layout/style/Loader.cpp
author Kyle Huey <khuey@kylehuey.com>
Tue, 11 Aug 2015 06:10:46 -0700
changeset 277167 a13c1f26e351dd6251da641fe7a9eb53790fc2d0
parent 275015 909e4b1913a9ce70d5aead33e13261f288d87904
child 277453 bab5913ea6cbb558457670e1785b0296cc13acc0
permissions -rw-r--r--
Bug 1179909: Refactor stable state handling. r=smaug This is motivated by three separate but related problems: 1. Our concept of recursion depth is broken for things that run from AfterProcessNextEvent observers (e.g. Promises). We decrement the recursionDepth counter before firing observers, so a Promise callback running at the lowest event loop depth has a recursion depth of 0 (whereas a regular nsIRunnable would be 1). This is a problem because it's impossible to distinguish a Promise running after a sync XHR's onreadystatechange handler from a top-level event (since the former runs with depth 2 - 1 = 1, and the latter runs with just 1). 2. The nsIThreadObserver mechanism that is used by a lot of code to run "after" the current event is a poor fit for anything that runs script. First, the order the observers fire in is the order they were added, not anything fixed by spec. Additionally, running script can cause the event loop to spin, which is a big source of pain here (bholley has some nasty bug caused by this). 3. We run Promises from different points in the code for workers and main thread. The latter runs from XPConnect's nsIThreadObserver callbacks, while the former runs from a hardcoded call to run Promises in the worker event loop. What workers do is particularly problematic because it means we can't get the right recursion depth no matter what we do to nsThread. The solve this, this patch does the following: 1. Consolidate some handling of microtasks and all handling of stable state from appshell and WorkerPrivate into CycleCollectedJSRuntime. 2. Make the recursionDepth counter only available to CycleCollectedJSRuntime (and its consumers) and remove it from the nsIThreadInternal and nsIThreadObserver APIs. 3. Adjust the recursionDepth counter so that microtasks run with the recursionDepth of the task they are associated with. 4. Introduce the concept of metastable state to replace appshell's RunBeforeNextEvent. Metastable state is reached after every microtask or task is completed. This provides the semantics that bent and I want for IndexedDB, where transactions autocommit at the end of a microtask and do not "spill" from one microtask into a subsequent microtask. This differs from appshell's RunBeforeNextEvent in two ways: a) It fires between microtasks, which was the motivation for starting this. b) It no longer ensures that we're at the same event loop depth in the native event queue. bent decided we don't care about this. 5. Reorder stable state to happen after microtasks such as Promises, per HTML. Right now we call the regular thread observers, including appshell, before the main thread observer (XPConnect), so stable state tasks happen before microtasks.

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: ft=cpp tw=78 sw=2 et ts=2
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * This Original Code has been modified by IBM Corporation.
 * Modifications made by IBM described herein are Copyright (c)
 * International Business Machines Corporation, 2000.  Modifications
 * to Mozilla code or documentation identified per MPL Section 3.3
 *
 * Date             Modified by     Description of modification
 * 04/20/2000       IBM Corp.      OS/2 VisualAge build.
 */

/* loading of CSS style sheets using the network APIs */

#include "mozilla/ArrayUtils.h"
#include "mozilla/LoadInfo.h"
#include "mozilla/MemoryReporting.h"

#include "mozilla/css/Loader.h"
#include "nsIRunnable.h"
#include "nsIUnicharStreamLoader.h"
#include "nsSyncLoadService.h"
#include "nsCOMPtr.h"
#include "nsString.h"
#include "nsIContent.h"
#include "nsIDocument.h"
#include "nsIDOMNode.h"
#include "nsIDOMDocument.h"
#include "nsIURI.h"
#include "nsNetUtil.h"
#include "nsIProtocolHandler.h"
#include "nsContentUtils.h"
#include "nsIScriptSecurityManager.h"
#include "nsContentPolicyUtils.h"
#include "nsIHttpChannel.h"
#include "nsIClassOfService.h"
#include "nsIScriptError.h"
#include "nsMimeTypes.h"
#include "nsIStyleSheetLinkingElement.h"
#include "nsICSSLoaderObserver.h"
#include "nsCSSParser.h"
#include "mozilla/CSSStyleSheet.h"
#include "mozilla/css/ImportRule.h"
#include "nsThreadUtils.h"
#include "nsGkAtoms.h"
#include "nsIThreadInternal.h"
#include "nsCORSListenerProxy.h"
#include "nsINetworkPredictor.h"
#include "mozilla/dom/ShadowRoot.h"
#include "mozilla/dom/URL.h"

#ifdef MOZ_XUL
#include "nsXULPrototypeCache.h"
#endif

#include "nsIMediaList.h"
#include "nsIDOMStyleSheet.h"
#include "nsError.h"

#include "nsIContentSecurityPolicy.h"

#include "mozilla/dom/EncodingUtils.h"
using mozilla::dom::EncodingUtils;

using namespace mozilla::dom;

/**
 * OVERALL ARCHITECTURE
 *
 * The CSS Loader gets requests to load various sorts of style sheets:
 * inline style from <style> elements, linked style, @import-ed child
 * sheets, non-document sheets.  The loader handles the following tasks:
 *
 * 1) Checking whether the load is allowed: CheckLoadAllowed()
 * 2) Creation of the actual style sheet objects: CreateSheet()
 * 3) setting of the right media, title, enabled state, etc on the
 *    sheet: PrepareSheet()
 * 4) Insertion of the sheet in the proper cascade order:
 *    InsertSheetInDoc() and InsertChildSheet()
 * 5) Load of the sheet: LoadSheet()
 * 6) Parsing of the sheet: ParseSheet()
 * 7) Cleanup: SheetComplete()
 *
 * The detailed documentation for these functions is found with the
 * function implementations.
 *
 * The following helper object is used:
 *    SheetLoadData -- a small class that is used to store all the
 *                     information needed for the loading of a sheet;
 *                     this class handles listening for the stream
 *                     loader completion and also handles charset
 *                     determination.
 */

namespace mozilla {
namespace css {

/*********************************************
 * Data needed to properly load a stylesheet *
 *********************************************/

class SheetLoadData final : public nsIRunnable,
                            public nsIUnicharStreamLoaderObserver,
                            public nsIThreadObserver
{
protected:
  virtual ~SheetLoadData(void);

public:
  // Data for loading a sheet linked from a document
  SheetLoadData(Loader* aLoader,
                const nsSubstring& aTitle,
                nsIURI* aURI,
                CSSStyleSheet* aSheet,
                nsIStyleSheetLinkingElement* aOwningElement,
                bool aIsAlternate,
                nsICSSLoaderObserver* aObserver,
                nsIPrincipal* aLoaderPrincipal,
                nsINode* aRequestingNode);

  // Data for loading a sheet linked from an @import rule
  SheetLoadData(Loader* aLoader,
                nsIURI* aURI,
                CSSStyleSheet* aSheet,
                SheetLoadData* aParentData,
                nsICSSLoaderObserver* aObserver,
                nsIPrincipal* aLoaderPrincipal,
                nsINode* aRequestingNode);

  // Data for loading a non-document sheet
  SheetLoadData(Loader* aLoader,
                nsIURI* aURI,
                CSSStyleSheet* aSheet,
                bool aSyncLoad,
                bool aAllowUnsafeRules,
                bool aUseSystemPrincipal,
                const nsCString& aCharset,
                nsICSSLoaderObserver* aObserver,
                nsIPrincipal* aLoaderPrincipal,
                nsINode* aRequestingNode);

  already_AddRefed<nsIURI> GetReferrerURI();

  void ScheduleLoadEventIfNeeded(nsresult aStatus);

  NS_DECL_ISUPPORTS
  NS_DECL_NSIRUNNABLE
  NS_DECL_NSITHREADOBSERVER
  NS_DECL_NSIUNICHARSTREAMLOADEROBSERVER

  // Hold a ref to the CSSLoader so we can call back to it to let it
  // know the load finished
  nsRefPtr<Loader>           mLoader;

  // Title needed to pull datas out of the pending datas table when
  // the preferred title is changed
  nsString                   mTitle;

  // Charset we decided to use for the sheet
  nsCString                  mCharset;

  // URI we're loading.  Null for inline sheets
  nsCOMPtr<nsIURI>           mURI;

  // Should be 1 for non-inline sheets.
  uint32_t                   mLineNumber;

  // The sheet we're loading data for
  nsRefPtr<CSSStyleSheet>    mSheet;

  // Linked list of datas for the same URI as us
  SheetLoadData*             mNext;  // strong ref

  // Load data for the sheet that @import-ed us if we were @import-ed
  // during the parse
  nsRefPtr<SheetLoadData>    mParentData;

  // Number of sheets we @import-ed that are still loading
  uint32_t                   mPendingChildren;

  // mSyncLoad is true when the load needs to be synchronous -- right
  // now only for LoadSheetSync and children of sync loads.
  bool                       mSyncLoad : 1;

  // mIsNonDocumentSheet is true if the load was triggered by LoadSheetSync or
  // LoadSheet or an @import from such a sheet.  Non-document sheet loads can
  // proceed even if we have no document.
  bool                       mIsNonDocumentSheet : 1;

  // mIsLoading is true from the moment we are placed in the loader's
  // "loading datas" table (right after the async channel is opened)
  // to the moment we are removed from said table (due to the load
  // completing or being cancelled).
  bool                       mIsLoading : 1;

  // mIsCancelled is set to true when a sheet load is stopped by
  // Stop() or StopLoadingSheet() (which was removed in Bug 556446).
  // SheetLoadData::OnStreamComplete() checks this to avoid parsing
  // sheets that have been cancelled and such.
  bool                       mIsCancelled : 1;

  // mMustNotify is true if the load data is being loaded async and
  // the original function call that started the load has returned.
  // This applies only to observer notifications; load/error events
  // are fired for any SheetLoadData that has a non-null
  // mOwningElement.
  bool                       mMustNotify : 1;

  // mWasAlternate is true if the sheet was an alternate when the load data was
  // created.
  bool                       mWasAlternate : 1;

  // mAllowUnsafeRules is true if we should allow unsafe rules to be parsed
  // in the loaded sheet.
  bool                       mAllowUnsafeRules : 1;

  // mUseSystemPrincipal is true if the system principal should be used for
  // this sheet, no matter what the channel principal is.  Only true for sync
  // loads.
  bool                       mUseSystemPrincipal : 1;

  // If true, this SheetLoadData is being used as a way to handle
  // async observer notification for an already-complete sheet.
  bool                       mSheetAlreadyComplete : 1;

  // This is the element that imported the sheet.  Needed to get the
  // charset set on it and to fire load/error events.
  nsCOMPtr<nsIStyleSheetLinkingElement> mOwningElement;

  // The observer that wishes to be notified of load completion
  nsCOMPtr<nsICSSLoaderObserver>        mObserver;

  // The principal that identifies who started loading us.
  nsCOMPtr<nsIPrincipal>                mLoaderPrincipal;

  // The node that identifies who started loading us.
  nsCOMPtr<nsINode>                     mRequestingNode;

  // The charset to use if the transport and sheet don't indicate one.
  // May be empty.  Must be empty if mOwningElement is non-null.
  nsCString                             mCharsetHint;

  // The status our load ended up with; this determines whether we
  // should fire error events or load events.  This gets initialized
  // by ScheduleLoadEventIfNeeded, and is only used after that has
  // been called.
  nsresult                              mStatus;

private:
  void FireLoadEvent(nsIThreadInternal* aThread);
};

#include "mozilla/Logging.h"

static PRLogModuleInfo *
GetLoaderLog()
{
  static PRLogModuleInfo *sLog;
  if (!sLog)
    sLog = PR_NewLogModule("nsCSSLoader");
  return sLog;
}

#define LOG_ERROR(args) MOZ_LOG(GetLoaderLog(), mozilla::LogLevel::Error, args)
#define LOG_WARN(args) MOZ_LOG(GetLoaderLog(), mozilla::LogLevel::Warning, args)
#define LOG_DEBUG(args) MOZ_LOG(GetLoaderLog(), mozilla::LogLevel::Debug, args)
#define LOG(args) LOG_DEBUG(args)

#define LOG_ERROR_ENABLED() MOZ_LOG_TEST(GetLoaderLog(), mozilla::LogLevel::Error)
#define LOG_WARN_ENABLED() MOZ_LOG_TEST(GetLoaderLog(), mozilla::LogLevel::Warning)
#define LOG_DEBUG_ENABLED() MOZ_LOG_TEST(GetLoaderLog(), mozilla::LogLevel::Debug)
#define LOG_ENABLED() LOG_DEBUG_ENABLED()

#define LOG_URI(format, uri)                        \
  PR_BEGIN_MACRO                                    \
    NS_ASSERTION(uri, "Logging null uri");          \
    if (LOG_ENABLED()) {                            \
      nsAutoCString _logURISpec;                    \
      uri->GetSpec(_logURISpec);                    \
      LOG((format, _logURISpec.get()));             \
    }                                               \
  PR_END_MACRO

// And some convenience strings...
static const char* const gStateStrings[] = {
  "eSheetStateUnknown",
  "eSheetNeedsParser",
  "eSheetPending",
  "eSheetLoading",
  "eSheetComplete"
};

/********************************
 * SheetLoadData implementation *
 ********************************/
NS_IMPL_ISUPPORTS(SheetLoadData, nsIUnicharStreamLoaderObserver, nsIRunnable,
                  nsIThreadObserver)

SheetLoadData::SheetLoadData(Loader* aLoader,
                             const nsSubstring& aTitle,
                             nsIURI* aURI,
                             CSSStyleSheet* aSheet,
                             nsIStyleSheetLinkingElement* aOwningElement,
                             bool aIsAlternate,
                             nsICSSLoaderObserver* aObserver,
                             nsIPrincipal* aLoaderPrincipal,
                             nsINode* aRequestingNode)
  : mLoader(aLoader),
    mTitle(aTitle),
    mURI(aURI),
    mLineNumber(1),
    mSheet(aSheet),
    mNext(nullptr),
    mPendingChildren(0),
    mSyncLoad(false),
    mIsNonDocumentSheet(false),
    mIsLoading(false),
    mIsCancelled(false),
    mMustNotify(false),
    mWasAlternate(aIsAlternate),
    mAllowUnsafeRules(false),
    mUseSystemPrincipal(false),
    mSheetAlreadyComplete(false),
    mOwningElement(aOwningElement),
    mObserver(aObserver),
    mLoaderPrincipal(aLoaderPrincipal),
    mRequestingNode(aRequestingNode)
{
  NS_PRECONDITION(mLoader, "Must have a loader!");
}

SheetLoadData::SheetLoadData(Loader* aLoader,
                             nsIURI* aURI,
                             CSSStyleSheet* aSheet,
                             SheetLoadData* aParentData,
                             nsICSSLoaderObserver* aObserver,
                             nsIPrincipal* aLoaderPrincipal,
                             nsINode* aRequestingNode)
  : mLoader(aLoader),
    mURI(aURI),
    mLineNumber(1),
    mSheet(aSheet),
    mNext(nullptr),
    mParentData(aParentData),
    mPendingChildren(0),
    mSyncLoad(false),
    mIsNonDocumentSheet(false),
    mIsLoading(false),
    mIsCancelled(false),
    mMustNotify(false),
    mWasAlternate(false),
    mAllowUnsafeRules(false),
    mUseSystemPrincipal(false),
    mSheetAlreadyComplete(false),
    mOwningElement(nullptr),
    mObserver(aObserver),
    mLoaderPrincipal(aLoaderPrincipal),
    mRequestingNode(aRequestingNode)
{
  NS_PRECONDITION(mLoader, "Must have a loader!");
  if (mParentData) {
    mSyncLoad = mParentData->mSyncLoad;
    mIsNonDocumentSheet = mParentData->mIsNonDocumentSheet;
    mAllowUnsafeRules = mParentData->mAllowUnsafeRules;
    mUseSystemPrincipal = mParentData->mUseSystemPrincipal;
    ++(mParentData->mPendingChildren);
  }

  NS_POSTCONDITION(!mUseSystemPrincipal || mSyncLoad,
                   "Shouldn't use system principal for async loads");
}

SheetLoadData::SheetLoadData(Loader* aLoader,
                             nsIURI* aURI,
                             CSSStyleSheet* aSheet,
                             bool aSyncLoad,
                             bool aAllowUnsafeRules,
                             bool aUseSystemPrincipal,
                             const nsCString& aCharset,
                             nsICSSLoaderObserver* aObserver,
                             nsIPrincipal* aLoaderPrincipal,
                             nsINode* aRequestingNode)
  : mLoader(aLoader),
    mURI(aURI),
    mLineNumber(1),
    mSheet(aSheet),
    mNext(nullptr),
    mPendingChildren(0),
    mSyncLoad(aSyncLoad),
    mIsNonDocumentSheet(true),
    mIsLoading(false),
    mIsCancelled(false),
    mMustNotify(false),
    mWasAlternate(false),
    mAllowUnsafeRules(aAllowUnsafeRules),
    mUseSystemPrincipal(aUseSystemPrincipal),
    mSheetAlreadyComplete(false),
    mOwningElement(nullptr),
    mObserver(aObserver),
    mLoaderPrincipal(aLoaderPrincipal),
    mRequestingNode(aRequestingNode),
    mCharsetHint(aCharset)
{
  NS_PRECONDITION(mLoader, "Must have a loader!");

  NS_POSTCONDITION(!mUseSystemPrincipal || mSyncLoad,
                   "Shouldn't use system principal for async loads");
}

SheetLoadData::~SheetLoadData()
{
  NS_IF_RELEASE(mNext);
}

NS_IMETHODIMP
SheetLoadData::Run()
{
  mLoader->HandleLoadEvent(this);
  return NS_OK;
}

NS_IMETHODIMP
SheetLoadData::OnDispatchedEvent(nsIThreadInternal* aThread)
{
  return NS_OK;
}

NS_IMETHODIMP
SheetLoadData::OnProcessNextEvent(nsIThreadInternal* aThread,
                                  bool aMayWait)
{
  // XXXkhuey this is insane!
  // We want to fire our load even before or after event processing,
  // whichever comes first.
  FireLoadEvent(aThread);
  return NS_OK;
}

NS_IMETHODIMP
SheetLoadData::AfterProcessNextEvent(nsIThreadInternal* aThread,
                                     bool aEventWasProcessed)
{
  // XXXkhuey this too!
  // We want to fire our load even before or after event processing,
  // whichever comes first.
  FireLoadEvent(aThread);
  return NS_OK;
}

void
SheetLoadData::FireLoadEvent(nsIThreadInternal* aThread)
{
  
  // First remove ourselves as a thread observer.  But we need to keep
  // ourselves alive while doing that!
  nsRefPtr<SheetLoadData> kungFuDeathGrip(this);
  aThread->RemoveObserver(this);

  // Now fire the event
  nsCOMPtr<nsINode> node = do_QueryInterface(mOwningElement);
  NS_ASSERTION(node, "How did that happen???");

  nsContentUtils::DispatchTrustedEvent(node->OwnerDoc(),
                                       node,
                                       NS_SUCCEEDED(mStatus) ?
                                         NS_LITERAL_STRING("load") :
                                         NS_LITERAL_STRING("error"),
                                       false, false);

  // And unblock onload
  if (mLoader->mDocument) {
    mLoader->mDocument->UnblockOnload(true);
  }  
}

void
SheetLoadData::ScheduleLoadEventIfNeeded(nsresult aStatus)
{
  if (!mOwningElement) {
    return;
  }

  mStatus = aStatus;

  nsCOMPtr<nsIThread> thread = do_GetMainThread();
  nsCOMPtr<nsIThreadInternal> internalThread = do_QueryInterface(thread);
  if (NS_SUCCEEDED(internalThread->AddObserver(this))) {
    // Make sure to block onload here
    if (mLoader->mDocument) {
      mLoader->mDocument->BlockOnload();
    }
  }
}

/*************************
 * Loader Implementation *
 *************************/

Loader::Loader(void)
  : mDocument(nullptr)
  , mDatasToNotifyOn(0)
  , mCompatMode(eCompatibility_FullStandards)
  , mEnabled(true)
#ifdef DEBUG
  , mSyncCallback(false)
#endif
{
}

Loader::Loader(nsIDocument* aDocument)
  : mDocument(aDocument)
  , mDatasToNotifyOn(0)
  , mCompatMode(eCompatibility_FullStandards)
  , mEnabled(true)
#ifdef DEBUG
  , mSyncCallback(false)
#endif
{
  // We can just use the preferred set, since there are no sheets in the
  // document yet (if there are, how did they get there? _we_ load the sheets!)
  // and hence the selected set makes no sense at this time.
  nsCOMPtr<nsIDOMDocument> domDoc = do_QueryInterface(mDocument);
  if (domDoc) {
    domDoc->GetPreferredStyleSheetSet(mPreferredSheet);
  }
}

Loader::~Loader()
{
  NS_ASSERTION(!mSheets || mSheets->mLoadingDatas.Count() == 0,
               "How did we get destroyed when there are loading data?");
  NS_ASSERTION(!mSheets || mSheets->mPendingDatas.Count() == 0,
               "How did we get destroyed when there are pending data?");
  // Note: no real need to revoke our stylesheet loaded events -- they
  // hold strong references to us, so if we're going away that means
  // they're all done.
}

void
Loader::DropDocumentReference(void)
{
  mDocument = nullptr;
  // Flush out pending datas just so we don't leak by accident.  These
  // loads should short-circuit through the mDocument check in
  // LoadSheet and just end up in SheetComplete immediately
  if (mSheets) {
    StartAlternateLoads();
  }
}

static PLDHashOperator
CollectNonAlternates(URIPrincipalReferrerPolicyAndCORSModeHashKey *aKey,
                     SheetLoadData* &aData,
                     void* aClosure)
{
  NS_PRECONDITION(aData, "Must have a data");
  NS_PRECONDITION(aClosure, "Must have an array");

  // Note that we don't want to affect what the selected style set is,
  // so use true for aHasAlternateRel.
  if (aData->mLoader->IsAlternate(aData->mTitle, true)) {
    return PL_DHASH_NEXT;
  }

  static_cast<Loader::LoadDataArray*>(aClosure)->AppendElement(aData);
  return PL_DHASH_REMOVE;
}

nsresult
Loader::SetPreferredSheet(const nsAString& aTitle)
{
#ifdef DEBUG
  nsCOMPtr<nsIDOMDocument> doc = do_QueryInterface(mDocument);
  if (doc) {
    nsAutoString currentPreferred;
    doc->GetLastStyleSheetSet(currentPreferred);
    if (DOMStringIsNull(currentPreferred)) {
      doc->GetPreferredStyleSheetSet(currentPreferred);
    }
    NS_ASSERTION(currentPreferred.Equals(aTitle),
                 "Unexpected argument to SetPreferredSheet");
  }
#endif

  mPreferredSheet = aTitle;

  // start any pending alternates that aren't alternates anymore
  if (mSheets) {
    LoadDataArray arr(mSheets->mPendingDatas.Count());
    mSheets->mPendingDatas.Enumerate(CollectNonAlternates, &arr);

    mDatasToNotifyOn += arr.Length();
    for (uint32_t i = 0; i < arr.Length(); ++i) {
      --mDatasToNotifyOn;
      LoadSheet(arr[i], eSheetNeedsParser);
    }
  }

  return NS_OK;
}

static const char kCharsetSym[] = "@charset \"";

static bool GetCharsetFromData(const char* aStyleSheetData,
                               uint32_t aDataLength,
                               nsACString& aCharset)
{
  aCharset.Truncate();
  if (aDataLength <= sizeof(kCharsetSym) - 1)
    return false;

  if (strncmp(aStyleSheetData,
              kCharsetSym,
              sizeof(kCharsetSym) - 1)) {
    return false;
  }

  for (uint32_t i = sizeof(kCharsetSym) - 1; i < aDataLength; ++i) {
    char c = aStyleSheetData[i];
    if (c == '"') {
      ++i;
      if (i < aDataLength && aStyleSheetData[i] == ';') {
        return true;
      }
      // fail
      break;
    }
    aCharset.Append(c);
  }

  // Did not see end quote or semicolon
  aCharset.Truncate();
  return false;
}

NS_IMETHODIMP
SheetLoadData::OnDetermineCharset(nsIUnicharStreamLoader* aLoader,
                                  nsISupports* aContext,
                                  nsACString const& aSegment,
                                  nsACString& aCharset)
{
  NS_PRECONDITION(!mOwningElement || mCharsetHint.IsEmpty(),
                  "Can't have element _and_ charset hint");

  LOG_URI("SheetLoadData::OnDetermineCharset for '%s'", mURI);

  // The precedence is (per CSS3 Syntax 2012-11-08 ED):
  // BOM
  // Channel
  // @charset rule
  // charset attribute on the referrer
  // encoding of the referrer
  // UTF-8

  aCharset.Truncate();

  if (nsContentUtils::CheckForBOM((const unsigned char*)aSegment.BeginReading(),
                                  aSegment.Length(),
                                  aCharset)) {
    // aCharset is now either "UTF-16BE", "UTF-16BE" or "UTF-8"
    // which will swallow the BOM.
    mCharset.Assign(aCharset);
    LOG(("  Setting from BOM to: %s", PromiseFlatCString(aCharset).get()));
    return NS_OK;
  }

  nsCOMPtr<nsIChannel> channel;
  nsAutoCString specified;
  aLoader->GetChannel(getter_AddRefs(channel));
  if (channel) {
    channel->GetContentCharset(specified);
    if (EncodingUtils::FindEncodingForLabel(specified, aCharset)) {
      mCharset.Assign(aCharset);
      LOG(("  Setting from HTTP to: %s", PromiseFlatCString(aCharset).get()));
      return NS_OK;
    }
  }

  if (GetCharsetFromData(aSegment.BeginReading(),
                         aSegment.Length(),
                         specified)) {
    if (EncodingUtils::FindEncodingForLabel(specified, aCharset)) {
      // FindEncodingForLabel currently never returns UTF-16LE but will
      // probably change to never return UTF-16 instead, so check both here
      // to avoid relying on the exact behavior.
      if (aCharset.EqualsLiteral("UTF-16") ||
          aCharset.EqualsLiteral("UTF-16BE") ||
          aCharset.EqualsLiteral("UTF-16LE")) {
        // Be consistent with HTML <meta> handling in face of impossibility.
        // When the @charset rule itself evidently was not UTF-16-encoded,
        // it saying UTF-16 has to be a lie.
        aCharset.AssignLiteral("UTF-8");
      }
      mCharset.Assign(aCharset);
      LOG(("  Setting from @charset rule to: %s",
          PromiseFlatCString(aCharset).get()));
      return NS_OK;
    }
  }

  // Now try the charset on the <link> or processing instruction
  // that loaded us
  if (mOwningElement) {
    nsAutoString specified16;
    mOwningElement->GetCharset(specified16);
    if (EncodingUtils::FindEncodingForLabel(specified16, aCharset)) {
      mCharset.Assign(aCharset);
      LOG(("  Setting from charset attribute to: %s",
          PromiseFlatCString(aCharset).get()));
      return NS_OK;
    }
  }

  // In the preload case, the value of the charset attribute on <link> comes
  // in via mCharsetHint instead.
  if (EncodingUtils::FindEncodingForLabel(mCharsetHint, aCharset)) {
    mCharset.Assign(aCharset);
      LOG(("  Setting from charset attribute (preload case) to: %s",
          PromiseFlatCString(aCharset).get()));
    return NS_OK;
  }

  // Try charset from the parent stylesheet.
  if (mParentData) {
    aCharset = mParentData->mCharset;
    if (!aCharset.IsEmpty()) {
      mCharset.Assign(aCharset);
      LOG(("  Setting from parent sheet to: %s",
          PromiseFlatCString(aCharset).get()));
      return NS_OK;
    }
  }

  if (mLoader->mDocument) {
    // no useful data on charset.  Try the document charset.
    aCharset = mLoader->mDocument->GetDocumentCharacterSet();
    MOZ_ASSERT(!aCharset.IsEmpty());
    mCharset.Assign(aCharset);
    LOG(("  Setting from document to: %s", PromiseFlatCString(aCharset).get()));
    return NS_OK;
  }

  aCharset.AssignLiteral("UTF-8");
  mCharset = aCharset;
  LOG(("  Setting from default to: %s", PromiseFlatCString(aCharset).get()));
  return NS_OK;
}

already_AddRefed<nsIURI>
SheetLoadData::GetReferrerURI()
{
  nsCOMPtr<nsIURI> uri;
  if (mParentData)
    uri = mParentData->mSheet->GetSheetURI();
  if (!uri && mLoader->mDocument)
    uri = mLoader->mDocument->GetDocumentURI();
  return uri.forget();
}

/*
 * Here we need to check that the load did not give us an http error
 * page and check the mimetype on the channel to make sure we're not
 * loading non-text/css data in standards mode.
 */
NS_IMETHODIMP
SheetLoadData::OnStreamComplete(nsIUnicharStreamLoader* aLoader,
                                nsISupports* aContext,
                                nsresult aStatus,
                                const nsAString& aBuffer)
{
  LOG(("SheetLoadData::OnStreamComplete"));
  NS_ASSERTION(!mLoader->mSyncCallback, "Synchronous callback from necko");

  if (mIsCancelled) {
    // Just return.  Don't call SheetComplete -- it's already been
    // called and calling it again will lead to an extra NS_RELEASE on
    // this data and a likely crash.
    return NS_OK;
  }

  if (!mLoader->mDocument && !mIsNonDocumentSheet) {
    // Sorry, we don't care about this load anymore
    LOG_WARN(("  No document and not non-document sheet; dropping load"));
    mLoader->SheetComplete(this, NS_BINDING_ABORTED);
    return NS_OK;
  }

  if (NS_FAILED(aStatus)) {
    LOG_WARN(("  Load failed: status 0x%x", aStatus));
    // Handle sheet not loading error because source was a tracking URL.
    // We make a note of this sheet node by including it in a dedicated
    // array of blocked tracking nodes under its parent document.
    //
    // Multiple sheet load instances might be tied to this request,
    // we annotate each one linked to a valid owning element (node).
    if (aStatus == NS_ERROR_TRACKING_URI) {
      nsIDocument* doc = mLoader->GetDocument();
      if (doc) {
        for (SheetLoadData* data = this; data; data = data->mNext) {
          // mOwningElement may be null but AddBlockTrackingNode can cope
          nsCOMPtr<nsIContent> content = do_QueryInterface(data->mOwningElement);
          doc->AddBlockedTrackingNode(content);
        }
      }
    }
    mLoader->SheetComplete(this, aStatus);
    return NS_OK;
  }

  nsCOMPtr<nsIChannel> channel;
  nsresult result = aLoader->GetChannel(getter_AddRefs(channel));
  if (NS_FAILED(result)) {
    LOG_WARN(("  No channel from loader"));
    mLoader->SheetComplete(this, result);
    return NS_OK;
  }

  nsCOMPtr<nsIURI> originalURI;
  channel->GetOriginalURI(getter_AddRefs(originalURI));

  // If the channel's original URI is "chrome:", we want that, since
  // the observer code in nsXULPrototypeCache depends on chrome stylesheets
  // having a chrome URI.  (Whether or not chrome stylesheets come through
  // this codepath seems nondeterministic.)
  // Otherwise we want the potentially-HTTP-redirected URI.
  nsCOMPtr<nsIURI> channelURI;
  NS_GetFinalChannelURI(channel, getter_AddRefs(channelURI));

  if (!channelURI || !originalURI) {
    NS_ERROR("Someone just violated the nsIRequest contract");
    LOG_WARN(("  Channel without a URI.  Bad!"));
    mLoader->SheetComplete(this, NS_ERROR_UNEXPECTED);
    return NS_OK;
  }

  nsCOMPtr<nsIPrincipal> principal;
  nsIScriptSecurityManager* secMan = nsContentUtils::GetSecurityManager();
  result = NS_ERROR_NOT_AVAILABLE;
  if (secMan) {  // Could be null if we already shut down
    if (mUseSystemPrincipal) {
      result = secMan->GetSystemPrincipal(getter_AddRefs(principal));
    } else {
      result = secMan->GetChannelResultPrincipal(channel, getter_AddRefs(principal));
    }
  }

  if (NS_FAILED(result)) {
    LOG_WARN(("  Couldn't get principal"));
    mLoader->SheetComplete(this, result);
    return NS_OK;
  }

  mSheet->SetPrincipal(principal);

  // If it's an HTTP channel, we want to make sure this is not an
  // error document we got.
  nsCOMPtr<nsIHttpChannel> httpChannel(do_QueryInterface(channel));
  if (httpChannel) {
    bool requestSucceeded;
    result = httpChannel->GetRequestSucceeded(&requestSucceeded);
    if (NS_SUCCEEDED(result) && !requestSucceeded) {
      LOG(("  Load returned an error page"));
      mLoader->SheetComplete(this, NS_ERROR_NOT_AVAILABLE);
      return NS_OK;
    }
  }

  nsAutoCString contentType;
  if (channel) {
    channel->GetContentType(contentType);
  }

  // In standards mode, a style sheet must have one of these MIME
  // types to be processed at all.  In quirks mode, we accept any
  // MIME type, but only if the style sheet is same-origin with the
  // requesting document or parent sheet.  See bug 524223.

  bool validType = contentType.EqualsLiteral("text/css") ||
    contentType.EqualsLiteral(UNKNOWN_CONTENT_TYPE) ||
    contentType.IsEmpty();

  if (!validType) {
    const char *errorMessage;
    uint32_t errorFlag;
    bool sameOrigin = true;

    if (mLoaderPrincipal) {
      bool subsumed;
      result = mLoaderPrincipal->Subsumes(principal, &subsumed);
      if (NS_FAILED(result) || !subsumed) {
        sameOrigin = false;
      }
    }

    if (sameOrigin && mLoader->mCompatMode == eCompatibility_NavQuirks) {
      errorMessage = "MimeNotCssWarn";
      errorFlag = nsIScriptError::warningFlag;
    } else {
      errorMessage = "MimeNotCss";
      errorFlag = nsIScriptError::errorFlag;
    }

    nsAutoCString spec;
    channelURI->GetSpec(spec);

    const nsAFlatString& specUTF16 = NS_ConvertUTF8toUTF16(spec);
    const nsAFlatString& ctypeUTF16 = NS_ConvertASCIItoUTF16(contentType);
    const char16_t *strings[] = { specUTF16.get(), ctypeUTF16.get() };

    nsCOMPtr<nsIURI> referrer = GetReferrerURI();
    nsContentUtils::ReportToConsole(errorFlag,
                                    NS_LITERAL_CSTRING("CSS Loader"),
                                    mLoader->mDocument,
                                    nsContentUtils::eCSS_PROPERTIES,
                                    errorMessage,
                                    strings, ArrayLength(strings),
                                    referrer);

    if (errorFlag == nsIScriptError::errorFlag) {
      LOG_WARN(("  Ignoring sheet with improper MIME type %s",
                contentType.get()));
      mLoader->SheetComplete(this, NS_ERROR_NOT_AVAILABLE);
      return NS_OK;
    }
  }

  // Enough to set the URIs on mSheet, since any sibling datas we have share
  // the same mInner as mSheet and will thus get the same URI.
  mSheet->SetURIs(channelURI, originalURI, channelURI);

  bool completed;
  result = mLoader->ParseSheet(aBuffer, this, completed);
  NS_ASSERTION(completed || !mSyncLoad, "sync load did not complete");
  return result;
}

bool
Loader::IsAlternate(const nsAString& aTitle, bool aHasAlternateRel)
{
  // A sheet is alternate if it has a nonempty title that doesn't match the
  // currently selected style set.  But if there _is_ no currently selected
  // style set, the sheet wasn't marked as an alternate explicitly, and aTitle
  // is nonempty, we should select the style set corresponding to aTitle, since
  // that's a preferred sheet.
  if (aTitle.IsEmpty()) {
    return false;
  }

  if (!aHasAlternateRel && mDocument && mPreferredSheet.IsEmpty()) {
    // There's no preferred set yet, and we now have a sheet with a title.
    // Make that be the preferred set.
    mDocument->SetHeaderData(nsGkAtoms::headerDefaultStyle, aTitle);
    // We're definitely not an alternate
    return false;
  }

  return !aTitle.Equals(mPreferredSheet);
}

/* static */ PLDHashOperator
Loader::RemoveEntriesWithURI(URIPrincipalReferrerPolicyAndCORSModeHashKey* aKey,
                             nsRefPtr<CSSStyleSheet>& aSheet,
                             void* aUserData)
{
  nsIURI* obsoleteURI = static_cast<nsIURI*>(aUserData);
  nsIURI* sheetURI = aKey->GetURI();
  bool areEqual;
  nsresult rv = sheetURI->Equals(obsoleteURI, &areEqual);
  if (NS_SUCCEEDED(rv) && areEqual) {
    return PL_DHASH_REMOVE;
  }
  return PL_DHASH_NEXT;
}

nsresult
Loader::ObsoleteSheet(nsIURI* aURI)
{
  if (!mSheets) {
    return NS_OK;
  }
  if (!aURI) {
    return NS_ERROR_INVALID_ARG;
  }
  mSheets->mCompleteSheets.Enumerate(RemoveEntriesWithURI, aURI);
  return NS_OK;
}

/**
 * CheckLoadAllowed will return success if the load is allowed,
 * failure otherwise.
 *
 * @param aSourcePrincipal the principal of the node or document or parent
 *                         sheet loading the sheet
 * @param aTargetURI the uri of the sheet to be loaded
 * @param aContext the node owning the sheet.  This is the element or document
 *                 owning the stylesheet (possibly indirectly, for child sheets)
 */
nsresult
Loader::CheckLoadAllowed(nsIPrincipal* aSourcePrincipal,
                         nsIURI* aTargetURI,
                         nsISupports* aContext)
{
  LOG(("css::Loader::CheckLoadAllowed"));

  nsresult rv;

  if (aSourcePrincipal) {
    // Check with the security manager
    nsIScriptSecurityManager *secMan = nsContentUtils::GetSecurityManager();
    rv =
      secMan->CheckLoadURIWithPrincipal(aSourcePrincipal, aTargetURI,
                                        nsIScriptSecurityManager::ALLOW_CHROME);
    if (NS_FAILED(rv)) { // failure is normal here; don't warn
      return rv;
    }

    LOG(("  Passed security check"));

    // Check with content policy

    int16_t shouldLoad = nsIContentPolicy::ACCEPT;
    rv = NS_CheckContentLoadPolicy(nsIContentPolicy::TYPE_STYLESHEET,
                                   aTargetURI,
                                   aSourcePrincipal,
                                   aContext,
                                   NS_LITERAL_CSTRING("text/css"),
                                   nullptr,                     //extra param
                                   &shouldLoad,
                                   nsContentUtils::GetContentPolicy(),
                                   nsContentUtils::GetSecurityManager());

    if (NS_FAILED(rv) || NS_CP_REJECTED(shouldLoad)) {
      LOG(("  Load blocked by content policy"));
      return NS_ERROR_CONTENT_BLOCKED;
    }
  }

  return NS_OK;
}

/**
 * CreateSheet() creates a CSSStyleSheet object for the given URI,
 * if any.  If there is no URI given, we just create a new style sheet
 * object.  Otherwise, we check for an existing style sheet object for
 * that uri in various caches and clone it if we find it.  Cloned
 * sheets will have the title/media/enabled state of the sheet they
 * are clones off; make sure to call PrepareSheet() on the result of
 * CreateSheet().
 */
nsresult
Loader::CreateSheet(nsIURI* aURI,
                    nsIContent* aLinkingContent,
                    nsIPrincipal* aLoaderPrincipal,
                    CORSMode aCORSMode,
                    ReferrerPolicy aReferrerPolicy,
                    bool aSyncLoad,
                    bool aHasAlternateRel,
                    const nsAString& aTitle,
                    StyleSheetState& aSheetState,
                    bool *aIsAlternate,
                    CSSStyleSheet** aSheet)
{
  LOG(("css::Loader::CreateSheet"));
  NS_PRECONDITION(aSheet, "Null out param!");

  if (!mSheets) {
    mSheets = new Sheets();
  }

  *aSheet = nullptr;
  aSheetState = eSheetStateUnknown;

  // Check the alternate state before doing anything else, because it
  // can mess with our hashtables.
  *aIsAlternate = IsAlternate(aTitle, aHasAlternateRel);

  if (aURI) {
    aSheetState = eSheetComplete;
    nsRefPtr<CSSStyleSheet> sheet;

    // First, the XUL cache
#ifdef MOZ_XUL
    if (IsChromeURI(aURI)) {
      nsXULPrototypeCache* cache = nsXULPrototypeCache::GetInstance();
      if (cache) {
        if (cache->IsEnabled()) {
          sheet = cache->GetStyleSheet(aURI);
          LOG(("  From XUL cache: %p", sheet.get()));
        }
      }
    }
#endif

    bool fromCompleteSheets = false;
    if (!sheet) {
      // Then our per-document complete sheets.
      URIPrincipalReferrerPolicyAndCORSModeHashKey key(aURI, aLoaderPrincipal, aCORSMode, aReferrerPolicy);

      mSheets->mCompleteSheets.Get(&key, getter_AddRefs(sheet));
      LOG(("  From completed: %p", sheet.get()));

      fromCompleteSheets = !!sheet;
    }

    if (sheet) {
      // This sheet came from the XUL cache or our per-document hashtable; it
      // better be a complete sheet.
      NS_ASSERTION(sheet->IsComplete(),
                   "Sheet thinks it's not complete while we think it is");

      // Make sure it hasn't been modified; if it has, we can't use it
      if (sheet->IsModified()) {
        LOG(("  Not cloning completed sheet %p because it's been modified",
             sheet.get()));
        sheet = nullptr;
        fromCompleteSheets = false;
      }
    }

    // Then loading sheets
    if (!sheet && !aSyncLoad) {
      aSheetState = eSheetLoading;
      SheetLoadData* loadData = nullptr;
      URIPrincipalReferrerPolicyAndCORSModeHashKey key(aURI, aLoaderPrincipal, aCORSMode, aReferrerPolicy);
      mSheets->mLoadingDatas.Get(&key, &loadData);
      if (loadData) {
        sheet = loadData->mSheet;
        LOG(("  From loading: %p", sheet.get()));

#ifdef DEBUG
        bool debugEqual;
        NS_ASSERTION((!aLoaderPrincipal && !loadData->mLoaderPrincipal) ||
                     (aLoaderPrincipal && loadData->mLoaderPrincipal &&
                      NS_SUCCEEDED(aLoaderPrincipal->
                                   Equals(loadData->mLoaderPrincipal,
                                          &debugEqual)) && debugEqual),
                     "Principals should be the same");
#endif
      }

      // Then alternate sheets
      if (!sheet) {
        aSheetState = eSheetPending;
        loadData = nullptr;
        mSheets->mPendingDatas.Get(&key, &loadData);
        if (loadData) {
          sheet = loadData->mSheet;
          LOG(("  From pending: %p", sheet.get()));

#ifdef DEBUG
          bool debugEqual;
          NS_ASSERTION((!aLoaderPrincipal && !loadData->mLoaderPrincipal) ||
                       (aLoaderPrincipal && loadData->mLoaderPrincipal &&
                        NS_SUCCEEDED(aLoaderPrincipal->
                                     Equals(loadData->mLoaderPrincipal,
                                            &debugEqual)) && debugEqual),
                       "Principals should be the same");
#endif
        }
      }
    }

    if (sheet) {
      // The sheet we have now should be either incomplete or unmodified
      NS_ASSERTION(!sheet->IsModified() || !sheet->IsComplete(),
                   "Unexpected modified complete sheet");
      NS_ASSERTION(sheet->IsComplete() || aSheetState != eSheetComplete,
                   "Sheet thinks it's not complete while we think it is");

      *aSheet = sheet->Clone(nullptr, nullptr, nullptr, nullptr).take();
      if (*aSheet && fromCompleteSheets &&
          !sheet->GetOwnerNode() && !sheet->GetParentSheet()) {
        // The sheet we're cloning isn't actually referenced by
        // anyone.  Replace it in the cache, so that if our CSSOM is
        // later modified we don't end up with two copies of our inner
        // hanging around.
        URIPrincipalReferrerPolicyAndCORSModeHashKey key(aURI, aLoaderPrincipal, aCORSMode, aReferrerPolicy);
        NS_ASSERTION((*aSheet)->IsComplete(),
                     "Should only be caching complete sheets");
        mSheets->mCompleteSheets.Put(&key, *aSheet);
      }
    }
  }

  if (!*aSheet) {
    aSheetState = eSheetNeedsParser;
    nsIURI *sheetURI;
    nsCOMPtr<nsIURI> baseURI;
    nsIURI* originalURI;
    if (!aURI) {
      // Inline style.  Use the document's base URL so that @import in
      // the inline sheet picks up the right base.
      NS_ASSERTION(aLinkingContent, "Inline stylesheet without linking content?");
      baseURI = aLinkingContent->GetBaseURI();
      sheetURI = aLinkingContent->OwnerDoc()->GetDocumentURI();
      originalURI = nullptr;
    } else {
      baseURI = aURI;
      sheetURI = aURI;
      originalURI = aURI;
    }

    nsRefPtr<CSSStyleSheet> sheet = new CSSStyleSheet(aCORSMode, aReferrerPolicy);
    sheet->SetURIs(sheetURI, originalURI, baseURI);
    sheet.forget(aSheet);
  }

  NS_ASSERTION(*aSheet, "We should have a sheet by now!");
  NS_ASSERTION(aSheetState != eSheetStateUnknown, "Have to set a state!");
  LOG(("  State: %s", gStateStrings[aSheetState]));

  return NS_OK;
}

/**
 * PrepareSheet() handles setting the media and title on the sheet, as
 * well as setting the enabled state based on the title and whether
 * the sheet had "alternate" in its rel.
 */
void
Loader::PrepareSheet(CSSStyleSheet* aSheet,
                     const nsSubstring& aTitle,
                     const nsSubstring& aMediaString,
                     nsMediaList* aMediaList,
                     Element* aScopeElement,
                     bool isAlternate)
{
  NS_PRECONDITION(aSheet, "Must have a sheet!");

  nsRefPtr<nsMediaList> mediaList(aMediaList);

  if (!aMediaString.IsEmpty()) {
    NS_ASSERTION(!aMediaList,
                 "must not provide both aMediaString and aMediaList");
    mediaList = new nsMediaList();

    nsCSSParser mediumParser(this);

    // We have aMediaString only when linked from link elements, style
    // elements, or PIs, so pass true.
    mediumParser.ParseMediaList(aMediaString, nullptr, 0, mediaList, true);
  }

  aSheet->SetMedia(mediaList);

  aSheet->SetTitle(aTitle);
  aSheet->SetEnabled(! isAlternate);
  aSheet->SetScopeElement(aScopeElement);
}

/**
 * InsertSheetInDoc handles ordering of sheets in the document.  Here
 * we have two types of sheets -- those with linking elements and
 * those without.  The latter are loaded by Link: headers.
 * The following constraints are observed:
 * 1) Any sheet with a linking element comes after all sheets without
 *    linking elements
 * 2) Sheets without linking elements are inserted in the order in
 *    which the inserting requests come in, since all of these are
 *    inserted during header data processing in the content sink
 * 3) Sheets with linking elements are ordered based on document order
 *    as determined by CompareDocumentPosition.
 */
nsresult
Loader::InsertSheetInDoc(CSSStyleSheet* aSheet,
                         nsIContent* aLinkingContent,
                         nsIDocument* aDocument)
{
  LOG(("css::Loader::InsertSheetInDoc"));
  NS_PRECONDITION(aSheet, "Nothing to insert");
  NS_PRECONDITION(aDocument, "Must have a document to insert into");

  // XXX Need to cancel pending sheet loads for this element, if any

  int32_t sheetCount = aDocument->GetNumberOfStyleSheets();

  /*
   * Start the walk at the _end_ of the list, since in the typical
   * case we'll just want to append anyway.  We want to break out of
   * the loop when insertionPoint points to just before the index we
   * want to insert at.  In other words, when we leave the loop
   * insertionPoint is the index of the stylesheet that immediately
   * precedes the one we're inserting.
   */
  int32_t insertionPoint;
  for (insertionPoint = sheetCount - 1; insertionPoint >= 0; --insertionPoint) {
    nsIStyleSheet *curSheet = aDocument->GetStyleSheetAt(insertionPoint);
    NS_ASSERTION(curSheet, "There must be a sheet here!");
    nsCOMPtr<nsIDOMStyleSheet> domSheet = do_QueryInterface(curSheet);
    NS_ASSERTION(domSheet, "All the \"normal\" sheets implement nsIDOMStyleSheet");
    nsCOMPtr<nsIDOMNode> sheetOwner;
    domSheet->GetOwnerNode(getter_AddRefs(sheetOwner));
    if (sheetOwner && !aLinkingContent) {
      // Keep moving; all sheets with a sheetOwner come after all
      // sheets without a linkingNode
      continue;
    }

    if (!sheetOwner) {
      // Aha!  The current sheet has no sheet owner, so we want to
      // insert after it no matter whether we have a linkingNode
      break;
    }

    nsCOMPtr<nsINode> sheetOwnerNode = do_QueryInterface(sheetOwner);
    NS_ASSERTION(aLinkingContent != sheetOwnerNode,
                 "Why do we still have our old sheet?");

    // Have to compare
    if (nsContentUtils::PositionIsBefore(sheetOwnerNode, aLinkingContent)) {
      // The current sheet comes before us, and it better be the first
      // such, because now we break
      break;
    }
  }

  ++insertionPoint; // adjust the index to the spot we want to insert in

  // XXX <meta> elements do not implement nsIStyleSheetLinkingElement;
  // need to fix this for them to be ordered correctly.
  nsCOMPtr<nsIStyleSheetLinkingElement>
    linkingElement = do_QueryInterface(aLinkingContent);
  if (linkingElement) {
    linkingElement->SetStyleSheet(aSheet); // This sets the ownerNode on the sheet
  }

  aDocument->BeginUpdate(UPDATE_STYLE);
  aDocument->InsertStyleSheetAt(aSheet, insertionPoint);
  aDocument->EndUpdate(UPDATE_STYLE);
  LOG(("  Inserting into document at position %d", insertionPoint));

  return NS_OK;
}

/**
 * InsertChildSheet handles ordering of @import-ed sheet in their
 * parent sheets.  Here we want to just insert based on order of the
 * @import rules that imported the sheets.  In theory we can't just
 * append to the end because the CSSOM can insert @import rules.  In
 * practice, we get the call to load the child sheet before the CSSOM
 * has finished inserting the @import rule, so we have no idea where
 * to put it anyway.  So just append for now.
 */
nsresult
Loader::InsertChildSheet(CSSStyleSheet* aSheet,
                         CSSStyleSheet* aParentSheet,
                         ImportRule* aParentRule)
{
  LOG(("css::Loader::InsertChildSheet"));
  NS_PRECONDITION(aSheet, "Nothing to insert");
  NS_PRECONDITION(aParentSheet, "Need a parent to insert into");
  NS_PRECONDITION(aParentSheet, "How did we get imported?");

  // child sheets should always start out enabled, even if they got
  // cloned off of top-level sheets which were disabled
  aSheet->SetEnabled(true);

  aParentSheet->AppendStyleSheet(aSheet);
  aParentRule->SetSheet(aSheet); // This sets the ownerRule on the sheet

  LOG(("  Inserting into parent sheet"));
  //  LOG(("  Inserting into parent sheet at position %d", insertionPoint));

  return NS_OK;
}

/**
 * LoadSheet handles the actual load of a sheet.  If the load is
 * supposed to be synchronous it just opens a channel synchronously
 * using the given uri, wraps the resulting stream in a converter
 * stream and calls ParseSheet.  Otherwise it tries to look for an
 * existing load for this URI and piggyback on it.  Failing all that,
 * a new load is kicked off asynchronously.
 */
nsresult
Loader::LoadSheet(SheetLoadData* aLoadData, StyleSheetState aSheetState)
{
  LOG(("css::Loader::LoadSheet"));
  NS_PRECONDITION(aLoadData, "Need a load data");
  NS_PRECONDITION(aLoadData->mURI, "Need a URI to load");
  NS_PRECONDITION(aLoadData->mSheet, "Need a sheet to load into");
  NS_PRECONDITION(aSheetState != eSheetComplete, "Why bother?");
  NS_PRECONDITION(!aLoadData->mUseSystemPrincipal || aLoadData->mSyncLoad,
                  "Shouldn't use system principal for async loads");
  NS_ASSERTION(mSheets, "mLoadingDatas should be initialized by now.");

  LOG_URI("  Load from: '%s'", aLoadData->mURI);

  nsresult rv = NS_OK;

  if (!mDocument && !aLoadData->mIsNonDocumentSheet) {
    // No point starting the load; just release all the data and such.
    LOG_WARN(("  No document and not non-document sheet; pre-dropping load"));
    SheetComplete(aLoadData, NS_BINDING_ABORTED);
    return NS_BINDING_ABORTED;
  }

  bool inherit = false;
  nsIPrincipal* triggeringPrincipal = aLoadData->mLoaderPrincipal;
  if (triggeringPrincipal) {
    rv = NS_URIChainHasFlags(aLoadData->mURI,
                             nsIProtocolHandler::URI_INHERITS_SECURITY_CONTEXT,
                             &inherit);
    inherit =
      ((NS_SUCCEEDED(rv) && inherit) ||
       (nsContentUtils::URIIsLocalFile(aLoadData->mURI) &&
        NS_SUCCEEDED(aLoadData->mLoaderPrincipal->
                     CheckMayLoad(aLoadData->mURI, false, false))));
  }
  else {
    triggeringPrincipal = nsContentUtils::GetSystemPrincipal();
  }

  if (aLoadData->mSyncLoad) {
    LOG(("  Synchronous load"));
    NS_ASSERTION(!aLoadData->mObserver, "Observer for a sync load?");
    NS_ASSERTION(aSheetState == eSheetNeedsParser,
                 "Sync loads can't reuse existing async loads");

    // Create a nsIUnicharStreamLoader instance to which we will feed
    // the data from the sync load.  Do this before creating the
    // channel to make error recovery simpler.
    nsCOMPtr<nsIUnicharStreamLoader> streamLoader;
    rv = NS_NewUnicharStreamLoader(getter_AddRefs(streamLoader), aLoadData);
    if (NS_FAILED(rv)) {
      LOG_ERROR(("  Failed to create stream loader for sync load"));
      SheetComplete(aLoadData, rv);
      return rv;
    }

    if (mDocument) {
      mozilla::net::PredictorLearn(aLoadData->mURI, mDocument->GetDocumentURI(),
                                   nsINetworkPredictor::LEARN_LOAD_SUBRESOURCE,
                                   mDocument);
    }

    // Just load it
    nsCOMPtr<nsIChannel> channel;
    // Note that we are calling NS_NewChannelWithTriggeringPrincipal() with both
    // a node and a principal.
    // This is because of a case where the node is the document being styled and
    // the principal is the stylesheet (perhaps from a different origin) that is
    // applying the styles.
    if (aLoadData->mRequestingNode) {
      rv = NS_NewChannelWithTriggeringPrincipal(getter_AddRefs(channel),
                                                aLoadData->mURI,
                                                aLoadData->mRequestingNode,
                                                triggeringPrincipal,
                                                nsILoadInfo::SEC_NORMAL,
                                                nsIContentPolicy::TYPE_OTHER);
    }
    else {
      // either we are loading something inside a document, in which case
      // we should always have a requestingNode, or we are loading something
      // outside a document, in which case the triggeringPrincipal
      // should always be the systemPrincipal.
      MOZ_ASSERT(nsContentUtils::IsSystemPrincipal(triggeringPrincipal));
      rv = NS_NewChannel(getter_AddRefs(channel),
                         aLoadData->mURI,
                         triggeringPrincipal,
                         nsILoadInfo::SEC_NORMAL,
                         nsIContentPolicy::TYPE_OTHER);
    }
    NS_ENSURE_SUCCESS(rv, rv);

    nsCOMPtr<nsIInputStream> stream;
    rv = channel->Open(getter_AddRefs(stream));

    if (NS_FAILED(rv)) {
      LOG_ERROR(("  Failed to open URI synchronously"));
      SheetComplete(aLoadData, rv);
      return rv;
    }

    // Force UA sheets to be UTF-8.
    // XXX this is only necessary because the default in
    // SheetLoadData::OnDetermineCharset is wrong (bug 521039).
    channel->SetContentCharset(NS_LITERAL_CSTRING("UTF-8"));

    // Manually feed the streamloader the contents of the stream.
    // This will call back into OnStreamComplete
    // and thence to ParseSheet.  Regardless of whether this fails,
    // SheetComplete has been called.
    return nsSyncLoadService::PushSyncStreamToListener(stream,
                                                       streamLoader,
                                                       channel);
  }

  SheetLoadData* existingData = nullptr;

  URIPrincipalReferrerPolicyAndCORSModeHashKey key(aLoadData->mURI,
                                     aLoadData->mLoaderPrincipal,
                                     aLoadData->mSheet->GetCORSMode(),
                                     aLoadData->mSheet->GetReferrerPolicy());
  if (aSheetState == eSheetLoading) {
    mSheets->mLoadingDatas.Get(&key, &existingData);
    NS_ASSERTION(existingData, "CreateSheet lied about the state");
  }
  else if (aSheetState == eSheetPending){
    mSheets->mPendingDatas.Get(&key, &existingData);
    NS_ASSERTION(existingData, "CreateSheet lied about the state");
  }

  if (existingData) {
    LOG(("  Glomming on to existing load"));
    SheetLoadData* data = existingData;
    while (data->mNext) {
      data = data->mNext;
    }
    data->mNext = aLoadData; // transfer ownership
    if (aSheetState == eSheetPending && !aLoadData->mWasAlternate) {
      // Kick the load off; someone cares about it right away

#ifdef DEBUG
      SheetLoadData* removedData;
      NS_ASSERTION(mSheets->mPendingDatas.Get(&key, &removedData) &&
                   removedData == existingData,
                   "Bad pending table.");
#endif

      mSheets->mPendingDatas.Remove(&key);

      LOG(("  Forcing load of pending data"));
      return LoadSheet(existingData, eSheetNeedsParser);
    }
    // All done here; once the load completes we'll be marked complete
    // automatically
    return NS_OK;
  }

#ifdef DEBUG
  mSyncCallback = true;
#endif
  nsCOMPtr<nsILoadGroup> loadGroup;
  if (mDocument) {
    loadGroup = mDocument->GetDocumentLoadGroup();
    NS_ASSERTION(loadGroup,
                 "No loadgroup for stylesheet; onload will fire early");
  }

  nsLoadFlags securityFlags = nsILoadInfo::SEC_NORMAL;
  if (inherit) {
    securityFlags |= nsILoadInfo::SEC_FORCE_INHERIT_PRINCIPAL;
  }

  nsCOMPtr<nsIChannel> channel;
  // Note we are calling NS_NewChannelWithTriggeringPrincipal here with a node
  // and a principal. This is because of a case where the node is the document
  // being styled and the principal is the stylesheet (perhaps from a different
  // origin)  that is applying the styles.
  if (aLoadData->mRequestingNode) {
    rv = NS_NewChannelWithTriggeringPrincipal(getter_AddRefs(channel),
                                              aLoadData->mURI,
                                              aLoadData->mRequestingNode,
                                              triggeringPrincipal,
                                              securityFlags,
                                              nsIContentPolicy::TYPE_STYLESHEET,
                                              loadGroup,
                                              nullptr,   // aCallbacks
                                              nsIChannel::LOAD_NORMAL |
                                              nsIChannel::LOAD_CLASSIFY_URI);
  }
  else {
    // either we are loading something inside a document, in which case
    // we should always have a requestingNode, or we are loading something
    // outside a document, in which case the triggeringPrincipal
    // should always be the systemPrincipal.
    MOZ_ASSERT(nsContentUtils::IsSystemPrincipal(triggeringPrincipal));
    rv = NS_NewChannel(getter_AddRefs(channel),
                       aLoadData->mURI,
                       triggeringPrincipal,
                       securityFlags,
                       nsIContentPolicy::TYPE_STYLESHEET,
                       loadGroup,
                       nullptr,   // aCallbacks
                       nsIChannel::LOAD_NORMAL |
                       nsIChannel::LOAD_CLASSIFY_URI);
  }

  if (NS_FAILED(rv)) {
#ifdef DEBUG
    mSyncCallback = false;
#endif
    LOG_ERROR(("  Failed to create channel"));
    SheetComplete(aLoadData, rv);
    return rv;
  }

  if (!aLoadData->mWasAlternate) {
    nsCOMPtr<nsIClassOfService> cos(do_QueryInterface(channel));
    if (cos) {
      cos->AddClassFlags(nsIClassOfService::Leader);
    }
  }

  nsCOMPtr<nsIHttpChannel> httpChannel(do_QueryInterface(channel));
  if (httpChannel) {
    // send a minimal Accept header for text/css
    httpChannel->SetRequestHeader(NS_LITERAL_CSTRING("Accept"),
                                  NS_LITERAL_CSTRING("text/css,*/*;q=0.1"),
                                  false);
    nsCOMPtr<nsIURI> referrerURI = aLoadData->GetReferrerURI();
    if (referrerURI)
      httpChannel->SetReferrerWithPolicy(referrerURI,
                                         aLoadData->mSheet->GetReferrerPolicy());

    // Set the initiator type
    nsCOMPtr<nsITimedChannel> timedChannel(do_QueryInterface(httpChannel));
    if (timedChannel) {
      if (aLoadData->mParentData) {
        timedChannel->SetInitiatorType(NS_LITERAL_STRING("css"));
      } else {
        timedChannel->SetInitiatorType(NS_LITERAL_STRING("link"));
      }
    }
  }

  // Now tell the channel we expect text/css data back....  We do
  // this before opening it, so it's only treated as a hint.
  channel->SetContentType(NS_LITERAL_CSTRING("text/css"));

  // We don't have to hold on to the stream loader.  The ownership
  // model is: Necko owns the stream loader, which owns the load data,
  // which owns us
  nsCOMPtr<nsIUnicharStreamLoader> streamLoader;
  rv = NS_NewUnicharStreamLoader(getter_AddRefs(streamLoader), aLoadData);
  if (NS_FAILED(rv)) {
#ifdef DEBUG
    mSyncCallback = false;
#endif
    LOG_ERROR(("  Failed to create stream loader"));
    SheetComplete(aLoadData, rv);
    return rv;
  }

  nsCOMPtr<nsIStreamListener> channelListener;
  CORSMode ourCORSMode = aLoadData->mSheet->GetCORSMode();
  if (ourCORSMode != CORS_NONE) {
    bool withCredentials = (ourCORSMode == CORS_USE_CREDENTIALS);
    LOG(("  Doing CORS-enabled load; credentials %d", withCredentials));
    nsRefPtr<nsCORSListenerProxy> corsListener =
      new nsCORSListenerProxy(streamLoader, aLoadData->mLoaderPrincipal,
			      withCredentials);
    rv = corsListener->Init(channel, DataURIHandling::Allow);
    if (NS_FAILED(rv)) {
#ifdef DEBUG
      mSyncCallback = false;
#endif
      LOG_ERROR(("  Initial CORS check failed"));
      SheetComplete(aLoadData, rv);
      return rv;
    }
    channelListener = corsListener;
  } else {
    channelListener = streamLoader;
  }

  if (mDocument) {
    mozilla::net::PredictorLearn(aLoadData->mURI, mDocument->GetDocumentURI(),
                                 nsINetworkPredictor::LEARN_LOAD_SUBRESOURCE,
                                 mDocument);
  }

  rv = channel->AsyncOpen(channelListener, nullptr);

#ifdef DEBUG
  mSyncCallback = false;
#endif

  if (NS_FAILED(rv)) {
    LOG_ERROR(("  Failed to create stream loader"));
    SheetComplete(aLoadData, rv);
    return rv;
  }

  mSheets->mLoadingDatas.Put(&key, aLoadData);
  aLoadData->mIsLoading = true;

  return NS_OK;
}

/**
 * ParseSheet handles parsing the data stream.  The main idea here is
 * to push the current load data onto the parse stack before letting
 * the CSS parser at the data stream.  That lets us handle @import
 * correctly.
 */
nsresult
Loader::ParseSheet(const nsAString& aInput,
                   SheetLoadData* aLoadData,
                   bool& aCompleted)
{
  LOG(("css::Loader::ParseSheet"));
  NS_PRECONDITION(aLoadData, "Must have load data");
  NS_PRECONDITION(aLoadData->mSheet, "Must have sheet to parse into");

  aCompleted = false;

  nsCSSParser parser(this, aLoadData->mSheet);

  // Push our load data on the stack so any kids can pick it up
  mParsingDatas.AppendElement(aLoadData);
  nsIURI* sheetURI = aLoadData->mSheet->GetSheetURI();
  nsIURI* baseURI = aLoadData->mSheet->GetBaseURI();
  nsresult rv = parser.ParseSheet(aInput, sheetURI, baseURI,
                                  aLoadData->mSheet->Principal(),
                                  aLoadData->mLineNumber,
                                  aLoadData->mAllowUnsafeRules);
  mParsingDatas.RemoveElementAt(mParsingDatas.Length() - 1);

  if (NS_FAILED(rv)) {
    LOG_ERROR(("  Low-level error in parser!"));
    SheetComplete(aLoadData, rv);
    return rv;
  }

  NS_ASSERTION(aLoadData->mPendingChildren == 0 || !aLoadData->mSyncLoad,
               "Sync load has leftover pending children!");

  if (aLoadData->mPendingChildren == 0) {
    LOG(("  No pending kids from parse"));
    aCompleted = true;
    SheetComplete(aLoadData, NS_OK);
  }
  // Otherwise, the children are holding strong refs to the data and
  // will call SheetComplete() on it when they complete.

  return NS_OK;
}

/**
 * SheetComplete is the do-it-all cleanup function.  It removes the
 * load data from the "loading" hashtable, adds the sheet to the
 * "completed" hashtable, massages the XUL cache, handles siblings of
 * the load data (other loads for the same URI), handles unblocking
 * blocked parent loads as needed, and most importantly calls
 * NS_RELEASE on the load data to destroy the whole mess.
 */
void
Loader::SheetComplete(SheetLoadData* aLoadData, nsresult aStatus)
{
  LOG(("css::Loader::SheetComplete"));

  // 8 is probably big enough for all our common cases.  It's not likely that
  // imports will nest more than 8 deep, and multiple sheets with the same URI
  // are rare.
  nsAutoTArray<nsRefPtr<SheetLoadData>, 8> datasToNotify;
  DoSheetComplete(aLoadData, aStatus, datasToNotify);

  // Now it's safe to go ahead and notify observers
  uint32_t count = datasToNotify.Length();
  mDatasToNotifyOn += count;
  for (uint32_t i = 0; i < count; ++i) {
    --mDatasToNotifyOn;

    SheetLoadData* data = datasToNotify[i];
    NS_ASSERTION(data && data->mMustNotify, "How did this data get here?");
    if (data->mObserver) {
      LOG(("  Notifying observer 0x%x for data 0x%x.  wasAlternate: %d",
           data->mObserver.get(), data, data->mWasAlternate));
      data->mObserver->StyleSheetLoaded(data->mSheet, data->mWasAlternate,
                                        aStatus);
    }

    nsTObserverArray<nsCOMPtr<nsICSSLoaderObserver> >::ForwardIterator iter(mObservers);
    nsCOMPtr<nsICSSLoaderObserver> obs;
    while (iter.HasMore()) {
      obs = iter.GetNext();
      LOG(("  Notifying global observer 0x%x for data 0x%s.  wasAlternate: %d",
           obs.get(), data, data->mWasAlternate));
      obs->StyleSheetLoaded(data->mSheet, data->mWasAlternate, aStatus);
    }
  }

  if (mSheets->mLoadingDatas.Count() == 0 && mSheets->mPendingDatas.Count() > 0) {
    LOG(("  No more loading sheets; starting alternates"));
    StartAlternateLoads();
  }
}

void
Loader::DoSheetComplete(SheetLoadData* aLoadData, nsresult aStatus,
                        LoadDataArray& aDatasToNotify)
{
  LOG(("css::Loader::DoSheetComplete"));
  NS_PRECONDITION(aLoadData, "Must have a load data!");
  NS_PRECONDITION(aLoadData->mSheet, "Must have a sheet");
  NS_ASSERTION(mSheets, "mLoadingDatas should be initialized by now.");

  LOG(("Load completed, status: 0x%x", aStatus));

  // Twiddle the hashtables
  if (aLoadData->mURI) {
    LOG_URI("  Finished loading: '%s'", aLoadData->mURI);
    // Remove the data from the list of loading datas
    if (aLoadData->mIsLoading) {
      URIPrincipalReferrerPolicyAndCORSModeHashKey key(aLoadData->mURI,
                                         aLoadData->mLoaderPrincipal,
                                         aLoadData->mSheet->GetCORSMode(),
                                         aLoadData->mSheet->GetReferrerPolicy());
#ifdef DEBUG
      SheetLoadData *loadingData;
      NS_ASSERTION(mSheets->mLoadingDatas.Get(&key, &loadingData) &&
                   loadingData == aLoadData,
                   "Bad loading table");
#endif

      mSheets->mLoadingDatas.Remove(&key);
      aLoadData->mIsLoading = false;
    }
  }

  // Go through and deal with the whole linked list.
  SheetLoadData* data = aLoadData;
  while (data) {
    if (!data->mSheetAlreadyComplete) {
      // If mSheetAlreadyComplete, then the sheet could well be modified between
      // when we posted the async call to SheetComplete and now, since the sheet
      // was page-accessible during that whole time.
      MOZ_ASSERT(!data->mSheet->IsModified(),
                 "should not get marked modified during parsing");
      data->mSheet->SetComplete();
      data->ScheduleLoadEventIfNeeded(aStatus);
    }
    if (data->mMustNotify && (data->mObserver || !mObservers.IsEmpty())) {
      // Don't notify here so we don't trigger script.  Remember the
      // info we need to notify, then do it later when it's safe.
      aDatasToNotify.AppendElement(data);

      // On append failure, just press on.  We'll fail to notify the observer,
      // but not much we can do about that....
    }

    NS_ASSERTION(!data->mParentData ||
                 data->mParentData->mPendingChildren != 0,
                 "Broken pending child count on our parent");

    // If we have a parent, our parent is no longer being parsed, and
    // we are the last pending child, then our load completion
    // completes the parent too.  Note that the parent _can_ still be
    // being parsed (eg if the child (us) failed to open the channel
    // or some such).
    if (data->mParentData &&
        --(data->mParentData->mPendingChildren) == 0 &&
        !mParsingDatas.Contains(data->mParentData)) {
      DoSheetComplete(data->mParentData, aStatus, aDatasToNotify);
    }

    data = data->mNext;
  }

  // Now that it's marked complete, put the sheet in our cache.
  // If we ever start doing this for failure aStatus, we'll need to
  // adjust the PostLoadEvent code that thinks anything already
  // complete must have loaded succesfully.
  if (NS_SUCCEEDED(aStatus) && aLoadData->mURI) {
    // Pick our sheet to cache carefully.  Ideally, we want to cache
    // one of the sheets that will be kept alive by a document or
    // parent sheet anyway, so that if someone then accesses it via
    // CSSOM we won't have extra clones of the inner lying around.
    data = aLoadData;
    CSSStyleSheet* sheet = aLoadData->mSheet;
    while (data) {
      if (data->mSheet->GetParentSheet() || data->mSheet->GetOwnerNode()) {
        sheet = data->mSheet;
        break;
      }
      data = data->mNext;
    }
#ifdef MOZ_XUL
    if (IsChromeURI(aLoadData->mURI)) {
      nsXULPrototypeCache* cache = nsXULPrototypeCache::GetInstance();
      if (cache && cache->IsEnabled()) {
        if (!cache->GetStyleSheet(aLoadData->mURI)) {
          LOG(("  Putting sheet in XUL prototype cache"));
          NS_ASSERTION(sheet->IsComplete(),
                       "Should only be caching complete sheets");
          cache->PutStyleSheet(sheet);
        }
      }
    }
    else {
#endif
      URIPrincipalReferrerPolicyAndCORSModeHashKey key(aLoadData->mURI,
                                         aLoadData->mLoaderPrincipal,
                                         aLoadData->mSheet->GetCORSMode(),
                                         aLoadData->mSheet->GetReferrerPolicy());
      NS_ASSERTION(sheet->IsComplete(),
                   "Should only be caching complete sheets");
      mSheets->mCompleteSheets.Put(&key, sheet);
#ifdef MOZ_XUL
    }
#endif
  }

  NS_RELEASE(aLoadData);  // this will release parents and siblings and all that
}

nsresult
Loader::LoadInlineStyle(nsIContent* aElement,
                        const nsAString& aBuffer,
                        uint32_t aLineNumber,
                        const nsAString& aTitle,
                        const nsAString& aMedia,
                        Element* aScopeElement,
                        nsICSSLoaderObserver* aObserver,
                        bool* aCompleted,
                        bool* aIsAlternate)
{
  LOG(("css::Loader::LoadInlineStyle"));
  NS_ASSERTION(mParsingDatas.Length() == 0, "We're in the middle of a parse?");

  *aCompleted = true;

  if (!mEnabled) {
    LOG_WARN(("  Not enabled"));
    return NS_ERROR_NOT_AVAILABLE;
  }

  NS_ENSURE_TRUE(mDocument, NS_ERROR_NOT_INITIALIZED);

  nsCOMPtr<nsIStyleSheetLinkingElement> owningElement(do_QueryInterface(aElement));
  NS_ASSERTION(owningElement, "Element is not a style linking element!");

  // Since we're not planning to load a URI, no need to hand a principal to the
  // load data or to CreateSheet().  Also, OK to use CORS_NONE for the CORS
  // mode and mDocument's ReferrerPolicy.
  StyleSheetState state;
  nsRefPtr<CSSStyleSheet> sheet;
  nsresult rv = CreateSheet(nullptr, aElement, nullptr, CORS_NONE,
                            mDocument->GetReferrerPolicy(), false, false,
                            aTitle, state, aIsAlternate, getter_AddRefs(sheet));
  NS_ENSURE_SUCCESS(rv, rv);
  NS_ASSERTION(state == eSheetNeedsParser,
               "Inline sheets should not be cached");

  LOG(("  Sheet is alternate: %d", *aIsAlternate));

  PrepareSheet(sheet, aTitle, aMedia, nullptr, aScopeElement, *aIsAlternate);

  if (aElement->HasFlag(NODE_IS_IN_SHADOW_TREE)) {
    ShadowRoot* containingShadow = aElement->GetContainingShadow();
    MOZ_ASSERT(containingShadow);
    containingShadow->InsertSheet(sheet, aElement);
  } else {
    rv = InsertSheetInDoc(sheet, aElement, mDocument);
    NS_ENSURE_SUCCESS(rv, rv);
  }

  SheetLoadData* data = new SheetLoadData(this, aTitle, nullptr, sheet,
                                          owningElement, *aIsAlternate,
                                          aObserver, nullptr, static_cast<nsINode*>(aElement));

  // We never actually load this, so just set its principal directly
  sheet->SetPrincipal(aElement->NodePrincipal());

  NS_ADDREF(data);
  data->mLineNumber = aLineNumber;
  // Parse completion releases the load data
  rv = ParseSheet(aBuffer, data, *aCompleted);
  NS_ENSURE_SUCCESS(rv, rv);

  // If aCompleted is true, |data| may well be deleted by now.
  if (!*aCompleted) {
    data->mMustNotify = true;
  }
  return rv;
}

nsresult
Loader::LoadStyleLink(nsIContent* aElement,
                      nsIURI* aURL,
                      const nsAString& aTitle,
                      const nsAString& aMedia,
                      bool aHasAlternateRel,
                      CORSMode aCORSMode,
                      ReferrerPolicy aReferrerPolicy,
                      nsICSSLoaderObserver* aObserver,
                      bool* aIsAlternate)
{
  LOG(("css::Loader::LoadStyleLink"));
  NS_PRECONDITION(aURL, "Must have URL to load");
  NS_ASSERTION(mParsingDatas.Length() == 0, "We're in the middle of a parse?");

  LOG_URI("  Link uri: '%s'", aURL);
  LOG(("  Link title: '%s'", NS_ConvertUTF16toUTF8(aTitle).get()));
  LOG(("  Link media: '%s'", NS_ConvertUTF16toUTF8(aMedia).get()));
  LOG(("  Link alternate rel: %d", aHasAlternateRel));

  if (!mEnabled) {
    LOG_WARN(("  Not enabled"));
    return NS_ERROR_NOT_AVAILABLE;
  }

  NS_ENSURE_TRUE(mDocument, NS_ERROR_NOT_INITIALIZED);

  nsIPrincipal* principal =
    aElement ? aElement->NodePrincipal() : mDocument->NodePrincipal();

  nsISupports* context = aElement;
  if (!context) {
    context = mDocument;
  }
  nsresult rv = CheckLoadAllowed(principal, aURL, context);
  if (NS_FAILED(rv)) return rv;

  LOG(("  Passed load check"));

  StyleSheetState state;
  nsRefPtr<CSSStyleSheet> sheet;
  rv = CreateSheet(aURL, aElement, principal, aCORSMode,
                   aReferrerPolicy, false,
                   aHasAlternateRel, aTitle, state, aIsAlternate,
                   getter_AddRefs(sheet));
  NS_ENSURE_SUCCESS(rv, rv);

  LOG(("  Sheet is alternate: %d", *aIsAlternate));

  PrepareSheet(sheet, aTitle, aMedia, nullptr, nullptr, *aIsAlternate);

  rv = InsertSheetInDoc(sheet, aElement, mDocument);
  NS_ENSURE_SUCCESS(rv, rv);

  nsCOMPtr<nsIStyleSheetLinkingElement> owningElement(do_QueryInterface(aElement));

  if (state == eSheetComplete) {
    LOG(("  Sheet already complete: 0x%p",
         static_cast<void*>(sheet.get())));
    if (aObserver || !mObservers.IsEmpty() || owningElement) {
      rv = PostLoadEvent(aURL, sheet, aObserver, *aIsAlternate,
                         owningElement);
      return rv;
    }

    return NS_OK;
  }

  // Now we need to actually load it
  nsCOMPtr<nsINode> requestingNode = do_QueryInterface(context);
  SheetLoadData* data = new SheetLoadData(this, aTitle, aURL, sheet,
                                          owningElement, *aIsAlternate,
                                          aObserver, principal, requestingNode);
  NS_ADDREF(data);

  // If we have to parse and it's an alternate non-inline, defer it
  if (aURL && state == eSheetNeedsParser && mSheets->mLoadingDatas.Count() != 0 &&
      *aIsAlternate) {
    LOG(("  Deferring alternate sheet load"));
    URIPrincipalReferrerPolicyAndCORSModeHashKey key(data->mURI,
                                                     data->mLoaderPrincipal,
                                                     data->mSheet->GetCORSMode(),
                                                     data->mSheet->GetReferrerPolicy());
    mSheets->mPendingDatas.Put(&key, data);

    data->mMustNotify = true;
    return NS_OK;
  }

  // Load completion will free the data
  rv = LoadSheet(data, state);
  NS_ENSURE_SUCCESS(rv, rv);

  data->mMustNotify = true;
  return rv;
}

static bool
HaveAncestorDataWithURI(SheetLoadData *aData, nsIURI *aURI)
{
  if (!aData->mURI) {
    // Inline style; this won't have any ancestors
    MOZ_ASSERT(!aData->mParentData,
               "How does inline style have a parent?");
    return false;
  }

  bool equal;
  if (NS_FAILED(aData->mURI->Equals(aURI, &equal)) || equal) {
    return true;
  }

  // Datas down the mNext chain have the same URI as aData, so we
  // don't have to compare to them.  But they might have different
  // parents, and we have to check all of those.
  while (aData) {
    if (aData->mParentData &&
        HaveAncestorDataWithURI(aData->mParentData, aURI)) {
      return true;
    }

    aData = aData->mNext;
  }

  return false;
}

nsresult
Loader::LoadChildSheet(CSSStyleSheet* aParentSheet,
                       nsIURI* aURL,
                       nsMediaList* aMedia,
                       ImportRule* aParentRule)
{
  LOG(("css::Loader::LoadChildSheet"));
  NS_PRECONDITION(aURL, "Must have a URI to load");
  NS_PRECONDITION(aParentSheet, "Must have a parent sheet");

  if (!mEnabled) {
    LOG_WARN(("  Not enabled"));
    return NS_ERROR_NOT_AVAILABLE;
  }

  LOG_URI("  Child uri: '%s'", aURL);

  nsCOMPtr<nsIDOMNode> owningNode;

  // check for an owning document: if none, don't bother walking up the parent
  // sheets
  if (aParentSheet->GetOwningDocument()) {
    nsCOMPtr<nsIDOMStyleSheet> nextParentSheet(aParentSheet);
    NS_ENSURE_TRUE(nextParentSheet, NS_ERROR_FAILURE); //Not a stylesheet!?

    nsCOMPtr<nsIDOMStyleSheet> topSheet;
    //traverse our way to the top-most sheet
    do {
      topSheet.swap(nextParentSheet);
      topSheet->GetParentStyleSheet(getter_AddRefs(nextParentSheet));
    } while (nextParentSheet);

    topSheet->GetOwnerNode(getter_AddRefs(owningNode));
  }

  nsISupports* context = owningNode;
  if (!context) {
    context = mDocument;
  }

  nsIPrincipal* principal = aParentSheet->Principal();
  nsresult rv = CheckLoadAllowed(principal, aURL, context);
  if (NS_FAILED(rv)) return rv;

  LOG(("  Passed load check"));

  SheetLoadData* parentData = nullptr;
  nsCOMPtr<nsICSSLoaderObserver> observer;

  int32_t count = mParsingDatas.Length();
  if (count > 0) {
    LOG(("  Have a parent load"));
    parentData = mParsingDatas.ElementAt(count - 1);
    // Check for cycles
    if (HaveAncestorDataWithURI(parentData, aURL)) {
      // Houston, we have a loop, blow off this child and pretend this never
      // happened
      LOG_ERROR(("  @import cycle detected, dropping load"));
      return NS_OK;
    }

    NS_ASSERTION(parentData->mSheet == aParentSheet,
                 "Unexpected call to LoadChildSheet");
  } else {
    LOG(("  No parent load; must be CSSOM"));
    // No parent load data, so the sheet will need to be notified when
    // we finish, if it can be, if we do the load asynchronously.
    observer = aParentSheet;
  }

  // Now that we know it's safe to load this (passes security check and not a
  // loop) do so.
  nsRefPtr<CSSStyleSheet> sheet;
  bool isAlternate;
  StyleSheetState state;
  const nsSubstring& empty = EmptyString();
  // For now, use CORS_NONE for child sheets
  rv = CreateSheet(aURL, nullptr, principal, CORS_NONE,
                   aParentSheet->GetReferrerPolicy(),
                   parentData ? parentData->mSyncLoad : false,
                   false, empty, state, &isAlternate, getter_AddRefs(sheet));
  NS_ENSURE_SUCCESS(rv, rv);

  PrepareSheet(sheet, empty, empty, aMedia, nullptr, isAlternate);

  rv = InsertChildSheet(sheet, aParentSheet, aParentRule);
  NS_ENSURE_SUCCESS(rv, rv);

  if (state == eSheetComplete) {
    LOG(("  Sheet already complete"));
    // We're completely done.  No need to notify, even, since the
    // @import rule addition/modification will trigger the right style
    // changes automatically.
    return NS_OK;
  }

  nsCOMPtr<nsINode> requestingNode = do_QueryInterface(context);
  SheetLoadData* data = new SheetLoadData(this, aURL, sheet, parentData,
                                          observer, principal, requestingNode);

  NS_ADDREF(data);
  bool syncLoad = data->mSyncLoad;

  // Load completion will release the data
  rv = LoadSheet(data, state);
  NS_ENSURE_SUCCESS(rv, rv);

  // If syncLoad is true, |data| will be deleted by now.
  if (!syncLoad) {
    data->mMustNotify = true;
  }
  return rv;
}

nsresult
Loader::LoadSheetSync(nsIURI* aURL, bool aAllowUnsafeRules,
                      bool aUseSystemPrincipal,
                      CSSStyleSheet** aSheet)
{
  LOG(("css::Loader::LoadSheetSync"));
  return InternalLoadNonDocumentSheet(aURL, aAllowUnsafeRules,
                                      aUseSystemPrincipal, nullptr,
                                      EmptyCString(), aSheet, nullptr);
}

nsresult
Loader::LoadSheet(nsIURI* aURL,
                  nsIPrincipal* aOriginPrincipal,
                  const nsCString& aCharset,
                  nsICSSLoaderObserver* aObserver,
                  CSSStyleSheet** aSheet)
{
  LOG(("css::Loader::LoadSheet(aURL, aObserver, aSheet) api call"));
  NS_PRECONDITION(aSheet, "aSheet is null");
  return InternalLoadNonDocumentSheet(aURL, false, false,
                                      aOriginPrincipal, aCharset,
                                      aSheet, aObserver);
}

nsresult
Loader::LoadSheet(nsIURI* aURL,
                  nsIPrincipal* aOriginPrincipal,
                  const nsCString& aCharset,
                  nsICSSLoaderObserver* aObserver,
                  CORSMode aCORSMode,
                  ReferrerPolicy aReferrerPolicy)
{
  LOG(("css::Loader::LoadSheet(aURL, aObserver) api call"));
  return InternalLoadNonDocumentSheet(aURL, false, false,
                                      aOriginPrincipal, aCharset,
                                      nullptr, aObserver, aCORSMode,
                                      aReferrerPolicy);
}

nsresult
Loader::InternalLoadNonDocumentSheet(nsIURI* aURL,
                                     bool aAllowUnsafeRules,
                                     bool aUseSystemPrincipal,
                                     nsIPrincipal* aOriginPrincipal,
                                     const nsCString& aCharset,
                                     CSSStyleSheet** aSheet,
                                     nsICSSLoaderObserver* aObserver,
                                     CORSMode aCORSMode,
                                     ReferrerPolicy aReferrerPolicy)
{
  NS_PRECONDITION(aURL, "Must have a URI to load");
  NS_PRECONDITION(aSheet || aObserver, "Sheet and observer can't both be null");
  NS_PRECONDITION(!aUseSystemPrincipal || !aObserver,
                  "Shouldn't load system-principal sheets async");
  NS_ASSERTION(mParsingDatas.Length() == 0, "We're in the middle of a parse?");

  LOG_URI("  Non-document sheet uri: '%s'", aURL);

  if (aSheet) {
    *aSheet = nullptr;
  }

  if (!mEnabled) {
    LOG_WARN(("  Not enabled"));
    return NS_ERROR_NOT_AVAILABLE;
  }

  nsresult rv = CheckLoadAllowed(aOriginPrincipal, aURL, mDocument);
  if (NS_FAILED(rv)) {
    return rv;
  }

  StyleSheetState state;
  bool isAlternate;
  nsRefPtr<CSSStyleSheet> sheet;
  bool syncLoad = (aObserver == nullptr);
  const nsSubstring& empty = EmptyString();

  rv = CreateSheet(aURL, nullptr, aOriginPrincipal, aCORSMode,
                   aReferrerPolicy, syncLoad, false,
                   empty, state, &isAlternate, getter_AddRefs(sheet));
  NS_ENSURE_SUCCESS(rv, rv);

  PrepareSheet(sheet, empty, empty, nullptr, nullptr, isAlternate);

  if (state == eSheetComplete) {
    LOG(("  Sheet already complete"));
    if (aObserver || !mObservers.IsEmpty()) {
      rv = PostLoadEvent(aURL, sheet, aObserver, false, nullptr);
    }
    if (aSheet) {
      sheet.swap(*aSheet);
    }
    return rv;
  }

  SheetLoadData* data =
    new SheetLoadData(this, aURL, sheet, syncLoad, aAllowUnsafeRules,
                      aUseSystemPrincipal, aCharset, aObserver,
                      aOriginPrincipal, mDocument);

  NS_ADDREF(data);
  rv = LoadSheet(data, state);
  NS_ENSURE_SUCCESS(rv, rv);

  if (aSheet) {
    sheet.swap(*aSheet);
  }
  if (aObserver) {
    data->mMustNotify = true;
  }

  return rv;
}

nsresult
Loader::PostLoadEvent(nsIURI* aURI,
                      CSSStyleSheet* aSheet,
                      nsICSSLoaderObserver* aObserver,
                      bool aWasAlternate,
                      nsIStyleSheetLinkingElement* aElement)
{
  LOG(("css::Loader::PostLoadEvent"));
  NS_PRECONDITION(aSheet, "Must have sheet");
  NS_PRECONDITION(aObserver || !mObservers.IsEmpty() || aElement,
                  "Must have observer or element");

  nsRefPtr<SheetLoadData> evt =
    new SheetLoadData(this, EmptyString(), // title doesn't matter here
                      aURI,
                      aSheet,
                      aElement,
                      aWasAlternate,
                      aObserver,
                      nullptr,
                      mDocument);
  NS_ENSURE_TRUE(evt, NS_ERROR_OUT_OF_MEMORY);

  if (!mPostedEvents.AppendElement(evt)) {
    return NS_ERROR_OUT_OF_MEMORY;
  }

  nsresult rv = NS_DispatchToCurrentThread(evt);
  if (NS_FAILED(rv)) {
    NS_WARNING("failed to dispatch stylesheet load event");
    mPostedEvents.RemoveElement(evt);
  } else {
    // We'll unblock onload when we handle the event.
    if (mDocument) {
      mDocument->BlockOnload();
    }

    // We want to notify the observer for this data.
    evt->mMustNotify = true;
    evt->mSheetAlreadyComplete = true;

    // If we get to this code, aSheet loaded correctly at some point, so
    // we can just use NS_OK for the status.  Note that we do this here
    // and not from inside our SheetComplete so that we don't end up
    // running the load event async.
    evt->ScheduleLoadEventIfNeeded(NS_OK);
  }

  return rv;
}

void
Loader::HandleLoadEvent(SheetLoadData* aEvent)
{
  // XXXbz can't assert this yet.... May not have an observer because
  // we're unblocking the parser
  // NS_ASSERTION(aEvent->mObserver, "Must have observer");
  NS_ASSERTION(aEvent->mSheet, "Must have sheet");

  // Very important: this needs to come before the SheetComplete call
  // below, so that HasPendingLoads() will test true as needed under
  // notifications we send from that SheetComplete call.
  mPostedEvents.RemoveElement(aEvent);

  if (!aEvent->mIsCancelled) {
    // SheetComplete will call Release(), so give it a reference to do
    // that with.
    NS_ADDREF(aEvent);
    SheetComplete(aEvent, NS_OK);
  }

  if (mDocument) {
    mDocument->UnblockOnload(true);
  }
}

static PLDHashOperator
StopLoadingSheetCallback(URIPrincipalReferrerPolicyAndCORSModeHashKey* aKey,
                         SheetLoadData*& aData,
                         void* aClosure)
{
  NS_PRECONDITION(aData, "Must have a data!");
  NS_PRECONDITION(aClosure, "Must have a loader");

  aData->mIsLoading = false; // we will handle the removal right here
  aData->mIsCancelled = true;

  static_cast<Loader::LoadDataArray*>(aClosure)->AppendElement(aData);

  return PL_DHASH_REMOVE;
}

nsresult
Loader::Stop()
{
  uint32_t pendingCount =
    mSheets ? mSheets->mPendingDatas.Count() : 0;
  uint32_t loadingCount =
    mSheets ? mSheets->mLoadingDatas.Count() : 0;
  LoadDataArray arr(pendingCount + loadingCount + mPostedEvents.Length());

  if (pendingCount) {
    mSheets->mPendingDatas.Enumerate(StopLoadingSheetCallback, &arr);
  }
  if (loadingCount) {
    mSheets->mLoadingDatas.Enumerate(StopLoadingSheetCallback, &arr);
  }

  uint32_t i;
  for (i = 0; i < mPostedEvents.Length(); ++i) {
    SheetLoadData* data = mPostedEvents[i];
    data->mIsCancelled = true;
    if (arr.AppendElement(data)) {
      // SheetComplete() calls Release(), so give this an extra ref.
      NS_ADDREF(data);
    }
#ifdef DEBUG
    else {
      NS_NOTREACHED("We preallocated this memory... shouldn't really fail, "
                    "except we never check that preallocation succeeds.");
    }
#endif
  }
  mPostedEvents.Clear();

  mDatasToNotifyOn += arr.Length();
  for (i = 0; i < arr.Length(); ++i) {
    --mDatasToNotifyOn;
    SheetComplete(arr[i], NS_BINDING_ABORTED);
  }
  return NS_OK;
}

bool
Loader::HasPendingLoads()
{
  return
    (mSheets && mSheets->mLoadingDatas.Count() != 0) ||
    (mSheets && mSheets->mPendingDatas.Count() != 0) ||
    mPostedEvents.Length() != 0 ||
    mDatasToNotifyOn != 0;
}

nsresult
Loader::AddObserver(nsICSSLoaderObserver* aObserver)
{
  NS_PRECONDITION(aObserver, "Must have observer");
  if (mObservers.AppendElementUnlessExists(aObserver)) {
    return NS_OK;
  }

  return NS_ERROR_OUT_OF_MEMORY;
}

void
Loader::RemoveObserver(nsICSSLoaderObserver* aObserver)
{
  mObservers.RemoveElement(aObserver);
}

static PLDHashOperator
CollectLoadDatas(URIPrincipalReferrerPolicyAndCORSModeHashKey *aKey,
                 SheetLoadData* &aData,
                 void* aClosure)
{
  static_cast<Loader::LoadDataArray*>(aClosure)->AppendElement(aData);
  return PL_DHASH_REMOVE;
}

void
Loader::StartAlternateLoads()
{
  NS_PRECONDITION(mSheets, "Don't call me!");
  LoadDataArray arr(mSheets->mPendingDatas.Count());
  mSheets->mPendingDatas.Enumerate(CollectLoadDatas, &arr);

  mDatasToNotifyOn += arr.Length();
  for (uint32_t i = 0; i < arr.Length(); ++i) {
    --mDatasToNotifyOn;
    LoadSheet(arr[i], eSheetNeedsParser);
  }
}

static PLDHashOperator
TraverseSheet(URIPrincipalReferrerPolicyAndCORSModeHashKey*,
              CSSStyleSheet* aSheet,
              void* aClosure)
{
  nsCycleCollectionTraversalCallback* cb =
    static_cast<nsCycleCollectionTraversalCallback*>(aClosure);
  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(*cb, "Sheet cache nsCSSLoader");
  cb->NoteXPCOMChild(NS_ISUPPORTS_CAST(nsIStyleSheet*, aSheet));
  return PL_DHASH_NEXT;
}

NS_IMPL_CYCLE_COLLECTION_CLASS(Loader)

NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(Loader)
  if (tmp->mSheets) {
    tmp->mSheets->mCompleteSheets.EnumerateRead(TraverseSheet, &cb);
  }
  nsTObserverArray<nsCOMPtr<nsICSSLoaderObserver>>::ForwardIterator
    it(tmp->mObservers);
  while (it.HasMore()) {
    ImplCycleCollectionTraverse(cb, it.GetNext(),
                                "mozilla::css::Loader.mObservers");
  }
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END

NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(Loader)
  if (tmp->mSheets) {
    tmp->mSheets->mCompleteSheets.Clear();
  }
  tmp->mObservers.Clear();
NS_IMPL_CYCLE_COLLECTION_UNLINK_END

NS_IMPL_CYCLE_COLLECTION_ROOT_NATIVE(Loader, AddRef)
NS_IMPL_CYCLE_COLLECTION_UNROOT_NATIVE(Loader, Release)

size_t
Loader::SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
{
  size_t n = aMallocSizeOf(this);

  if (mSheets) {
    n += mSheets->mCompleteSheets.ShallowSizeOfExcludingThis(aMallocSizeOf);
    for (auto iter = mSheets->mCompleteSheets.ConstIter();
         !iter.Done();
         iter.Next()) {
      // If aSheet has a parent, then its parent will report it so we don't
      // have to worry about it here. Likewise, if aSheet has an owning node,
      // then the document that node is in will report it.
      const nsRefPtr<CSSStyleSheet>& aSheet = iter.Data();
      n += (aSheet->GetOwnerNode() || aSheet->GetParentSheet())
         ? 0
         : aSheet->SizeOfIncludingThis(aMallocSizeOf);
    }
  }
  n += mObservers.ShallowSizeOfExcludingThis(aMallocSizeOf);

  // Measurement of the following members may be added later if DMD finds it is
  // worthwhile:
  // - mLoadingDatas: transient, and should be small
  // - mPendingDatas: transient, and should be small
  // - mParsingDatas: transient, and should be small
  // - mPostedEvents: transient, and should be small
  //
  // The following members aren't measured:
  // - mDocument, because it's a weak backpointer
  // - mPreferredSheet, because it can be a shared string

  return n;
}

} // namespace css
} // namespace mozilla