xpcom/io/nsIScriptableBase64Encoder.idl
author Henri Sivonen <hsivonen@hsivonen.fi>
Fri, 06 Jul 2018 10:44:43 +0300
changeset 489140 4ef0f163fdeb9afeddd87b37bfd987298c038542
parent 98983 f4157e8c410708d76703f19e4dfb61859bfe32d8
permissions -rw-r--r--
Bug 1402247 - Use encoding_rs for XPCOM string encoding conversions. r=Nika,erahm,froydnj. Correctness improvements: * UTF errors are handled safely per spec instead of dangerously truncating strings. * There are fewer converter implementations. Performance improvements: * The old code did exact buffer length math, which meant doing UTF math twice on each input string (once for length calculation and another time for conversion). Exact length math is more complicated when handling errors properly, which the old code didn't do. The new code does UTF math on the string content only once (when converting) but risks allocating more than once. There are heuristics in place to lower the probability of reallocation in cases where the double math avoidance isn't enough of a saving to absorb an allocation and memcpy. * Previously, in UTF-16 <-> UTF-8 conversions, an ASCII prefix was optimized but a single non-ASCII code point pessimized the rest of the string. The new code tries to get back on the fast ASCII path. * UTF-16 to Latin1 conversion guarantees less about handling of out-of-range input to eliminate an operation from the inner loop on x86/x86_64. * When assigning to a pre-existing string, the new code tries to reuse the old buffer instead of first releasing the old buffer and then allocating a new one. * When reallocating from the new code, the memcpy covers only the data that is part of the logical length of the old string instead of memcpying the whole capacity. (For old callers old excess memcpy behavior is preserved due to bogus callers. See bug 1472113.) * UTF-8 strings in XPConnect that are in the Latin1 range are passed to SpiderMonkey as Latin1. New features: * Conversion between UTF-8 and Latin1 is added in order to enable faster future interop between Rust code (or otherwise UTF-8-using code) and text node and SpiderMonkey code that uses Latin1. MozReview-Commit-ID: JaJuExfILM9

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 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/. */

#include "nsISupports.idl"

interface nsIInputStream;

/**
 * nsIScriptableBase64Encoder efficiently encodes the contents
 * of a nsIInputStream to a Base64 string.  This avoids the need
 * to read the entire stream into a buffer, and only then do the
 * Base64 encoding.
 *
 *  If you already have a buffer full of data, you should use
 *  btoa instead!
 */
[scriptable, uuid(9479c864-d1f9-45ab-b7b9-28b907bd2ba9)]
interface nsIScriptableBase64Encoder : nsISupports
{
  /**
   *  These methods take an nsIInputStream and return a narrow or wide
   *  string with the contents of the nsIInputStream base64 encoded.
   *
   *  The stream passed in must support ReadSegments and must not be
   *  a non-blocking stream that will return NS_BASE_STREAM_WOULD_BLOCK.
   *  If either of these restrictions are violated we will abort.
   */
  ACString encodeToCString(in nsIInputStream stream, in unsigned long length);
  AString encodeToString(in nsIInputStream stream, in unsigned long length);
};