xpcom/io/nsIScriptableInputStream.idl
author Henri Sivonen <hsivonen@hsivonen.fi>
Fri, 06 Jul 2018 10:44:43 +0300
changeset 489140 4ef0f163fdeb9afeddd87b37bfd987298c038542
parent 108154 14e988e17b792ef5f50feb9aa96dbf9d71052215
child 538050 020c8c871c0d3b3920fe95935cfef06501976c0f
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: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* 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;

/**
 * nsIScriptableInputStream provides scriptable access to an nsIInputStream
 * instance.
 */
[scriptable, uuid(3fce9015-472a-4080-ac3e-cd875dbe361e)]
interface nsIScriptableInputStream : nsISupports
{ 
    /** 
     * Closes the stream. 
     */
    void close();

    /**
     * Wrap the given nsIInputStream with this nsIScriptableInputStream. 
     *
     * @param aInputStream parameter providing the stream to wrap 
     */ 
    void init(in nsIInputStream aInputStream); 

    /**
     * Return the number of bytes currently available in the stream 
     *
     * @return the number of bytes 
     *
     * @throws NS_BASE_STREAM_CLOSED if called after the stream has been closed
     */ 
    unsigned long long available(); 

    /**
     * Read data from the stream.
     *
     * WARNING: If the data contains a null byte, then this method will return
     * a truncated string.
     *
     * @param aCount the maximum number of bytes to read 
     *
     * @return the data, which will be an empty string if the stream is at EOF.
     *
     * @throws NS_BASE_STREAM_CLOSED if called after the stream has been closed
     * @throws NS_ERROR_NOT_INITIALIZED if init was not called
     */ 
    string read(in unsigned long aCount); 

    /**
     * Read data from the stream, including NULL bytes.
     *
     * @param aCount the maximum number of bytes to read.
     *
     * @return the data from the stream, which will be an empty string if EOF
     *         has been reached.
     *
     * @throws NS_BASE_STREAM_WOULD_BLOCK if reading from the input stream
     *         would block the calling thread (non-blocking mode only).
     * @throws NS_ERROR_FAILURE if there are not enough bytes available to read
     *         aCount amount of data.
     */
    ACString readBytes(in unsigned long aCount);
};