gecko-dev/xpcom/io/nsISeekableStream.idl
Andrea Marchesini 4ebf5b4364 Bug 1496581 - Split nsISeekableStream in 2 classes: nsISeekableStream and nsITellableStream, f=mayhemer, r=froydnj
In the current code there are 3 main issues:

1. nsFileStream is not really thread-safe. There is nothing to protect the
internal members and we see crashes.

2. nsPipeInputStream doesn't implement ::Seek() method and that caused issues
in devtools when a nsHttpChannel sends POST data using a pipe. In order to fix
this, bug 1494176 added a check in nsHttpChannel: if the stream doesn't
implement ::Seek(), let's clone it. This was an hack around nsPipeInputStream,
and it's bad.

3. When nsHttpChannel sends POST data using a file stream, nsFileStream does
I/O on main-thread because of the issue 2. Plus, ::Seek() is called on the
main-thread causing issue 1.

Note that nsPipeInputStream implements only ::Tell(), of the nsISeekableStream
methods. It doesn't implement ::Seek() and it doesn't implement ::SetEOF().

With this patch I want to fix point 2 and point 3 (and consequentially issue 1
- but we need a separate fix for it - follow up). The patch does:

1. it splits nsISeekableStream in 2 interfaces: nsITellableStream and
nsISeekableStream.
2. nsPipeInputStream implements only nsITellableStream.  Doing this, we don't
need the ::Seek() check for point 2 in nsHttpChannel: a simple QI check is
enough.
3. Because we don't call ::Seek() in nsHttpChannel, nsFileStream doesn't do I/O
on the main-thread, and we don't crash doing so.
2018-10-18 13:35:35 +02:00

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/* -*- Mode: C++; 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 "nsITellableStream.idl"
/*
* nsISeekableStream
*
* Note that a stream might not implement all methods (e.g., a readonly stream
* won't implement setEOF)
*/
#include "nsISupports.idl"
[scriptable, uuid(8429d350-1040-4661-8b71-f2a6ba455980)]
interface nsISeekableStream : nsITellableStream
{
/*
* Sets the stream pointer to the value of the 'offset' parameter
*/
const int32_t NS_SEEK_SET = 0;
/*
* Sets the stream pointer to its current location plus the value
* of the offset parameter.
*/
const int32_t NS_SEEK_CUR = 1;
/*
* Sets the stream pointer to the size of the stream plus the value
* of the offset parameter.
*/
const int32_t NS_SEEK_END = 2;
/**
* seek
*
* This method moves the stream offset of the steam implementing this
* interface.
*
* @param whence specifies how to interpret the 'offset' parameter in
* setting the stream offset associated with the implementing
* stream.
*
* @param offset specifies a value, in bytes, that is used in conjunction
* with the 'whence' parameter to set the stream offset of the
* implementing stream. A negative value causes seeking in
* the reverse direction.
*
* @throws NS_BASE_STREAM_CLOSED if called on a closed stream.
*/
void seek(in long whence, in long long offset);
/**
* setEOF
*
* This method truncates the stream at the current offset.
*
* @throws NS_BASE_STREAM_CLOSED if called on a closed stream.
*/
void setEOF();
};