1960252 - nsBufferedOutputStream SetEOF() doesn't account for unwritten data in buffer

Status: NEW

(Core :: Networking: File, defect, P2)

Description

[Ben Campbell]

Calling SetEOF() to truncate an nsBufferedOutputStream doesn't take into account unflushed data in the buffer.

It uses nsBufferedStream::SetEOF(), which just calls SetEOF() on the underlying stream:
https://searchfox.org/comm-central/rev/b56347bd5a63f051bdc994ed4051088b37df4c99/mozilla/netwerk/base/nsBufferedStreams.cpp#246

But if there's unwritten data in the buffer, it'll get written out at the next Flush().
This is confusing because - from the callers point of view - it was written out before the SetEOF() call, and thus should have been truncated.

Comment 1

[Ben Campbell]

Attachment: seteof_test.patch

An xpcshell test to illustrate the issue.

Comment 2

[Ben Campbell]

It needs a buffer-aware nsBufferedOutputStream::SetEOF(). But just calling Flush() before the underlying-stream SetEOF() isn't enough. The Flush() changes the position within the file, so the SetEOF() will occur at an unexpected position (unexpected to the caller, anyway).