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.
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