wireproto: compress data from a generator
Currently, the "getbundle" wire protocol command obtains a generator of
data, converts it to a util.chunkbuffer, then converts it back to a
generator via the protocol's groupchunks() implementation. For the SSH
protocol, groupchunks() simply reads 4kb chunks then write()s the
data to a file descriptor. For the HTTP protocol, groupchunks() reads
32kb chunks, feeds those into a zlib compressor, emits compressed data
as it is available, and that is sent to the WSGI layer, where it is
likely turned into HTTP chunked transfer chunks as is or further
buffered and turned into a larger chunk.
For both the SSH and HTTP protocols, there is inefficiency from using
util.chunkbuffer.
For SSH, emitting consistent 4kb chunks sounds nice. However, the file
descriptor it is writing to is almost certainly buffered. That means
that a Python .write() probably doesn't translate into exactly what is
written to the I/O layer.
For HTTP, we're going through an intermediate layer to zlib compress
data. So all util.chunkbuffer is doing is ensuring that the chunks we
feed into the zlib compressor are of uniform size. This means more CPU
time in Python buffering and emitting chunks in util.chunkbuffer but
fewer function calls to zlib.
This patch introduces and implements a new wire protocol abstract
method: compresschunks(). It is like groupchunks() except it operates
on a generator instead of something with a .read(). The SSH
implementation simply proxies chunks. The HTTP implementation uses
zlib compression.
To avoid duplicate code, the HTTP groupchunks() has been reimplemented
in terms of compresschunks().
To prove this all works, the "getbundle" wire protocol command has been
switched to compresschunks(). This removes the util.chunkbuffer from
that command. Now, data essentially streams straight from the
changegroup emitter to the wire, possibly through a zlib compressor.
Generators all the way, baby.
There were slim to no performance changes on the server as measured
with the mozilla-central repository. This is likely because CPU
time is dominated by reading revlogs, producing the changegroup, and
zlib compressing the output stream. Still, this brings us a little
closer to our ideal of using generators everywhere.
$ cat > makepatch.py <<EOF
> f = file('eol.diff', 'wb')
> w = f.write
> w('test message\n')
> w('diff --git a/a b/a\n')
> w('--- a/a\n')
> w('+++ b/a\n')
> w('@@ -1,5 +1,5 @@\n')
> w(' a\n')
> w('-bbb\r\n')
> w('+yyyy\r\n')
> w(' cc\r\n')
> w(' \n')
> w(' d\n')
> w('-e\n')
> w('\ No newline at end of file\n')
> w('+z\r\n')
> w('\ No newline at end of file\r\n')
> EOF
$ hg init repo
$ cd repo
$ echo '\.diff' > .hgignore
Test different --eol values
$ $PYTHON -c 'file("a", "wb").write("a\nbbb\ncc\n\nd\ne")'
$ hg ci -Am adda
adding .hgignore
adding a
$ python ../makepatch.py
invalid eol
$ hg --config patch.eol='LFCR' import eol.diff
applying eol.diff
abort: unsupported line endings type: LFCR
[255]
$ hg revert -a
force LF
$ hg --traceback --config patch.eol='LF' import eol.diff
applying eol.diff
$ cat a
a
yyyy
cc
d
e (no-eol)
$ hg st
force CRLF
$ hg up -C 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg --traceback --config patch.eol='CRLF' import eol.diff
applying eol.diff
$ cat a
a\r (esc)
yyyy\r (esc)
cc\r (esc)
\r (esc)
d\r (esc)
e (no-eol)
$ hg st
auto EOL on LF file
$ hg up -C 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg --traceback --config patch.eol='auto' import eol.diff
applying eol.diff
$ cat a
a
yyyy
cc
d
e (no-eol)
$ hg st
auto EOL on CRLF file
$ $PYTHON -c 'file("a", "wb").write("a\r\nbbb\r\ncc\r\n\r\nd\r\ne")'
$ hg commit -m 'switch EOLs in a'
$ hg --traceback --config patch.eol='auto' import eol.diff
applying eol.diff
$ cat a
a\r (esc)
yyyy\r (esc)
cc\r (esc)
\r (esc)
d\r (esc)
e (no-eol)
$ hg st
auto EOL on new file or source without any EOL
$ $PYTHON -c 'file("noeol", "wb").write("noeol")'
$ hg add noeol
$ hg commit -m 'add noeol'
$ $PYTHON -c 'file("noeol", "wb").write("noeol\r\nnoeol\n")'
$ $PYTHON -c 'file("neweol", "wb").write("neweol\nneweol\r\n")'
$ hg add neweol
$ hg diff --git > noeol.diff
$ hg revert --no-backup noeol neweol
$ rm neweol
$ hg --traceback --config patch.eol='auto' import -m noeol noeol.diff
applying noeol.diff
$ cat noeol
noeol\r (esc)
noeol
$ cat neweol
neweol
neweol\r (esc)
$ hg st
Test --eol and binary patches
$ $PYTHON -c 'file("b", "wb").write("a\x00\nb\r\nd")'
$ hg ci -Am addb
adding b
$ $PYTHON -c 'file("b", "wb").write("a\x00\nc\r\nd")'
$ hg diff --git > bin.diff
$ hg revert --no-backup b
binary patch with --eol
$ hg import --config patch.eol='CRLF' -m changeb bin.diff
applying bin.diff
$ cat b
a\x00 (esc)
c\r (esc)
d (no-eol)
$ hg st
$ cd ..