httppeer: use compression engine API for decompressing responses

In preparation for supporting multiple compression formats on the
wire protocol, we need all users of the wire protocol to use
compression engine APIs.

This commit ports the HTTP wire protocol client to use the
compression engine API.

The code for handling the HTTPException is a bit hacky. Essentially,
HTTPException could be thrown by any read() from the socket. However,
as part of porting the API, we no longer have a generator wrapping
the socket and we don't have a single place where we can trap the
exception. We solve this by introducing a proxy class that intercepts
read() and converts the exception appropriately.

In the future, we could introduce a new compression engine API that
supports emitting a generator of decompressed chunks. This would
eliminate the need for the proxy class. As I said when I introduced
the decompressorreader() API, I'm not fond of it and would support
transitioning to something better. This can be done as a follow-up,
preferably once all the code is using the compression engine API and
we have a better idea of the API needs of all the consumers.

mercurial/httppeer.py

@@ -12,7 +12,6 b' import errno'
 import os
 import socket
 import tempfile
-import zlib
 
 from .i18n import _
 from .node import nullid
@@ -30,16 +29,26 b' httplib = util.httplib'
 urlerr = util.urlerr
 urlreq = util.urlreq
 
-def zgenerator(f):
-    zd = zlib.decompressobj()
+# FUTURE: consider refactoring this API to use generators. This will
+# require a compression engine API to emit generators.
+def decompressresponse(response, engine):
     try:
-        for chunk in util.filechunkiter(f):
-            while chunk:
-                yield zd.decompress(chunk, 2**18)
-                chunk = zd.unconsumed_tail
+        reader = engine.decompressorreader(response)
     except httplib.HTTPException:
         raise IOError(None, _('connection ended unexpectedly'))
-    yield zd.flush()
+
+    # We need to wrap reader.read() so HTTPException on subsequent
+    # reads is also converted.
+    origread = reader.read
+    class readerproxy(reader.__class__):
+        def read(self, *args, **kwargs):
+            try:
+                return origread(*args, **kwargs)
+            except httplib.HTTPException:
+                raise IOError(None, _('connection ended unexpectedly'))
+
+    reader.__class__ = readerproxy
+    return reader
 
 class httppeer(wireproto.wirepeer):
     def __init__(self, ui, path):
@@ -202,7 +211,7 b' class httppeer(wireproto.wirepeer):'
                                       (safeurl, version))
 
         if _compressible:
-            return util.chunkbuffer(zgenerator(resp))
+            return decompressresponse(resp, util.compengines['zlib'])
 
         return resp