fbconduit extension

Summary: Adds a template method to fetch hash translations from scmquery

Test Plan:
  [ericsumner@dev2048 ~/fbcode] time hg log -T '{node} {mirrornode("git")}\n' --config extensions.conduit=~/fb-hgext/fbconduit.py -r 'master~5::master' --config fbconduit.reponame=fbcode
  744def84d4821ae847ca9e2c31147ec495b0ff2a e498cef35914c5a7a8de648888e47b0d6c452044
  86d589bbed310cac765d1d2822f350c66f55ee30 a49473c0f0a0eaa532f0f25f8e632015dc57de87
  74e5eddf18a9e911b561d2f2f79c433971e36234 608e41cd9c4e8a0ba8dcd3f53162fed656354db0
  95a4cce9686558864af97631142a23eee1ffd1b0 228cbfc779da14306ae43002317bf59be9b3844d
  9ec5dfd21c5360bcff66ddd3db4747742da9bd56 115df93aa18a5003323f5419bbd135a9a08d96b9
  721fd7f98313aec4513bf86817bf98e01238ebdc 170cde24839d9213efa11f4f965402fd5e13cc9b

  real  0m0.407s
  user  0m0.229s
  sys 0m0.080s
  [ericsumner@dev2048 ~/fbcode] time hg log -T '{node} {mirrornode("git")}\n' --config extensions.conduit=~/fb-hgext/fbconduit.py -r 'ancestor(.,master)::master' --config fbconduit.reponame=fbcode | wc -l
  157

  real  0m2.718s
  user  0m0.504s
  sys 0m0.066s

Reviewers: #sourcecontrol, durham

Reviewed By: #sourcecontrol, durham

Subscribers: sid0, durham, lcharignon

Differential Revision: https://phabricator.fb.com/D2070465

fbconduit.py

@@ -0,0 +1,103 @@
+# fbconduit.py
+#
+# An extension to query remote servers for extra information via conduit RPC
+#
+# Copyright 2015 Facebook, Inc.
+
+from mercurial import templater
+import json
+from urllib import urlencode
+import httplib
+
+conduit_host = None
+conduit_path = None
+connection = None
+
+MAX_CONNECT_RETRIES = 3
+
+class ConduitError(Exception):
+    pass
+
+class HttpError(Exception):
+    pass
+
+def extsetup(ui):
+    global conduit_host, conduit_path
+    conduit_host = ui.config('fbconduit', 'host')
+    conduit_path = ui.config('fbconduit', 'path')
+    
+    if not conduit_host:
+        ui.warn('No conduit host specified in config; disabling fbconduit\n')
+        return
+    templater.funcs['mirrornode'] = mirrornode
+
+def _call_conduit(method, **kwargs):
+    global connection, conduit_host, conduit_path
+
+    # start connection
+    if connection is None:
+        connection = httplib.HTTPSConnection(conduit_host)
+
+    # send request
+    path = conduit_path + method
+    args = urlencode({'params': json.dumps(kwargs)})
+    for attempt in xrange(MAX_CONNECT_RETRIES):
+        try:
+            connection.request('POST', path, args, {'Connection': 'Keep-Alive'})
+            break;
+        except httplib.HTTPException as e:
+            connection.connect()
+    else:
+        raise e
+
+    # read http response
+    response = connection.getresponse()
+    if response.status != 200:
+        raise HttpError(response.reason)
+    result = response.read()
+
+    # strip jsonp header and parse
+    assert result.startswith('for(;;);')
+    result = json.loads(result[8:])
+
+    # check for conduit errors
+    if result['error_code']:
+        raise ConduitError(result['error_info'])
+
+    # return RPC result
+    return result['result']
+
+    # don't close the connection b/c we want to avoid the connection overhead
+
+def mirrornode(ctx, mapping, args):
+    '''template: find this commit in other repositories'''
+
+    reponame = mapping['repo'].ui.config('fbconduit', 'reponame')
+    if not reponame:
+        # We don't know who we are, so we can't ask for a translation
+        return ''
+
+    if mapping['ctx'].mutable():
+        # Local commits don't have translations
+        return ''
+
+    node = mapping['ctx'].hex()
+    args = [f(ctx, mapping, a) for f, a in args]
+    if len(args) == 1:
+        torepo, totype = reponame, args[0]
+    else:
+        torepo, totype = args
+
+    try:
+        result = _call_conduit('scmquery.get.mirrored.revs',
+            from_repo=reponame,
+            from_scm='hg',
+            to_repo=torepo,
+            to_scm=totype,
+            revs=[node]
+        )
+    except ConduitError as e:
+        if 'unknown revision' not in str(e.args):
+            mapping['repo'].ui.warn(str(e.args) + '\n')
+        return ''
+    return result.get(node, '')