httppeer: basic implementation of capabilities interface

This is a bit crude. The capabilities mechanism for version 2 of
the wire protocol is a bit different from version 1. And code
in core is relying on strings passed to capable() matching strings
advertised by the "capabilities" wire protocol command. I may
refactor the internal checking mechanism to be a bit more
abstract or based on interfaces. Time will tell...

Differential Revision: https://phab.mercurial-scm.org/D3256

mercurial/httppeer.py

@@ -517,7 +517,7 b' class httppeer(wireproto.wirepeer):'
         raise exception
 
 # TODO implement interface for version 2 peers
[e-mail](repository.ipeerconnection)
[e-mail](repository.ipeerconnection, repository.ipeercapabilities)
 class httpv2peer(object):
     def __init__(self, ui, repourl, apipath, opener, requestbuilder,
                  apidescriptor):
@@ -552,6 +552,33 b' class httpv2peer(object):'
 
     # End of ipeerconnection.
 
+    # Start of ipeercapabilities.
+
+    def capable(self, name):
+        # The capabilities used internally historically map to capabilities
+        # advertised from the "capabilities" wire protocol command. However,
+        # version 2 of that command works differently.
+
+        # Maps to commands that are available.
+        if name in ('branchmap', 'getbundle', 'known', 'lookup', 'pushkey'):
+            return True
+
+        # Other concepts.
+        if name in ('bundle2',):
+            return True
+
+        return False
+
+    def requirecap(self, name, purpose):
+        if self.capable(name):
+            return
+
+        raise error.CapabilityError(
+            _('cannot %s; client or remote repository does not support the %r '
+              'capability') % (purpose, name))
+
+    # End of ipeercapabilities.
+
     # TODO require to be part of a batched primitive, use futures.
     def _call(self, name, **args):
         """Call a wire protocol command with arguments."""

tests/test-check-interfaces.py

@@ -94,6 +94,8 b' def main():'
 
     ziverify.verifyClass(repository.ipeerconnection,
                          httppeer.httpv2peer)
+    ziverify.verifyClass(repository.ipeercapabilities,
+                         httppeer.httpv2peer)
     checkzobject(httppeer.httpv2peer(None, '', None, None, None, None))
 
     ziverify.verifyClass(repository.ipeerbase,