bundle2: specify what capabilities will be used for

bundle2: specify what capabilities will be used for

We currently assume there is a symmetric relationship of bundle2
capabilities between client and server. However, this may not always be
the case.

We need a bundle2 capability to advertise bundle2 streaming clone support
on servers to differentiate it from the existing, legacy streaming clone
support.

However, servers may wish to disable streaming clone support. If bundle2
capabilities were the same between client and server, a client (which
may also be a server) that has disabled streaming clone support would
not be able to perform a streaming clone itself!

This commit introduces a "role" argument to bundle2.getrepocaps() that
explicitly defines the role being performed. This will allow us (and
extensions) to alter bundle2 capabilities depending on the operation
being performed.

Differential Revision: https://phab.mercurial-scm.org/D1923

--- a/mercurial/bundle2.py	Sat Jan 20 15:43:02 2018 -0800
+++ b/mercurial/bundle2.py	Sat Jan 20 13:54:36 2018 -0800
@@ -1490,11 +1490,18 @@
                 'stream': ('v2',),
                }
 
-def getrepocaps(repo, allowpushback=False):
+def getrepocaps(repo, allowpushback=False, role=None):
     """return the bundle2 capabilities for a given repo
 
     Exists to allow extensions (like evolution) to mutate the capabilities.
+
+    The returned value is used for servers advertising their capabilities as
+    well as clients advertising their capabilities to servers as part of
+    bundle2 requests. The ``role`` argument specifies which is which.
     """
+    if role not in ('client', 'server'):
+        raise error.ProgrammingError('role argument must be client or server')
+
     caps = capabilities.copy()
     caps['changegroup'] = tuple(sorted(
         changegroup.supportedincomingversions(repo)))

--- a/mercurial/bundlerepo.py	Sat Jan 20 15:43:02 2018 -0800
+++ b/mercurial/bundlerepo.py	Sat Jan 20 13:54:36 2018 -0800
@@ -543,7 +543,7 @@
             kwargs = {}
             kwargs[r'common'] = common
             kwargs[r'heads'] = rheads
-            kwargs[r'bundlecaps'] = exchange.caps20to10(repo)
+            kwargs[r'bundlecaps'] = exchange.caps20to10(repo, role='client')
             kwargs[r'cg'] = True
             b2 = other.getbundle('incoming', **kwargs)
             fname = bundle = changegroup.writechunks(ui, b2._forwardchunks(),

--- a/mercurial/exchange.py	Sat Jan 20 15:43:02 2018 -0800
+++ b/mercurial/exchange.py	Sat Jan 20 13:54:36 2018 -0800
@@ -1015,7 +1015,8 @@
 
     # create reply capability
     capsblob = bundle2.encodecaps(bundle2.getrepocaps(pushop.repo,
-                                                      allowpushback=pushback))
+                                                      allowpushback=pushback,
+                                                      role='client'))
     bundler.newpart('replycaps', data=capsblob)
     replyhandlers = []
     for partgenname in b2partsgenorder:
@@ -1448,7 +1449,7 @@
     """pull data using bundle2
 
     For now, the only supported data are changegroup."""
-    kwargs = {'bundlecaps': caps20to10(pullop.repo)}
+    kwargs = {'bundlecaps': caps20to10(pullop.repo, role='client')}
 
     # make ui easier to access
     ui = pullop.repo.ui
@@ -1680,10 +1681,10 @@
             pullop.repo.invalidatevolatilesets()
     return tr
 
-def caps20to10(repo):
+def caps20to10(repo, role):
     """return a set with appropriate options to use bundle20 during getbundle"""
     caps = {'HG20'}
-    capsblob = bundle2.encodecaps(bundle2.getrepocaps(repo))
+    capsblob = bundle2.encodecaps(bundle2.getrepocaps(repo, role=role))
     caps.add('bundle2=' + urlreq.quote(capsblob))
     return caps
 

--- a/mercurial/localrepo.py	Sat Jan 20 15:43:02 2018 -0800
+++ b/mercurial/localrepo.py	Sat Jan 20 13:54:36 2018 -0800
@@ -577,7 +577,8 @@
     def _restrictcapabilities(self, caps):
         if self.ui.configbool('experimental', 'bundle2-advertise'):
             caps = set(caps)
-            capsblob = bundle2.encodecaps(bundle2.getrepocaps(self))
+            capsblob = bundle2.encodecaps(bundle2.getrepocaps(self,
+                                                              role='client'))
             caps.add('bundle2=' + urlreq.quote(capsblob))
         return caps
 

--- a/mercurial/wireproto.py	Sat Jan 20 15:43:02 2018 -0800
+++ b/mercurial/wireproto.py	Sat Jan 20 13:54:36 2018 -0800
@@ -780,7 +780,7 @@
         else:
             caps.append('streamreqs=%s' % ','.join(sorted(requiredformats)))
     if repo.ui.configbool('experimental', 'bundle2-advertise'):
-        capsblob = bundle2.encodecaps(bundle2.getrepocaps(repo))
+        capsblob = bundle2.encodecaps(bundle2.getrepocaps(repo, role='server'))
         caps.append('bundle2=' + urlreq.quote(capsblob))
     caps.append('unbundle=%s' % ','.join(bundle2.bundlepriority))