exchange: extract bundle specification components into own attributes

An upcoming patch will enable clients to prefer certain bundles over
others. The idea is that we define values of attributes from manifests
that are desirable.

The BUNDLESPEC attribute is a complex value consisting of multiple
parts. Clients may wish to only prefer one of these parts. Having to
specify every combination of BUNDLESPEC would be annoying. So, we
extract the components of BUNDLESPEC into their own attributes so
clients can easily filter on a sub-component.

mercurial/exchange.py

@@ -1603,7 +1603,7 b' def _maybeapplyclonebundle(pullop):'
         return
 
     res = remote._call('clonebundles')
-    entries = parseclonebundlesmanifest(res)
+    entries = parseclonebundlesmanifest(repo, res)
     if not entries:
         repo.ui.note(_('no clone bundles available on remote; '
                        'falling back to regular clone\n'))
@@ -1640,7 +1640,7 b' def _maybeapplyclonebundle(pullop):'
                           hint=_('consider contacting the server '
                                  'operator if this error persists'))
 
-def parseclonebundlesmanifest(s):
+def parseclonebundlesmanifest(repo, s):
     """Parses the raw text of a clone bundles manifest.
 
     Returns a list of dicts. The dicts have a ``URL`` key corresponding
@@ -1654,7 +1654,23 b' def parseclonebundlesmanifest(s):'
         attrs = {'URL': fields[0]}
         for rawattr in fields[1:]:
             key, value = rawattr.split('=', 1)
-            attrs[urllib.unquote(key)] = urllib.unquote(value)
+            key = urllib.unquote(key)
+            value = urllib.unquote(value)
+            attrs[key] = value
+
+            # Parse BUNDLESPEC into components. This makes client-side
+            # preferences easier to specify since you can prefer a single
+            # component of the BUNDLESPEC.
+            if key == 'BUNDLESPEC':
+                try:
+                    comp, version = parsebundlespec(repo, value,
+                                                    externalnames=True)
+                    attrs['COMPRESSION'] = comp
+                    attrs['VERSION'] = version
+                except error.InvalidBundleSpecification:
+                    pass
+                except error.UnsupportedBundleSpecification:
+                    pass
 
         m.append(attrs)