--- a/mercurial/wireproto.py	Tue Mar 06 15:08:33 2018 -0800
+++ b/mercurial/wireproto.py	Wed Mar 07 16:02:24 2018 -0800
@@ -592,10 +592,12 @@
 
 class commandentry(object):
     """Represents a declared wire protocol command."""
-    def __init__(self, func, args='', transports=None):
+    def __init__(self, func, args='', transports=None,
+                 permission='push'):
         self.func = func
         self.args = args
         self.transports = transports or set()
+        self.permission = permission
 
     def _merge(self, func, args):
         """Merge this instance with an incoming 2-tuple.
@@ -605,7 +607,8 @@
         data not captured by the 2-tuple and a new instance containing
         the union of the two objects is returned.
         """
-        return commandentry(func, args=args, transports=set(self.transports))
+        return commandentry(func, args=args, transports=set(self.transports),
+                            permission=self.permission)
 
     # Old code treats instances as 2-tuples. So expose that interface.
     def __iter__(self):
@@ -643,7 +646,8 @@
             else:
                 # Use default values from @wireprotocommand.
                 v = commandentry(v[0], args=v[1],
-                                 transports=set(wireprototypes.TRANSPORTS))
+                                 transports=set(wireprototypes.TRANSPORTS),
+                                 permission='push')
         else:
             raise ValueError('command entries must be commandentry instances '
                              'or 2-tuples')
@@ -672,12 +676,8 @@
 
 commands = commanddict()
 
-# Maps wire protocol name to operation type. This is used for permissions
-# checking. All defined @wireiprotocommand should have an entry in this
-# dict.
-permissions = {}
-
-def wireprotocommand(name, args='', transportpolicy=POLICY_ALL):
+def wireprotocommand(name, args='', transportpolicy=POLICY_ALL,
+                     permission='push'):
     """Decorator to declare a wire protocol command.
 
     ``name`` is the name of the wire protocol command being provided.
@@ -688,6 +688,12 @@
     ``transportpolicy`` is a POLICY_* constant denoting which transports
     this wire protocol command should be exposed to. By default, commands
     are exposed to all wire protocol transports.
+
+    ``permission`` defines the permission type needed to run this command.
+    Can be ``push`` or ``pull``. These roughly map to read-write and read-only,
+    respectively. Default is to assume command requires ``push`` permissions
+    because otherwise commands not declaring their permissions could modify
+    a repository that is supposed to be read-only.
     """
     if transportpolicy == POLICY_ALL:
         transports = set(wireprototypes.TRANSPORTS)
@@ -701,14 +707,18 @@
         raise error.Abort(_('invalid transport policy value: %s') %
                           transportpolicy)
 
+    if permission not in ('push', 'pull'):
+        raise error.Abort(_('invalid wire protocol permission; got %s; '
+                            'expected "push" or "pull"') % permission)
+
     def register(func):
-        commands[name] = commandentry(func, args=args, transports=transports)
+        commands[name] = commandentry(func, args=args, transports=transports,
+                                      permission=permission)
         return func
     return register
 
 # TODO define a more appropriate permissions type to use for this.
-permissions['batch'] = 'pull'
-@wireprotocommand('batch', 'cmds *')
+@wireprotocommand('batch', 'cmds *', permission='pull')
 def batch(repo, proto, cmds, others):
     repo = repo.filtered("served")
     res = []
@@ -725,11 +735,9 @@
         # checking on each batched command.
         # TODO formalize permission checking as part of protocol interface.
         if util.safehasattr(proto, 'checkperm'):
-            # Assume commands with no defined permissions are writes / for
-            # pushes. This is the safest from a security perspective because
-            # it doesn't allow commands with undefined semantics from
-            # bypassing permissions checks.
-            proto.checkperm(permissions.get(op, 'push'))
+            perm = commands[op].permission
+            assert perm in ('push', 'pull')
+            proto.checkperm(perm)
 
         if spec:
             keys = spec.split()
@@ -758,8 +766,8 @@
 
     return bytesresponse(';'.join(res))
 
-permissions['between'] = 'pull'
-@wireprotocommand('between', 'pairs', transportpolicy=POLICY_V1_ONLY)
+@wireprotocommand('between', 'pairs', transportpolicy=POLICY_V1_ONLY,
+                  permission='pull')
 def between(repo, proto, pairs):
     pairs = [decodelist(p, '-') for p in pairs.split(" ")]
     r = []
@@ -768,8 +776,7 @@
 
     return bytesresponse(''.join(r))
 
-permissions['branchmap'] = 'pull'
-@wireprotocommand('branchmap')
+@wireprotocommand('branchmap', permission='pull')
 def branchmap(repo, proto):
     branchmap = repo.branchmap()
     heads = []
@@ -780,8 +787,8 @@
 
     return bytesresponse('\n'.join(heads))
 
-permissions['branches'] = 'pull'
-@wireprotocommand('branches', 'nodes', transportpolicy=POLICY_V1_ONLY)
+@wireprotocommand('branches', 'nodes', transportpolicy=POLICY_V1_ONLY,
+                  permission='pull')
 def branches(repo, proto, nodes):
     nodes = decodelist(nodes)
     r = []
@@ -790,8 +797,7 @@
 
     return bytesresponse(''.join(r))
 
-permissions['clonebundles'] = 'pull'
-@wireprotocommand('clonebundles', '')
+@wireprotocommand('clonebundles', '', permission='pull')
 def clonebundles(repo, proto):
     """Server command for returning info for available bundles to seed clones.
 
@@ -843,13 +849,12 @@
 
 # If you are writing an extension and consider wrapping this function. Wrap
 # `_capabilities` instead.
-permissions['capabilities'] = 'pull'
-@wireprotocommand('capabilities')
+@wireprotocommand('capabilities', permission='pull')
 def capabilities(repo, proto):
     return bytesresponse(' '.join(_capabilities(repo, proto)))
 
-permissions['changegroup'] = 'pull'
-@wireprotocommand('changegroup', 'roots', transportpolicy=POLICY_V1_ONLY)
+@wireprotocommand('changegroup', 'roots', transportpolicy=POLICY_V1_ONLY,
+                  permission='pull')
 def changegroup(repo, proto, roots):
     nodes = decodelist(roots)
     outgoing = discovery.outgoing(repo, missingroots=nodes,
@@ -858,9 +863,9 @@
     gen = iter(lambda: cg.read(32768), '')
     return streamres(gen=gen)
 
-permissions['changegroupsubset'] = 'pull'
 @wireprotocommand('changegroupsubset', 'bases heads',
-                  transportpolicy=POLICY_V1_ONLY)
+                  transportpolicy=POLICY_V1_ONLY,
+                  permission='pull')
 def changegroupsubset(repo, proto, bases, heads):
     bases = decodelist(bases)
     heads = decodelist(heads)
@@ -870,16 +875,15 @@
     gen = iter(lambda: cg.read(32768), '')
     return streamres(gen=gen)
 
-permissions['debugwireargs'] = 'pull'
-@wireprotocommand('debugwireargs', 'one two *')
+@wireprotocommand('debugwireargs', 'one two *',
+                  permission='pull')
 def debugwireargs(repo, proto, one, two, others):
     # only accept optional args from the known set
     opts = options('debugwireargs', ['three', 'four'], others)
     return bytesresponse(repo.debugwireargs(one, two,
                                             **pycompat.strkwargs(opts)))
 
-permissions['getbundle'] = 'pull'
-@wireprotocommand('getbundle', '*')
+@wireprotocommand('getbundle', '*', permission='pull')
 def getbundle(repo, proto, others):
     opts = options('getbundle', gboptsmap.keys(), others)
     for k, v in opts.iteritems():
@@ -945,14 +949,12 @@
 
     return streamres(gen=chunks, prefer_uncompressed=not prefercompressed)
 
-permissions['heads'] = 'pull'
-@wireprotocommand('heads')
+@wireprotocommand('heads', permission='pull')
 def heads(repo, proto):
     h = repo.heads()
     return bytesresponse(encodelist(h) + '\n')
 
-permissions['hello'] = 'pull'
-@wireprotocommand('hello')
+@wireprotocommand('hello', permission='pull')
 def hello(repo, proto):
     """Called as part of SSH handshake to obtain server info.
 
@@ -967,14 +969,12 @@
     caps = capabilities(repo, proto).data
     return bytesresponse('capabilities: %s\n' % caps)
 
-permissions['listkeys'] = 'pull'
-@wireprotocommand('listkeys', 'namespace')
+@wireprotocommand('listkeys', 'namespace', permission='pull')
 def listkeys(repo, proto, namespace):
     d = sorted(repo.listkeys(encoding.tolocal(namespace)).items())
     return bytesresponse(pushkeymod.encodekeys(d))
 
-permissions['lookup'] = 'pull'
-@wireprotocommand('lookup', 'key')
+@wireprotocommand('lookup', 'key', permission='pull')
 def lookup(repo, proto, key):
     try:
         k = encoding.tolocal(key)
@@ -986,14 +986,12 @@
         success = 0
     return bytesresponse('%d %s\n' % (success, r))
 
-permissions['known'] = 'pull'
-@wireprotocommand('known', 'nodes *')
+@wireprotocommand('known', 'nodes *', permission='pull')
 def known(repo, proto, nodes, others):
     v = ''.join(b and '1' or '0' for b in repo.known(decodelist(nodes)))
     return bytesresponse(v)
 
-permissions['pushkey'] = 'push'
-@wireprotocommand('pushkey', 'namespace key old new')
+@wireprotocommand('pushkey', 'namespace key old new', permission='push')
 def pushkey(repo, proto, namespace, key, old, new):
     # compatibility with pre-1.8 clients which were accidentally
     # sending raw binary nodes rather than utf-8-encoded hex
@@ -1014,8 +1012,7 @@
     output = output.getvalue() if output else ''
     return bytesresponse('%d\n%s' % (int(r), output))
 
-permissions['stream_out'] = 'pull'
-@wireprotocommand('stream_out')
+@wireprotocommand('stream_out', permission='pull')
 def stream(repo, proto):
     '''If the server supports streaming clone, it advertises the "stream"
     capability with a value representing the version and flags of the repo
@@ -1023,8 +1020,7 @@
     '''
     return streamres_legacy(streamclone.generatev1wireproto(repo))
 
-permissions['unbundle'] = 'push'
-@wireprotocommand('unbundle', 'heads')
+@wireprotocommand('unbundle', 'heads', permission='push')
 def unbundle(repo, proto, heads):
     their_heads = decodelist(heads)