diff mercurial/wireprotov2server.py @ 39637:c7a7c7e844e5

wireprotov2: define and implement "manifestdata" command

The added command can be used for obtaining manifest data.
Given a manifest path and set of manifest nodes, data about
manifests can be retrieved.

Unlike changeset data, we wish to emit deltas to describe
manifest revisions. So the command uses the relatively new
API for building delta requests and emitting them.

The code calls into deltaparent(), which I'm not very keen of.
There's still work to be done in delta generation land so
implementation details of storage (e.g. exactly one delta
is stored/available) don't creep into higher levels. But we
can worry about this later (there is already a TODO on
imanifestorage tracking this).

On the subject of parent deltas, the server assumes parent revisions
exist on the receiving end. This is obviously wrong for shallow
clone. I've added TODOs to add a mechanism to the command to
allow clients to specify desired behavior. This shouldn't be
too difficult to implement.

Another big change is that the client must explicitly request
manifest nodes to retrieve. This is a major departure from
"getbundle," where the server derives relevant manifests as it
iterates changesets and sends them automatically. As implemented,
the client must transmit each requested node to the server. At
20 bytes per node, we're looking at 2 MB per 100,000 nodes. Plus
wire encoding overhead. This isn't ideal for clients with limited
upload bandwidth. I plan to address this in the future by allowing
alternate mechanisms for defining the revisions to retrieve. One
idea is to define a range of changeset revisions whose manifest
revisions to retrieve (similar to how "changesetdata" works).
We almost certainly want an API to look up an individual manifest
by node. And that's where I've chosen to start with the implementation.
Again, a theme of this early exchangev2 work is I want to start by
building primitives for accessing raw repository data first and see
how far we can get with those before we need more complexity.

Differential Revision: https://phab.mercurial-scm.org/D4488

--- a/mercurial/wireprotov2server.py	Wed Aug 22 14:51:11 2018 -0700
+++ b/mercurial/wireprotov2server.py	Wed Sep 05 09:09:52 2018 -0700
@@ -11,8 +11,11 @@
 from .i18n import _
 from .node import (
     nullid,
+    nullrev,
 )
 from . import (
+    changegroup,
+    dagop,
     discovery,
     encoding,
     error,
@@ -411,6 +414,67 @@
 
     return proto.addcapabilities(repo, caps)
 
+def builddeltarequests(store, nodes):
+    """Build a series of revision delta requests against a backend store.
+
+    Returns a list of revision numbers in the order they should be sent
+    and a list of ``irevisiondeltarequest`` instances to be made against
+    the backend store.
+    """
+    # We sort and send nodes in DAG order because this is optimal for
+    # storage emission.
+    # TODO we may want a better storage API here - one where we can throw
+    # a list of nodes and delta preconditions over a figurative wall and
+    # have the storage backend figure it out for us.
+    revs = dagop.linearize({store.rev(n) for n in nodes}, store.parentrevs)
+
+    requests = []
+
+    for rev in revs:
+        node = store.node(rev)
+        parents = store.parents(node)
+        deltaparent = store.node(store.deltaparent(rev))
+
+        # There is a delta in storage. That means we can send the delta
+        # efficiently.
+        #
+        # But, the delta may be against a revision the receiver doesn't
+        # have (e.g. shallow clone or when the delta isn't against a parent
+        # revision). For now, we ignore the problem of shallow clone. As
+        # long as a delta exists against a parent, we send it.
+        # TODO allow arguments to control this behavior, as the receiver
+        # may not have the base revision in some scenarios.
+        if deltaparent != nullid and deltaparent in parents:
+            basenode = deltaparent
+
+        # Else there is no delta parent in storage or the delta that is
+        # # there isn't suitable. Let's use a delta against a parent
+        # revision, if possible.
+        #
+        # There is room to check if the delta parent is in the ancestry of
+        # this node. But there isn't an API on the manifest storage object
+        # for that. So ignore this case for now.
+
+        elif parents[0] != nullid:
+            basenode = parents[0]
+        elif parents[1] != nullid:
+            basenode = parents[1]
+
+        # No potential bases to delta against. Send a full revision.
+        else:
+            basenode = nullid
+
+        requests.append(changegroup.revisiondeltarequest(
+            node=node,
+            p1node=parents[0],
+            p2node=parents[1],
+            # Receiver deals with linknode resolution.
+            linknode=nullid,
+            basenode=basenode,
+        ))
+
+    return revs, requests
+
 def wireprotocommand(name, args=None, permission='push'):
     """Decorator to declare a wire protocol command.
 
@@ -630,6 +694,87 @@
 
     yield node
 
+@wireprotocommand('manifestdata',
+                  args={
+                      'nodes': [b'0123456...'],
+                      'fields': [b'parents', b'revision'],
+                      'tree': b'',
+                  },
+                  permission='pull')
+def manifestdata(repo, proto, nodes=None, fields=None, tree=None):
+    fields = fields or set()
+
+    if nodes is None:
+        raise error.WireprotoCommandError(
+            'nodes argument must be defined')
+
+    if tree is None:
+        raise error.WireprotoCommandError(
+            'tree argument must be defined')
+
+    store = repo.manifestlog.getstorage(tree)
+
+    # Validate the node is known and abort on unknown revisions.
+    for node in nodes:
+        try:
+            store.rev(node)
+        except error.LookupError:
+            raise error.WireprotoCommandError(
+                'unknown node: %s', (node,))
+
+    revs, requests = builddeltarequests(store, nodes)
+
+    yield {
+        b'totalitems': len(revs),
+    }
+
+    if b'revision' in fields:
+        deltas = store.emitrevisiondeltas(requests)
+    else:
+        deltas = None
+
+    for rev in revs:
+        node = store.node(rev)
+
+        if deltas is not None:
+            delta = next(deltas)
+        else:
+            delta = None
+
+        d = {
+            b'node': node,
+        }
+
+        if b'parents' in fields:
+            d[b'parents'] = store.parents(node)
+
+        if b'revision' in fields:
+            assert delta is not None
+            assert delta.flags == 0
+            assert d[b'node'] == delta.node
+
+            if delta.revision is not None:
+                revisiondata = delta.revision
+                d[b'revisionsize'] = len(revisiondata)
+            else:
+                d[b'deltabasenode'] = delta.basenode
+                revisiondata = delta.delta
+                d[b'deltasize'] = len(revisiondata)
+        else:
+            revisiondata = None
+
+        yield d
+
+        if revisiondata is not None:
+            yield revisiondata
+
+    if deltas is not None:
+        try:
+            next(deltas)
+            raise error.ProgrammingError('should not have more deltas')
+        except GeneratorExit:
+            pass
+
 @wireprotocommand('pushkey',
                   args={
                       'namespace': b'ns',