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diff mercurial/help/internals/wireprotocolv2.txt @ 39653:c7a7c7e844e5

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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
author Gregory Szorc <gregory.szorc@gmail.com>
date Wed, 05 Sep 2018 09:09:52 -0700
parents 9dffa99f9158
children 0e03e6a44dee
line wrap: on
line diff
--- a/mercurial/help/internals/wireprotocolv2.txt	Wed Aug 22 14:51:11 2018 -0700
+++ b/mercurial/help/internals/wireprotocolv2.txt	Wed Sep 05 09:09:52 2018 -0700
@@ -258,6 +258,80 @@
 
 On success, returns a bytestring containing the resolved node.
 
+manifestdata
+------------
+
+Obtain various data related to manifests (which are lists of files in
+a revision).
+
+The command accepts the following arguments:
+
+fields
+   (set of bytestring) Which data associated with manifests to fetch.
+   The following values are recognized:
+
+   parents
+      Parent nodes for the manifest.
+
+   revision
+      The raw revision data for the manifest.
+
+nodes
+   (array of bytestring) Manifest nodes whose data to retrieve.
+
+tree
+   (bytestring) Path to manifest to retrieve. The empty bytestring represents
+   the root manifest. All other values represent directories/trees within
+   the repository.
+
+TODO allow specifying revisions via alternate means (such as from changeset
+revisions or ranges)
+TODO consider recursive expansion of manifests (with path filtering for
+narrow use cases)
+TODO more control over whether to emit fulltexts or deltas
+
+The response bytestream starts with a CBOR map describing the data that
+follows. It has the following bytestring keys:
+
+totalitems
+   (unsigned integer) Total number of manifest revisions whose data is
+   being returned.
+
+Following the header map is a series of 0 or more CBOR values. The first
+value is always a map describing a manifest revision. If this map has the
+``deltasize`` or ``revisionsize`` keys, a bytestring containing the delta
+or revision, respectively, will immediately follow the map. Otherwise
+the next value will be a map describing the next manifest revision.
+
+Each map has the following bytestring keys:
+
+node
+   (bytestring) The node of the manifest revision whose data is represented.
+
+deltabasenode
+   (bytestring) The node that the delta representation of this revision is
+   computed against. Only present if the ``revision`` field is requested and
+   a delta is being emitted.
+
+deltasize
+   (unsigned integer) The size of the delta data that follows this map.
+   Only present if the ``revision`` field is requested and a delta is
+   being emitted.
+
+parents
+   (array of bytestring) The nodes of the parents of this manifest revision.
+   Only present if the ``parents`` field is requested.
+
+revisionsize
+   (unsigned integer) The size of the fulltext revision data that follows
+   this map. Only present if the ``revision`` field is requested and a fulltext
+   revision is being emitted.
+
+When ``revision`` data is requested, the server chooses to emit either fulltext
+revision data or a delta. What the server decides can be inferred by looking
+for the presence of the ``deltasize`` or ``revisionsize`` keys in the map.
+Servers MUST NOT define both keys.
+
 pushkey
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