Document the underlying protocol used by shallow repositories and --depth commands.

Explain the exchange that occurs between a client and server when
the client is requesting shallow history and/or is already using
a shallow repository.

Signed-off-by: Alex Neronskiy <zakmagnus@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/technical/pack-protocol.txt b/Documentation/technical/pack-protocol.txt
index ce69f57b5d7a0dc36c9a5da6e702142706be58ea..a7004c63e7ff5a4fe237267121a5b7c76a4c5496 100644 (file)
--- a/Documentation/technical/pack-protocol.txt
+++ b/Documentation/technical/pack-protocol.txt
@@ -187,27 +187,28 @@ the client already is up-to-date.
 
 Otherwise, it enters the negotiation phase, where the client and
 server determine what the minimal packfile necessary for transport is,
 
 Otherwise, it enters the negotiation phase, where the client and
 server determine what the minimal packfile necessary for transport is,

-by telling the server what objects it wants and what objects it has,
-so the server can make a packfile that only contains the objects that the
-client needs.  The client will also send a list of the capabilities it
-wants to be in effect, out of what the server said it could do with the
-first 'want' line.
+by telling the server what objects it wants, its shallow objects
+(if any), and the maximum commit depth it wants (if any).  The client
+will also send a list of the capabilities it wants to be in effect,
+out of what the server said it could do with the first 'want' line.

 
 ----
   upload-request    =  want-list
 
 ----
   upload-request    =  want-list

-                      have-list
-                      compute-end
+                      *shallow-line
+                      *1depth-request
+                      flush-pkt

 
   want-list         =  first-want
                       *additional-want
 
   want-list         =  first-want
                       *additional-want

-                      flush-pkt
+
+  shallow-line      =  PKT_LINE("shallow" SP obj-id)
+
+  depth-request     =  PKT_LINE("deepen" SP depth)

 
   first-want        =  PKT-LINE("want" SP obj-id SP capability-list LF)
   additional-want   =  PKT-LINE("want" SP obj-id LF)
 
 
   first-want        =  PKT-LINE("want" SP obj-id SP capability-list LF)
   additional-want   =  PKT-LINE("want" SP obj-id LF)
 

-  have-list         =  *have-line
-  have-line         =  PKT-LINE("have" SP obj-id LF)
-  compute-end       =  flush-pkt / PKT-LINE("done")
+  depth             =  1*DIGIT

 ----
 
 Clients MUST send all the obj-ids it wants from the reference
 ----
 
 Clients MUST send all the obj-ids it wants from the reference


@@ -216,21 +217,64 @@ discovery phase as 'want' lines. Clients MUST send at least one
 obj-id in a 'want' command which did not appear in the response
 obtained through ref discovery.
 
 obj-id in a 'want' command which did not appear in the response
 obtained through ref discovery.
 

-If client is requesting a shallow clone, it will now send a 'deepen'
-line with the depth it is requesting.
+The client MUST write all obj-ids which it only has shallow copies
+of (meaning that it does not have the parents of a commit) as
+'shallow' lines so that the server is aware of the limitations of
+the client's history. Clients MUST NOT mention an obj-id which
+it does not know exists on the server.
+
+The client now sends the maximum commit history depth it wants for
+this transaction, which is the number of commits it wants from the
+tip of the history, if any, as a 'deepen' line.  A depth of 0 is the
+same as not making a depth request. The client does not want to receive
+any commits beyond this depth, nor objects needed only to complete
+those commits. Commits whose parents are not received as a result are
+defined as shallow and marked as such in the server. This information
+is sent back to the client in the next step.
+
+Once all the 'want's and 'shallow's (and optional 'deepen') are
+transferred, clients MUST send a flush-pkt, to tell the server side
+that it is done sending the list.
+
+Otherwise, if the client sent a positive depth request, the server
+will determine which commits will and will not be shallow and
+send this information to the client. If the client did not request
+a positive depth, this step is skipped.

 
 

-Once all the "want"s (and optional 'deepen') are transferred,
-clients MUST send a flush-pkt, to tell the server side that it is
-done sending the list.
+----
+  shallow-update   =  *shallow-line
+                     *unshallow-line
+                     flush-pkt

 
 

-TODO: shallow/unshallow response and document the deepen command in the ABNF.
+  shallow-line     =  PKT-LINE("shallow" SP obj-id)
+
+  unshallow-line   =  PKT-LINE("unshallow" SP obj-id)
+----
+
+If the client has requested a positive depth, the server will compute
+the set of commits which are no deeper than the desired depth, starting
+at the client's wants. The server writes 'shallow' lines for each
+commit whose parents will not be sent as a result. The server writes
+an 'unshallow' line for each commit which the client has indicated is
+shallow, but is no longer shallow at the currently requested depth
+(that is, its parents will now be sent). The server MUST NOT mark
+as unshallow anything which the client has not indicated was shallow.

 
 Now the client will send a list of the obj-ids it has using 'have'
 
 Now the client will send a list of the obj-ids it has using 'have'

-lines.  In multi_ack mode, the canonical implementation will send up
-to 32 of these at a time, then will send a flush-pkt.  The canonical
-implementation will skip ahead and send the next 32 immediately,
-so that there is always a block of 32 "in-flight on the wire" at a
-time.
+lines, so the server can make a packfile that only contains the objects
+that the client needs. In multi_ack mode, the canonical implementation
+will send up to 32 of these at a time, then will send a flush-pkt. The
+canonical implementation will skip ahead and send the next 32 immediately,
+so that there is always a block of 32 "in-flight on the wire" at a time.
+
+----
+  upload-haves      =  have-list
+                      compute-end
+
+  have-list         =  *have-line
+  have-line         =  PKT-LINE("have" SP obj-id LF)
+  compute-end       =  flush-pkt / PKT-LINE("done")
+----

 
 If the server reads 'have' lines, it then will respond by ACKing any
 of the obj-ids the client said it had that the server also has. The
 
 If the server reads 'have' lines, it then will respond by ACKing any
 of the obj-ids the client said it had that the server also has. The