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upload-pack: implement ref-in-want

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Currently, while performing packfile negotiation, clients are only
allowed to specify their desired objects using object ids.  This causes
a vulnerability to failure when an object turns non-existent during
negotiation, which may happen if, for example, the desired repository is
provided by multiple Git servers in a load-balancing arrangement and
there exists replication delay.

In order to eliminate this vulnerability, implement the ref-in-want
feature for the 'fetch' command in protocol version 2.  This feature
enables the 'fetch' command to support requests in the form of ref names
through a new "want-ref <ref>" parameter.  At the conclusion of
negotiation, the server will send a list of all of the wanted references
(as provided by "want-ref" lines) in addition to the generated packfile.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Brandon Williams
2018-06-27 15:30:17 -07:00
committed by Junio C Hamano
parent 4bcd37d3bc
commit 516e2b76bd
4 changed files with 260 additions and 1 deletions
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28
Documentation/technical/protocol-v2.txt
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@ -299,12 +299,21 @@ included in the client's request:
for use with partial clone and partial fetch operations. See
`rev-list` for possible "filter-spec" values.
If the 'ref-in-want' feature is advertised, the following argument can
be included in the client's request as well as the potential addition of
the 'wanted-refs' section in the server's response as explained below.
want-ref <ref>
Indicates to the server that the client wants to retrieve a
particular ref, where <ref> is the full name of a ref on the
server.
The response of `fetch` is broken into a number of sections separated by
delimiter packets (0001), with each section beginning with its section
header.
output = *section
section = (acknowledgments | shallow-info | packfile)
section = (acknowledgments | shallow-info | wanted-refs | packfile)
(flush-pkt | delim-pkt)
acknowledgments = PKT-LINE("acknowledgments" LF)
@ -319,6 +328,10 @@ header.
shallow = "shallow" SP obj-id
unshallow = "unshallow" SP obj-id
wanted-refs = PKT-LINE("wanted-refs" LF)
*PKT-LINE(wanted-ref LF)
wanted-ref = obj-id SP refname
packfile = PKT-LINE("packfile" LF)
*PKT-LINE(%x01-03 *%x00-ff)
@ -379,6 +392,19 @@ header.
* This section is only included if a packfile section is also
included in the response.
wanted-refs section
* This section is only included if the client has requested a
ref using a 'want-ref' line and if a packfile section is also
included in the response.
* Always begins with the section header "wanted-refs".
* The server will send a ref listing ("<oid> <refname>") for
each reference requested using 'want-ref' lines.
* The server MUST NOT send any refs which were not requested
using 'want-ref' lines.
packfile section
* This section is only included if the client has sent 'want'
lines in its request and either requested that no more