send-pack: don't send a thin pack to a server which doesn't support it
Up to now git has assumed that all servers are able to fix thin packs. This is however not always the case. Document the 'no-thin' capability and prevent send-pack from generating a thin pack if the server advertises it. Signed-off-by: Carlos Martín Nieto <cmn@elego.de> Helped-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Carlos Martín Nieto committed
Nov 23, 2013 at 17:07 UTC
1ba98a79f1b991e6f2b1d01ac392ba2edadc3ca1
2 files changed
+25
-8
Documentation/technical/protocol-capabilities.txt
+23
-8
@@ -72,14 +72,29 @@ interleaved with S-R-Q.
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thin-pack
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---------
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-This capability means that the server can send a 'thin' pack, a pack
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-which does not contain base objects; if those base objects are available
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-on client side. Client requests 'thin-pack' capability when it
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-understands how to "thicken" it by adding required delta bases making
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-it self-contained.
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-
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-Client MUST NOT request 'thin-pack' capability if it cannot turn a thin
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-pack into a self-contained pack.
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+A thin pack is one with deltas which reference base objects not
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+contained within the pack (but are known to exist at the receiving
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+end). This can reduce the network traffic significantly, but it
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+requires the receiving end to know how to "thicken" these packs by
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+adding the missing bases to the pack.
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+
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+The upload-pack server advertises 'thin-pack' when it can generate
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+and send a thin pack. A client requests the 'thin-pack' capability
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+when it understands how to "thicken" it, notifying the server that
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+it can receive such a pack. A client MUST NOT request the
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+'thin-pack' capability if it cannot turn a thin pack into a
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+self-contained pack.
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+
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+Receive-pack, on the other hand, is assumed by default to be able to
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+handle thin packs, but can ask the client not to use the feature by
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+advertising the 'no-thin' capability. A client MUST NOT send a thin
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+pack if the server advertises the 'no-thin' capability.
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+
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+The reasons for this asymmetry are historical. The receive-pack
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+program did not exist until after the invention of thin packs, so
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+historically the reference implementation of receive-pack always
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+understood thin packs. Adding 'no-thin' later allowed receive-pack
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+to disable the feature in a backwards-compatible manner.
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side-band, side-band-64k
send-pack.c
+2
@@ -206,6 +206,8 @@ int send_pack(struct send_pack_args *args,
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quiet_supported = 1;
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if (server_supports("agent"))
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agent_supported = 1;
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+ if (server_supports("no-thin"))
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+ args->use_thin_pack = 0;
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if (!remote_refs) {
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fprintf(stderr, "No refs in common and none specified; doing nothing.\n"