git/fetch-pack.c, branch v2.20.2

fetch-pack: be more precise in parsing v2 response

2018-11-01T05:30:22Z

Each section in a protocol v2 response is followed by either a DELIM packet (indicating more sections to follow) or a FLUSH packet (indicating none to follow). But when parsing the "acknowledgments" section, do_fetch_pack_v2() is liberal in accepting both, but determines whether to continue reading or not based solely on the contents of the "acknowledgments" section, not on whether DELIM or FLUSH was read. There is no issue with a protocol-compliant server, but can result in confusing error messages when communicating with a server that serves unexpected additional sections. Consider a server that sends "new-section" after "acknowledgments": - client writes request - client reads the "acknowledgments" section which contains no "ready", then DELIM - since there was no "ready", client needs to continue negotiation, and writes request - client reads "new-section", and reports to the end user "expected 'acknowledgments', received 'new-section'" For the person debugging the involved Git implementation(s), the error message is confusing in that "new-section" was not received in response to the latest request, but to the first one. One solution is to always continue reading after DELIM, but in this case, we can do better. We know from the protocol that "ready" means at least the packfile section is coming (hence, DELIM) and that no "ready" means that no sections are to follow (hence, FLUSH). So teach process_acks() to enforce this. Signed-off-by: Jonathan Tan Signed-off-by: Junio C Hamano

Merge branch 'tb/filter-alternate-refs'

2018-10-19T04:34:08Z

When pushing into a repository that borrows its objects from an alternate object store, "git receive-pack" that responds to the push request on the other side lists the tips of refs in the alternate to reduce the amount of objects transferred. This sometimes is detrimental when the number of refs in the alternate is absurdly large, in which case the bandwidth saved in potentially fewer objects transferred is wasted in excessively large ref advertisement. The alternate refs that are advertised are now configurable with a pair of configuration variables. * tb/filter-alternate-refs: transport.c: introduce core.alternateRefsPrefixes transport.c: introduce core.alternateRefsCommand transport.c: extract 'fill_alternate_refs_command' transport: drop refnames from for_each_alternate_ref

Merge branch 'jt/avoid-ls-refs'

2018-10-19T04:34:07Z

Over some transports, fetching objects with an exact commit object name can be done without first seeing the ref advertisements. The code has been optimized to exploit this. * jt/avoid-ls-refs: fetch: do not list refs if fetching only hashes transport: list refs before fetch if necessary transport: do not list refs if possible transport: allow skipping of ref listing

Merge branch 'jt/non-blob-lazy-fetch'

2018-10-19T04:34:07Z

A partial clone that is configured to lazily fetch missing objects will on-demand issue a "git fetch" request to the originating repository to fill not-yet-obtained objects. The request has been optimized for requesting a tree object (and not the leaf blob objects contained in it) by telling the originating repository that no blobs are needed. * jt/non-blob-lazy-fetch: fetch-pack: exclude blobs when lazy-fetching trees fetch-pack: avoid object flags if no_dependents

transport: drop refnames from for_each_alternate_ref

2018-10-09T05:30:02Z

None of the current callers use the refname parameter we pass to their callbacks. In theory somebody _could_ do so, but it's actually quite weird if you think about it: it's a ref in somebody else's repository. So the name has no meaning locally, and in fact there may be duplicates if there are multiple alternates. The users of this interface really only care about seeing some ref tips, since that promises that the alternate has the full commit graph reachable from there. So let's keep the information we pass back to the bare minimum. Signed-off-by: Jeff King Signed-off-by: Taylor Blau Acked-by: Jeff King Signed-off-by: Junio C Hamano

transport: do not list refs if possible

2018-10-07T00:53:15Z

When all refs to be fetched are exact OIDs, it is possible to perform a fetch without requiring the remote to list refs if protocol v2 is used. Teach Git to do this. This currently has an effect only for lazy fetches done from partial clones. The change necessary to likewise optimize "git fetch

" will be done in a subsequent patch. Signed-off-by: Jonathan Tan Signed-off-by: Junio C Hamano

fetch-pack: load tip_oids eagerly iff needed

2018-10-04T18:12:13Z

tip_oids_contain() lazily loads refs into an oidset at its first call. It abuses the internal (sub)member .map.tablesize of that oidset to check if it has done that already. Determine if the oidset needs to be populated upfront and then do that instead. This duplicates a loop, but simplifies the existing one by separating concerns between the two. Signed-off-by: Rene Scharfe Signed-off-by: Junio C Hamano

fetch-pack: factor out is_unmatched_ref()

2018-10-04T18:12:13Z

Move the code to determine if a request is unmatched to its own little helper. This allows us to reuse it in a subsequent patch. Signed-off-by: Rene Scharfe Signed-off-by: Junio C Hamano

fetch-pack: exclude blobs when lazy-fetching trees

2018-10-04T13:03:49Z

A partial clone with missing trees can be obtained using "git clone --filter=tree:none ". In such a repository, when a tree needs to be lazily fetched, any tree or blob it directly or indirectly references is fetched as well, regardless of whether the original command required those objects, or if the local repository already had some of them. This is because the fetch protocol, which the lazy fetch uses, does not allow clients to request that only the wanted objects be sent, which would be the ideal solution. This patch implements a partial solution: specify the "blob:none" filter, somewhat reducing the fetch payload. This change has no effect when lazily fetching blobs (due to how filters work). And if lazily fetching a commit (such repositories are difficult to construct and is not a use case we support very well, but it is possible), referenced commits and trees are still fetched - only the blobs are not fetched. The necessary code change is done in fetch_pack() instead of somewhere closer to where the "filter" instruction is written to the wire so that only one part of the code needs to be changed in order for users of all protocol versions to benefit from this optimization. Signed-off-by: Jonathan Tan Signed-off-by: Junio C Hamano

fetch-pack: avoid object flags if no_dependents

2018-10-04T13:00:53Z

When fetch_pack() is invoked as part of another Git command (due to a lazy fetch from a partial clone, for example), it uses object flags that may already be used by the outer Git command. The commit that introduced the lazy fetch feature (88e2f9ed8e ("introduce fetch-object: fetch one promisor object", 2017-12-05)) tried to avoid this overlap, but it did not avoid it totally. It was successful in avoiding writing COMPLETE, but did not avoid reading COMPLETE, and did not avoid writing and reading ALTERNATE. Ensure that no flags are written or read by fetch_pack() in the case where it is used to perform a lazy fetch. To do this, it is sufficient to avoid checking completeness of wanted refs (unnecessary in the case of lazy fetches), and to avoid negotiation-related work (in the current implementation, already, no negotiation is performed). After that was done, the lack of overlap was verified by checking all direct and indirect usages of COMPLETE and ALTERNATE - that they are read or written only if no_dependents is false. There are other possible solutions to this issue: (1) Split fetch-pack.{c,h} into a flag-using part and a non-flag-using part, and whenever no_dependents is set, only use the non-flag-using part. (2) Make fetch_pack() be able to be used with arbitrary repository objects. fetch_pack() should then create its own repository object based on the given repository object, with its own object hashtable, so that the flags do not conflict. (1) is possible but invasive - some functions would need to be split; and such invasiveness would potentially be unnecessary if we ever were to need (2) anyway. (2) would be useful if we were to support, say, submodules that were partial clones themselves, but I don't know when or if the Git project plans to support those. Signed-off-by: Jonathan Tan Signed-off-by: Junio C Hamano