gitgit-fetch

Retrieve specific commit from a remote Git repository

Is there any way to retrieve only one specific commit from a remote Git repo without cloning it on my PC? The structure of remote repo is absolutely same as that of mine and hence there won't be any conflicts but I have no idea how to do this and I don't want to clone that huge repository.

I am new to git, is there any way?

Solution

  • Starting with Git version 2.5+ (Q2 2015), fetching a single commit (without cloning the full repo) is actually possible.

    See commit 68ee628 by Fredrik Medley (moroten), 21 May 2015.
    (Merged by Junio C Hamano -- gitster -- in commit a9d3493, 01 Jun 2015)

    You now have a new config (on the server side)

    uploadpack.allowReachableSHA1InWant

    Allow upload-pack to accept a fetch request that asks for an object that is reachable from any ref tip. However, note that calculating object reachability is computationally expensive.
    Defaults to false.

    If you combine that server-side configuration with a shallow clone (git fetch --depth=1), you can ask for a single commit (see t/t5516-fetch-push.sh:

    git fetch --depth=1 ../testrepo/.git <full-length SHA1>

    You can use the git cat-file command to see that the commit has been fetched:

    git cat-file commit <full-length SHA1>

    "git upload-pack" that serves "git fetch" can be told to serve commits that are not at the tip of any ref, as long as they are reachable from a ref, with uploadpack.allowReachableSHA1InWant configuration variable.

    As noted by matt in the comments:

    Note that SHA must be the full unabbreviated SHA, otherwise Git will claim it couldn't find the commit

    The full documentation is:

    upload-pack: optionally allow fetching reachable sha1

    With uploadpack.allowReachableSHA1InWant configuration option set on the server side, "git fetch" can make a request with a "want" line that names an object that has not been advertised (likely to have been obtained out of band or from a submodule pointer).
    Only objects reachable from the branch tips, i.e. the union of advertised branches and branches hidden by transfer.hideRefs, will be processed.
    Note that there is an associated cost of having to walk back the history to check the reachability.

    This feature can be used when obtaining the content of a certain commit, for which the sha1 is known, without the need of cloning the whole repository, especially if a shallow fetch is used.

    Useful cases are e.g.

    • repositories containing large files in the history,
    • fetching only the needed data for a submodule checkout,
    • when sharing a sha1 without telling which exact branch it belongs to and in Gerrit, if you think in terms of commits instead of change numbers.
      (The Gerrit case has already been solved through allowTipSHA1InWant as every Gerrit change has a ref.)

    Git 2.6 (Q3 2015) will improve that model.
    See commit 2bc31d1, commit cc118a6 (28 Jul 2015) by Jeff King (peff).
    (Merged by Junio C Hamano -- gitster -- in commit 824a0be, 19 Aug 2015)

    refs: support negative transfer.hideRefs

    If you hide a hierarchy of refs using the transfer.hideRefs config, there is no way to later override that config to "unhide" it.
    This patch implements a "negative" hide which causes matches to immediately be marked as unhidden, even if another match would hide it.
    We take care to apply the matches in reverse-order from how they are fed to us by the config machinery, as that lets our usual "last one wins" config precedence work (and entries in .git/config, for example, will override /etc/gitconfig).

    So you can now do:

    git config --system transfer.hideRefs refs/secret
git config transfer.hideRefs '!refs/secret/not-so-secret'

    to hide refs/secret in all repos, except for one public bit in one specific repo.

    Git 2.7 (Nov/Dec 2015) will improve again:

    See commit 948bfa2, commit 00b293e (05 Nov 2015), commit 78a766a, commit 92cab49, commit 92cab49, commit 92cab49 (03 Nov 2015), commit 00b293e, commit 00b293e (05 Nov 2015), and commit 92cab49, commit 92cab49, commit 92cab49, commit 92cab49 (03 Nov 2015) by Lukas Fleischer (lfos).
    Helped-by: Eric Sunshine (sunshineco).
    (Merged by Jeff King -- peff -- in commit dbba85e, 20 Nov 2015)

    config.txt: document the semantics of hideRefs with namespaces

    Right now, there is no clear definition of how transfer.hideRefs should behave when a namespace is set.
    Explain that hideRefs prefixes match stripped names in that case. This is how hideRefs patterns are currently handled in receive-pack.

    hideRefs: add support for matching full refs

    In addition to matching stripped refs, one can now add hideRefs patterns that the full (unstripped) ref is matched against.
    To distinguish between stripped and full matches, those new patterns must be prefixed with a circumflex (^).

    Hence the new documentation:

    transfer.hideRefs:

    If a namespace is in use, the namespace prefix is stripped from each reference before it is matched against transfer.hiderefs patterns.
    For example, if refs/heads/master is specified in transfer.hideRefs and the current namespace is foo, then refs/namespaces/foo/refs/heads/master is omitted from the advertisements but refs/heads/master and refs/namespaces/bar/refs/heads/master are still advertised as so-called "have" lines.
    In order to match refs before stripping, add a ^ in front of the ref name. If you combine ! and ^, ! must be specified first.

    R.. mentions in the comments the config uploadpack.allowAnySHA1InWant, which allows upload-pack to accept a fetch request that asks for any object at all. (Defaults to false).

    See commit f8edeaa (Nov. 2016, Git v2.11.1) by David "novalis" Turner (novalis):

    upload-pack: optionally allow fetching any sha1

    It seems a little silly to do a reachabilty check in the case where we trust the user to access absolutely everything in the repository.

    Also, it's racy in a distributed system -- perhaps one server advertises a ref, but another has since had a force-push to that ref, and perhaps the two HTTP requests end up directed to these different servers.

    With Git 2.34 (Q4 2021), "git upload-pack"(man) which runs on the other side of git fetch(man) forgot to take the ref namespaces into account when handling want-ref requests.

    See commit 53a66ec, commit 3955140, commit bac01c6 (13 Aug 2021) by Kim Altintop (kim).
    (Merged by Junio C Hamano -- gitster -- in commit 1ab13eb, 10 Sep 2021)

    docs: clarify the interaction of transfer.hideRefs and namespaces

    Signed-off-by: Kim Altintop
    Reviewed-by: Jonathan Tan

    Expand the section about namespaces in the documentation of transfer.hideRefs to point out the subtle differences between upload-pack and receive-pack.

    3955140 ("upload-pack.c: treat want-ref relative to namespace", 2021-07-30, Git v2.34.0 -- merge listed in batch #5) taught upload-pack to reject want-refs for hidden refs, which is now mentioned.
    It is clarified that at no point the name of a hidden ref is revealed, but the object id it points to may.

    git config now includes in its man page:

    reference before it is matched against transfer.hiderefs patterns. In order to match refs before stripping, add a ^ in front of the ref name. If you combine ! and ^, ! must be specified first.

    git config now includes in its man page:

    is omitted from the advertisements. If uploadpack.allowRefInWant is set, upload-pack will treat want-ref refs/heads/master in a protocol v2 fetch command as if refs/namespaces/foo/refs/heads/master did not exist. receive-pack, on the other hand, will still advertise the object id the ref is pointing to without mentioning its name (a so-called ".have" line).

    With Git 2.39 (Q4 2022), "git receive-pack"(man) used to use all the local refs as the boundary for checking connectivity of the data git push(man) sent, but now it uses only the refs that it advertised to the pusher.
    In a repository with the .hideRefs configuration, this reduces the resources needed to perform the check.

    See commit bcec678, commit 5ff36c9, commit 8c1bc2a, commit 1e9f273, commit 05b9425, commit 9b67eb6, commit 5eeb9aa (17 Nov 2022) by Patrick Steinhardt (pks-t).
    (Merged by Junio C Hamano -- gitster -- in commit f8828f9, 23 Nov 2022)

    revision: add new parameter to exclude hidden refs

    Signed-off-by: Patrick Steinhardt
    Signed-off-by: Taylor Blau

    Users can optionally hide refs from remote users in git-upload-pack(1), git-receive-pack(1) and others via the transfer.hideRefs, but there is not an easy way to obtain the list of all visible or hidden refs right now.
    We'll require just that though for a performance improvement in our connectivity check.

    Add a new option --exclude-hidden= that excludes any hidden refs from the next pseudo-ref like --all or --branches.

    rev-list-options now includes in its man page:

    --exclude-hidden=[receive|uploadpack]

    Do not include refs that would be hidden by git-receive-pack or git-upload-pack by consulting the appropriate receive.hideRefs or uploadpack.hideRefs configuration along with transfer.hideRefs (see git config). This option affects the next pseudo-ref option --all or --glob and is cleared after processing them.

    And:

    rev-parse: add --exclude-hidden= option

    Signed-off-by: Patrick Steinhardt
    Signed-off-by: Taylor Blau

    Add a new --exclude-hidden= option that is similar to the one we just added to git-rev-list(1).
    Given a section name uploadpack or receive as argument, it causes us to exclude all references that would be hidden by the respective $section.hideRefs configuration.

    git rev-parse now includes in its man page:

    --exclude-hidden=[receive|uploadpack]

    Do not include refs that would be hidden by git-receive-pack or git-upload-pack by consulting the appropriate receive.hideRefs or uploadpack.hideRefs configuration along with transfer.hideRefs (see git config). This option affects the next pseudo-ref option --all or --glob and is cleared after processing them.