diff options
authorTaylor Blau <>2018-10-08 18:09:28 (GMT)
committerJunio C Hamano <>2018-10-09 05:30:03 (GMT)
commit89284c1d6ca03480a93f9d95a2460a09390f3c40 (patch)
parent1e5f31d444436cfab1b1aef3026ffbd925f5a818 (diff)
transport.c: introduce core.alternateRefsCommand
When in a repository containing one or more alternates, Git would sometimes like to list references from those alternates. For example, 'git receive-pack' lists the "tips" pointed to by references in those alternates as special ".have" references. Listing ".have" references is designed to make pushing changes from upstream to a fork a lightweight operation, by advertising to the pusher that the fork already has the objects (via its alternate). Thus, the client can avoid sending them. However, when the alternate (upstream, in the previous example) has a pathologically large number of references, the initial advertisement is too expensive. In fact, it can dominate any such optimization where the pusher avoids sending certain objects. Introduce "core.alternateRefsCommand" in order to provide a facility to limit or filter alternate references. This can be used, for example, to filter out references the alternate does not wish to send (for space concerns, or otherwise) during the initial advertisement. Let the repository that has alternates configure this command to avoid trusting the alternate to provide us a safe command to run in the shell. To find the alternate, pass its absolute path as the first argument. Signed-off-by: Taylor Blau <> Acked-by: Jeff King <> Signed-off-by: Junio C Hamano <>
3 files changed, 59 insertions, 4 deletions
diff --git a/Documentation/config.txt b/Documentation/config.txt
index eb66a11..00224de 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -616,6 +616,17 @@ core.preferSymlinkRefs::
This is sometimes needed to work with old scripts that
expect HEAD to be a symbolic link.
+ When advertising tips of available history from an alternate, use the shell to
+ execute the specified command instead of linkgit:git-for-each-ref[1]. The
+ first argument is the absolute path of the alternate. Output must contain one
+ hex object id per line (i.e., the same as produce by `git for-each-ref
+ --format='%(objectname)'`).
+Note that you cannot generally put `git for-each-ref` directly into the config
+value, as it does not take a repository path as an argument (but you can wrap
+the command above in a shell script).
If true this repository is assumed to be 'bare' and has no
working directory associated with it. If this is the case a
diff --git a/t/ b/t/
new file mode 100755
index 0000000..49d0fe4
--- /dev/null
+++ b/t/
@@ -0,0 +1,33 @@
+test_description='git receive-pack with alternate ref filtering'
+. ./
+test_expect_success 'setup' '
+ test_commit base &&
+ git clone -s --bare . fork &&
+ git checkout -b public/branch master &&
+ test_commit public &&
+ git checkout -b private/branch master &&
+ test_commit private
+extract_haves () {
+ depacketize | perl -lne '/^(\S+) \.have/ and print $1'
+test_expect_success 'with core.alternateRefsCommand' '
+ write_script fork/alternate-refs <<-\EOF &&
+ git --git-dir="$1" for-each-ref \
+ --format="%(objectname)" \
+ refs/heads/public/
+ test_config -C fork core.alternateRefsCommand alternate-refs &&
+ git rev-parse public/branch >expect &&
+ printf "0000" | git receive-pack fork >actual &&
+ extract_haves <actual >actual.haves &&
+ test_cmp expect actual.haves
diff --git a/transport.c b/transport.c
index 25d8ea7..19baec7 100644
--- a/transport.c
+++ b/transport.c
@@ -1328,10 +1328,21 @@ literal_copy:
static void fill_alternate_refs_command(struct child_process *cmd,
const char *repo_path)
- cmd->git_cmd = 1;
- argv_array_pushf(&cmd->args, "--git-dir=%s", repo_path);
- argv_array_push(&cmd->args, "for-each-ref");
- argv_array_push(&cmd->args, "--format=%(objectname)");
+ const char *value;
+ if (!git_config_get_value("core.alternateRefsCommand", &value)) {
+ cmd->use_shell = 1;
+ argv_array_push(&cmd->args, value);
+ argv_array_push(&cmd->args, repo_path);
+ } else {
+ cmd->git_cmd = 1;
+ argv_array_pushf(&cmd->args, "--git-dir=%s", repo_path);
+ argv_array_push(&cmd->args, "for-each-ref");
+ argv_array_push(&cmd->args, "--format=%(objectname)");
+ }
cmd->env = local_repo_env;
cmd->out = -1;