When cloning an empty repository served by standard git, "git clone" produces
the following reassuring message:

        $ git clone git://localhost/tmp/empty
        Cloning into 'empty'...
        warning: You appear to have cloned an empty repository.
        Checking connectivity... done.

Meanwhile when cloning an empty repository served by JGit, the output is more

        $ git clone git://localhost/tmp/empty
        Cloning into 'empty'...
        Checking connectivity... done.
        warning: remote HEAD refers to nonexistent ref, unable to checkout.

This is a common command to run immediately after creating a remote repository
as preparation for adding content to populate it and pushing. The warning is
confusing and needlessly worrying.

The cause is that, since v3.1.0.201309270735-rc1~22 (Advertise capabilities
with no refs in upload service., 2013-08-08), JGit's ref advertisement includes
a ref named capabilities^{} to advertise its capabilities on, while git's ref
advertisement is empty in this case. This allows the client to learn about the
server's capabilities and is needed, for example, for fetch-by-sha1 to work
when no refs are advertised.

This also affects "ls-remote". For example, against an empty repository served
by JGit:

        $ git ls-remote git://localhost/tmp/empty
        0000000000000000000000000000000000000000        capabilities^{}

Git advertises the same capabilities^{} ref in its ref advertisement for push
but since it never remembered to do so for fetch, the client forgot to handle
this case. Handle it.

In this aspect, JGit is compliant with the specification in pack-protocol.txt.
Because git client versions without this fix are expected to exist in the wild
for a while, we should not change the server to always send the capabilities^{}
line when there are no refs to advertise yet.  A transition will take multiple

 1. This patch, which updates the client

 2. Update pack-protocol to clarify that both server behaviors must be

 3. Add a configuration variable to allow git upload-pack to advertise
    capabilities when there are no refs to advertise.  Leave it disabled
    by default since git clients can't be counted on to have this patch (1)

 4. After a year or so, flip the default for that server configuration
    variable to true.

Signed-off-by: Jonathan Tan <jonathanta...@google.com>
 connect.c            |  3 +++
 t/t5512-ls-remote.sh | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/connect.c b/connect.c
index 722dc3f..0c2221e 100644
--- a/connect.c
+++ b/connect.c
@@ -165,6 +165,9 @@ struct ref **get_remote_heads(int in, char *src_buf, size_t 
+               if (!strcmp(name, "capabilities^{}"))
+                       continue;
                if (!check_ref(name, flags))
                ref = alloc_ref(buffer + GIT_SHA1_HEXSZ + 1);
diff --git a/t/t5512-ls-remote.sh b/t/t5512-ls-remote.sh
index 819b9dd..2de52f5 100755
--- a/t/t5512-ls-remote.sh
+++ b/t/t5512-ls-remote.sh
@@ -207,5 +207,44 @@ test_expect_success 'ls-remote --symref omits filtered-out 
matches' '
        test_cmp expect actual
+test_lazy_prereq GIT_DAEMON '
+       test_tristate GIT_TEST_GIT_DAEMON &&
+       test "$GIT_TEST_GIT_DAEMON" != false
+# This test spawns a daemon, so run it only if the user would be OK with
+# testing with git-daemon.
+test_expect_success PIPE,JGIT,GIT_DAEMON 'indicate no refs in 
standards-compliant empty remote' '
+       JGIT_DAEMON_PID= &&
+       git init --bare empty.git &&
+       touch empty.git/git-daemon-export-ok &&
+       mkfifo jgit_daemon_output &&
+       {
+               jgit daemon --port="$JGIT_DAEMON_PORT" . >jgit_daemon_output &
+               JGIT_DAEMON_PID=$!
+       } &&
+       test_when_finished kill "$JGIT_DAEMON_PID" &&
+       {
+               read line &&
+               case $line in
+               Exporting*)
+                       ;;
+               *)
+                       echo "Expected: Exporting" &&
+                       false;;
+               esac &&
+               read line &&
+               case $line in
+               "Listening on"*)
+                       ;;
+               *)
+                       echo "Expected: Listening on" &&
+                       false;;
+               esac
+       } <jgit_daemon_output &&
+       test_expect_code 2 git ls-remote --exit-code 

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