The dumb HTTP transport tries to read the remote HEAD reference by
downloading the "HEAD" file and then parsing it via `http_fetch_ref()`.
This function will either parse the file as an object ID in case it is
exactly `the_hash_algo->hexsz` long, or otherwise it will check whether
the reference starts with "ref :" and parse it as a symbolic ref.
This is broken when parsing detached HEADs of a remote SHA256 repository
because we never update `the_hash_algo` to the discovered remote object
hash. Consequently, `the_hash_algo` will always be the fallback SHA1
hash algorithm, which will cause us to fail parsing HEAD altogteher when
it contains a SHA256 object ID.
Fix this issue by setting up `the_hash_algo` via `repo_set_hash_algo()`.
While at it, let's make the expected SHA1 fallback explicit in our code,
which also addresses an upcoming issue where we are going to remove the
SHA1 fallback for `the_hash_algo`.
Signed-off-by: Patrick Steinhardt <ps@xxxxxx>
---
remote-curl.c | 19 ++++++++++++++++++-
t/t5550-http-fetch-dumb.sh | 15 +++++++++++++++
2 files changed, 33 insertions(+), 1 deletion(-)
diff --git a/remote-curl.c b/remote-curl.c
index 0b6d7815fd..004b707fdf 100644
--- a/remote-curl.c
+++ b/remote-curl.c
@@ -266,12 +266,23 @@ static struct ref *parse_git_refs(struct discovery *heads, int for_push)
return list;
}
+/*
+ * Try to detect the hash algorithm used by the remote repository when using
+ * the dumb HTTP transport. As dumb transports cannot tell us the object hash
+ * directly have to derive it from the advertised ref lengths.
+ */
static const struct git_hash_algo *detect_hash_algo(struct discovery *heads)
{
const char *p = memchr(heads->buf, '\t', heads->len);
int algo;
+
+ /*
+ * In case the remote has no refs we have no way to reliably determine
+ * the object hash used by that repository. In that case we simply fall
+ * back to SHA1, which may or may not be correct.
+ */
if (!p)
- return the_hash_algo;
+ return &hash_algos[GIT_HASH_SHA1];
algo = hash_algo_by_length((p - heads->buf) / 2);
if (algo == GIT_HASH_UNKNOWN)
@@ -295,6 +306,12 @@ static struct ref *parse_info_refs(struct discovery *heads)
"is this a git repository?",
transport_anonymize_url(url.buf));
+ /*
+ * Set the repository's hash algo to whatever we have just detected.
+ * This ensures that we can correctly parse the remote references.
+ */
+ repo_set_hash_algo(the_repository, hash_algo_by_ptr(options.hash_algo));
+
data = heads->buf;
start = NULL;
mid = data;
diff --git a/t/t5550-http-fetch-dumb.sh b/t/t5550-http-fetch-dumb.sh
index 4c3b32785d..5f16cbc58d 100755
--- a/t/t5550-http-fetch-dumb.sh
+++ b/t/t5550-http-fetch-dumb.sh
@@ -55,6 +55,21 @@ test_expect_success 'list refs from outside any repository' '
test_cmp expect actual
'
+
+test_expect_success 'list detached HEAD from outside any repository' '
+ git clone --mirror "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" \
+ "$HTTPD_DOCUMENT_ROOT_PATH/repo-detached.git" &&
+ git -C "$HTTPD_DOCUMENT_ROOT_PATH/repo-detached.git" \
+ update-ref --no-deref HEAD refs/heads/main &&
+ git -C "$HTTPD_DOCUMENT_ROOT_PATH/repo-detached.git" update-server-info &&
+ cat >expect <<-EOF &&
+ $(git rev-parse main) HEAD
+ $(git rev-parse main) refs/heads/main
+ EOF
+ nongit git ls-remote "$HTTPD_URL/dumb/repo-detached.git" >actual &&
+ test_cmp expect actual
+'
+
test_expect_success 'create password-protected repository' '
mkdir -p "$HTTPD_DOCUMENT_ROOT_PATH/auth/dumb/" &&
cp -Rf "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" \
--
2.44.GIT
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