connect: tighten check for unexpected early hang up

A server hanging up immediately to mark access being denied does not
send any .have refs, shallow lines, or anything else before hanging
up.  If the server has sent anything, then the hangup is unexpected.

That is, if the server hangs up after a shallow line but before sending
any refs, then git should tell me so:

	fatal: The remote end hung up upon initial contact

instead of suggesting an access control problem:

	fatal: Could not read from remote repository.
	Please make sure you have the correct access rights
	and the repository exists.

Noticed while examining this code.  This case isn't likely to come up
in practice but tightening the check makes the code easier to read and
manipulate.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

connect.c

@@ -43,9 +43,9 @@ int check_ref_type(const struct ref *ref, int flags)
 	return check_ref(ref->name, flags);
 }
 
-static void die_initial_contact(int got_at_least_one_head)
+static void die_initial_contact(int unexpected)
 {
-	if (got_at_least_one_head)
+	if (unexpected)
 		die("The remote end hung up upon initial contact");
 	else
 		die("Could not read from remote repository.\n\n"
@@ -115,10 +115,17 @@ struct ref **get_remote_heads(int in, char *src_buf, size_t src_len,
 			      struct sha1_array *shallow_points)
 {
 	struct ref **orig_list = list;
-	int got_at_least_one_head = 0;
+
+	/*
+	 * A hang-up after seeing some response from the other end
+	 * means that it is unexpected, as we know the other end is
+	 * willing to talk to us.  A hang-up before seeing any
+	 * response does not necessarily mean an ACL problem, though.
+	 */
+	int saw_response;
 
 	*list = NULL;
-	for (;;) {
+	for (saw_response = 0; ; saw_response = 1) {
 		struct ref *ref;
 		struct object_id old_oid;
 		char *name;
@@ -131,7 +138,7 @@ struct ref **get_remote_heads(int in, char *src_buf, size_t src_len,
 				  PACKET_READ_GENTLE_ON_EOF |
 				  PACKET_READ_CHOMP_NEWLINE);
 		if (len < 0)
-			die_initial_contact(got_at_least_one_head);
+			die_initial_contact(saw_response);
 
 		if (!len)
 			break;
@@ -171,7 +178,6 @@ struct ref **get_remote_heads(int in, char *src_buf, size_t src_len,
 		oidcpy(&ref->old_oid, &old_oid);
 		*list = ref;
 		list = &ref->next;
-		got_at_least_one_head = 1;
 	}
 
 	annotate_refs_with_symref_info(*orig_list);