Support mandatory capabilities

Add support for marking capability as mandatory for hosting git version
to understand. This is useful for helpers which require various types
of assistance from main git binary.

Signed-off-by: Ilari Liusvaara <ilari.liusvaara@elisanet.fi>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 23 insertions, 7 deletions

diff --git a/Documentation/git-remote-helpers.txt b/Documentation/git-remote-helpers.txt
index 5cfdc0cfc5..20a05fe9d8 100644
--- a/Documentation/git-remote-helpers.txt
+++ b/Documentation/git-remote-helpers.txt
@@ -25,7 +25,10 @@ Commands are given by the caller on the helper's standard input, one per line.
 
 'capabilities'::
 	Lists the capabilities of the helper, one per line, ending
-	with a blank line.
+	with a blank line. Each capability may be preceeded with '*'.
+	This marks them mandatory for git version using the remote
+	helper to understand (unknown mandatory capability is fatal
+	error).
 
 'list'::
 	Lists the refs, one per line, in the format "<value> <name>
diff --git a/transport-helper.c b/transport-helper.c
index a721dc25be..4b17aaa237 100644
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -93,25 +93,38 @@ static struct child_process *get_helper(struct transport *transport)
 
 	data->out = xfdopen(helper->out, "r");
 	while (1) {
+		const char *capname;
+		int mandatory = 0;
 		recvline(data, &buf);
 
 		if (!*buf.buf)
 			break;
+
+		if (*buf.buf == '*') {
+			capname = buf.buf + 1;
+			mandatory = 1;
+		} else
+			capname = buf.buf;
+
 		if (debug)
-			fprintf(stderr, "Debug: Got cap %s\n", buf.buf);
-		if (!strcmp(buf.buf, "fetch"))
+			fprintf(stderr, "Debug: Got cap %s\n", capname);
+		if (!strcmp(capname, "fetch"))
 			data->fetch = 1;
-		if (!strcmp(buf.buf, "option"))
+		else if (!strcmp(capname, "option"))
 			data->option = 1;
-		if (!strcmp(buf.buf, "push"))
+		else if (!strcmp(capname, "push"))
 			data->push = 1;
-		if (!strcmp(buf.buf, "import"))
+		else if (!strcmp(capname, "import"))
 			data->import = 1;
-		if (!data->refspecs && !prefixcmp(buf.buf, "refspec ")) {
+		else if (!data->refspecs && !prefixcmp(capname, "refspec ")) {
 			ALLOC_GROW(refspecs,
 				   refspec_nr + 1,
 				   refspec_alloc);
 			refspecs[refspec_nr++] = strdup(buf.buf + strlen("refspec "));
+		} else if (mandatory) {
+			die("Unknown madatory capability %s. This remote "
+			    "helper probably needs newer version of Git.\n",
+			    capname);
 		}
 	}
 	if (refspecs) {