connect: request remote refs using v2

Teach the client to be able to request a remote's refs using protocol
v2.  This is done by having a client issue a 'ls-refs' request to a v2
server.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

connect.c

@@ -12,9 +12,11 @@
 #include "sha1-array.h"
 #include "transport.h"
 #include "strbuf.h"
+#include "version.h"
 #include "protocol.h"
 
-static char *server_capabilities;
+static char *server_capabilities_v1;
+static struct argv_array server_capabilities_v2 = ARGV_ARRAY_INIT;
 static const char *parse_feature_value(const char *, const char *, int *);
 
 static int check_ref(const char *name, unsigned int flags)
@@ -62,6 +64,33 @@ static void die_initial_contact(int unexpected)
 		      "and the repository exists."));
 }
 
+/* Checks if the server supports the capability 'c' */
+int server_supports_v2(const char *c, int die_on_error)
+{
+	int i;
+
+	for (i = 0; i < server_capabilities_v2.argc; i++) {
+		const char *out;
+		if (skip_prefix(server_capabilities_v2.argv[i], c, &out) &&
+		    (!*out || *out == '='))
+			return 1;
+	}
+
+	if (die_on_error)
+		die("server doesn't support '%s'", c);
+
+	return 0;
+}
+
+static void process_capabilities_v2(struct packet_reader *reader)
+{
+	while (packet_reader_read(reader) == PACKET_READ_NORMAL)
+		argv_array_push(&server_capabilities_v2, reader->line);
+
+	if (reader->status != PACKET_READ_FLUSH)
+		die("expected flush after capabilities");
+}
+
 enum protocol_version discover_version(struct packet_reader *reader)
 {
 	enum protocol_version version = protocol_unknown_version;
@@ -84,7 +113,7 @@ enum protocol_version discover_version(struct packet_reader *reader)
 
 	switch (version) {
 	case protocol_v2:
-		die("support for protocol v2 not implemented yet");
+		process_capabilities_v2(reader);
 		break;
 	case protocol_v1:
 		/* Read the peeked version line */
@@ -128,7 +157,7 @@ reject:
 static void annotate_refs_with_symref_info(struct ref *ref)
 {
 	struct string_list symref = STRING_LIST_INIT_DUP;
-	const char *feature_list = server_capabilities;
+	const char *feature_list = server_capabilities_v1;
 
 	while (feature_list) {
 		int len;
@@ -157,7 +186,7 @@ static void process_capabilities(const char *line, int *len)
 	int nul_location = strlen(line);
 	if (nul_location == *len)
 		return;
-	server_capabilities = xstrdup(line + nul_location + 1);
+	server_capabilities_v1 = xstrdup(line + nul_location + 1);
 	*len = nul_location;
 }
 
@@ -292,6 +321,105 @@ struct ref **get_remote_heads(struct packet_reader *reader,
 	return list;
 }
 
+/* Returns 1 when a valid ref has been added to `list`, 0 otherwise */
+static int process_ref_v2(const char *line, struct ref ***list)
+{
+	int ret = 1;
+	int i = 0;
+	struct object_id old_oid;
+	struct ref *ref;
+	struct string_list line_sections = STRING_LIST_INIT_DUP;
+	const char *end;
+
+	/*
+	 * Ref lines have a number of fields which are space deliminated.  The
+	 * first field is the OID of the ref.  The second field is the ref
+	 * name.  Subsequent fields (symref-target and peeled) are optional and
+	 * don't have a particular order.
+	 */
+	if (string_list_split(&line_sections, line, ' ', -1) < 2) {
+		ret = 0;
+		goto out;
+	}
+
+	if (parse_oid_hex(line_sections.items[i++].string, &old_oid, &end) ||
+	    *end) {
+		ret = 0;
+		goto out;
+	}
+
+	ref = alloc_ref(line_sections.items[i++].string);
+
+	oidcpy(&ref->old_oid, &old_oid);
+	**list = ref;
+	*list = &ref->next;
+
+	for (; i < line_sections.nr; i++) {
+		const char *arg = line_sections.items[i].string;
+		if (skip_prefix(arg, "symref-target:", &arg))
+			ref->symref = xstrdup(arg);
+
+		if (skip_prefix(arg, "peeled:", &arg)) {
+			struct object_id peeled_oid;
+			char *peeled_name;
+			struct ref *peeled;
+			if (parse_oid_hex(arg, &peeled_oid, &end) || *end) {
+				ret = 0;
+				goto out;
+			}
+
+			peeled_name = xstrfmt("%s^{}", ref->name);
+			peeled = alloc_ref(peeled_name);
+
+			oidcpy(&peeled->old_oid, &peeled_oid);
+			**list = peeled;
+			*list = &peeled->next;
+
+			free(peeled_name);
+		}
+	}
+
+out:
+	string_list_clear(&line_sections, 0);
+	return ret;
+}
+
+struct ref **get_remote_refs(int fd_out, struct packet_reader *reader,
+			     struct ref **list, int for_push,
+			     const struct argv_array *ref_prefixes)
+{
+	int i;
+	*list = NULL;
+
+	if (server_supports_v2("ls-refs", 1))
+		packet_write_fmt(fd_out, "command=ls-refs\n");
+
+	if (server_supports_v2("agent", 0))
+		packet_write_fmt(fd_out, "agent=%s", git_user_agent_sanitized());
+
+	packet_delim(fd_out);
+	/* When pushing we don't want to request the peeled tags */
+	if (!for_push)
+		packet_write_fmt(fd_out, "peel\n");
+	packet_write_fmt(fd_out, "symrefs\n");
+	for (i = 0; ref_prefixes && i < ref_prefixes->argc; i++) {
+		packet_write_fmt(fd_out, "ref-prefix %s\n",
+				 ref_prefixes->argv[i]);
+	}
+	packet_flush(fd_out);
+
+	/* Process response from server */
+	while (packet_reader_read(reader) == PACKET_READ_NORMAL) {
+		if (!process_ref_v2(reader->line, &list))
+			die("invalid ls-refs response: %s", reader->line);
+	}
+
+	if (reader->status != PACKET_READ_FLUSH)
+		die("expected flush after ref listing");
+
+	return list;
+}
+
 static const char *parse_feature_value(const char *feature_list, const char *feature, int *lenp)
 {
 	int len;
@@ -336,7 +464,7 @@ int parse_feature_request(const char *feature_list, const char *feature)
 
 const char *server_feature_value(const char *feature, int *len)
 {
-	return parse_feature_value(server_capabilities, feature, len);
+	return parse_feature_value(server_capabilities_v1, feature, len);
 }
 
 int server_supports(const char *feature)