transport: log received server session ID

When a client receives a session-id capability from a protocol v0, v1,
or v2 server, log the received session ID via a trace2 data event.

Signed-off-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t5705-session-id-in-capabilities.sh

@@ -0,0 +1,64 @@
+#!/bin/sh
+
+test_description='session ID in capabilities'
+
+. ./test-lib.sh
+
+REPO="$(pwd)/repo"
+LOCAL_PRISTINE="$(pwd)/local_pristine"
+
+test_expect_success 'setup repos for session ID capability tests' '
+	git init "$REPO" &&
+	test_commit -C "$REPO" a &&
+	git clone "file://$REPO" "$LOCAL_PRISTINE" &&
+	test_commit -C "$REPO" b
+'
+
+for PROTO in 0 1 2
+do
+	test_expect_success "session IDs not advertised by default (fetch v${PROTO})" '
+		test_when_finished "rm -rf local tr2-client-events" &&
+		cp -r "$LOCAL_PRISTINE" local &&
+		GIT_TRACE2_EVENT="$(pwd)/tr2-client-events" \
+		git -c protocol.version=$PROTO -C local fetch origin &&
+		test -z "$(grep \"key\":\"server-sid\" tr2-client-events)"
+	'
+
+	test_expect_success "session IDs not advertised by default (push v${PROTO})" '
+		test_when_finished "rm -rf local tr2-client-events" &&
+		cp -r "$LOCAL_PRISTINE" local &&
+		git -C local pull --no-rebase origin &&
+		GIT_TRACE2_EVENT_NESTING=5 \
+		GIT_TRACE2_EVENT="$(pwd)/tr2-client-events" \
+		git -c protocol.version=$PROTO -C local push origin &&
+		test -z "$(grep \"key\":\"server-sid\" tr2-client-events)"
+	'
+done
+
+test_expect_success 'enable SID advertisement' '
+	git -C "$REPO" config transfer.advertiseSID true &&
+	git -C "$LOCAL_PRISTINE" config transfer.advertiseSID true
+'
+
+for PROTO in 0 1 2
+do
+	test_expect_success "session IDs advertised (fetch v${PROTO})" '
+		test_when_finished "rm -rf local tr2-client-events" &&
+		cp -r "$LOCAL_PRISTINE" local &&
+		GIT_TRACE2_EVENT="$(pwd)/tr2-client-events" \
+		git -c protocol.version=$PROTO -C local fetch origin &&
+		grep \"key\":\"server-sid\" tr2-client-events
+	'
+
+	test_expect_success "session IDs advertised (push v${PROTO})" '
+		test_when_finished "rm -rf local tr2-client-events" &&
+		cp -r "$LOCAL_PRISTINE" local &&
+		git -C local pull --no-rebase origin &&
+		GIT_TRACE2_EVENT_NESTING=5 \
+		GIT_TRACE2_EVENT="$(pwd)/tr2-client-events" \
+		git -c protocol.version=$PROTO -C local push origin &&
+		grep \"key\":\"server-sid\" tr2-client-events
+	'
+done
+
+test_done

transport.c

@@ -286,6 +286,8 @@ static struct ref *handshake(struct transport *transport, int for_push,
 	struct git_transport_data *data = transport->data;
 	struct ref *refs = NULL;
 	struct packet_reader reader;
+	int sid_len;
+	const char *server_sid;
 
 	connect_setup(transport, for_push);
 
@@ -297,6 +299,8 @@ static struct ref *handshake(struct transport *transport, int for_push,
 	data->version = discover_version(&reader);
 	switch (data->version) {
 	case protocol_v2:
+		if (server_feature_v2("session-id", &server_sid))
+			trace2_data_string("transfer", NULL, "server-sid", server_sid);
 		if (must_list_refs)
 			get_remote_refs(data->fd[1], &reader, &refs, for_push,
 					ref_prefixes,
@@ -310,6 +314,12 @@ static struct ref *handshake(struct transport *transport, int for_push,
 				 for_push ? REF_NORMAL : 0,
 				 &data->extra_have,
 				 &data->shallow);
+		server_sid = server_feature_value("session-id", &sid_len);
+		if (server_sid) {
+			char *sid = xstrndup(server_sid, sid_len);
+			trace2_data_string("transfer", NULL, "server-sid", sid);
+			free(sid);
+		}
 		break;
 	case protocol_unknown_version:
 		BUG("unknown protocol version");