Merge branch 'dl/remote-curl-deadlock-fix'

On-the-wire protocol v2 easily falls into a deadlock between the
remote-curl helper and the fetch-pack process when the server side
prematurely throws an error and disconnects.  The communication has
been updated to make it more robust.

* dl/remote-curl-deadlock-fix:
  stateless-connect: send response end packet
  pkt-line: define PACKET_READ_RESPONSE_END
  remote-curl: error on incomplete packet
  pkt-line: extern packet_length()
  transport: extract common fetch_pack() call
  remote-curl: remove label indentation
  remote-curl: fix typo

Author: gitster

Documentation/gitremote-helpers.txt

@@ -405,7 +405,9 @@ Supported if the helper has the "connect" capability.
 	trying to fall back).  After line feed terminating the positive
 	(empty) response, the output of the service starts.  Messages
 	(both request and response) must consist of zero or more
-	PKT-LINEs, terminating in a flush packet. The client must not
+	PKT-LINEs, terminating in a flush packet. Response messages will
+	then have a response end packet after the flush packet to
+	indicate the end of a response.  The client must not
 	expect the server to store any state in between request-response
 	pairs.  After the connection ends, the remote helper exits.
 +

Documentation/technical/protocol-v2.txt

@@ -33,6 +33,8 @@ In protocol v2 these special packets will have the following semantics:
 
   * '0000' Flush Packet (flush-pkt) - indicates the end of a message
   * '0001' Delimiter Packet (delim-pkt) - separates sections of a message
+  * '0002' Message Packet (response-end-pkt) - indicates the end of a response
+    for stateless connections
 
 Initial Client Request
 ----------------------

builtin/fetch-pack.c

@@ -224,7 +224,7 @@ int cmd_fetch_pack(int argc, const char **argv, const char *prefix)
 	version = discover_version(&reader);
 	switch (version) {
 	case protocol_v2:
-		get_remote_refs(fd[1], &reader, &ref, 0, NULL, NULL);
+		get_remote_refs(fd[1], &reader, &ref, 0, NULL, NULL, args.stateless_rpc);
 		break;
 	case protocol_v1:
 	case protocol_v0:

connect.c

@@ -127,6 +127,7 @@ enum protocol_version discover_version(struct packet_reader *reader)
 		die_initial_contact(0);
 	case PACKET_READ_FLUSH:
 	case PACKET_READ_DELIM:
+	case PACKET_READ_RESPONSE_END:
 		version = protocol_v0;
 		break;
 	case PACKET_READ_NORMAL:
@@ -310,6 +311,7 @@ struct ref **get_remote_heads(struct packet_reader *reader,
 			state = EXPECTING_DONE;
 			break;
 		case PACKET_READ_DELIM:
+		case PACKET_READ_RESPONSE_END:
 			die(_("invalid packet"));
 		}
 
@@ -404,10 +406,21 @@ static int process_ref_v2(const char *line, struct ref ***list)
 	return ret;
 }
 
+void check_stateless_delimiter(int stateless_rpc,
+			      struct packet_reader *reader,
+			      const char *error)
+{
+	if (!stateless_rpc)
+		return; /* not in stateless mode, no delimiter expected */
+	if (packet_reader_read(reader) != PACKET_READ_RESPONSE_END)
+		die("%s", error);
+}
+
 struct ref **get_remote_refs(int fd_out, struct packet_reader *reader,
 			     struct ref **list, int for_push,
 			     const struct argv_array *ref_prefixes,
-			     const struct string_list *server_options)
+			     const struct string_list *server_options,
+			     int stateless_rpc)
 {
 	int i;
 	*list = NULL;
@@ -444,6 +457,9 @@ struct ref **get_remote_refs(int fd_out, struct packet_reader *reader,
 	if (reader->status != PACKET_READ_FLUSH)
 		die(_("expected flush after ref listing"));
 
+	check_stateless_delimiter(stateless_rpc, reader,
+				  _("expected response end packet after ref listing"));
+
 	return list;
 }
 

connect.h

@@ -22,4 +22,8 @@ int server_supports_v2(const char *c, int die_on_error);
 int server_supports_feature(const char *c, const char *feature,
 			    int die_on_error);
 
+void check_stateless_delimiter(int stateless_rpc,
+			       struct packet_reader *reader,
+			       const char *error);
+
 #endif

fetch-pack.c

@@ -1451,6 +1451,13 @@ enum fetch_state {
 	FETCH_DONE,
 };
 
+static void do_check_stateless_delimiter(const struct fetch_pack_args *args,
+					 struct packet_reader *reader)
+{
+	check_stateless_delimiter(args->stateless_rpc, reader,
+				  _("git fetch-pack: expected response end packet"));
+}
+
 static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 				    int fd[2],
 				    const struct ref *orig_ref,
@@ -1535,13 +1542,18 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 			/* Process ACKs/NAKs */
 			switch (process_acks(negotiator, &reader, &common)) {
 			case READY:
+				/*
+				 * Don't check for response delimiter; get_pack() will
+				 * read the rest of this response.
+				 */
 				state = FETCH_GET_PACK;
 				break;
 			case COMMON_FOUND:
 				in_vain = 0;
 				seen_ack = 1;
 				/* fallthrough */
 			case NO_COMMON_FOUND:
+				do_check_stateless_delimiter(args, &reader);
 				state = FETCH_SEND_REQUEST;
 				break;
 			}
@@ -1561,6 +1573,7 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 			process_section_header(&reader, "packfile", 0);
 			if (get_pack(args, fd, pack_lockfile, sought, nr_sought))
 				die(_("git fetch-pack: fetch failed."));
+			do_check_stateless_delimiter(args, &reader);
 
 			state = FETCH_DONE;
 			break;

pkt-line.c

@@ -99,6 +99,13 @@ void packet_delim(int fd)
 		die_errno(_("unable to write delim packet"));
 }
 
+void packet_response_end(int fd)
+{
+	packet_trace("0002", 4, 1);
+	if (write_in_full(fd, "0002", 4) < 0)
+		die_errno(_("unable to write stateless separator packet"));
+}
+
 int packet_flush_gently(int fd)
 {
 	packet_trace("0000", 4, 1);
@@ -306,10 +313,10 @@ static int get_packet_data(int fd, char **src_buf, size_t *src_size,
 	return ret;
 }
 
-static int packet_length(const char *linelen)
+int packet_length(const char lenbuf_hex[4])
 {
-	int val = hex2chr(linelen);
-	return (val < 0) ? val : (val << 8) | hex2chr(linelen + 2);
+	int val = hex2chr(lenbuf_hex);
+	return (val < 0) ? val : (val << 8) | hex2chr(lenbuf_hex + 2);
 }
 
 enum packet_read_status packet_read_with_status(int fd, char **src_buffer,
@@ -337,6 +344,10 @@ enum packet_read_status packet_read_with_status(int fd, char **src_buffer,
 		packet_trace("0001", 4, 0);
 		*pktlen = 0;
 		return PACKET_READ_DELIM;
+	} else if (len == 2) {
+		packet_trace("0002", 4, 0);
+		*pktlen = 0;
+		return PACKET_READ_RESPONSE_END;
 	} else if (len < 4) {
 		die(_("protocol error: bad line length %d"), len);
 	}

pkt-line.h

@@ -22,6 +22,7 @@
  */
 void packet_flush(int fd);
 void packet_delim(int fd);
+void packet_response_end(int fd);
 void packet_write_fmt(int fd, const char *fmt, ...) __attribute__((format (printf, 2, 3)));
 void packet_buf_flush(struct strbuf *buf);
 void packet_buf_delim(struct strbuf *buf);
@@ -74,6 +75,15 @@ int write_packetized_from_buf(const char *src_in, size_t len, int fd_out);
 int packet_read(int fd, char **src_buffer, size_t *src_len, char
 		*buffer, unsigned size, int options);
 
+/*
+ * Convert a four hex digit packet line length header into its numeric
+ * representation.
+ *
+ * If lenbuf_hex contains non-hex characters, return -1. Otherwise, return the
+ * numeric value of the length header.
+ */
+int packet_length(const char lenbuf_hex[4]);
+
 /*
  * Read a packetized line into a buffer like the 'packet_read()' function but
  * returns an 'enum packet_read_status' which indicates the status of the read.
@@ -85,6 +95,7 @@ enum packet_read_status {
 	PACKET_READ_NORMAL,
 	PACKET_READ_FLUSH,
 	PACKET_READ_DELIM,
+	PACKET_READ_RESPONSE_END,
 };
 enum packet_read_status packet_read_with_status(int fd, char **src_buffer,
 						size_t *src_len, char *buffer,

remote-curl.c

@@ -601,6 +601,8 @@ static int rpc_read_from_out(struct rpc_state *rpc, int options,
 		case PACKET_READ_FLUSH:
 			memcpy(buf - 4, "0000", 4);
 			break;
+		case PACKET_READ_RESPONSE_END:
+			die(_("remote server sent stateless separator"));
 		}
 	}
 
@@ -643,7 +645,7 @@ static size_t rpc_out(void *ptr, size_t eltsize,
 			return 0;
 		}
 		/*
-		 * If avail is non-zerp, the line length for the flush still
+		 * If avail is non-zero, the line length for the flush still
 		 * hasn't been fully sent. Proceed with sending the line
 		 * length.
 		 */
@@ -679,9 +681,55 @@ static curlioerr rpc_ioctl(CURL *handle, int cmd, void *clientp)
 }
 #endif
 
+struct check_pktline_state {
+	char len_buf[4];
+	int len_filled;
+	int remaining;
+};
+
+static void check_pktline(struct check_pktline_state *state, const char *ptr, size_t size)
+{
+	while (size) {
+		if (!state->remaining) {
+			int digits_remaining = 4 - state->len_filled;
+			if (digits_remaining > size)
+				digits_remaining = size;
+			memcpy(&state->len_buf[state->len_filled], ptr, digits_remaining);
+			state->len_filled += digits_remaining;
+			ptr += digits_remaining;
+			size -= digits_remaining;
+
+			if (state->len_filled == 4) {
+				state->remaining = packet_length(state->len_buf);
+				if (state->remaining < 0) {
+					die(_("remote-curl: bad line length character: %.4s"), state->len_buf);
+				} else if (state->remaining == 2) {
+					die(_("remote-curl: unexpected response end packet"));
+				} else if (state->remaining < 4) {
+					state->remaining = 0;
+				} else {
+					state->remaining -= 4;
+				}
+				state->len_filled = 0;
+			}
+		}
+
+		if (state->remaining) {
+			int remaining = state->remaining;
+			if (remaining > size)
+				remaining = size;
+			ptr += remaining;
+			size -= remaining;
+			state->remaining -= remaining;
+		}
+	}
+}
+
 struct rpc_in_data {
 	struct rpc_state *rpc;
 	struct active_request_slot *slot;
+	int check_pktline;
+	struct check_pktline_state pktline_state;
 };
 
 /*
@@ -702,6 +750,8 @@ static size_t rpc_in(char *ptr, size_t eltsize,
 		return size;
 	if (size)
 		data->rpc->any_written = 1;
+	if (data->check_pktline)
+		check_pktline(&data->pktline_state, ptr, size);
 	write_or_die(data->rpc->in, ptr, size);
 	return size;
 }
@@ -778,7 +828,7 @@ static curl_off_t xcurl_off_t(size_t len)
  * If flush_received is true, do not attempt to read any more; just use what's
  * in rpc->buf.
  */
-static int post_rpc(struct rpc_state *rpc, int flush_received)
+static int post_rpc(struct rpc_state *rpc, int stateless_connect, int flush_received)
 {
 	struct active_request_slot *slot;
 	struct curl_slist *headers = http_copy_default_headers();
@@ -920,6 +970,8 @@ static int post_rpc(struct rpc_state *rpc, int flush_received)
 	curl_easy_setopt(slot->curl, CURLOPT_WRITEFUNCTION, rpc_in);
 	rpc_in_data.rpc = rpc;
 	rpc_in_data.slot = slot;
+	rpc_in_data.check_pktline = stateless_connect;
+	memset(&rpc_in_data.pktline_state, 0, sizeof(rpc_in_data.pktline_state));
 	curl_easy_setopt(slot->curl, CURLOPT_FILE, &rpc_in_data);
 	curl_easy_setopt(slot->curl, CURLOPT_FAILONERROR, 0);
 
@@ -936,6 +988,14 @@ static int post_rpc(struct rpc_state *rpc, int flush_received)
 	if (!rpc->any_written)
 		err = -1;
 
+	if (rpc_in_data.pktline_state.len_filled)
+		err = error(_("%d bytes of length header were received"), rpc_in_data.pktline_state.len_filled);
+	if (rpc_in_data.pktline_state.remaining)
+		err = error(_("%d bytes of body are still expected"), rpc_in_data.pktline_state.remaining);
+
+	if (stateless_connect)
+		packet_response_end(rpc->in);
+
 	curl_slist_free_all(headers);
 	free(gzip_body);
 	return err;
@@ -985,7 +1045,7 @@ static int rpc_service(struct rpc_state *rpc, struct discovery *heads,
 			break;
 		rpc->pos = 0;
 		rpc->len = n;
-		err |= post_rpc(rpc, 0);
+		err |= post_rpc(rpc, 0, 0);
 	}
 
 	close(client.in);
@@ -1276,7 +1336,7 @@ static void parse_push(struct strbuf *buf)
 	if (ret)
 		exit(128); /* error already reported */
 
- free_specs:
+free_specs:
 	argv_array_clear(&specs);
 }
 
@@ -1342,7 +1402,7 @@ static int stateless_connect(const char *service_name)
 			BUG("The entire rpc->buf should be larger than LARGE_PACKET_MAX");
 		if (status == PACKET_READ_EOF)
 			break;
-		if (post_rpc(&rpc, status == PACKET_READ_FLUSH))
+		if (post_rpc(&rpc, 1, status == PACKET_READ_FLUSH))
 			/* We would have an err here */
 			break;
 		/* Reset the buffer for next request */

remote.h

@@ -179,7 +179,8 @@ struct ref **get_remote_heads(struct packet_reader *reader,
 struct ref **get_remote_refs(int fd_out, struct packet_reader *reader,
 			     struct ref **list, int for_push,
 			     const struct argv_array *ref_prefixes,
-			     const struct string_list *server_options);
+			     const struct string_list *server_options,
+			     int stateless_rpc);
 
 int resolve_remote_symref(struct ref *ref, struct ref *list);