lightningd: always do incremental parsing of JSON inputs.

time lightning-cli -R --network=regtest --lightning-dir /tmp/ltests-k8jhvtty/test_pay_stress_1/lightning-1/ listpays > /dev/null

Before:
	real	0m42.741s
	user	0m0.149s
	sys	0m0.016s

After:
	real	0m13.674s
	user	0m0.131s
	sys	0m0.024s

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Fixed: JSON-RPC: significant speedups for plugins which create large JSON replies (e.g. listpays on large nodes).

lightningd/jsonrpc.c

@@ -89,6 +89,10 @@ struct json_connection {
 	/* How much has just been filled. */
 	size_t len_read;
 
+	/* JSON parsing state. */
+	jsmn_parser input_parser;
+	jsmntok_t *input_toks;
+
 	/* Our commands */
 	struct list_head commands;
 
@@ -912,9 +916,7 @@ static struct io_plan *stream_out_complete(struct io_conn *conn,
 static struct io_plan *read_json(struct io_conn *conn,
 				 struct json_connection *jcon)
 {
-	jsmntok_t *toks;
 	bool complete;
-	jsmn_parser parser;
 
 	if (jcon->len_read)
 		log_io(jcon->log, LOG_IO_IN, NULL, "",
@@ -931,9 +933,8 @@ static struct io_plan *read_json(struct io_conn *conn,
 		return io_wait(conn, conn, read_json, jcon);
 	}
 
-	toks = toks_alloc(jcon->buffer);
-	jsmn_init(&parser);
-	if (!json_parse_input(&parser, &toks, jcon->buffer, jcon->used,
+	if (!json_parse_input(&jcon->input_parser, &jcon->input_toks,
+			      jcon->buffer, jcon->used,
 			      &complete)) {
 		json_command_malformed(jcon, "null",
 				       "Invalid token in json input");
@@ -944,30 +945,36 @@ static struct io_plan *read_json(struct io_conn *conn,
 		goto read_more;
 
 	/* Empty buffer? (eg. just whitespace). */
-	if (tal_count(toks) == 1) {
+	if (tal_count(jcon->input_toks) == 1) {
 		jcon->used = 0;
+
+		/* Reset parser. */
+		jsmn_init(&jcon->input_parser);
+		toks_reset(jcon->input_toks);
 		goto read_more;
 	}
 
-	parse_request(jcon, toks);
+	parse_request(jcon, jcon->input_toks);
 
 	/* Remove first {}. */
-	memmove(jcon->buffer, jcon->buffer + toks[0].end,
-		tal_count(jcon->buffer) - toks[0].end);
-	jcon->used -= toks[0].end;
+	memmove(jcon->buffer, jcon->buffer + jcon->input_toks[0].end,
+		tal_count(jcon->buffer) - jcon->input_toks[0].end);
+	jcon->used -= jcon->input_toks[0].end;
+
+	/* Reset parser. */
+	jsmn_init(&jcon->input_parser);
+	toks_reset(jcon->input_toks);
 
 	/* If we have more to process, try again.  FIXME: this still gets
 	 * first priority in io_loop, so can starve others.  Hack would be
 	 * a (non-zero) timer, but better would be to have io_loop avoid
 	 * such livelock */
 	if (jcon->used) {
-		tal_free(toks);
 		jcon->len_read = 0;
 		return io_always(conn, read_json, jcon);
 	}
 
 read_more:
-	tal_free(toks);
 	return io_read_partial(conn, jcon->buffer + jcon->used,
 			       tal_count(jcon->buffer) - jcon->used,
 			       &jcon->len_read, read_json, jcon);
@@ -986,6 +993,8 @@ static struct io_plan *jcon_connected(struct io_conn *conn,
 	jcon->buffer = tal_arr(jcon, char, 64);
 	jcon->js_arr = tal_arr(jcon, struct json_stream *, 0);
 	jcon->len_read = 0;
+	jsmn_init(&jcon->input_parser);
+	jcon->input_toks = toks_alloc(jcon);
 	list_head_init(&jcon->commands);
 
 	/* We want to log on destruction, so we free this in destructor. */

lightningd/plugin.c

@@ -386,22 +386,16 @@ static const char *plugin_read_json_one(struct plugin *plugin,
 					bool *complete,
 					bool *destroyed)
 {
-	jsmntok_t *toks;
 	const jsmntok_t *jrtok, *idtok;
 	struct plugin_destroyed *pd;
 	const char *err;
-	jsmn_parser parser;
 
 	*destroyed = false;
 	/* Note that in the case of 'plugin stop' this can free request (since
 	 * plugin is parent), so detect that case */
 
-	/* FIXME: This could be done more efficiently by storing the
-	 * toks and doing an incremental parse, like lightning-cli
-	 * does. */
-	toks = toks_alloc(plugin);
-	jsmn_init(&parser);
-	if (!json_parse_input(&parser, &toks, plugin->buffer, plugin->used,
+	if (!json_parse_input(&plugin->parser, &plugin->toks,
+			      plugin->buffer, plugin->used,
 			      complete)) {
 		return tal_fmt(plugin,
 			       "Failed to parse JSON response '%.*s'",
@@ -410,21 +404,21 @@ static const char *plugin_read_json_one(struct plugin *plugin,
 
 	if (!*complete) {
 		/* We need more. */
-		tal_free(toks);
 		return NULL;
 	}
 
 	/* Empty buffer? (eg. just whitespace). */
-	if (tal_count(toks) == 1) {
-		tal_free(toks);
+	if (tal_count(plugin->toks) == 1) {
 		plugin->used = 0;
+		jsmn_init(&plugin->parser);
+		toks_reset(plugin->toks);
 		/* We need more. */
 		*complete = false;
 		return NULL;
 	}
 
-	jrtok = json_get_member(plugin->buffer, toks, "jsonrpc");
-	idtok = json_get_member(plugin->buffer, toks, "id");
+	jrtok = json_get_member(plugin->buffer, plugin->toks, "jsonrpc");
+	idtok = json_get_member(plugin->buffer, plugin->toks, "id");
 
 	if (!jrtok) {
 		return tal_fmt(
@@ -445,7 +439,7 @@ static const char *plugin_read_json_one(struct plugin *plugin,
 		 *
 		 * https://www.jsonrpc.org/specification#notification
 		 */
-		err = plugin_notification_handle(plugin, toks);
+		err = plugin_notification_handle(plugin, plugin->toks);
 
 	} else {
 		/* When a rpc call is made, the Server MUST reply with
@@ -475,7 +469,7 @@ static const char *plugin_read_json_one(struct plugin *plugin,
 		 *
 		 * https://www.jsonrpc.org/specification#response_object
 		 */
-		err = plugin_response_handle(plugin, toks, idtok);
+		err = plugin_response_handle(plugin, plugin->toks, idtok);
 	}
 
 	/* Corner case: rpc_command hook can destroy plugin for 'plugin
@@ -484,10 +478,11 @@ static const char *plugin_read_json_one(struct plugin *plugin,
 		*destroyed = true;
 	} else {
 		/* Move this object out of the buffer */
-		memmove(plugin->buffer, plugin->buffer + toks[0].end,
-			tal_count(plugin->buffer) - toks[0].end);
-		plugin->used -= toks[0].end;
-		tal_free(toks);
+		memmove(plugin->buffer, plugin->buffer + plugin->toks[0].end,
+			tal_count(plugin->buffer) - plugin->toks[0].end);
+		plugin->used -= plugin->toks[0].end;
+		jsmn_init(&plugin->parser);
+		toks_reset(plugin->toks);
 	}
 	return err;
 }
@@ -1306,6 +1301,8 @@ const char *plugin_send_getmanifest(struct plugin *p)
 
 	log_debug(p->plugins->log, "started(%u) %s", p->pid, p->cmd);
 	p->buffer = tal_arr(p, char, 64);
+	jsmn_init(&p->parser);
+	p->toks = toks_alloc(p);
 
 	/* Create two connections, one read-only on top of p->stdout, and one
 	 * write-only on p->stdin */

lightningd/plugin.h

@@ -56,6 +56,8 @@ struct plugin {
 	/* Stuff we read */
 	char *buffer;
 	size_t used, len_read;
+	jsmn_parser parser;
+	jsmntok_t *toks;
 
 	/* Our json_streams. Since multiple streams could start
 	 * returning data at once, we always service these in order,