fixup! json: Only start parsing once we're sure we have a message

lightningd/plugin.c

@@ -492,22 +492,17 @@ static struct io_plan *plugin_read_json(struct io_conn *conn,
 {
 	bool success;
 	bool have_full;
-	int offset = plugin->used >= 1 ? 1 : 0;
 
 	log_io(plugin->log, LOG_IO_IN, NULL, "",
 	       plugin->buffer + plugin->used, plugin->len_read);
 
-	/* Peek into the buffer increment we just read (including a tiny
-	 * overlap if we're not at the start) to see if we have a '}'
-	 * separator. If not we can skip the JSON attempt.
-	 *
-	 * Our JSON parser is pretty good at incremental parsing, but
+	/* Our JSON parser is pretty good at incremental parsing, but
 	 * `getrawblock` gives a giant 2MB token, which forces it to re-parse
 	 * every time until we have all of it. However, we can't complete a
 	 * JSON object without a '}', so we do a cheaper check here.
-	*/
-	have_full = memmem(plugin->buffer + plugin->used - offset,
-			   plugin->len_read + offset, "}", 1);
+	 */
+	have_full = memchr(plugin->buffer + plugin->used, '}',
+			   plugin->len_read);
 
 	plugin->used += plugin->len_read;
 	if (plugin->used == tal_count(plugin->buffer))