jsonrpc: add json_tok_short_channel_id helper.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/jsonrpc.c

@@ -388,6 +388,14 @@ void json_add_short_channel_id(struct json_result *response,
 			type_to_string(response, struct short_channel_id, id));
 }
 
+bool json_tok_short_channel_id(const char *buffer, const jsmntok_t *tok,
+			       struct short_channel_id *scid)
+{
+	return short_channel_id_from_str(buffer + tok->start,
+					 tok->end - tok->start,
+					 scid);
+}
+
 void json_add_address(struct json_result *response, const char *fieldname,
 		      const struct wireaddr *addr)
 {

lightningd/jsonrpc.h

@@ -76,6 +76,10 @@ void json_add_txid(struct json_result *result, const char *fieldname,
 bool json_tok_pubkey(const char *buffer, const jsmntok_t *tok,
 		     struct pubkey *pubkey);
 
+/* Extract a short_channel_id from this */
+bool json_tok_short_channel_id(const char *buffer, const jsmntok_t *tok,
+			       struct short_channel_id *scid);
+
 /* '"fieldname" : "1234:5:6"' */
 void json_add_short_channel_id(struct json_result *response,
 			       const char *fieldname,

lightningd/pay.c

@@ -299,8 +299,7 @@ static void json_sendpay(struct command *cmd,
 			return;
 		}
 
-		if (!short_channel_id_from_str(buffer + chantok->start,
-					       chantok->end - chantok->start,
+		if (!json_tok_short_channel_id(buffer, chantok,
 					       &route[n_hops].channel_id)) {
 			command_fail(cmd, "route %zu invalid channel_id", n_hops);
 			return;