bitcoin/tx: fix type of outpoint (n is a u32), simplify json_to_outpoint

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

bitcoin/tx.h

@@ -24,7 +24,7 @@ struct bitcoin_txid {
 
 struct bitcoin_outpoint {
 	struct bitcoin_txid txid;
-	u16 n;
+	u32 n;
 };
 
 /* Define bitcoin_txid_eq */

common/json_helpers.c

@@ -96,26 +96,13 @@ bool json_to_txid(const char *buffer, const jsmntok_t *tok,
 bool json_to_outpoint(const char *buffer, const jsmntok_t *tok,
 		      struct bitcoin_outpoint *op)
 {
-	size_t len = tok->end - tok->start;
-	char str[len + 1];
+	jsmntok_t t1, t2;
 
-	if (len < 66)
-		return NULL;
-
-	memcpy(str, buffer+tok->start, len);
-	str[len] = 0x00;
-
-	if (str[64] != ':')
-		return NULL;
-
-	if (!bitcoin_txid_from_hex(str, 64, &op->txid))
+	if (!split_tok(buffer, tok, ':', &t1, &t2))
 		return false;
 
-	op->n = atoi(str + 65);
-	if (op->n < 0)
-		return false;
-
-	return true;
+	return json_to_txid(buffer, &t1, &op->txid)
+		&& json_to_u32(buffer, &t2, &op->n);
 }
 
 bool json_to_channel_id(const char *buffer, const jsmntok_t *tok,