common/amount: accept 0msat in parse_amount_sat()

Changelog-fixed: bcli now handles 0msat outputs in gettxout.

Co-authored-by: Rusty Russell <rusty@rustcorp.com.au>

common/amount.c

@@ -181,6 +181,7 @@ bool parse_amount_msat(struct amount_msat *msat, const char *s, size_t slen)
  *  [0-9]+ => satoshi.
  *  [0-9]+sat => satoshi.
  *  [0-9]+000msat => satoshi.
+ *  0msat => 0 satoshi
  *  [0-9]+.[0-9]{1,8}btc => satoshi.
  */
 bool parse_amount_sat(struct amount_sat *sat, const char *s, size_t slen)
@@ -198,8 +199,12 @@ bool parse_amount_sat(struct amount_sat *sat, const char *s, size_t slen)
 	if (!post_decimal_ptr && memeqstr(suffix_ptr, suffix_len, "sat"))
 		return from_number(&sat->satoshis, s, whole_number_len, 0);
 	if (!post_decimal_ptr && memeqstr(suffix_ptr, suffix_len, "msat")) {
-		if (!memends(s, whole_number_len, "000", strlen("000")))
+		if (!memends(s, whole_number_len, "000", strlen("000"))) {
+			if (memeqstr(s, whole_number_len, "0"))
+				return from_number(&sat->satoshis, s,
+						   whole_number_len, 0);
 			return false;
+		}
 		return from_number(&sat->satoshis, s, whole_number_len - 3, 0);
 	}
 	if (post_decimal_ptr && memeqstr(suffix_ptr, suffix_len, "btc"))

common/test/run-amount.c

@@ -101,7 +101,7 @@ int main(void)
 	PASS_SAT(&sat, "1000msat", 1);
 	PASS_SAT(&sat, "1000000msat", 1000);
 	PASS_SAT(&sat, "2100000000000000000msat", 2100000000000000ULL);
-	FAIL_SAT(&sat, "0msat");
+	PASS_SAT(&sat, "0msat", 0);
 	FAIL_SAT(&sat, "100msat");
 	FAIL_SAT(&sat, "2000000000000000999msat");
 	FAIL_SAT(&sat, "-1000msat");