amount: correctly parse amount strings we generate

This:
	- Allows `.*btc` amounts (without post-decimal)
	- Avoids creating decimals when amount is 0 btc
	- Corrects our handling of the suffixes (memeqstr would
	  sometimes return false because of null-termination)

Changelog-Fixed: We are now able to parse any amount string (XXXmsat, XX.XXXbtc, ..) we create.

Signed-off-by: Antoine Poinsot <darosior@protonmail.com>

common/amount.c

@@ -33,6 +33,9 @@ const char *fmt_amount_msat_btc(const tal_t *ctx,
 				const struct amount_msat *msat,
 				bool append_unit)
 {
+	if (msat->millisatoshis == 0)
+		return tal_fmt(ctx, append_unit ? "0btc" : "0");
+
 	return tal_fmt(ctx, "%"PRIu64".%011"PRIu64"%s",
 		       msat->millisatoshis / MSAT_PER_BTC,
 		       msat->millisatoshis % MSAT_PER_BTC,
@@ -49,6 +52,9 @@ const char *fmt_amount_sat_btc(const tal_t *ctx,
 			       const struct amount_sat *sat,
 			       bool append_unit)
 {
+	if (sat->satoshis == 0)
+		return tal_fmt(ctx, append_unit ? "0btc" : "0");
+
 	return tal_fmt(ctx, "%"PRIu64".%08"PRIu64"%s",
 		       sat->satoshis / SAT_PER_BTC,
 		       sat->satoshis % SAT_PER_BTC,
@@ -80,7 +86,8 @@ static bool breakup(const char *str, size_t slen,
 	*suffix_len = 0;
 
 	for (i = 0;; i++) {
-		if (i >= slen)
+		/* The string may be null-terminated. */
+		if (i >= slen || str[i] == '\0')
 			return i != 0;
 		if (cisdigit(str[i]))
 			(*whole_number_len)++;
@@ -93,7 +100,7 @@ static bool breakup(const char *str, size_t slen,
 		*post_decimal_ptr = str + i;
 		for (;; i++) {
 			/* True if > 0 decimals. */
-			if (i >= slen)
+			if (i >= slen || str[i] == '\0')
 				return str + i != *post_decimal_ptr;
 			if (cisdigit(str[i]))
 				(*post_decimal_len)++;
@@ -168,14 +175,18 @@ bool parse_amount_msat(struct amount_msat *msat, const char *s, size_t slen)
 
 	if (!post_decimal_ptr && !suffix_ptr)
 		return from_number(&msat->millisatoshis, s, whole_number_len, 0);
-	if (!post_decimal_ptr && memeqstr(suffix_ptr, suffix_len, "msat"))
+	if (!post_decimal_ptr && memstarts_str(suffix_ptr, suffix_len, "msat"))
 		return from_number(&msat->millisatoshis, s, whole_number_len, 0);
-	if (!post_decimal_ptr && memeqstr(suffix_ptr, suffix_len, "sat"))
+	if (!post_decimal_ptr && memstarts_str(suffix_ptr, suffix_len, "sat"))
 		return from_number(&msat->millisatoshis, s, whole_number_len, 3);
-	if (post_decimal_ptr && memeqstr(suffix_ptr, suffix_len, "btc"))
+	if (memstarts_str(suffix_ptr, suffix_len, "btc")) {
+		if (post_decimal_len > 0)
 			return from_numbers(&msat->millisatoshis,
 					    s, whole_number_len, 11,
 					    post_decimal_ptr, post_decimal_len);
+		return from_number(&msat->millisatoshis, s, whole_number_len, 11);
+	}
+
 	return false;
 }
 
@@ -198,21 +209,24 @@ bool parse_amount_sat(struct amount_sat *sat, const char *s, size_t slen)
 
 	if (!post_decimal_ptr && !suffix_ptr)
 		return from_number(&sat->satoshis, s, whole_number_len, 0);
-	if (!post_decimal_ptr && memeqstr(suffix_ptr, suffix_len, "sat"))
+	if (!post_decimal_ptr && memstarts_str(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 (!post_decimal_ptr && memstarts_str(suffix_ptr, suffix_len, "msat")) {
 		if (!memends(s, whole_number_len, "000", strlen("000"))) {
-			if (memeqstr(s, whole_number_len, "0"))
+			if (memstarts_str(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"))
+	if (memstarts_str(suffix_ptr, suffix_len, "btc")) {
+		if (post_decimal_len > 0)
 			return from_numbers(&sat->satoshis,
 					    s, whole_number_len, 8,
 					    post_decimal_ptr, post_decimal_len);
+		return from_number(&sat->satoshis, s, whole_number_len, 8);
+	}
 
 	return false;
 }

common/test/run-amount.c

@@ -128,7 +128,6 @@ int main(void)
 	PASS_MSAT(&msat, "1.234567890btc", 123456789000);
 	PASS_MSAT(&msat, "1.2345678901btc", 123456789010);
 	PASS_MSAT(&msat, "1.23456789012btc", 123456789012);
-	FAIL_MSAT(&msat, "1btc");
 	FAIL_MSAT(&msat, "1.000000000000btc");
 	FAIL_MSAT(&msat, "-1.23456789btc");
 	FAIL_MSAT(&msat, "-1.23456789012btc");
@@ -177,7 +176,6 @@ int main(void)
 	PASS_SAT(&sat, "1.2345678btc", 123456780);
 	PASS_SAT(&sat, "1.23456789btc", 123456789);
 	FAIL_SAT(&sat, "1.234567890btc");
-	FAIL_SAT(&sat, "1btc");
 	FAIL_SAT(&sat, "-1.23456789btc");
 
 	/* Overflowingly big. */