bolt11: expose routine to parse bolt11 string except signature.

This means we can hand around unsigned bolt11s.

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

common/bolt11.c

@@ -550,24 +550,25 @@ struct bolt11 *new_bolt11(const tal_t *ctx,
 	return b11;
 }
 
-/* Decodes and checks signature; returns NULL on error. */
-struct bolt11 *bolt11_decode(const tal_t *ctx, const char *str,
-			     const struct feature_set *our_features,
-			     const char *description,
-			     const struct chainparams *must_be_chain,
-			     char **fail)
+/* Extracts signature but does not check it. */
+struct bolt11 *bolt11_decode_nosig(const tal_t *ctx, const char *str,
+				   const struct feature_set *our_features,
+				   const char *description,
+				   const struct chainparams *must_be_chain,
+				   struct sha256 *hash,
+				   u5 **sig,
+				   bool *have_n,
+				   char **fail)
 {
 	char *hrp, *amountstr, *prefix;
 	u5 *data;
 	size_t data_len;
 	struct bolt11 *b11 = new_bolt11(ctx, NULL);
-	u8 sig_and_recid[65];
-	secp256k1_ecdsa_recoverable_signature sig;
 	struct hash_u5 hu5;
-	struct sha256 hash;
-	bool have_p = false, have_n = false, have_d = false, have_h = false,
+	bool have_p = false, have_d = false, have_h = false,
 		have_x = false, have_c = false, have_s = false;
 
+	*have_n = false;
 	b11->routes = tal_arr(b11, struct route_info *, 0);
 
 	/* BOLT #11:
@@ -737,7 +738,7 @@ struct bolt11 *bolt11_decode(const tal_t *ctx, const char *str,
 		case 'n':
 			problem = decode_n(b11, &hu5, &data,
 					   &data_len, data_length,
-					   &have_n);
+					   have_n);
 			break;
 
 		case 'x':
@@ -795,7 +796,31 @@ struct bolt11 *bolt11_decode(const tal_t *ctx, const char *str,
 					   "h: does not match description");
 	}
 
-	hash_u5_done(&hu5, &hash);
+	hash_u5_done(&hu5, hash);
+	*sig = tal_dup_arr(ctx, u5, data, data_len, 0);
+	return b11;
+}
+
+/* Decodes and checks signature; returns NULL on error. */
+struct bolt11 *bolt11_decode(const tal_t *ctx, const char *str,
+			     const struct feature_set *our_features,
+			     const char *description,
+			     const struct chainparams *must_be_chain,
+			     char **fail)
+{
+	u5 *sigdata;
+	size_t data_len;
+	u8 sig_and_recid[65];
+	secp256k1_ecdsa_recoverable_signature sig;
+	struct bolt11 *b11;
+	struct sha256 hash;
+	bool have_n;
+
+	b11 = bolt11_decode_nosig(ctx, str, our_features, description,
+				  must_be_chain, &hash, &sigdata, &have_n,
+				  fail);
+	if (!b11)
+		return NULL;
 
 	/* BOLT #11:
 	 *
@@ -807,7 +832,8 @@ struct bolt11 *bolt11_decode(const tal_t *ctx, const char *str,
 	 * boundary, with a trailing byte containing the recovery ID
 	 * (0, 1, 2, or 3).
 	 */
-	if (!pull_bits(NULL, &data, &data_len, sig_and_recid, 520, false))
+	data_len = tal_count(sigdata);
+	if (!pull_bits(NULL, &sigdata, &data_len, sig_and_recid, 520, false))
 		return decode_fail(b11, fail, "signature truncated");
 
 	assert(data_len == 0);

common/bolt11.h

@@ -94,6 +94,16 @@ struct bolt11 *bolt11_decode(const tal_t *ctx, const char *str,
 			     const struct chainparams *must_be_chain,
 			     char **fail);
 
+/* Extracts signature but does not check it. */
+struct bolt11 *bolt11_decode_nosig(const tal_t *ctx, const char *str,
+				   const struct feature_set *our_features,
+				   const char *description,
+				   const struct chainparams *must_be_chain,
+				   struct sha256 *hash,
+				   u5 **sig,
+				   bool *have_n,
+				   char **fail);
+
 /* Initialize an empty bolt11 struct with optional amount */
 struct bolt11 *new_bolt11(const tal_t *ctx,
 			  const struct amount_msat *msat TAKES);