invoice: add fallback address to invoice command

* Modifies invoice command to have the following format
  invoice <msatoshi> <label> <desc> <?expiry> <?fallbackaddr>
* Adds support for Segwit bcrt1 addresses for withdraw
* Add test case for fallback address in invoice creation
* Create a common json_tok_address_scriptpubkey to be used
  by invoice and withdraw commands.

lightningd/jsonrpc.c

@@ -1,11 +1,15 @@
 /* Code for JSON_RPC API */
 /* eg: { "method" : "dev-echo", "params" : [ "hello", "Arabella!" ], "id" : "1" } */
 #include <arpa/inet.h>
+#include <bitcoin/address.h>
+#include <bitcoin/base58.h>
+#include <bitcoin/script.h>
 #include <ccan/array_size/array_size.h>
 #include <ccan/err/err.h>
 #include <ccan/io/io.h>
 #include <ccan/str/hex/hex.h>
 #include <ccan/tal/str/str.h>
+#include <common/bech32.h>
 #include <common/json.h>
 #include <common/memleak.h>
 #include <common/version.h>
@@ -792,3 +796,97 @@ void setup_jsonrpc(struct lightningd *ld, const char *rpc_filename)
 	/* Technically this is a leak, but there's only one */
 	notleak(io_new_listener(ld, fd, incoming_jcon_connected, ld));
 }
+
+/**
+ * segwit_addr_net_decode - Try to decode a Bech32 address and detect
+ * testnet/mainnet/regtest
+ *
+ * This processes the address and returns a string if it is a Bech32
+ * address specified by BIP173. The string is set whether it is
+ * testnet ("tb"),  mainnet ("bc"), or regtest ("bcrt")
+ * It does not check, witness version and program size restrictions.
+ *
+ *  Out: witness_version: Pointer to an int that will be updated to contain
+ *                 the witness program version (between 0 and 16 inclusive).
+ *       witness_program: Pointer to a buffer of size 40 that will be updated
+ *                 to contain the witness program bytes.
+ *       witness_program_len: Pointer to a size_t that will be updated to
+ *                 contain the length of bytes in witness_program.
+ *  In:  addrz:    Pointer to the null-terminated address.
+ *  Returns string containing the human readable segment of bech32 address
+ */
+static const char* segwit_addr_net_decode(int *witness_version,
+				   uint8_t *witness_program,
+				   size_t *witness_program_len,
+				   const char *addrz)
+{
+	const char *network[] = { "bc", "tb", "bcrt" };
+	for (int i = 0; i < sizeof(network) / sizeof(*network); ++i) {
+		if (segwit_addr_decode(witness_version,
+				       witness_program, witness_program_len,
+				       network[i], addrz))
+			return network[i];
+	}
+
+	return NULL;
+}
+
+const char *json_tok_address_scriptpubkey(const tal_t *cxt, const char *buffer,
+					  const jsmntok_t *tok, const u8 **scriptpubkey)
+{
+	struct bitcoin_address p2pkh_destination;
+	struct ripemd160 p2sh_destination;
+	int witness_version;
+	/* segwit_addr_net_decode requires a buffer of size 40, and will
+	 * not write to the buffer if the address is too long, so a buffer
+	 * of fixed size 40 will not overflow. */
+	uint8_t witness_program[40];
+	size_t witness_program_len;
+	bool witness_ok;
+
+	char *addrz;
+	const char *bip173;
+	bool testnet;
+
+	bip173 = NULL;
+	if (bitcoin_from_base58(&testnet, &p2pkh_destination,
+				buffer + tok->start, tok->end - tok->start)) {
+		*scriptpubkey = scriptpubkey_p2pkh(cxt, &p2pkh_destination);
+		bip173 = chainparams_for_network(testnet ? "testnet" : "bitcoin")->bip173_name;
+	} else if (p2sh_from_base58(&testnet, &p2sh_destination,
+				    buffer + tok->start, tok->end - tok->start)) {
+		*scriptpubkey = scriptpubkey_p2sh_hash(cxt, &p2sh_destination);
+		bip173 = chainparams_for_network(testnet ? "testnet" : "bitcoin")->bip173_name;
+	}
+	/* Insert other parsers that accept pointer+len here. */
+
+	if (bip173) return bip173;
+
+	/* Generate null-terminated address. */
+	addrz = tal_dup_arr(cxt, char, buffer + tok->start, tok->end - tok->start, 1);
+	addrz[tok->end - tok->start] = '\0';
+
+	bip173 = segwit_addr_net_decode(&witness_version, witness_program,
+					&witness_program_len, addrz);
+
+	if (bip173) {
+		witness_ok = false;
+		if (witness_version == 0 && (witness_program_len == 20 ||
+					     witness_program_len == 32)) {
+			witness_ok = true;
+		}
+		/* Insert other witness versions here. */
+
+		if (witness_ok) {
+			*scriptpubkey = scriptpubkey_witness_raw(cxt, witness_version,
+								 witness_program, witness_program_len);
+		}
+		else {
+			bip173 = NULL;
+		}
+	}
+	/* Insert other parsers that accept null-terminated string here. */
+
+	tal_free(addrz);
+	return bip173;
+}