From e26d294b60fea497bb3b05d03348dafe56873511 Mon Sep 17 00:00:00 2001
From: ZmnSCPxj <ZmnSCPxj@protonmail.com>
Date: Mon, 11 Dec 2017 03:43:11 +0000
Subject: [PATCH] Add support for withdrawing to BECH32 addresses.

Fixes: #428
---
 wallet/walletrpc.c | 83 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 82 insertions(+), 1 deletion(-)

diff --git a/wallet/walletrpc.c b/wallet/walletrpc.c
index 116ae48fd..b76baaedc 100644
--- a/wallet/walletrpc.c
+++ b/wallet/walletrpc.c
@@ -2,6 +2,7 @@
 #include <bitcoin/base58.h>
 #include <bitcoin/script.h>
 #include <ccan/tal/str/str.h>
+#include <common/bech32.h>
 #include <common/key_derive.h>
 #include <common/status.h>
 #include <common/utxo.h>
@@ -69,6 +70,51 @@ static void wallet_withdrawal_broadcast(struct bitcoind *bitcoind,
 	}
 }
 
+/**
+ * segwit_addr_net_decode - Try to decode a Bech32 address and detect
+ * testnet/mainnet
+ *
+ * This processes the address and returns true if it is a Bech32
+ * address specified by BIP173. If it returns true, then *testnet is
+ * set whether it is testnet "tb" address or false if mainnet "bc"
+ * address. It does not check, witness version and program size
+ * restrictions.
+ *
+ *  Out: testnet:  Pointer to a bool that will be updated to true if the
+ *                 address is testnet, or false if mainnet.
+ *       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 true if successful, false if fail (on fail, none of the out
+ *  parameters are modified).
+ */
+static bool segwit_addr_net_decode(bool *testnet, int *witness_version,
+				   uint8_t *witness_program,
+				   size_t *witness_program_len,
+				   const char *addrz)
+{
+	/* segwit_addr_decode itself expects a prog buffer (which we pass
+	 * witness_program as) of size 40, so segwit_addr_net_decode
+	 * inherits that requirement. It will not write to that buffer
+	 * if the input address is too long, so no buffer overflow risk. */
+	if (segwit_addr_decode(witness_version,
+			       witness_program, witness_program_len,
+			       "bc", addrz)) {
+		*testnet = false;
+		return true;
+	} else if (segwit_addr_decode(witness_version,
+				      witness_program, witness_program_len,
+				      "tb", addrz)) {
+		*testnet = true;
+		return true;
+	}
+	return false;
+}
+
 /**
  * scriptpubkey_from_address - Determine scriptpubkey from a given address
  *
@@ -82,8 +128,18 @@ static u8 *scriptpubkey_from_address(const tal_t *cxt, bool *testnet,
 {
 	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;
 	u8 *script = NULL;
 
+	char *addrz;
+	bool my_testnet;
+
 	if (bitcoin_from_base58(testnet, &p2pkh_destination,
 				addr, addrlen)) {
 		script = scriptpubkey_p2pkh(cxt, &p2pkh_destination);
@@ -91,8 +147,33 @@ static u8 *scriptpubkey_from_address(const tal_t *cxt, bool *testnet,
 				    addr, addrlen)) {
 		script = scriptpubkey_p2sh_hash(cxt, &p2sh_destination);
 	}
-	/* TODO Insert other supported addresses here. */
+	/* Insert other parsers that accept pointer+len here. */
+
+	if (script) return script;
+
+	/* Generate null-terminated address. */
+	addrz = tal_dup_arr(cxt, char, addr, addrlen, 1);
+	addrz[addrlen] = '\0';
+
+	if (segwit_addr_net_decode(&my_testnet, &witness_version,
+				   witness_program, &witness_program_len,
+				   addrz)) {
+		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) {
+			*testnet = my_testnet;
+			script = scriptpubkey_witness_raw(cxt, witness_version,
+							  witness_program,
+							  witness_program_len);
+		}
+	}
+	/* Insert other parsers that accept null-terminated string here. */
 
+	tal_free(addrz);
 	return script;
 }