rgb-cln/lightningd/bolt11.c

#include <bitcoin/address.h>
#include <bitcoin/base58.h>
#include <bitcoin/chainparams.h>
#include <bitcoin/script.h>
#include <ccan/array_size/array_size.h>
#include <ccan/cast/cast.h>
#include <ccan/endian/endian.h>
#include <ccan/structeq/structeq.h>
#include <ccan/tal/str/str.h>
#include <common/utils.h>
#include <errno.h>
#include <hsmd/gen_hsm_wire.h>
#include <inttypes.h>
#include <lightningd/bech32.h>
#include <lightningd/bolt11.h>
#include <lightningd/hsm_control.h>
#include <lightningd/jsonrpc.h>
#include <lightningd/lightningd.h>
#include <lightningd/log.h>
#include <secp256k1_recovery.h>
#include <stdarg.h>
#include <stdio.h>
#include <wire/wire.h>
#include <wire/wire_sync.h>

/* 1000 * 10^8 millisatoshi == 1 bitcoin */
#define MSAT_PER_BTC 100000000000ULL

struct multiplier {
        const char letter;
        /* We can't represent p postfix to msat, so we multiply this by 10 */
        u64 m10;
};

/* BOLT #11:
 *
 * The following `multiplier` letters are defined:
 *
 * * `m` (milli): multiply by 0.001
 * * `u` (micro): multiply by 0.000001
 * * `n` (nano): multiply by 0.000000001
 * * `p` (pico): multiply by 0.000000000001
 */
static struct multiplier multipliers[] = {
        { 'm', 10 * MSAT_PER_BTC / 1000 },
        { 'u', 10 * MSAT_PER_BTC / 1000000 },
        { 'n', 10 * MSAT_PER_BTC / 1000000000 },
        { 'p', 10 * MSAT_PER_BTC / 1000000000000ULL }
};

/* If pad is false, we discard any bits which don't fit in the last byte.
 * Otherwise we add an extra byte */
static bool pull_bits(struct hash_u5 *hu5,
                      u5 **data, size_t *data_len, void *dst, size_t nbits,
                      bool pad)
{
        size_t n5 = nbits / 5;
        size_t len = 0;

        if (nbits % 5)
                n5++;

        if (*data_len < n5)
                return false;
        if (!bech32_convert_bits(dst, &len, 8, *data, n5, 5, pad))
                return false;
        if (hu5)
                hash_u5(hu5, *data, n5);
        *data += n5;
        *data_len -= n5;

        return true;
}

/* For pulling fields where we should have checked it will succeed already. */
#ifndef NDEBUG
#define pull_bits_certain(hu5, data, data_len, dst, nbits, pad)             \
        assert(pull_bits((hu5), (data), (data_len), (dst), (nbits), (pad)))
#else
#define pull_bits_certain pull_bits
#endif

/* Helper for pulling a variable-length big-endian int. */
static bool pull_uint(struct hash_u5 *hu5,
                      u5 **data, size_t *data_len,
                      u64 *val, size_t databits)
{
        be64 be_val;

        /* Too big. */
        if (databits > sizeof(be_val) * CHAR_BIT)
                return false;
        if (!pull_bits(hu5, data, data_len, &be_val, databits, true))
                return false;
        *val = be64_to_cpu(be_val) >> (sizeof(be_val) * CHAR_BIT - databits);
        return true;
}

static size_t num_u8(size_t num_u5)
{
        return (num_u5 * 5 + 4) / 8;
}

/* Frees bolt11, returns NULL. */
static struct bolt11 *decode_fail(struct bolt11 *b11, char **fail,
                                  const char *fmt, ...)
        PRINTF_FMT(3,4);

static struct bolt11 *decode_fail(struct bolt11 *b11, char **fail,
                                  const char *fmt, ...)
{
        va_list ap;

        va_start(ap, fmt);
        *fail = tal_vfmt(tal_parent(b11), fmt, ap);
        va_end(ap);
        return tal_free(b11);
}

/*
 * These handle specific fields in the payment request; returning the problem
 * if any, or NULL.
 */
static char *unknown_field(struct bolt11 *b11,
                           struct hash_u5 *hu5,
                           u5 **data, size_t *data_len,
                           u5 type, size_t length)
{
        struct bolt11_field *extra = tal(b11, struct bolt11_field);
        u8 u8data[num_u8(length)];

        extra->tag = type;
        extra->data = tal_dup_arr(extra, u5, *data, length, 0);
        list_add_tail(&b11->extra_fields, &extra->list);

        pull_bits_certain(hu5, data, data_len, u8data, length, false);
        (*data) += length;
        (*data_len) -= length;
        return NULL;
}

/* BOLT #11:
 *
 * `p` (1): `data_length` 52.  256-bit SHA256 payment_hash: preimage of this
 * provides proof of payment.
 */
static void decode_p(struct bolt11 *b11,
                     struct hash_u5 *hu5,
                     u5 **data, size_t *data_len,
                     size_t data_length, bool *have_p)
{
        /* BOLT #11:
         *
         * A payer SHOULD use the first `p` field did not skip as the payment
         * hash.
         */
        if (*have_p) {
                unknown_field(b11, hu5, data, data_len, 'p', data_length);
                return;
        }

        /* BOLT #11:
         *
         * A reader MUST skip over unknown fields, an `f` field with unknown
         * `version`, or a `p`, `h`, or `n` field which does not have
         * `data_length` 52, 52, or 53 respectively. */
        if (data_length != 52) {
                unknown_field(b11, hu5, data, data_len, 'p', data_length);
                return;
        }

        pull_bits_certain(hu5, data, data_len, &b11->payment_hash, 256, false);
        *have_p = true;
}

/* BOLT #11:
 *
 * `d` (13): `data_length` variable.  short description of purpose of payment
 * (ASCII), e.g. '1 cup of coffee'
 */
static void decode_d(struct bolt11 *b11,
                     struct hash_u5 *hu5,
                     u5 **data, size_t *data_len,
                     size_t data_length, bool *have_d)
{
        if (*have_d) {
                unknown_field(b11, hu5, data, data_len, 'd', data_length);
                return;
        }

        b11->description = tal_arrz(b11, char, num_u8(data_length) + 1);
        pull_bits_certain(hu5, data, data_len, (u8 *)b11->description,
                          data_length*5, false);
        *have_d = true;
}

/* BOLT #11:
 *
 * `h` (23): `data_length` 52.  256-bit description of purpose of payment
 * (SHA256).  This is used to commit to an associated description which is too
 * long to fit, such as may be contained in a web page.
 */
static void decode_h(struct bolt11 *b11,
                     struct hash_u5 *hu5,
                     u5 **data, size_t *data_len,
                     size_t data_length, bool *have_h)
{
        if (*have_h) {
                unknown_field(b11, hu5, data, data_len, 'h', data_length);
                return;
        }

        /* BOLT #11:
         *
         * A reader MUST skip over unknown fields, an `f` field with unknown
         * `version`, or a `p`, `h`, or `n` field which does not have
         * `data_length` 52, 52, or 53 respectively. */
        if (data_length != 52) {
                unknown_field(b11, hu5, data, data_len, 'h', data_length);
                return;
        }

        b11->description_hash = tal(b11, struct sha256);
        pull_bits_certain(hu5, data, data_len, b11->description_hash, 256,
                          false);
        *have_h = true;
}

/* BOLT #11:
 *
 * `x` (6): `data_length` variable.  `expiry` time in seconds
 * (big-endian). Default is 3600 (1 hour) if not specified.
 */
#define DEFAULT_X 3600
static char *decode_x(struct bolt11 *b11,
                      struct hash_u5 *hu5,
                      u5 **data, size_t *data_len,
                      size_t data_length, bool *have_x)
{
        if (*have_x)
                return unknown_field(b11, hu5, data, data_len, 'x',
                                     data_length);

        /* FIXME: Put upper limit in bolt 11 */
        if (!pull_uint(hu5, data, data_len, &b11->expiry, data_length * 5))
                return tal_fmt(b11, "x: length %zu chars is excessive",
                               *data_len);
        return NULL;
}

static char *decode_n(struct bolt11 *b11,
                      struct hash_u5 *hu5,
                      u5 **data, size_t *data_len,
                      size_t data_length, bool *have_n)
{
        u8 der[PUBKEY_DER_LEN];

        if (*have_n)
                return unknown_field(b11, hu5, data, data_len, 'n',
                                     data_length);

        /* BOLT #11:
         *
         * A reader MUST skip over unknown fields, an `f` field with unknown
         * `version`, or a `p`, `h`, or `n` field which does not have
         * `data_length` 52, 52, or 53 respectively. */
        if (data_length != 53)
                return unknown_field(b11, hu5, data, data_len, 'n',
                                     data_length);

        pull_bits_certain(hu5, data, data_len, der, data_length * 5, false);
        if (!pubkey_from_der(der, sizeof(der), &b11->receiver_id))
                return tal_fmt(b11, "n: invalid pubkey %.*s",
                               (int)sizeof(der), der);

        *have_n = true;
        return NULL;
}

/* BOLT #11:
 *
 * `f` (9): `data_length` variable, depending on version. Fallback on-chain
 * address: for bitcoin, this starts with a 5 bit `version`; a witness program
 * or P2PKH or P2SH address.
 */
static char *decode_f(struct bolt11 *b11,
                      struct hash_u5 *hu5,
                      u5 **data, size_t *data_len,
                      size_t data_length, bool *have_f)
{
        u64 version;

        if (*have_f)
                return unknown_field(b11, hu5, data, data_len, 'f',
                                     data_length);

        if (!pull_uint(hu5, data, data_len, &version, 5))
                return tal_fmt(b11, "f: data_length %zu short", data_length);
        data_length--;

        /* BOLT #11:
         *
         * For bitcoin payments, a writer MUST set an `f` field to a
         * valid witness version and program, or `17` followed by a
         * public key hash, or `18` followed by a script hash. */
        if (version == 17) {
                /* Pay to pubkey hash (P2PKH) */
                struct bitcoin_address pkhash;
                if (num_u8(data_length) != sizeof(pkhash))
                        return tal_fmt(b11, "f: pkhash length %zu",
                                       data_length);

                pull_bits_certain(hu5, data, data_len, &pkhash, data_length*5,
                                  false);
                b11->fallback = scriptpubkey_p2pkh(b11, &pkhash);
                return NULL;
        } else if (version == 18) {
                /* Pay to pubkey script hash (P2SH) */
                struct ripemd160 shash;
                if (num_u8(data_length) != sizeof(shash))
                        return tal_fmt(b11, "f: p2sh length %zu",
                                       data_length);

                pull_bits_certain(hu5, data, data_len, &shash, data_length*5,
                                  false);
                b11->fallback = scriptpubkey_p2sh_hash(b11, &shash);
        } else if (version < 17) {
                u8 *f = tal_arr(b11, u8, data_length * 5 / 8);
                if (version == 0) {
                        if (tal_len(f) != 20 && tal_len(f) != 32)
                                return tal_fmt(b11,
                                               "f: witness v0 bad length %zu",
                                               data_length);
                }
                pull_bits_certain(hu5, data, data_len, f, data_length * 5,
                                  false);
                b11->fallback = scriptpubkey_witness_raw(b11, version,
                                                         f, tal_len(f));
                tal_free(f);
        } else
                return unknown_field(b11, hu5, data, data_len, 'f',
                                     data_length);

        *have_f = true;
        return NULL;
}

static bool fromwire_route_info(const u8 **cursor, size_t *max,
                                struct route_info *route_info)
{
        fromwire_pubkey(cursor, max, &route_info->pubkey);
        fromwire_short_channel_id(cursor, max, &route_info->short_channel_id);
        route_info->fee = fromwire_u64(cursor, max);
        route_info->cltv_expiry_delta = fromwire_u16(cursor, max);
        return *cursor != NULL;
}

static void towire_route_info(u8 **pptr, const struct route_info *route_info)
{
        towire_pubkey(pptr, &route_info->pubkey);
        towire_short_channel_id(pptr, &route_info->short_channel_id);
        towire_u64(pptr, route_info->fee);
        towire_u16(pptr, route_info->cltv_expiry_delta);
}

/* BOLT #11:
 *
 * `r` (3): `data_length` variable.  One or more entries containing
 * extra routing information for a private route; there may be more
 * than one `r` field, too.
 *
 *   * `pubkey` (264 bits)
 *   * `short_channel_id` (64 bits)
 *   * `fee` (64 bits, big-endian)
 *   * `cltv_expiry_delta` (16 bits, big-endian)
 */
static char *decode_r(struct bolt11 *b11,
                      struct hash_u5 *hu5,
                      u5 **data, size_t *data_len,
                      size_t data_length)
{
        tal_t *tmpctx = tal_tmpctx(b11);
        size_t rlen = data_length * 5 / 8;
        u8 *r8 = tal_arr(tmpctx, u8, rlen);
        size_t n = 0;
        struct route_info *r = tal_arr(tmpctx, struct route_info, n);
        const u8 *cursor = r8;

        /* Route hops don't split in 5 bit boundaries, so convert whole thing */
        pull_bits_certain(hu5, data, data_len, r8, data_length * 5, false);

        do {
                tal_resize(&r, n+1);
                if (!fromwire_route_info(&cursor, &rlen, &r[n])) {
                        tal_free(tmpctx);
                        return tal_fmt(b11, "r: hop %zu truncated", n);
                }
                n++;
        } while (rlen);

        /* Append route */
        n = tal_count(b11->routes);
        tal_resize(&b11->routes, n+1);
        b11->routes[n] = tal_steal(b11, r);

        tal_free(tmpctx);
        return NULL;
}

struct bolt11 *new_bolt11(const tal_t *ctx, u64 *msatoshi)
{
        struct bolt11 *b11 = tal(ctx, struct bolt11);

        list_head_init(&b11->extra_fields);
        b11->description = NULL;
        b11->description_hash = NULL;
        b11->fallback = NULL;
        b11->routes = NULL;
        b11->msatoshi = NULL;

        if (msatoshi)
                b11->msatoshi = tal_dup(b11, u64, msatoshi);
        return b11;
}

/* Decodes and checks signature; returns NULL on error. */
struct bolt11 *bolt11_decode(const tal_t *ctx, const char *str,
                             const char *description, char **fail)
{
        char *hrp, *amountstr, *prefix;
        u5 *data;
        size_t data_len;
        struct bolt11 *b11 = new_bolt11(ctx, NULL);
        tal_t *tmpctx = tal_tmpctx(b11);
        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,
                have_x = false, have_f = false;

        b11->routes = tal_arr(b11, struct route_info *, 0);

        hrp = tal_arr(tmpctx, char, strlen(str) - 6);
        data = tal_arr(tmpctx, u5, strlen(str) - 8);

        if (!bech32_decode(hrp, data, &data_len, str, (size_t)-1))
                return decode_fail(b11, fail, "Bad bech32 string");

        /* For signature checking at the end. */
        hash_u5_init(&hu5, hrp);

        /* BOLT #11:
         *
         * The human readable part consists of two sections:
         * 1. `prefix`: `ln` + BIP-0173 currency prefix (e.g. `lnbc`, `lntb`)
         * 1. `amount`: optional number in that currency, followed by optional
         *    `multiplier`.
         */
        prefix = tal_strndup(tmpctx, hrp, strcspn(hrp, "0123456789"));

        /* BOLT #11:
         *
         * A reader MUST fail if it does not understand the `prefix`.
         */
        if (!strstarts(prefix, "ln"))
                return decode_fail(b11, fail,
                                   "Prefix '%s' does not start with ln", prefix);

        b11->chain = chainparams_by_bip173(prefix + 2);
        if (!b11->chain)
                return decode_fail(b11, fail, "Unknown chain %s", prefix + 2);

        /* BOLT #11:
         *
         * A reader SHOULD fail if `amount` contains a non-digit, or
         * is followed by anything except a `multiplier` in the table
         * above. */
        amountstr = tal_strdup(tmpctx, hrp + strlen(prefix));
        if (streq(amountstr, "")) {
                /* BOLT #11:
                 *
                 * A reader SHOULD indicate if amount is unspecified
                 */
                b11->msatoshi = NULL;
        } else {
                u64 m10 = 10;
                u64 amount;
                char *end;

                /* Gather and trim multiplier */
                end = amountstr + strlen(amountstr)-1;
                for (size_t i = 0; i < ARRAY_SIZE(multipliers); i++) {
                        if (*end == multipliers[i].letter) {
                                m10 = multipliers[i].m10;
                                *end = '\0';
                                break;
                        }
                }

                /* BOLT #11:
                 *
                 * A reader SHOULD fail if `amount` contains a non-digit, or
                 * is followed by anything except a `multiplier` in the table
                 * above.
                 */
                amount = strtoull(amountstr, &end, 10);
                if (amount == ULLONG_MAX && errno == ERANGE)
                        return decode_fail(b11, fail,
                                           "Invalid amount '%s'", amountstr);
                if (!*amountstr || *end)
                        return decode_fail(b11, fail,
                                           "Invalid amount postfix '%s'", end);

                /* Convert to millisatoshis. */
                b11->msatoshi = tal(b11, u64);
                *b11->msatoshi = amount * m10 / 10;
        }

        /* BOLT #11:
         *
         * The data part consists of multiple sections:
         *
         * 1. `timestamp`: seconds-since-1970 (35 bits, big-endian)
         * 1. Zero or more tagged parts.
         * 1. `signature`: bitcoin-style signature of above. (520 bits)
         */
        if (!pull_uint(&hu5, &data, &data_len, &b11->timestamp, 35))
                return decode_fail(b11, fail, "Can't get 35-bit timestamp");

        b11->expiry = DEFAULT_X;

        while (data_len > 520 / 5) {
                const char *problem = NULL;
                u64 type, data_length;

                /* BOLT #11:
                 *
                 * Each Tagged Field is of format:
                 *
                 * 1. `type` (5 bits)
                 * 1. `data_length` (10 bits, big-endian)
                 * 1. `data` (`data_length` x 5 bits)
                 */
                if (!pull_uint(&hu5, &data, &data_len, &type, 5)
                    || !pull_uint(&hu5, &data, &data_len, &data_length, 10))
                        return decode_fail(b11, fail,
                                           "Can't get tag and length");

                /* Can't exceed total data remaining. */
                if (data_length > data_len)
                        return decode_fail(b11, fail, "%c: truncated",
                                           bech32_charset[type]);

                switch (bech32_charset[type]) {
                case 'p':
                        decode_p(b11, &hu5, &data, &data_len, data_length,
                                 &have_p);
                        break;

                case 'd':
                        decode_d(b11, &hu5, &data, &data_len, data_length,
                                 &have_d);
                        break;

                case 'h':
                        decode_h(b11, &hu5, &data, &data_len, data_length,
                                 &have_h);
                        break;

                case 'n':
                        problem = decode_n(b11, &hu5, &data,
                                           &data_len, data_length,
                                           &have_n);
                        break;

                case 'x':
                        problem = decode_x(b11, &hu5, &data,
                                           &data_len, data_length,
                                           &have_x);
                        break;

                case 'f':
                        problem = decode_f(b11, &hu5, &data,
                                           &data_len, data_length,
                                           &have_f);
                        break;
                case 'r':
                        problem = decode_r(b11, &hu5, &data, &data_len,
                                           data_length);
                        break;
                default:
                        unknown_field(b11, &hu5, &data, &data_len,
                                      bech32_charset[type], data_length);
                }
                if (problem)
                        return decode_fail(b11, fail, "%s", problem);
        }

        if (!have_p)
                return decode_fail(b11, fail, "No valid 'p' field found");

        if (have_h) {
                struct sha256 sha;

                /* BOLT #11:
                 *
                 * A reader MUST check that the SHA-2 256 in the `h` field
                 * exactly matches the hashed description.
                 */
                if (!description)
                        return decode_fail(b11, fail,
                                           "h: no description to check");
                sha256(&sha, description, strlen(description));
                if (!structeq(b11->description_hash, &sha))
                        return decode_fail(b11, fail,
                                           "h: does not match description");
        }

        hash_u5_done(&hu5, &hash);

        /* BOLT #11:
         *
         * A writer MUST set `signature` to a valid 512-bit secp256k1
         * signature of the SHA2 256-bit hash of the Human Readable Part
         * concatenated with the Data Part and zero bits appended to the next
         * byte 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))
                return decode_fail(b11, fail, "signature truncated");

        assert(data_len == 0);

        if (!secp256k1_ecdsa_recoverable_signature_parse_compact
            (secp256k1_ctx, &sig, sig_and_recid, sig_and_recid[64]))
                return decode_fail(b11, fail, "signature invalid");

        secp256k1_ecdsa_recoverable_signature_convert(secp256k1_ctx,
                                                      &b11->sig, &sig);

        /* BOLT #11:
         *
         * A reader MUST check that the `signature` is valid (see the `n`
         * tagged field specified below).
         *...
         * A reader MUST use the `n` field to validate the signature instead of
         * performing signature recovery if a valid `n` field is provided.
         */
        if (!have_n) {
                if (!secp256k1_ecdsa_recover(secp256k1_ctx,
                                             &b11->receiver_id.pubkey,
                                             &sig,
                                             (const u8 *)&hash))
                        return decode_fail(b11, fail,
                                           "signature recovery failed");
        } else {
                if (!secp256k1_ecdsa_verify(secp256k1_ctx, &b11->sig,
                                            (const u8 *)&hash,
                                            &b11->receiver_id.pubkey))
                        return decode_fail(b11, fail, "invalid signature");
        }

        tal_free(tmpctx);
        return b11;
}

static size_t num_u5(size_t num_u8)
{
        return (num_u8 * 8 + 7) / 5;
}

static u8 get_bit(const u8 *src, size_t bitoff)
{
        return ((src[bitoff / 8] >> (7 - (bitoff % 8))) & 1);
}

/* Returns now many u5s were appended. */
static void push_bits(u5 **data, const void *src, size_t nbits)
{
        size_t i, b;
        size_t data_len = tal_len(*data);

        for (i = 0; i < nbits; i += b) {
                tal_resize(data, data_len+1);
                (*data)[data_len] = 0;
                for (b = 0; b < 5; b++) {
                        (*data)[data_len] <<= 1;
                        /* If we need bits we don't have, zero */
                        if (i+b < nbits)
                                (*data)[data_len] |= get_bit(src, i+b);
                }
                data_len++;
        }
}

/* Helper for pushing a variable-length big-endian int. */
static void push_varlen_uint(u5 **data, u64 val, size_t nbits)
{
        be64 be_val = cpu_to_be64(val << (64 - nbits));
        push_bits(data, &be_val, nbits);
}

/* BOLT #11:
 *
 * Each Tagged Field is of format:
 *
 * 1. `type` (5 bits)
 * 1. `data_length` (10 bits, big-endian)
 * 1. `data` (`data_length` x 5 bits)
 */
static void push_field(u5 **data, char type, const void *src, size_t nbits)
{
        assert(bech32_charset_rev[(unsigned char)type] >= 0);
        push_varlen_uint(data, bech32_charset_rev[(unsigned char)type], 5);
        push_varlen_uint(data, (nbits + 4) / 5, 10);
        push_bits(data, src, nbits);
}

/* BOLT #11:
 *
 * SHOULD use the minimum `data_length` possible.
 */
static void push_varlen_field(u5 **data, char type, u64 val)
{
        assert(bech32_charset_rev[(unsigned char)type] >= 0);
        push_varlen_uint(data, bech32_charset_rev[(unsigned char)type], 5);

        for (size_t nbits = 5; nbits < 65; nbits++) {
                if ((val >> nbits) == 0) {
                        push_varlen_uint(data, nbits / 5, 10);
                        push_varlen_uint(data, val,  nbits);
                        return;
                }
        }
        /* Can't be encoded in <= 60 bits. */
        abort();
}

static void encode_p(u5 **data, const struct sha256 *hash)
{
        push_field(data, 'p', hash, 256);
}

static void encode_d(u5 **data, const char *description)
{
        push_field(data, 'd', description, strlen(description) * CHAR_BIT);
}

static void encode_h(u5 **data, const struct sha256 *hash)
{
        push_field(data, 'h', hash, 256);
}

static void encode_n(u5 **data, const struct pubkey *id)
{
        u8 der[PUBKEY_DER_LEN];

        pubkey_to_der(der, id);
        push_field(data, 'n', der, sizeof(der) * CHAR_BIT);
}

static void encode_x(u5 **data, u64 expiry)
{
        push_varlen_field(data, 'x', expiry);
}

static void encode_f(u5 **data, const u8 *fallback)
{
        struct bitcoin_address pkh;
        struct ripemd160 sh;
        struct sha256 wsh;

        /* BOLT #11:
         *
         * For bitcoin payments, a writer MUST set an `f` field to a valid
         * witness version and program, or `17` followed by a public key hash,
         * or `18` followed by a script hash.
         */
        if (is_p2pkh(fallback, &pkh)) {
                u8 v17[1 + sizeof(pkh)];
                v17[0] = 17;
                memcpy(v17+1, &pkh, sizeof(pkh));
                push_field(data, 'f', v17, sizeof(v17) * CHAR_BIT);
        } else if (is_p2sh(fallback, &sh)) {
                u8 v18[1 + sizeof(sh)];
                v18[0] = 18;
                memcpy(v18+1, &sh, sizeof(sh));
                push_field(data, 'f', v18, sizeof(v18) * CHAR_BIT);
        } else if (is_p2wpkh(fallback, &pkh)) {
                u8 v0[1 + sizeof(pkh)];
                v0[0] = 0;
                memcpy(v0+1, &pkh, sizeof(pkh));
                push_field(data, 'f', v0, sizeof(v0) * CHAR_BIT);
        } else if (is_p2wsh(fallback, &wsh)) {
                u8 v0[1 + sizeof(wsh)];
                v0[0] = 0;
                memcpy(v0+1, &wsh, sizeof(wsh));
                push_field(data, 'f', v0, sizeof(v0) * CHAR_BIT);
        } else if (tal_len(fallback)
                   && fallback[0] >= 0x50
                   && fallback[0] < (0x50+16)) {
                /* Other (future) witness versions: turn OP_N into N */
                u8 *f = tal_dup_arr(NULL, u8,
                                    fallback, tal_len(fallback), 0);
                f[0] -= 0x50;
                push_field(data, 'f', f, tal_len(f) * CHAR_BIT);
                tal_free(f);
        } else {
                /* Copy raw. */
                push_field(data, 'f',
                           fallback, tal_len(fallback) * CHAR_BIT);
        }
}

static void encode_r(u5 **data, const struct route_info *r)
{
        u8 *rinfo = tal_arr(NULL, u8, 0);

        for (size_t i = 0; i < tal_count(r); i++)
                towire_route_info(&rinfo, r);

        push_field(data, 'r', rinfo, tal_len(rinfo) * CHAR_BIT);
        tal_free(rinfo);
}

static void encode_extra(u5 **data, const struct bolt11_field *extra)
{
        size_t len;

        push_varlen_uint(data, extra->tag, 5);
        push_varlen_uint(data, tal_count(extra->data), 10);

        /* extra->data is already u5s, so do this raw. */
        len = tal_len(*data);
        tal_resize(data, len + tal_count(extra->data));
        memcpy(*data + len, extra->data, tal_count(extra->data));
}

/* Encodes, even if it's nonsense. */
char *bolt11_encode(const tal_t *ctx,
                    struct lightningd *ld,
                    const struct bolt11 *b11, bool n_field)
{
        tal_t *tmpctx = tal_tmpctx(ctx);
        u5 *data = tal_arr(tmpctx, u5, 0);
        char *hrp, *output;
        char postfix;
        u64 amount;
        struct bolt11_field *extra;
        secp256k1_ecdsa_recoverable_signature rsig;
        u8 sig_and_recid[65];
        u8 *hrpu8, *msg;
        int recid;
        size_t i;

        /* BOLT #11:
         *
         * A writer MUST encode `amount` as a positive decimal integer
         * with no leading zeroes, SHOULD use the shortest
         * representation possible.
         */
        if (b11->msatoshi) {
                if (*b11->msatoshi % MSAT_PER_BTC == 0) {
                        postfix = '\0';
                        amount = *b11->msatoshi / MSAT_PER_BTC;
                } else {
                        for (i = 0; i < ARRAY_SIZE(multipliers)-1; i++) {
                                if (!(*b11->msatoshi * 10 % multipliers[i].m10))
                                        break;
                        }
                        postfix = multipliers[i].letter;
                        amount = *b11->msatoshi * 10 / multipliers[i].m10;
                }
                hrp = tal_fmt(tmpctx, "ln%s%"PRIu64"%c",
                              b11->chain->bip173_name, amount, postfix);
        } else
                hrp = tal_fmt(tmpctx, "ln%s", b11->chain->bip173_name);

        /* BOLT #11:
         *
         * 1. `timestamp`: seconds-since-1970 (35 bits, big-endian)
         * 1. Zero or more tagged parts.
         * 1. `signature`: bitcoin-style signature of above. (520 bits)
         */
        push_varlen_uint(&data, b11->timestamp, 35);

        /* BOLT #11:
         *
         * If a writer offers more than one of any field type, it MUST
         * specify the most-preferred field first, followed by
         * less-preferred fields in order.
         */
        /* Thus we do built-in fields, then extras last. */
        encode_p(&data, &b11->payment_hash);

        if (b11->description)
                encode_d(&data, b11->description);

        if (b11->description_hash)
                encode_h(&data, b11->description_hash);

        if (n_field)
                encode_n(&data, &b11->receiver_id);

        if (b11->expiry != DEFAULT_X)
                encode_x(&data, b11->expiry);

        if (b11->fallback)
                encode_f(&data, b11->fallback);

        for (size_t i = 0; i < tal_count(b11->routes); i++)
                encode_r(&data, b11->routes[i]);

        list_for_each(&b11->extra_fields, extra, list)
                encode_extra(&data, extra);

        /* FIXME: towire_ should check this? */
        if (tal_len(data) > 65535)
                return tal_free(tmpctx);

        /* Need exact length here */
        hrpu8 = tal_dup_arr(tmpctx, u8, (const u8 *)hrp, strlen(hrp), 0);
        msg = towire_hsmctl_sign_invoice(tmpctx, data, hrpu8);

	if (!wire_sync_write(ld->hsm_fd, take(msg)))
		fatal("Could not write to HSM: %s", strerror(errno));

	msg = hsm_sync_read(tmpctx, ld);
        if (!fromwire_hsmctl_sign_invoice_reply(msg, NULL, &rsig))
		fatal("HSM gave bad sign_invoice_reply %s",
		      tal_hex(msg, msg));

        secp256k1_ecdsa_recoverable_signature_serialize_compact(
                secp256k1_ctx,
                sig_and_recid,
                &recid,
                &rsig);
        sig_and_recid[64] = recid;

        push_bits(&data, sig_and_recid, sizeof(sig_and_recid) * CHAR_BIT);

        output = tal_arr(ctx, char, strlen(hrp) + tal_count(data) + 8);
        if (!bech32_encode(output, hrp, data, tal_count(data), (size_t)-1))
                output = tal_free(output);

        tal_free(tmpctx);
        return output;
}

static PRINTF_FMT(2,3) void *bad(const char *abortstr, const char *fmt, ...)
{
	if (abortstr) {
                va_list ap;

                va_start(ap, fmt);
                fprintf(stderr, "%s: ", abortstr);
                vfprintf(stderr, fmt, ap);
                fprintf(stderr, "\n");
		abort();
	}
	return NULL;
}

struct bolt11 *bolt11_out_check(const struct bolt11 *b11, const char *abortstr)
{
        struct bolt11_field *extra;

        /* BOLT #11:
         *
         * For channels with `chain_hash` identifying the Bitcoin blockchain,
         * the sending node MUST set the 4 most significant bytes of
         * `amount_msat` to zero.
         */
        if (*b11->msatoshi >= 1ULL << 32)
                return bad(abortstr, "msatoshi %"PRIu64" too large",
                           *b11->msatoshi);

        if (!b11->description && !b11->description_hash)
                return bad(abortstr, "No description or description_hash");

        if (b11->description && b11->description_hash)
                return bad(abortstr, "Both description or description_hash");

        if (b11->description && num_u5(strlen(b11->description)) > 1024)
                return bad(abortstr, "Description too long");

        /* FIXME: Check fallback is known type. */
        if (b11->fallback && tal_count(b11->fallback) == 0)
                return bad(abortstr, "Empty fallback");

        if (!list_check(&b11->extra_fields, abortstr))
                return bad(abortstr, "Invalid extras list");

        list_for_each(&b11->extra_fields, extra, list) {
                if (bech32_charset_rev[(unsigned char)extra->tag] < 0)
                        return bad(abortstr, "Invalid extra type %c (0x%02x)",
                                   extra->tag, extra->tag);

                if (tal_len(extra->data) >= 1024)
                        return bad(abortstr, "Extra %c too long", extra->tag);
        }
        return cast_const(struct bolt11 *, b11);
}

static void json_decodepay(struct command *cmd,
                           const char *buffer, const jsmntok_t *params)
{
	jsmntok_t *bolt11tok, *desctok;
	struct bolt11 *b11;
	struct json_result *response;
        char *str, *desc, *fail;

	if (!json_get_params(buffer, params,
			     "bolt11", &bolt11tok,
			     "?description", &desctok,
			     NULL)) {
		command_fail(cmd, "Need bolt11 string");
		return;
	}

        str = tal_strndup(cmd, buffer + bolt11tok->start,
                          bolt11tok->end - bolt11tok->start);

        if (desctok)
                desc = tal_strndup(cmd, buffer + desctok->start,
                                   desctok->end - desctok->start);
        else
                desc = NULL;

	b11 = bolt11_decode(cmd, str, desc, &fail);

	if (!b11) {
		command_fail(cmd, "Invalid bolt11: %s", fail);
		return;
	}

	response = new_json_result(cmd);
	json_object_start(response, NULL);

	json_add_string(response, "currency", b11->chain->bip173_name);
	json_add_u64(response, "timestamp", b11->timestamp);
	json_add_u64(response, "expiry", b11->expiry);
	json_add_pubkey(response, "payee", &b11->receiver_id);
        if (b11->msatoshi)
                json_add_u64(response, "msatoshi", *b11->msatoshi);
        if (b11->description)
                json_add_string(response, "description", b11->description);
        if (b11->description_hash)
                json_add_hex(response, "description_hash",
                             b11->description_hash,
                             sizeof(*b11->description_hash));
        if (tal_len(b11->fallback)) {
                struct bitcoin_address pkh;
                struct ripemd160 sh;
                struct sha256 wsh;

                json_object_start(response, "fallback");
                if (is_p2pkh(b11->fallback, &pkh)) {
                        json_add_string(response, "type", "P2PKH");
                        json_add_string(response, "addr",
                                        bitcoin_to_base58(cmd,
                                                          b11->chain->testnet,
                                                          &pkh));
                } else if (is_p2sh(b11->fallback, &sh)) {
                        json_add_string(response, "type", "P2SH");
                        json_add_string(response, "addr",
                                        p2sh_to_base58(cmd,
                                                       b11->chain->testnet,
                                                       &sh));
                } else if (is_p2wpkh(b11->fallback, &pkh)) {
                        char out[73 + strlen(b11->chain->bip173_name)];
                        json_add_string(response, "type", "P2WPKH");
                        if (segwit_addr_encode(out, b11->chain->bip173_name, 0,
                                               (const u8 *)&pkh, sizeof(pkh)))
                                json_add_string(response, "addr", out);
                } else if (is_p2wsh(b11->fallback, &wsh)) {
                        char out[73 + strlen(b11->chain->bip173_name)];
                        json_add_string(response, "type", "P2WSH");
                        if (segwit_addr_encode(out, b11->chain->bip173_name, 0,
                                               (const u8 *)&wsh, sizeof(wsh)))
                                json_add_string(response, "addr", out);
                }
                json_add_hex(response, "hex",
                             b11->fallback, tal_len(b11->fallback));
                json_object_end(response);
        }

        if (tal_count(b11->routes)) {
                size_t i, n;

                json_array_start(response, "routes");
                for (i = 0; i < tal_count(b11->routes); i++) {
                        json_array_start(response, NULL);
                        for (n = 0; n < tal_count(b11->routes[i]); n++) {
                                json_object_start(response, NULL);
                                json_add_pubkey(response, "pubkey",
                                                &b11->routes[i][n].pubkey);
                                json_add_short_channel_id(response,
                                                          "short_channel_id",
                                                          &b11->routes[i][n]
                                                          .short_channel_id);
                                json_add_u64(response, "fee",
                                             b11->routes[i][n].fee);
                                json_add_num(response, "cltv_expiry_delta",
                                             b11->routes[i][n]
                                             .cltv_expiry_delta);
                                json_object_end(response);
                        }
                        json_array_end(response);
                }
                json_array_end(response);
        }

        if (!list_empty(&b11->extra_fields)) {
                struct bolt11_field *extra;

                json_array_start(response, "extra");
                list_for_each(&b11->extra_fields, extra, list) {
                        char *data = tal_arr(cmd, char, tal_len(extra->data)+1);
                        size_t i;

                        for (i = 0; i < tal_len(extra->data); i++)
                                data[i] = bech32_charset[extra->data[i]];
                        data[i] = '\0';
                        json_object_start(response, NULL);
                        json_add_string(response, "tag",
                                        tal_fmt(data, "%c", extra->tag));
                        json_add_string(response, "data", data);
                        tal_free(data);
                        json_object_end(response);
                }
                json_array_end(response);
        }

	json_add_hex(response, "payment_hash",
                     &b11->payment_hash, sizeof(b11->payment_hash));

	json_add_string(response, "signature",
                        type_to_string(cmd, secp256k1_ecdsa_signature,
                                       &b11->sig));
	json_object_end(response);
	command_success(cmd, response);
}

static const struct json_command decodepay_command = {
	"decodepay",
	json_decodepay,
	"Parse and decode {bolt11} if possible",
	"Returns a verbose description on success"
};
AUTODATA(json_command, &decodepay_command);