_ Git - rust-lightning/blob - lightning/src/ln/chan_utils.rs

   1 //! Various utilities for building scripts and deriving keys related to channels. These are
   2 //! largely of interest for those implementing chain::keysinterface::ChannelKeys message signing
   3 //! by hand.
   4
   5 use bitcoin::blockdata::script::{Script,Builder};
   6 use bitcoin::blockdata::opcodes;
   7 use bitcoin::blockdata::transaction::{TxIn,TxOut,OutPoint,Transaction, SigHashType};
   8 use bitcoin::consensus::encode::{self, Decodable, Encodable};
   9 use bitcoin::util::bip143;
  10
  11 use bitcoin_hashes::{Hash, HashEngine};
  12 use bitcoin_hashes::sha256::Hash as Sha256;
  13 use bitcoin_hashes::ripemd160::Hash as Ripemd160;
  14 use bitcoin_hashes::hash160::Hash as Hash160;
  15 use bitcoin_hashes::sha256d::Hash as Sha256dHash;
  16
  17 use ln::channelmanager::{PaymentHash, PaymentPreimage};
  18 use ln::msgs::DecodeError;
  19 use util::ser::{Readable, Writeable, Writer, WriterWriteAdaptor};
  20
  21 use secp256k1::key::{SecretKey,PublicKey};
  22 use secp256k1::{Secp256k1, Signature};
  23 use secp256k1;
  24
  25 pub(super) const HTLC_SUCCESS_TX_WEIGHT: u64 = 703;
  26 pub(super) const HTLC_TIMEOUT_TX_WEIGHT: u64 = 663;
  27
  28 #[derive(PartialEq)]
  29 pub(crate) enum HTLCType {
  30         AcceptedHTLC,
  31         OfferedHTLC
  32 }
  33
  34 impl HTLCType {
  35         /// Check if a given tx witnessScript len matchs one of a pre-signed HTLC
  36         pub(crate) fn scriptlen_to_htlctype(witness_script_len: usize) ->  Option<HTLCType> {
  37                 if witness_script_len == 133 {
  38                         Some(HTLCType::OfferedHTLC)
  39                 } else if witness_script_len >= 136 && witness_script_len <= 139 {
  40                         Some(HTLCType::AcceptedHTLC)
  41                 } else {
  42                         None
  43                 }
  44         }
  45 }
  46
  47 // Various functions for key derivation and transaction creation for use within channels. Primarily
  48 // used in Channel and ChannelMonitor.
  49
  50 pub(super) fn build_commitment_secret(commitment_seed: &[u8; 32], idx: u64) -> [u8; 32] {
  51         let mut res: [u8; 32] = commitment_seed.clone();
  52         for i in 0..48 {
  53                 let bitpos = 47 - i;
  54                 if idx & (1 << bitpos) == (1 << bitpos) {
  55                         res[bitpos / 8] ^= 1 << (bitpos & 7);
  56                         res = Sha256::hash(&res).into_inner();
  57                 }
  58         }
  59         res
  60 }
  61
  62 /// Derives a per-commitment-transaction private key (eg an htlc key or payment key) from the base
  63 /// private key for that type of key and the per_commitment_point (available in TxCreationKeys)
  64 pub fn derive_private_key<T: secp256k1::Signing>(secp_ctx: &Secp256k1<T>, per_commitment_point: &PublicKey, base_secret: &SecretKey) -> Result<SecretKey, secp256k1::Error> {
  65         let mut sha = Sha256::engine();
  66         sha.input(&per_commitment_point.serialize());
  67         sha.input(&PublicKey::from_secret_key(&secp_ctx, &base_secret).serialize());
  68         let res = Sha256::from_engine(sha).into_inner();
  69
  70         let mut key = base_secret.clone();
  71         key.add_assign(&res)?;
  72         Ok(key)
  73 }
  74
  75 pub(super) fn derive_public_key<T: secp256k1::Signing>(secp_ctx: &Secp256k1<T>, per_commitment_point: &PublicKey, base_point: &PublicKey) -> Result<PublicKey, secp256k1::Error> {
  76         let mut sha = Sha256::engine();
  77         sha.input(&per_commitment_point.serialize());
  78         sha.input(&base_point.serialize());
  79         let res = Sha256::from_engine(sha).into_inner();
  80
  81         let hashkey = PublicKey::from_secret_key(&secp_ctx, &SecretKey::from_slice(&res)?);
  82         base_point.combine(&hashkey)
  83 }
  84
  85 /// Derives a revocation key from its constituent parts.
  86 /// Note that this is infallible iff we trust that at least one of the two input keys are randomly
  87 /// generated (ie our own).
  88 pub(super) fn derive_private_revocation_key<T: secp256k1::Signing>(secp_ctx: &Secp256k1<T>, per_commitment_secret: &SecretKey, revocation_base_secret: &SecretKey) -> Result<SecretKey, secp256k1::Error> {
  89         let revocation_base_point = PublicKey::from_secret_key(&secp_ctx, &revocation_base_secret);
  90         let per_commitment_point = PublicKey::from_secret_key(&secp_ctx, &per_commitment_secret);
  91
  92         let rev_append_commit_hash_key = {
  93                 let mut sha = Sha256::engine();
  94                 sha.input(&revocation_base_point.serialize());
  95                 sha.input(&per_commitment_point.serialize());
  96
  97                 Sha256::from_engine(sha).into_inner()
  98         };
  99         let commit_append_rev_hash_key = {
 100                 let mut sha = Sha256::engine();
 101                 sha.input(&per_commitment_point.serialize());
 102                 sha.input(&revocation_base_point.serialize());
 103
 104                 Sha256::from_engine(sha).into_inner()
 105         };
 106
 107         let mut part_a = revocation_base_secret.clone();
 108         part_a.mul_assign(&rev_append_commit_hash_key)?;
 109         let mut part_b = per_commitment_secret.clone();
 110         part_b.mul_assign(&commit_append_rev_hash_key)?;
 111         part_a.add_assign(&part_b[..])?;
 112         Ok(part_a)
 113 }
 114
 115 pub(super) fn derive_public_revocation_key<T: secp256k1::Verification>(secp_ctx: &Secp256k1<T>, per_commitment_point: &PublicKey, revocation_base_point: &PublicKey) -> Result<PublicKey, secp256k1::Error> {
 116         let rev_append_commit_hash_key = {
 117                 let mut sha = Sha256::engine();
 118                 sha.input(&revocation_base_point.serialize());
 119                 sha.input(&per_commitment_point.serialize());
 120
 121                 Sha256::from_engine(sha).into_inner()
 122         };
 123         let commit_append_rev_hash_key = {
 124                 let mut sha = Sha256::engine();
 125                 sha.input(&per_commitment_point.serialize());
 126                 sha.input(&revocation_base_point.serialize());
 127
 128                 Sha256::from_engine(sha).into_inner()
 129         };
 130
 131         let mut part_a = revocation_base_point.clone();
 132         part_a.mul_assign(&secp_ctx, &rev_append_commit_hash_key)?;
 133         let mut part_b = per_commitment_point.clone();
 134         part_b.mul_assign(&secp_ctx, &commit_append_rev_hash_key)?;
 135         part_a.combine(&part_b)
 136 }
 137
 138 /// The set of public keys which are used in the creation of one commitment transaction.
 139 /// These are derived from the channel base keys and per-commitment data.
 140 pub struct TxCreationKeys {
 141         /// The per-commitment public key which was used to derive the other keys.
 142         pub per_commitment_point: PublicKey,
 143         /// The revocation key which is used to allow the owner of the commitment transaction to
 144         /// provide their counterparty the ability to punish them if they broadcast an old state.
 145         pub revocation_key: PublicKey,
 146         /// A's HTLC Key
 147         pub a_htlc_key: PublicKey,
 148         /// B's HTLC Key
 149         pub b_htlc_key: PublicKey,
 150         /// A's Payment Key (which isn't allowed to be spent from for some delay)
 151         pub a_delayed_payment_key: PublicKey,
 152         /// B's Payment Key
 153         pub b_payment_key: PublicKey,
 154 }
 155
 156 impl TxCreationKeys {
 157         pub(super) fn new<T: secp256k1::Signing + secp256k1::Verification>(secp_ctx: &Secp256k1<T>, per_commitment_point: &PublicKey, a_delayed_payment_base: &PublicKey, a_htlc_base: &PublicKey, b_revocation_base: &PublicKey, b_payment_base: &PublicKey, b_htlc_base: &PublicKey) -> Result<TxCreationKeys, secp256k1::Error> {
 158                 Ok(TxCreationKeys {
 159                         per_commitment_point: per_commitment_point.clone(),
 160                         revocation_key: derive_public_revocation_key(&secp_ctx, &per_commitment_point, &b_revocation_base)?,
 161                         a_htlc_key: derive_public_key(&secp_ctx, &per_commitment_point, &a_htlc_base)?,
 162                         b_htlc_key: derive_public_key(&secp_ctx, &per_commitment_point, &b_htlc_base)?,
 163                         a_delayed_payment_key: derive_public_key(&secp_ctx, &per_commitment_point, &a_delayed_payment_base)?,
 164                         b_payment_key: derive_public_key(&secp_ctx, &per_commitment_point, &b_payment_base)?,
 165                 })
 166         }
 167 }
 168
 169 /// Gets the "to_local" output redeemscript, ie the script which is time-locked or spendable by
 170 /// the revocation key
 171 pub(super) fn get_revokeable_redeemscript(revocation_key: &PublicKey, to_self_delay: u16, delayed_payment_key: &PublicKey) -> Script {
 172         Builder::new().push_opcode(opcodes::all::OP_IF)
 173                       .push_slice(&revocation_key.serialize())
 174                       .push_opcode(opcodes::all::OP_ELSE)
 175                       .push_int(to_self_delay as i64)
 176                       .push_opcode(opcodes::all::OP_CSV)
 177                       .push_opcode(opcodes::all::OP_DROP)
 178                       .push_slice(&delayed_payment_key.serialize())
 179                       .push_opcode(opcodes::all::OP_ENDIF)
 180                       .push_opcode(opcodes::all::OP_CHECKSIG)
 181                       .into_script()
 182 }
 183
 184 #[derive(Clone, PartialEq)]
 185 /// Information about an HTLC as it appears in a commitment transaction
 186 pub struct HTLCOutputInCommitment {
 187         /// Whether the HTLC was "offered" (ie outbound in relation to this commitment transaction).
 188         /// Note that this is not the same as whether it is ountbound *from us*. To determine that you
 189         /// need to compare this value to whether the commitment transaction in question is that of
 190         /// the remote party or our own.
 191         pub offered: bool,
 192         /// The value, in msat, of the HTLC. The value as it appears in the commitment transaction is
 193         /// this divided by 1000.
 194         pub amount_msat: u64,
 195         /// The CLTV lock-time at which this HTLC expires.
 196         pub cltv_expiry: u32,
 197         /// The hash of the preimage which unlocks this HTLC.
 198         pub payment_hash: PaymentHash,
 199         /// The position within the commitment transactions' outputs. This may be None if the value is
 200         /// below the dust limit (in which case no output appears in the commitment transaction and the
 201         /// value is spent to additional transaction fees).
 202         pub transaction_output_index: Option<u32>,
 203 }
 204
 205 #[inline]
 206 pub(super) fn get_htlc_redeemscript_with_explicit_keys(htlc: &HTLCOutputInCommitment, a_htlc_key: &PublicKey, b_htlc_key: &PublicKey, revocation_key: &PublicKey) -> Script {
 207         let payment_hash160 = Ripemd160::hash(&htlc.payment_hash.0[..]).into_inner();
 208         if htlc.offered {
 209                 Builder::new().push_opcode(opcodes::all::OP_DUP)
 210                               .push_opcode(opcodes::all::OP_HASH160)
 211                               .push_slice(&Hash160::hash(&revocation_key.serialize())[..])
 212                               .push_opcode(opcodes::all::OP_EQUAL)
 213                               .push_opcode(opcodes::all::OP_IF)
 214                               .push_opcode(opcodes::all::OP_CHECKSIG)
 215                               .push_opcode(opcodes::all::OP_ELSE)
 216                               .push_slice(&b_htlc_key.serialize()[..])
 217                               .push_opcode(opcodes::all::OP_SWAP)
 218                               .push_opcode(opcodes::all::OP_SIZE)
 219                               .push_int(32)
 220                               .push_opcode(opcodes::all::OP_EQUAL)
 221                               .push_opcode(opcodes::all::OP_NOTIF)
 222                               .push_opcode(opcodes::all::OP_DROP)
 223                               .push_int(2)
 224                               .push_opcode(opcodes::all::OP_SWAP)
 225                               .push_slice(&a_htlc_key.serialize()[..])
 226                               .push_int(2)
 227                               .push_opcode(opcodes::all::OP_CHECKMULTISIG)
 228                               .push_opcode(opcodes::all::OP_ELSE)
 229                               .push_opcode(opcodes::all::OP_HASH160)
 230                               .push_slice(&payment_hash160)
 231                               .push_opcode(opcodes::all::OP_EQUALVERIFY)
 232                               .push_opcode(opcodes::all::OP_CHECKSIG)
 233                               .push_opcode(opcodes::all::OP_ENDIF)
 234                               .push_opcode(opcodes::all::OP_ENDIF)
 235                               .into_script()
 236         } else {
 237                 Builder::new().push_opcode(opcodes::all::OP_DUP)
 238                               .push_opcode(opcodes::all::OP_HASH160)
 239                               .push_slice(&Hash160::hash(&revocation_key.serialize())[..])
 240                               .push_opcode(opcodes::all::OP_EQUAL)
 241                               .push_opcode(opcodes::all::OP_IF)
 242                               .push_opcode(opcodes::all::OP_CHECKSIG)
 243                               .push_opcode(opcodes::all::OP_ELSE)
 244                               .push_slice(&b_htlc_key.serialize()[..])
 245                               .push_opcode(opcodes::all::OP_SWAP)
 246                               .push_opcode(opcodes::all::OP_SIZE)
 247                               .push_int(32)
 248                               .push_opcode(opcodes::all::OP_EQUAL)
 249                               .push_opcode(opcodes::all::OP_IF)
 250                               .push_opcode(opcodes::all::OP_HASH160)
 251                               .push_slice(&payment_hash160)
 252                               .push_opcode(opcodes::all::OP_EQUALVERIFY)
 253                               .push_int(2)
 254                               .push_opcode(opcodes::all::OP_SWAP)
 255                               .push_slice(&a_htlc_key.serialize()[..])
 256                               .push_int(2)
 257                               .push_opcode(opcodes::all::OP_CHECKMULTISIG)
 258                               .push_opcode(opcodes::all::OP_ELSE)
 259                               .push_opcode(opcodes::all::OP_DROP)
 260                               .push_int(htlc.cltv_expiry as i64)
 261                               .push_opcode(opcodes::all::OP_CLTV)
 262                               .push_opcode(opcodes::all::OP_DROP)
 263                               .push_opcode(opcodes::all::OP_CHECKSIG)
 264                               .push_opcode(opcodes::all::OP_ENDIF)
 265                               .push_opcode(opcodes::all::OP_ENDIF)
 266                               .into_script()
 267         }
 268 }
 269
 270 /// note here that 'a_revocation_key' is generated using b_revocation_basepoint and a's
 271 /// commitment secret. 'htlc' does *not* need to have its previous_output_index filled.
 272 #[inline]
 273 pub fn get_htlc_redeemscript(htlc: &HTLCOutputInCommitment, keys: &TxCreationKeys) -> Script {
 274         get_htlc_redeemscript_with_explicit_keys(htlc, &keys.a_htlc_key, &keys.b_htlc_key, &keys.revocation_key)
 275 }
 276
 277 /// Gets the redeemscript for a funding output from the two funding public keys.
 278 /// Note that the order of funding public keys does not matter.
 279 pub fn make_funding_redeemscript(a: &PublicKey, b: &PublicKey) -> Script {
 280         let our_funding_key = a.serialize();
 281         let their_funding_key = b.serialize();
 282
 283         let builder = Builder::new().push_opcode(opcodes::all::OP_PUSHNUM_2);
 284         if our_funding_key[..] < their_funding_key[..] {
 285                 builder.push_slice(&our_funding_key)
 286                         .push_slice(&their_funding_key)
 287         } else {
 288                 builder.push_slice(&their_funding_key)
 289                         .push_slice(&our_funding_key)
 290         }.push_opcode(opcodes::all::OP_PUSHNUM_2).push_opcode(opcodes::all::OP_CHECKMULTISIG).into_script()
 291 }
 292
 293 /// panics if htlc.transaction_output_index.is_none()!
 294 pub fn build_htlc_transaction(prev_hash: &Sha256dHash, feerate_per_kw: u64, to_self_delay: u16, htlc: &HTLCOutputInCommitment, a_delayed_payment_key: &PublicKey, revocation_key: &PublicKey) -> Transaction {
 295         let mut txins: Vec<TxIn> = Vec::new();
 296         txins.push(TxIn {
 297                 previous_output: OutPoint {
 298                         txid: prev_hash.clone(),
 299                         vout: htlc.transaction_output_index.expect("Can't build an HTLC transaction for a dust output"),
 300                 },
 301                 script_sig: Script::new(),
 302                 sequence: 0,
 303                 witness: Vec::new(),
 304         });
 305
 306         let total_fee = if htlc.offered {
 307                         feerate_per_kw * HTLC_TIMEOUT_TX_WEIGHT / 1000
 308                 } else {
 309                         feerate_per_kw * HTLC_SUCCESS_TX_WEIGHT / 1000
 310                 };
 311
 312         let mut txouts: Vec<TxOut> = Vec::new();
 313         txouts.push(TxOut {
 314                 script_pubkey: get_revokeable_redeemscript(revocation_key, to_self_delay, a_delayed_payment_key).to_v0_p2wsh(),
 315                 value: htlc.amount_msat / 1000 - total_fee //TODO: BOLT 3 does not specify if we should add amount_msat before dividing or if we should divide by 1000 before subtracting (as we do here)
 316         });
 317
 318         Transaction {
 319                 version: 2,
 320                 lock_time: if htlc.offered { htlc.cltv_expiry } else { 0 },
 321                 input: txins,
 322                 output: txouts,
 323         }
 324 }
 325
 326 /// Signs a transaction created by build_htlc_transaction. If the transaction is an
 327 /// HTLC-Success transaction (ie htlc.offered is false), preimage must be set!
 328 pub(crate) fn sign_htlc_transaction<T: secp256k1::Signing>(tx: &mut Transaction, their_sig: &Signature, preimage: &Option<PaymentPreimage>, htlc: &HTLCOutputInCommitment, a_htlc_key: &PublicKey, b_htlc_key: &PublicKey, revocation_key: &PublicKey, per_commitment_point: &PublicKey, htlc_base_key: &SecretKey, secp_ctx: &Secp256k1<T>) -> Result<(Signature, Script), ()> {
 329         if tx.input.len() != 1 { return Err(()); }
 330         if tx.input[0].witness.len() != 0 { return Err(()); }
 331
 332         let htlc_redeemscript = get_htlc_redeemscript_with_explicit_keys(&htlc, a_htlc_key, b_htlc_key, revocation_key);
 333
 334         let our_htlc_key = derive_private_key(secp_ctx, per_commitment_point, htlc_base_key).map_err(|_| ())?;
 335         let sighash = hash_to_message!(&bip143::SighashComponents::new(&tx).sighash_all(&tx.input[0], &htlc_redeemscript, htlc.amount_msat / 1000)[..]);
 336         let local_tx = PublicKey::from_secret_key(&secp_ctx, &our_htlc_key) == *a_htlc_key;
 337         let our_sig = secp_ctx.sign(&sighash, &our_htlc_key);
 338
 339         tx.input[0].witness.push(Vec::new()); // First is the multisig dummy
 340
 341         if local_tx { // b, then a
 342                 tx.input[0].witness.push(their_sig.serialize_der().to_vec());
 343                 tx.input[0].witness.push(our_sig.serialize_der().to_vec());
 344         } else {
 345                 tx.input[0].witness.push(our_sig.serialize_der().to_vec());
 346                 tx.input[0].witness.push(their_sig.serialize_der().to_vec());
 347         }
 348         tx.input[0].witness[1].push(SigHashType::All as u8);
 349         tx.input[0].witness[2].push(SigHashType::All as u8);
 350
 351         if htlc.offered {
 352                 tx.input[0].witness.push(Vec::new());
 353                 assert!(preimage.is_none());
 354         } else {
 355                 tx.input[0].witness.push(preimage.unwrap().0.to_vec());
 356         }
 357
 358         tx.input[0].witness.push(htlc_redeemscript.as_bytes().to_vec());
 359
 360         Ok((our_sig, htlc_redeemscript))
 361 }
 362
 363 #[derive(Clone)]
 364 /// We use this to track local commitment transactions and put off signing them until we are ready
 365 /// to broadcast. Eventually this will require a signer which is possibly external, but for now we
 366 /// just pass in the SecretKeys required.
 367 pub(crate) struct LocalCommitmentTransaction {
 368         tx: Transaction
 369 }
 370 impl LocalCommitmentTransaction {
 371         #[cfg(test)]
 372         pub fn dummy() -> Self {
 373                 Self { tx: Transaction {
 374                         version: 2,
 375                         input: Vec::new(),
 376                         output: Vec::new(),
 377                         lock_time: 0,
 378                 } }
 379         }
 380
 381         pub fn new_missing_local_sig(mut tx: Transaction, their_sig: &Signature, our_funding_key: &PublicKey, their_funding_key: &PublicKey) -> LocalCommitmentTransaction {
 382                 if tx.input.len() != 1 { panic!("Tried to store a commitment transaction that had input count != 1!"); }
 383                 if tx.input[0].witness.len() != 0 { panic!("Tried to store a signed commitment transaction?"); }
 384
 385                 tx.input[0].witness.push(Vec::new()); // First is the multisig dummy
 386
 387                 if our_funding_key.serialize()[..] < their_funding_key.serialize()[..] {
 388                         tx.input[0].witness.push(Vec::new());
 389                         tx.input[0].witness.push(their_sig.serialize_der().to_vec());
 390                         tx.input[0].witness[2].push(SigHashType::All as u8);
 391                 } else {
 392                         tx.input[0].witness.push(their_sig.serialize_der().to_vec());
 393                         tx.input[0].witness[1].push(SigHashType::All as u8);
 394                         tx.input[0].witness.push(Vec::new());
 395                 }
 396
 397                 Self { tx }
 398         }
 399
 400         pub fn txid(&self) -> Sha256dHash {
 401                 self.tx.txid()
 402         }
 403
 404         pub fn has_local_sig(&self) -> bool {
 405                 if self.tx.input.len() != 1 { panic!("Commitment transactions must have input count == 1!"); }
 406                 if self.tx.input[0].witness.len() == 4 {
 407                         assert!(!self.tx.input[0].witness[1].is_empty());
 408                         assert!(!self.tx.input[0].witness[2].is_empty());
 409                         true
 410                 } else {
 411                         assert_eq!(self.tx.input[0].witness.len(), 3);
 412                         assert!(self.tx.input[0].witness[0].is_empty());
 413                         assert!(self.tx.input[0].witness[1].is_empty() || self.tx.input[0].witness[2].is_empty());
 414                         false
 415                 }
 416         }
 417
 418         pub fn add_local_sig<T: secp256k1::Signing>(&mut self, funding_key: &SecretKey, funding_redeemscript: &Script, channel_value_satoshis: u64, secp_ctx: &Secp256k1<T>) {
 419                 if self.has_local_sig() { return; }
 420                 let sighash = hash_to_message!(&bip143::SighashComponents::new(&self.tx)
 421                         .sighash_all(&self.tx.input[0], funding_redeemscript, channel_value_satoshis)[..]);
 422                 let our_sig = secp_ctx.sign(&sighash, funding_key);
 423
 424                 if self.tx.input[0].witness[1].is_empty() {
 425                         self.tx.input[0].witness[1] = our_sig.serialize_der().to_vec();
 426                         self.tx.input[0].witness[1].push(SigHashType::All as u8);
 427                 } else {
 428                         self.tx.input[0].witness[2] = our_sig.serialize_der().to_vec();
 429                         self.tx.input[0].witness[2].push(SigHashType::All as u8);
 430                 }
 431
 432                 self.tx.input[0].witness.push(funding_redeemscript.as_bytes().to_vec());
 433         }
 434
 435         pub fn without_valid_witness(&self) -> &Transaction { &self.tx }
 436         pub fn with_valid_witness(&self) -> &Transaction {
 437                 assert!(self.has_local_sig());
 438                 &self.tx
 439         }
 440 }
 441 impl PartialEq for LocalCommitmentTransaction {
 442         // We dont care whether we are signed in equality comparison
 443         fn eq(&self, o: &Self) -> bool {
 444                 self.txid() == o.txid()
 445         }
 446 }
 447 impl Writeable for LocalCommitmentTransaction {
 448         fn write<W: Writer>(&self, writer: &mut W) -> Result<(), ::std::io::Error> {
 449                 if let Err(e) = self.tx.consensus_encode(&mut WriterWriteAdaptor(writer)) {
 450                         match e {
 451                                 encode::Error::Io(e) => return Err(e),
 452                                 _ => panic!("local tx must have been well-formed!"),
 453                         }
 454                 }
 455                 Ok(())
 456         }
 457 }
 458 impl<R: ::std::io::Read> Readable<R> for LocalCommitmentTransaction {
 459         fn read(reader: &mut R) -> Result<Self, DecodeError> {
 460                 let tx = match Transaction::consensus_decode(reader.by_ref()) {
 461                         Ok(tx) => tx,
 462                         Err(e) => match e {
 463                                 encode::Error::Io(ioe) => return Err(DecodeError::Io(ioe)),
 464                                 _ => return Err(DecodeError::InvalidValue),
 465                         },
 466                 };
 467
 468                 if tx.input.len() != 1 {
 469                         // Ensure tx didn't hit the 0-input ambiguity case.
 470                         return Err(DecodeError::InvalidValue);
 471                 }
 472                 Ok(Self { tx })
 473         }
 474 }