Merge #994: Add a LockTime type

0ed78e5 Add lock time types (Tobin C. Harding)
1390ee1 Add a max scriptnum constant (Tobin C. Harding)

Pull request description:

  Implement a `LockTime` type that adds support for lock time values based on nLockTime and OP_CHECKLOCKTIMEVERIFY.

  For example usage in `rust-miniscript` please see rust-bitcoin/rust-miniscript#408.

  ### Notes:

  I probably should have opened a new PR, this is a total re-write and very different from what is being discussed below, sorry, my bad.

  This is just half of the 'timelock' story, its the easier half. The reason I switched terminology from timelock to locktime is that we have to compare two u32s so it does not make sense to call them _both_ timelocks.

  If I have missed, or apparently ignored, anything you said reviewers please accept my apology in advance, it was not intentional. The thread of discussion is long and this topic is complex. Please do restate your views liberally :)

  Here is a useful blog post I used while touching up on timelock specifics: https://medium.com/summa-technology/bitcoins-time-locks-27e0c362d7a1. It links to all the relevant bips too.

ACKs for top commit:
  Kixunil:
    ACK 0ed78e5
  apoelstra:
    ACK 0ed78e5

Tree-SHA512: 486fcce859b38fa1e8e6b11cd2f494462d6d7d1d9030d096ce6b260f6c9d0342b8952afe35152bdf3afe323a234a8165ac3d6c946304afcc13406d7a0489d75a

examples/ecdsa-psbt.rs

@@ -43,8 +43,8 @@ use bitcoin::util::bip32::{
 };
 use bitcoin::util::psbt::{self, Input, Psbt, PsbtSighashType};
 use bitcoin::{
-    Address, Amount, Network, OutPoint, PrivateKey, PublicKey, Script, Sequence, Transaction, TxIn,
-    TxOut, Txid, Witness,
+    Address, Amount, Network, OutPoint, PackedLockTime, PrivateKey, PublicKey, Script, Sequence,
+    Transaction, TxIn, TxOut, Txid, Witness,
 };
 
 use self::psbt_sign::*;
@@ -207,7 +207,7 @@ impl WatchOnly {
 
         let tx = Transaction {
             version: 2,
-            lock_time: 0,
+            lock_time: PackedLockTime::ZERO,
             input: vec![TxIn {
                 previous_output: OutPoint {
                     txid: Txid::from_hex(INPUT_UTXO_TXID)?,

src/blockdata/constants.rs

@@ -16,6 +16,7 @@ use crate::hashes::hex::{self, HexIterator};
 use crate::hashes::{Hash, sha256d};
 use crate::blockdata::opcodes;
 use crate::blockdata::script;
+use crate::blockdata::locktime::PackedLockTime;
 use crate::blockdata::transaction::{OutPoint, Transaction, TxOut, TxIn, Sequence};
 use crate::blockdata::block::{Block, BlockHeader};
 use crate::blockdata::witness::Witness;
@@ -53,6 +54,8 @@ pub const SCRIPT_ADDRESS_PREFIX_TEST: u8 = 196; // 0xc4
 pub const MAX_SCRIPT_ELEMENT_SIZE: usize = 520;
 /// How may blocks between halvings.
 pub const SUBSIDY_HALVING_INTERVAL: u32 = 210_000;
+/// Maximum allowed value for an integer in Script.
+pub const MAX_SCRIPTNUM_VALUE: u32 = 0x80000000; // 2^31
 
 /// In Bitcoind this is insanely described as ~((u256)0 >> 32)
 pub fn max_target(_: Network) -> Uint256 {
@@ -71,7 +74,7 @@ fn bitcoin_genesis_tx() -> Transaction {
     // Base
     let mut ret = Transaction {
         version: 1,
-        lock_time: 0,
+        lock_time: PackedLockTime::ZERO,
         input: vec![],
         output: vec![],
     };
@@ -199,6 +202,7 @@ mod test {
     use crate::hashes::hex::{ToHex, FromHex};
     use crate::network::constants::Network;
     use crate::consensus::encode::serialize;
+    use crate::blockdata::locktime::PackedLockTime;
 
     #[test]
     fn bitcoin_genesis_first_transaction() {
@@ -216,7 +220,7 @@ mod test {
         assert_eq!(serialize(&gen.output[0].script_pubkey),
                    Vec::from_hex("434104678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5fac").unwrap());
         assert_eq!(gen.output[0].value, 50 * COIN_VALUE);
-        assert_eq!(gen.lock_time, 0);
+        assert_eq!(gen.lock_time, PackedLockTime::ZERO);
 
         assert_eq!(gen.wtxid().to_hex(), "4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b");
     }