From 9c90b39ebd7418c5512a774e189ebacd1c1d7cb3 Mon Sep 17 00:00:00 2001
From: Steven Roose <steven@stevenroose.org>
Date: Tue, 21 Jul 2020 11:30:17 +0200
Subject: [PATCH] Add Block::coinbase and Block::bip34_block_height

---
 src/blockdata/block.rs | 86 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)

diff --git a/src/blockdata/block.rs b/src/blockdata/block.rs
index 5aad6d33..af2a7b78 100644
--- a/src/blockdata/block.rs
+++ b/src/blockdata/block.rs
@@ -20,6 +20,8 @@
 //! these blocks and the blockchain.
 //!
 
+use std::fmt;
+
 use util;
 use util::Error::{BlockBadTarget, BlockBadProofOfWork};
 use util::hash::bitcoin_merkle_root;
@@ -30,6 +32,7 @@ use consensus::encode::Encodable;
 use network::constants::Network;
 use blockdata::transaction::Transaction;
 use blockdata::constants::{max_target, WITNESS_SCALE_FACTOR};
+use blockdata::script;
 use VarInt;
 
 /// A block header, which contains all the block's information except
@@ -242,8 +245,71 @@ impl Block {
         let txs_weight: usize = self.txdata.iter().map(Transaction::get_weight).sum();
         base_weight + txs_weight
     }
+
+    /// Get the coinbase transaction, if one is present.
+    pub fn coinbase(&self) -> Option<&Transaction> {
+        self.txdata.first()
+    }
+
+    /// Get the block height as encoded into the coinbase according to BIP34.
+    /// Returns [None] if not present.
+    pub fn bip34_block_height(&self) -> Result<u64, Bip34Error> {
+        // Citing the spec:
+        // Add height as the first item in the coinbase transaction's scriptSig,
+        // and increase block version to 2. The format of the height is
+        // "serialized CScript" -- first byte is number of bytes in the number
+        // (will be 0x03 on main net for the next 150 or so years with 2^23-1
+        // blocks), following bytes are little-endian representation of the
+        // number (including a sign bit). Height is the height of the mined
+        // block in the block chain, where the genesis block is height zero (0).
+
+        if self.header.version < 2 {
+            return Err(Bip34Error::Unsupported);
+        }
+
+        let cb = self.coinbase().ok_or(Bip34Error::NotPresent)?;
+        let input = cb.input.first().ok_or(Bip34Error::NotPresent)?;
+        let push = input.script_sig.instructions_minimal().next().ok_or(Bip34Error::NotPresent)?;
+        match push.map_err(|_| Bip34Error::NotPresent)? {
+            script::Instruction::PushBytes(b) if b.len() <= 8 => {
+                // Expand the push to exactly 8 bytes (LE).
+                let mut full = [0; 8];
+                full[0..b.len()].copy_from_slice(&b[..]);
+                Ok(util::endian::slice_to_u64_le(&full))
+            }
+            script::Instruction::PushBytes(b) if b.len() > 8 => {
+                Err(Bip34Error::UnexpectedPush(b.to_vec()))
+            }
+            _ => Err(Bip34Error::NotPresent),
+        }
+    }
 }
 
+/// An error when looking up a BIP34 block height.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Bip34Error {
+    /// The block does not support BIP34 yet.
+    Unsupported,
+    /// No push was present where the BIP34 push was expected.
+    NotPresent,
+    /// The BIP34 push was larger than 8 bytes.
+    UnexpectedPush(Vec<u8>),
+}
+
+impl fmt::Display for Bip34Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            Bip34Error::Unsupported => write!(f, "block doesn't support BIP34"),
+            Bip34Error::NotPresent => write!(f, "BIP34 push not present in block's coinbase"),
+            Bip34Error::UnexpectedPush(ref p) => {
+                write!(f, "unexpected byte push of > 8 bytes: {:?}", p)
+            }
+        }
+    }
+}
+
+impl ::std::error::Error for Bip34Error {}
+
 #[cfg(test)]
 mod tests {
     use hashes::hex::FromHex;
@@ -251,6 +317,26 @@ mod tests {
     use blockdata::block::{Block, BlockHeader};
     use consensus::encode::{deserialize, serialize};
 
+    #[test]
+    fn test_coinbase_and_bip34() {
+        // testnet block 100,000
+        let block_hex = "0200000035ab154183570282ce9afc0b494c9fc6a3cfea05aa8c1add2ecc56490000000038ba3d78e4500a5a7570dbe61960398add4410d278b21cd9708e6d9743f374d544fc055227f1001c29c1ea3b0101000000010000000000000000000000000000000000000000000000000000000000000000ffffffff3703a08601000427f1001c046a510100522cfabe6d6d0000000000000000000068692066726f6d20706f6f6c7365727665726aac1eeeed88ffffffff0100f2052a010000001976a914912e2b234f941f30b18afbb4fa46171214bf66c888ac00000000";
+        let block: Block = deserialize(&Vec::<u8>::from_hex(block_hex).unwrap()).unwrap();
+
+        let cb_txid = "d574f343976d8e70d91cb278d21044dd8a396019e6db70755a0a50e4783dba38";
+        assert_eq!(block.coinbase().unwrap().txid().to_string(), cb_txid);
+
+        assert_eq!(block.bip34_block_height(), Ok(100_000));
+
+
+        // block with 9-byte bip34 push
+        let bad_hex = "0200000035ab154183570282ce9afc0b494c9fc6a3cfea05aa8c1add2ecc56490000000038ba3d78e4500a5a7570dbe61960398add4410d278b21cd9708e6d9743f374d544fc055227f1001c29c1ea3b0101000000010000000000000000000000000000000000000000000000000000000000000000ffffffff3d09a08601112233445566000427f1001c046a510100522cfabe6d6d0000000000000000000068692066726f6d20706f6f6c7365727665726aac1eeeed88ffffffff0100f2052a010000001976a914912e2b234f941f30b18afbb4fa46171214bf66c888ac00000000";
+        let bad: Block = deserialize(&Vec::<u8>::from_hex(bad_hex).unwrap()).unwrap();
+
+        let push = Vec::<u8>::from_hex("a08601112233445566").unwrap();
+        assert_eq!(bad.bip34_block_height(), Err(super::Bip34Error::UnexpectedPush(push)));
+    }
+
     #[test]
     fn block_test() {
         let some_block = Vec::from_hex("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").unwrap();