Merge pull request #461 from TheBlueMatt/2020-08-mut-sighash

Expose the witnesses of the tx being hashed in SigHashCache

src/util/bip143.rs

@@ -25,6 +25,8 @@ use blockdata::script::Script;
 use blockdata::transaction::{Transaction, TxIn, SigHashType};
 use consensus::encode::Encodable;
 
+use std::ops::{Deref, DerefMut};
+
 /// Parts of a sighash which are common across inputs or signatures, and which are
 /// sufficient (in conjunction with a private key) to sign the transaction
 #[derive(Clone, PartialEq, Eq, Debug)]
@@ -102,9 +104,9 @@ impl SighashComponents {
 }
 
 /// A replacement for SigHashComponents which supports all sighash modes
-pub struct SigHashCache<'a> {
+pub struct SigHashCache<R: Deref<Target=Transaction>> {
     /// Access to transaction required for various introspection
-    tx: &'a Transaction,
+    tx: R,
     /// Hash of all the previous outputs, computed as required
     hash_prevouts: Option<sha256d::Hash>,
     /// Hash of all the input sequence nos, computed as required
@@ -113,12 +115,12 @@ pub struct SigHashCache<'a> {
     hash_outputs: Option<sha256d::Hash>,
 }
 
-impl<'a> SigHashCache<'a> {
+impl<R: Deref<Target=Transaction>> SigHashCache<R> {
     /// Compute the sighash components from an unsigned transaction and auxiliary
     /// in a lazy manner when required.
     /// For the generated sighashes to be valid, no fields in the transaction may change except for
     /// script_sig and witnesses.
-    pub fn new(tx: &Transaction) -> SigHashCache {
+    pub fn new(tx: R) -> Self {
         SigHashCache {
             tx: tx,
             hash_prevouts: None,
@@ -189,15 +191,17 @@ impl<'a> SigHashCache<'a> {
             zero_hash.consensus_encode(&mut enc).unwrap();
         }
 
-        let txin = &self.tx.input[input_index];
+        {
+            let txin = &self.tx.input[input_index];
 
-        txin
-            .previous_output
-            .consensus_encode(&mut enc)
-            .unwrap();
-        script_code.consensus_encode(&mut enc).unwrap();
-        value.consensus_encode(&mut enc).unwrap();
-        txin.sequence.consensus_encode(&mut enc).unwrap();
+            txin
+                .previous_output
+                .consensus_encode(&mut enc)
+                .unwrap();
+            script_code.consensus_encode(&mut enc).unwrap();
+            value.consensus_encode(&mut enc).unwrap();
+            txin.sequence.consensus_encode(&mut enc).unwrap();
+        }
 
         if sighash != SigHashType::Single && sighash != SigHashType::None {
             self.hash_outputs().consensus_encode(&mut enc).unwrap();
@@ -215,6 +219,32 @@ impl<'a> SigHashCache<'a> {
     }
 }
 
+impl<R: DerefMut<Target=Transaction>> SigHashCache<R> {
+    /// When the SigHashCache is initialized with a mutable reference to a transaction instead of a
+    /// regular reference, this method is available to allow modification to the witnesses.
+    ///
+    /// This allows in-line signing such as
+    /// ```
+    /// use bitcoin::blockdata::transaction::{Transaction, SigHashType};
+    /// use bitcoin::util::bip143::SigHashCache;
+    /// use bitcoin::Script;
+    ///
+    /// let mut tx_to_sign = Transaction { version: 2, lock_time: 0, input: Vec::new(), output: Vec::new() };
+    /// let input_count = tx_to_sign.input.len();
+    ///
+    /// let mut sig_hasher = SigHashCache::new(&mut tx_to_sign);
+    /// for inp in 0..input_count {
+    ///     let prevout_script = Script::new();
+    ///     let _sighash = sig_hasher.signature_hash(inp, &prevout_script, 42, SigHashType::All);
+    ///     // ... sign the sighash
+    ///     sig_hasher.access_witness(inp).push(Vec::new());
+    /// }
+    /// ```
+    pub fn access_witness(&mut self, input_index: usize) -> &mut Vec<Vec<u8>> {
+        &mut self.tx.input[input_index].witness
+    }
+}
+
 #[cfg(test)]
 #[allow(deprecated)]
 mod tests {