Expose serialized data for transaction signatures

src/blockdata/transaction.rs

@@ -307,30 +307,34 @@ impl Transaction {
         Wtxid::from_engine(enc)
     }
 
-    /// Computes a signature hash for a given input index with a given sighash flag.
+    /// Encodes the signing data from which a signature hash for a given input index with a given
-    /// To actually produce a scriptSig, this hash needs to be run through an
+    /// sighash flag can be computed.  To actually produce a scriptSig, this hash needs to be run
-    /// ECDSA signer, the SigHashType appended to the resulting sig, and a
+    /// through an ECDSA signer, the SigHashType appended to the resulting sig, and a script
-    /// script written around this, but this is the general (and hard) part.
+    /// written around this, but this is the general (and hard) part.
     ///
-    /// *Warning* This does NOT attempt to support OP_CODESEPARATOR. In general
+    /// *Warning* This does NOT attempt to support OP_CODESEPARATOR. In general this would require
-    /// this would require evaluating `script_pubkey` to determine which separators
+    /// evaluating `script_pubkey` to determine which separators get evaluated and which don't,
-    /// get evaluated and which don't, which we don't have the information to
+    /// which we don't have the information to determine.
-    /// determine.
     ///
-    /// # Panics
+    /// # Panics Panics if `input_index` is greater than or equal to `self.input.len()`
-    /// Panics if `input_index` is greater than or equal to `self.input.len()`
     ///
-    pub fn signature_hash(&self, input_index: usize, script_pubkey: &Script, sighash_u32: u32) -> SigHash {
+    pub fn encode_signing_data_to<Write: io::Write>(
+        &self,
+        mut writer: Write,
+        input_index: usize,
+        script_pubkey: &Script,
+        sighash_u32: u32
+    ) {
         assert!(input_index < self.input.len());  // Panic on OOB
 
         let (sighash, anyone_can_pay) = SigHashType::from_u32(sighash_u32).split_anyonecanpay_flag();
 
         // Special-case sighash_single bug because this is easy enough.
         if sighash == SigHashType::Single && input_index >= self.output.len() {
-            return SigHash::from_slice(&[1, 0, 0, 0, 0, 0, 0, 0,
+            writer.write_all(&[1, 0, 0, 0, 0, 0, 0, 0,
-                                               0, 0, 0, 0, 0, 0, 0, 0,
+                               0, 0, 0, 0, 0, 0, 0, 0,
-                                               0, 0, 0, 0, 0, 0, 0, 0,
+                               0, 0, 0, 0, 0, 0, 0, 0,
-                                               0, 0, 0, 0, 0, 0, 0, 0]).unwrap();
+                               0, 0, 0, 0, 0, 0, 0, 0]).unwrap();
         }
 
         // Build tx to sign
@@ -373,10 +377,27 @@ impl Transaction {
             _ => unreachable!()
         };
         // hash the result
-        let mut engine = SigHash::engine();
+        tx.consensus_encode(&mut writer).unwrap();
-        tx.consensus_encode(&mut engine).unwrap();
         let sighash_arr = endian::u32_to_array_le(sighash_u32);
-        sighash_arr.consensus_encode(&mut engine).unwrap();
+        sighash_arr.consensus_encode(&mut writer).unwrap();
+    }
+
+    /// Computes a signature hash for a given input index with a given sighash flag.
+    /// To actually produce a scriptSig, this hash needs to be run through an
+    /// ECDSA signer, the SigHashType appended to the resulting sig, and a
+    /// script written around this, but this is the general (and hard) part.
+    ///
+    /// *Warning* This does NOT attempt to support OP_CODESEPARATOR. In general
+    /// this would require evaluating `script_pubkey` to determine which separators
+    /// get evaluated and which don't, which we don't have the information to
+    /// determine.
+    ///
+    /// # Panics
+    /// Panics if `input_index` is greater than or equal to `self.input.len()`
+    ///
+    pub fn signature_hash(&self, input_index: usize, script_pubkey: &Script, sighash_u32: u32) -> SigHash {
+        let mut engine = SigHash::engine();
+        self.encode_signing_data_to(&mut engine, input_index, script_pubkey, sighash_u32);
         SigHash::from_engine(engine)
     }
 

src/util/bip143.rs

@@ -25,6 +25,7 @@ use blockdata::script::Script;
 use blockdata::transaction::{Transaction, TxIn, SigHashType};
 use consensus::encode::Encodable;
 
+use std::io;
 use std::ops::{Deref, DerefMut};
 
 /// Parts of a sighash which are common across inputs or signatures, and which are
@@ -168,27 +169,32 @@ impl<R: Deref<Target=Transaction>> SigHashCache<R> {
         })
     }
 
-    /// Compute the BIP143 sighash for any flag type. See SighashComponents::sighash_all simpler
+    /// Encode the BIP143 signing data for any flag type into a given object implementing a
-    /// API for the most common case
+    /// std::io::Write trait.
-    pub fn signature_hash(&mut self, input_index: usize, script_code: &Script, value: u64, sighash_type: SigHashType) -> SigHash {
+    pub fn encode_signing_data_to<Write: io::Write>(
-
+        &mut self,
+        mut writer: Write,
+        input_index: usize,
+        script_code: &Script,
+        value: u64,
+        sighash_type: SigHashType,
+    ) {
         let zero_hash = sha256d::Hash::default();
 
         let (sighash, anyone_can_pay) = sighash_type.split_anyonecanpay_flag();
 
-        let mut enc = SigHash::engine();
+        self.tx.version.consensus_encode(&mut writer).unwrap();
-        self.tx.version.consensus_encode(&mut enc).unwrap();
 
         if !anyone_can_pay {
-            self.hash_prevouts().consensus_encode(&mut enc).unwrap();
+            self.hash_prevouts().consensus_encode(&mut writer).unwrap();
         } else {
-            zero_hash.consensus_encode(&mut enc).unwrap();
+            zero_hash.consensus_encode(&mut writer).unwrap();
         }
 
         if !anyone_can_pay && sighash != SigHashType::Single && sighash != SigHashType::None {
-            self.hash_sequence().consensus_encode(&mut enc).unwrap();
+            self.hash_sequence().consensus_encode(&mut writer).unwrap();
         } else {
-            zero_hash.consensus_encode(&mut enc).unwrap();
+            zero_hash.consensus_encode(&mut writer).unwrap();
         }
 
         {
@@ -196,25 +202,32 @@ impl<R: Deref<Target=Transaction>> SigHashCache<R> {
 
             txin
                 .previous_output
-                .consensus_encode(&mut enc)
+                .consensus_encode(&mut writer)
                 .unwrap();
-            script_code.consensus_encode(&mut enc).unwrap();
+            script_code.consensus_encode(&mut writer).unwrap();
-            value.consensus_encode(&mut enc).unwrap();
+            value.consensus_encode(&mut writer).unwrap();
-            txin.sequence.consensus_encode(&mut enc).unwrap();
+            txin.sequence.consensus_encode(&mut writer).unwrap();
         }
 
         if sighash != SigHashType::Single && sighash != SigHashType::None {
-            self.hash_outputs().consensus_encode(&mut enc).unwrap();
+            self.hash_outputs().consensus_encode(&mut writer).unwrap();
         } else if sighash == SigHashType::Single && input_index < self.tx.output.len() {
             let mut single_enc = SigHash::engine();
             self.tx.output[input_index].consensus_encode(&mut single_enc).unwrap();
-            SigHash::from_engine(single_enc).consensus_encode(&mut enc).unwrap();
+            SigHash::from_engine(single_enc).consensus_encode(&mut writer).unwrap();
         } else {
-            zero_hash.consensus_encode(&mut enc).unwrap();
+            zero_hash.consensus_encode(&mut writer).unwrap();
         }
 
-        self.tx.lock_time.consensus_encode(&mut enc).unwrap();
+        self.tx.lock_time.consensus_encode(&mut writer).unwrap();
-        sighash_type.as_u32().consensus_encode(&mut enc).unwrap();
+        sighash_type.as_u32().consensus_encode(&mut writer).unwrap();
+    }
+
+    /// Compute the BIP143 sighash for any flag type. See SighashComponents::sighash_all simpler
+    /// API for the most common case
+    pub fn signature_hash(&mut self, input_index: usize, script_code: &Script, value: u64, sighash_type: SigHashType) -> SigHash {
+        let mut enc = SigHash::engine();
+        self.encode_signing_data_to(&mut enc, input_index, script_code, value, sighash_type);
         SigHash::from_engine(enc)
     }
 }