Factor out `io::Error` from sighash errors

The hadnling of `io::Error` in sighash had a few problems:

* It used `io::ErrorKind` instead of `io::Error` losing inforation
* Changing `io::ErrorKind` to `io::Error` would disable `PartialEq`&co
* The `Io` error wariants were duplicated

It turns out all of these can be solved by moving the `Io` variant into
a separate error.

bitcoin/src/crypto/sighash.rs

@@ -582,8 +582,8 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
         annex: Option<Annex>,
         leaf_hash_code_separator: Option<(TapLeafHash, u32)>,
         sighash_type: TapSighashType,
-    ) -> Result<(), TaprootError> {
+    ) -> Result<(), SigningDataError<TaprootError>> {
-        prevouts.check_all(self.tx.borrow())?;
+        prevouts.check_all(self.tx.borrow()).map_err(SigningDataError::sighash)?;
 
         let (sighash, anyone_can_pay) = sighash_type.split_anyonecanpay_flag();
 
@@ -608,8 +608,8 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
         //     sha_sequences (32): the SHA256 of the serialization of all input nSequence.
         if !anyone_can_pay {
             self.common_cache().prevouts.consensus_encode(writer)?;
-            self.taproot_cache(prevouts.get_all()?).amounts.consensus_encode(writer)?;
+            self.taproot_cache(prevouts.get_all().map_err(SigningDataError::sighash)?).amounts.consensus_encode(writer)?;
-            self.taproot_cache(prevouts.get_all()?).script_pubkeys.consensus_encode(writer)?;
+            self.taproot_cache(prevouts.get_all().map_err(SigningDataError::sighash)?).script_pubkeys.consensus_encode(writer)?;
             self.common_cache().sequences.consensus_encode(writer)?;
         }
 
@@ -637,8 +637,8 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
         //      scriptPubKey (35): scriptPubKey of the previous output spent by this input, serialized as script inside CTxOut. Its size is always 35 bytes.
         //      nSequence (4): nSequence of this input.
         if anyone_can_pay {
-            let txin = &self.tx.borrow().tx_in(input_index)?;
+            let txin = &self.tx.borrow().tx_in(input_index).map_err(SigningDataError::sighash)?;
-            let previous_output = prevouts.get(input_index)?;
+            let previous_output = prevouts.get(input_index).map_err(SigningDataError::sighash)?;
             txin.previous_output.consensus_encode(writer)?;
             previous_output.value.consensus_encode(writer)?;
             previous_output.script_pubkey.consensus_encode(writer)?;
@@ -669,7 +669,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
                 .ok_or(TaprootError::SingleMissingOutput(SingleMissingOutputError {
                     input_index,
                     outputs_length: self.tx.borrow().output.len(),
-                }))?
+                })).map_err(SigningDataError::Sighash)?
                 .consensus_encode(&mut enc)?;
             let hash = sha256::Hash::from_engine(enc);
             hash.consensus_encode(writer)?;
@@ -705,7 +705,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
             annex,
             leaf_hash_code_separator,
             sighash_type,
-        )?;
+        ).map_err(SigningDataError::unwrap_sighash)?;
         Ok(TapSighash::from_engine(enc))
     }
 
@@ -724,7 +724,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
             None,
             None,
             sighash_type,
-        )?;
+        ).map_err(SigningDataError::unwrap_sighash)?;
         Ok(TapSighash::from_engine(enc))
     }
 
@@ -747,7 +747,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
             None,
             Some((leaf_hash.into(), 0xFFFFFFFF)),
             sighash_type,
-        )?;
+        ).map_err(SigningDataError::unwrap_sighash)?;
         Ok(TapSighash::from_engine(enc))
     }
 
@@ -764,7 +764,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
         script_code: &Script,
         value: Amount,
         sighash_type: EcdsaSighashType,
-    ) -> Result<(), SegwitV0Error> {
+    ) -> Result<(), SigningDataError<SegwitV0Error>> {
         let zero_hash = sha256d::Hash::all_zeros();
 
         let (sighash, anyone_can_pay) = sighash_type.split_anyonecanpay_flag();
@@ -787,7 +787,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
         }
 
         {
-            let txin = &self.tx.borrow().tx_in(input_index)?;
+            let txin = &self.tx.borrow().tx_in(input_index).map_err(SigningDataError::sighash)?;
             txin.previous_output.consensus_encode(writer)?;
             script_code.consensus_encode(writer)?;
             value.consensus_encode(writer)?;
@@ -831,7 +831,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
             &script_code,
             value,
             sighash_type,
-        )?;
+        ).map_err(SigningDataError::unwrap_sighash)?;
         Ok(SegwitV0Sighash::from_engine(enc))
     }
 
@@ -850,7 +850,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
             witness_script,
             value,
             sighash_type,
-        )?;
+        ).map_err(SigningDataError::unwrap_sighash)?;
         Ok(SegwitV0Sighash::from_engine(enc))
     }
 
@@ -882,10 +882,10 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
         input_index: usize,
         script_pubkey: &Script,
         sighash_type: U,
-    ) -> EncodeSigningDataResult<LegacyError> {
+    ) -> EncodeSigningDataResult<SigningDataError<LegacyError>> {
         // Validate input_index.
         if let Err(e) = self.tx.borrow().tx_in(input_index) {
-            return EncodeSigningDataResult::WriteResult(Err(e.into()));
+            return EncodeSigningDataResult::WriteResult(Err(SigningDataError::Sighash(e.into())));
         }
         let sighash_type: u32 = sighash_type.into();
 
@@ -977,7 +977,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
                 script_pubkey,
                 sighash_type,
             )
-            .map_err(|e| LegacyError::Io(e.kind())),
+            .map_err(Into::into),
         )
     }
 
@@ -1013,10 +1013,7 @@ impl<R: Borrow<Transaction>> SighashCache<R> {
         {
             Ok(true) => Ok(LegacySighash::from_byte_array(UINT256_ONE)),
             Ok(false) => Ok(LegacySighash::from_engine(engine)),
-            Err(e) => match e {
+            Err(e) => Err(match e.unwrap_sighash() { LegacyError::InputsIndex(error) => error }),
-                LegacyError::InputsIndex(e) => Err(e),
-                LegacyError::Io(_) => unreachable!("engines don't error"),
-            },
         }
     }
 
@@ -1145,9 +1142,6 @@ impl<'a> Encodable for Annex<'a> {
 pub enum TaprootError {
     /// Index out of bounds when accessing transaction input vector.
     InputsIndex(transaction::InputsIndexError),
-    /// Can happen only when using `*_encode_signing_*` methods with custom writers, engines
-    /// like those used in `*_signature_hash` methods do not error.
-    Io(io::ErrorKind),
     /// Using `SIGHASH_SINGLE` requires an output at the same index is the input.
     SingleMissingOutput(SingleMissingOutputError),
     /// Prevouts size error.
@@ -1166,7 +1160,6 @@ impl fmt::Display for TaprootError {
 
         match *self {
             InputsIndex(ref e) => write_err!(f, "inputs index"; e),
-            Io(error_kind) => write!(f, "write failed: {:?}", error_kind),
             SingleMissingOutput(ref e) => write_err!(f, "sighash single"; e),
             PrevoutsSize(ref e) => write_err!(f, "prevouts size"; e),
             PrevoutsIndex(ref e) => write_err!(f, "prevouts index"; e),
@@ -1187,7 +1180,7 @@ impl std::error::Error for TaprootError {
             PrevoutsSize(ref e) => Some(e),
             PrevoutsIndex(ref e) => Some(e),
             PrevoutsKind(ref e) => Some(e),
-            Io(_) | InvalidSighashType(_) => None,
+            InvalidSighashType(_) => None,
         }
     }
 }
@@ -1196,10 +1189,6 @@ impl From<transaction::InputsIndexError> for TaprootError {
     fn from(e: transaction::InputsIndexError) -> Self { Self::InputsIndex(e) }
 }
 
-impl From<io::Error> for TaprootError {
-    fn from(e: io::Error) -> Self { Self::Io(e.kind()) }
-}
-
 impl From<PrevoutsSizeError> for TaprootError {
     fn from(e: PrevoutsSizeError) -> Self { Self::PrevoutsSize(e) }
 }
@@ -1255,8 +1244,6 @@ impl From<SegwitV0Error> for P2wpkhError {
 pub enum SegwitV0Error {
     /// Index out of bounds when accessing transaction input vector.
     InputsIndex(transaction::InputsIndexError),
-    /// Writer errored during consensus encoding.
-    Io(io::ErrorKind),
 }
 
 impl fmt::Display for SegwitV0Error {
@@ -1265,7 +1252,6 @@ impl fmt::Display for SegwitV0Error {
 
         match *self {
             InputsIndex(ref e) => write_err!(f, "inputs index"; e),
-            Io(error_kind) => write!(f, "write failed: {:?}", error_kind),
         }
     }
 }
@@ -1278,7 +1264,6 @@ impl std::error::Error for SegwitV0Error {
 
         match *self {
             InputsIndex(ref e) => Some(e),
-            Io(_) => None,
         }
     }
 }
@@ -1287,10 +1272,6 @@ impl From<transaction::InputsIndexError> for SegwitV0Error {
     fn from(e: transaction::InputsIndexError) -> Self { Self::InputsIndex(e) }
 }
 
-impl From<io::Error> for SegwitV0Error {
-    fn from(e: io::Error) -> Self { Self::Io(e.kind()) }
-}
-
 /// Using `SIGHASH_SINGLE` requires an output at the same index as the input.
 #[derive(Debug, Clone, PartialEq, Eq)]
 #[non_exhaustive]
@@ -1356,8 +1337,6 @@ impl std::error::Error for AnnexError {
 pub enum LegacyError {
     /// Index out of bounds when accessing transaction input vector.
     InputsIndex(transaction::InputsIndexError),
-    /// Writer errored during consensus encoding.
-    Io(io::ErrorKind),
 }
 
 impl fmt::Display for LegacyError {
@@ -1366,7 +1345,6 @@ impl fmt::Display for LegacyError {
 
         match *self {
             InputsIndex(ref e) => write_err!(f, "inputs index"; e),
-            Io(error_kind) => write!(f, "write failed: {:?}", error_kind),
         }
     }
 }
@@ -1378,7 +1356,6 @@ impl std::error::Error for LegacyError {
 
         match *self {
             InputsIndex(ref e) => Some(e),
-            Io(_) => None,
         }
     }
 }
@@ -1387,10 +1364,6 @@ impl From<transaction::InputsIndexError> for LegacyError {
     fn from(e: transaction::InputsIndexError) -> Self { Self::InputsIndex(e) }
 }
 
-impl From<io::Error> for LegacyError {
-    fn from(e: io::Error) -> Self { Self::Io(e.kind()) }
-}
-
 fn is_invalid_use_of_sighash_single(sighash: u32, input_index: usize, outputs_len: usize) -> bool {
     let ty = EcdsaSighashType::from_consensus(sighash);
     ty == EcdsaSighashType::Single && input_index >= outputs_len
@@ -1464,6 +1437,59 @@ impl<E> EncodeSigningDataResult<E> {
     }
 }
 
+/// Error returned when writing signing data fails.
+#[derive(Debug)]
+pub enum SigningDataError<E> {
+    /// Can happen only when using `*_encode_signing_*` methods with custom writers, engines
+    /// like those used in `*_signature_hash` methods do not error.
+    Io(io::Error),
+    /// An argument to the called sighash function was invalid.
+    Sighash(E),
+}
+
+impl<E> SigningDataError<E> {
+    /// Returns the sighash variant, panicking if it's IO.
+    ///
+    /// This is used when encoding to hash engine when we know that IO doesn't fail.
+    fn unwrap_sighash(self) -> E {
+        match self {
+            Self::Sighash(error) => error,
+            Self::Io(error) => panic!("hash engine error {}", error),
+        }
+    }
+
+    fn sighash<E2: Into<E>>(error: E2) -> Self {
+        Self::Sighash(error.into())
+    }
+}
+
+// We cannot simultaneously impl `From<E>`. it was determined that this alternative requires less
+// manual `map_err` calls.
+impl<E> From<io::Error> for SigningDataError<E> {
+    fn from(value: io::Error) -> Self {
+        Self::Io(value)
+    }
+}
+
+impl<E: fmt::Display> fmt::Display for SigningDataError<E> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Self::Io(error) => write_err!(f, "failed to write sighash data"; error),
+            Self::Sighash(error) => write_err!(f, "failed to compute sighash data"; error),
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl<E: std::error::Error + 'static> std::error::Error for SigningDataError<E> {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            SigningDataError::Io(error) => Some(error),
+            SigningDataError::Sighash(error) => Some(error),
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use std::str::FromStr;