feat(bitcoin): introduce hash-like types

Types like "Txid", "BlockHash", "DescriptorId" are all just 32 byte
arrays that represent hashes with different meanings. Currently they
are represented as strings at the FFI layer, but they are also
meaningful arrays of bytes. Particularly if a user wants to implement
persistence over the FFI layer, they would want to efficiently
serialize these types.

Here I am introducing a new group of types that all implement display,
allow serialization to bytes, and may be constructed from an array of
bytes. I went with a "rule of 3s" here, and also introduced a macro to
do these implementations because there was a lot of boilerplate
involved.

Note that all of these are included in the wallet changeset, which is
required to represent in-full for FFI-layer custom persistence.

Author: rustaceanrob

bdk-ffi/src/bitcoin.rs

@@ -1,27 +1,31 @@
 use crate::error::{
-    AddressParseError, ExtractTxError, FeeRateError, FromScriptError, PsbtError, PsbtParseError,
-    TransactionError,
+    AddressParseError, ExtractTxError, FeeRateError, FromScriptError, HashParseError, PsbtError,
+    PsbtParseError, TransactionError,
 };
 use crate::error::{ParseAmountError, PsbtFinalizeError};
-use crate::{impl_from_core_type, impl_into_core_type};
+use crate::{impl_from_core_type, impl_hash_like, impl_into_core_type};
 
 use bdk_wallet::bitcoin::address::NetworkChecked;
 use bdk_wallet::bitcoin::address::NetworkUnchecked;
 use bdk_wallet::bitcoin::address::{Address as BdkAddress, AddressData as BdkAddressData};
 use bdk_wallet::bitcoin::blockdata::block::Header as BdkHeader;
+use bdk_wallet::bitcoin::consensus::encode::deserialize;
 use bdk_wallet::bitcoin::consensus::encode::serialize;
 use bdk_wallet::bitcoin::consensus::Decodable;
+use bdk_wallet::bitcoin::hashes::sha256::Hash as BitcoinSha256Hash;
 use bdk_wallet::bitcoin::io::Cursor;
 use bdk_wallet::bitcoin::secp256k1::Secp256k1;
 use bdk_wallet::bitcoin::Amount as BdkAmount;
+use bdk_wallet::bitcoin::BlockHash as BitcoinBlockHash;
 use bdk_wallet::bitcoin::FeeRate as BdkFeeRate;
 use bdk_wallet::bitcoin::Network;
+use bdk_wallet::bitcoin::OutPoint as BdkOutPoint;
 use bdk_wallet::bitcoin::Psbt as BdkPsbt;
 use bdk_wallet::bitcoin::ScriptBuf as BdkScriptBuf;
 use bdk_wallet::bitcoin::Transaction as BdkTransaction;
 use bdk_wallet::bitcoin::TxIn as BdkTxIn;
 use bdk_wallet::bitcoin::TxOut as BdkTxOut;
-use bdk_wallet::bitcoin::{OutPoint as BdkOutPoint, Txid};
+use bdk_wallet::bitcoin::Txid as BitcoinTxid;
 use bdk_wallet::miniscript::psbt::PsbtExt;
 use bdk_wallet::serde_json;
 
@@ -51,7 +55,7 @@ impl From<&BdkOutPoint> for OutPoint {
 impl From<OutPoint> for BdkOutPoint {
     fn from(outpoint: OutPoint) -> Self {
         BdkOutPoint {
-            txid: Txid::from_str(&outpoint.txid).unwrap(),
+            txid: BitcoinTxid::from_str(&outpoint.txid).unwrap(),
             vout: outpoint.vout,
         }
     }
@@ -575,6 +579,34 @@ impl From<&BdkTxOut> for TxOut {
     }
 }
 
+/// A bitcoin Block hash
+#[derive(uniffi::Object)]
+#[uniffi::export(Display)]
+pub struct BlockHash(BitcoinBlockHash);
+
+impl_hash_like!(BlockHash, BitcoinBlockHash);
+
+/// A bitcoin transaction identifier
+#[derive(uniffi::Object)]
+#[uniffi::export(Display)]
+pub struct Txid(BitcoinTxid);
+
+impl_hash_like!(Txid, BitcoinTxid);
+
+/// A collision-proof unique identifier for a descriptor.
+#[derive(uniffi::Object)]
+#[uniffi::export(Display)]
+pub struct DescriptorId(BitcoinSha256Hash);
+
+impl_hash_like!(DescriptorId, BitcoinSha256Hash);
+
+/// The merkle root of the merkle tree corresponding to a block's transactions.
+#[derive(uniffi::Object)]
+#[uniffi::export(Display)]
+pub struct TxMerkleNode(BitcoinSha256Hash);
+
+impl_hash_like!(TxMerkleNode, BitcoinSha256Hash);
+
 #[cfg(test)]
 mod tests {
     use crate::bitcoin::Address;

bdk-ffi/src/error.rs

@@ -1507,6 +1507,12 @@ impl From<BdkEncodeError> for TransactionError {
     }
 }
 
+#[derive(Debug, thiserror::Error, uniffi::Error)]
+pub enum HashParseError {
+    #[error("invalid hash: expected length 32 bytes, got {len} bytes")]
+    InvalidHash { len: u32 },
+}
+
 impl From<BdkSqliteError> for SqliteError {
     fn from(error: BdkSqliteError) -> Self {
         SqliteError::Sqlite {

bdk-ffi/src/macros.rs

@@ -19,3 +19,32 @@ macro_rules! impl_into_core_type {
         }
     };
 }
+
+#[macro_export]
+macro_rules! impl_hash_like {
+    ($ffi_type:ident, $core_type:ident) => {
+        #[uniffi::export]
+        impl $ffi_type {
+            /// Construct a hash-like type from 32 bytes.
+            #[uniffi::constructor]
+            fn from_bytes(bytes: Vec<u8>) -> Result<Self, HashParseError> {
+                let hash_like: $core_type = deserialize(&bytes).map_err(|_| {
+                    let len = bytes.len() as u32;
+                    HashParseError::InvalidHash { len }
+                })?;
+                Ok(Self(hash_like))
+            }
+
+            /// Serialize this type into a 32 byte array.
+            fn serialize(&self) -> Vec<u8> {
+                serialize(&self.0)
+            }
+        }
+
+        impl std::fmt::Display for $ffi_type {
+            fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+                self.0.fmt(f)
+            }
+        }
+    };
+}