Merge rust-bitcoin/rust-bitcoin#2310: use arrayvec to represent witness programs internally

01df1417c7 use arrayvec to represent witness programs (conduition)

Pull request description:

  Fixes https://github.com/rust-bitcoin/rust-bitcoin/issues/2261

  Introduces a new constructor, `WitnessProgram::from_bytes`, which creates a witness program by copying the program content from a byte slice.

ACKs for top commit:
  Kixunil:
    ACK 01df1417c7
  apoelstra:
    ACK 01df1417c7

Tree-SHA512: 73b8f2785674cd99c3f5dfe0e2180ed256942a0c29bcb1d357e0bd84fddee5e62f3f230c6cd55a37322bc3a6011467e9b7dcf24d903b20f35c095a1a1f9a29ce

bitcoin/src/address/mod.rs

@@ -44,7 +44,7 @@ use crate::blockdata::constants::{
 };
 use crate::blockdata::script::witness_program::WitnessProgram;
 use crate::blockdata::script::witness_version::WitnessVersion;
-use crate::blockdata::script::{self, PushBytesBuf, Script, ScriptBuf, ScriptHash};
+use crate::blockdata::script::{self, Script, ScriptBuf, ScriptHash};
 use crate::crypto::key::{
     CompressedPublicKey, PubkeyHash, PublicKey, TweakedPublicKey, UntweakedPublicKey,
 };
@@ -520,10 +520,8 @@ impl Address {
         } else if script.is_witness_program() {
             let opcode = script.first_opcode().expect("is_witness_program guarantees len > 4");
 
-            let buf = PushBytesBuf::try_from(script.as_bytes()[2..].to_vec())
-                .expect("is_witness_program guarantees len <= 42 bytes");
             let version = WitnessVersion::try_from(opcode)?;
-            let program = WitnessProgram::new(version, buf)?;
+            let program = WitnessProgram::new(version, &script.as_bytes()[2..])?;
             Ok(Address::from_witness_program(program, network))
         } else {
             Err(Error::UnrecognizedScript)
@@ -727,8 +725,7 @@ impl FromStr for Address<NetworkUnchecked> {
     fn from_str(s: &str) -> Result<Address<NetworkUnchecked>, ParseError> {
         if let Ok((hrp, witness_version, data)) = bech32::segwit::decode(s) {
             let version = WitnessVersion::try_from(witness_version)?;
-            let buf = PushBytesBuf::try_from(data).expect("bech32 guarantees valid program length");
-            let program = WitnessProgram::new(version, buf)
+            let program = WitnessProgram::new(version, &data)
                 .expect("bech32 guarantees valid program length for witness");
 
             let hrp = KnownHrp::from_hrp(hrp)?;
@@ -924,10 +921,10 @@ mod tests {
     #[test]
     fn test_non_existent_segwit_version() {
         // 40-byte program
-        let program = PushBytesBuf::from(hex!(
+        let program = hex!(
             "654f6ea368e0acdfd92976b7c2103a1b26313f430654f6ea368e0acdfd92976b7c2103a1b26313f4"
-        ));
-        let program = WitnessProgram::new(WitnessVersion::V13, program).expect("valid program");
+        );
+        let program = WitnessProgram::new(WitnessVersion::V13, &program).expect("valid program");
 
         let addr = Address::from_witness_program(program, Bitcoin);
         roundtrips(&addr, Bitcoin);

bitcoin/src/blockdata/script/witness_program.rs

@@ -10,13 +10,20 @@
 use core::fmt;
 
 use hashes::Hash as _;
+use internals::array_vec::ArrayVec;
 use secp256k1::{Secp256k1, Verification};
 
 use crate::blockdata::script::witness_version::WitnessVersion;
-use crate::blockdata::script::{PushBytes, PushBytesBuf, PushBytesErrorReport, Script};
+use crate::blockdata::script::{PushBytes, Script};
 use crate::crypto::key::{CompressedPublicKey, TapTweak, TweakedPublicKey, UntweakedPublicKey};
 use crate::taproot::TapNodeHash;
 
+/// The minimum byte size of a segregated witness program.
+pub const MIN_SIZE: usize = 2;
+
+/// The maximum byte size of a segregated witness program.
+pub const MAX_SIZE: usize = 40;
+
 /// The segregated witness program.
 ///
 /// The segregated witness program is technically only the program bytes _excluding_ the witness
@@ -27,43 +34,41 @@ pub struct WitnessProgram {
     /// The segwit version associated with this witness program.
     version: WitnessVersion,
     /// The witness program (between 2 and 40 bytes).
-    program: PushBytesBuf,
+    program: ArrayVec<u8, MAX_SIZE>,
 }
 
 impl WitnessProgram {
-    /// Creates a new witness program.
-    pub fn new<P>(version: WitnessVersion, program: P) -> Result<Self, Error>
-    where
-        P: TryInto<PushBytesBuf>,
-        <P as TryInto<PushBytesBuf>>::Error: PushBytesErrorReport,
-    {
+    /// Creates a new witness program, copying the content from the given byte slice.
+    pub fn new(version: WitnessVersion, bytes: &[u8]) -> Result<Self, Error> {
         use Error::*;
 
-        let program = program.try_into().map_err(|error| InvalidLength(error.input_len()))?;
-        if program.len() < 2 || program.len() > 40 {
-            return Err(InvalidLength(program.len()));
+        let program_len = bytes.len();
+        if program_len < MIN_SIZE || program_len > MAX_SIZE {
+            return Err(InvalidLength(program_len));
         }
 
         // Specific segwit v0 check. These addresses can never spend funds sent to them.
-        if version == WitnessVersion::V0 && (program.len() != 20 && program.len() != 32) {
-            return Err(InvalidSegwitV0Length(program.len()));
+        if version == WitnessVersion::V0 && (program_len != 20 && program_len != 32) {
+            return Err(InvalidSegwitV0Length(program_len));
         }
+
+        let program = ArrayVec::from_slice(bytes);
         Ok(WitnessProgram { version, program })
     }
 
     /// Creates a [`WitnessProgram`] from a 20 byte pubkey hash.
     fn new_p2wpkh(program: [u8; 20]) -> Self {
-        WitnessProgram { version: WitnessVersion::V0, program: program.into() }
+        WitnessProgram { version: WitnessVersion::V0, program: ArrayVec::from_slice(&program) }
     }
 
     /// Creates a [`WitnessProgram`] from a 32 byte script hash.
     fn new_p2wsh(program: [u8; 32]) -> Self {
-        WitnessProgram { version: WitnessVersion::V0, program: program.into() }
+        WitnessProgram { version: WitnessVersion::V0, program: ArrayVec::from_slice(&program) }
     }
 
     /// Creates a [`WitnessProgram`] from a 32 byte serialize taproot xonly pubkey.
     fn new_p2tr(program: [u8; 32]) -> Self {
-        WitnessProgram { version: WitnessVersion::V1, program: program.into() }
+        WitnessProgram { version: WitnessVersion::V1, program: ArrayVec::from_slice(&program) }
     }
 
     /// Creates a [`WitnessProgram`] from `pk` for a P2WPKH output.
@@ -99,7 +104,12 @@ impl WitnessProgram {
     pub fn version(&self) -> WitnessVersion { self.version }
 
     /// Returns the witness program.
-    pub fn program(&self) -> &PushBytes { &self.program }
+    pub fn program(&self) -> &PushBytes {
+        self.program
+            .as_slice()
+            .try_into()
+            .expect("witness programs are always smaller than max size of PushBytes")
+    }
 
     /// Returns true if this witness program is for a P2WPKH output.
     pub fn is_p2wpkh(&self) -> bool {

bitcoin/src/lib.rs

@@ -39,6 +39,7 @@
 // Exclude clippy lints we don't think are valuable
 #![allow(clippy::needless_question_mark)] // https://github.com/rust-bitcoin/rust-bitcoin/pull/2134
 #![allow(clippy::uninhabited_references)] // falsely claims that 100% safe code is UB
+#![allow(clippy::manual_range_contains)] // more readable than clippy's format
 
 // Disable 16-bit support at least for now as we can't guarantee it yet.
 #[cfg(target_pointer_width = "16")]

bitcoin/src/psbt/mod.rs

@@ -2087,7 +2087,7 @@ mod tests {
         psbt.inputs[0].bip32_derivation = map;
 
         // Second input is unspendable by us e.g., from another wallet that supports future upgrades.
-        let unknown_prog = WitnessProgram::new(WitnessVersion::V4, vec![0xaa; 34]).unwrap();
+        let unknown_prog = WitnessProgram::new(WitnessVersion::V4, &[0xaa; 34]).unwrap();
         let txout_unknown_future = TxOut {
             value: Amount::from_sat(10),
             script_pubkey: ScriptBuf::new_witness_program(&unknown_prog),