Add support for pay to anchor outputs

Add support for the newly created Pay2Anchor output-type.

See https://github.com/bitcoin/bitcoin/pull/30352

bitcoin/src/address/mod.rs

@@ -91,6 +91,8 @@ pub enum AddressType {
     P2wsh,
     /// Pay to taproot.
     P2tr,
+    /// Pay to anchor.
+    P2a
 }
 
 impl fmt::Display for AddressType {
@@ -101,6 +103,7 @@ impl fmt::Display for AddressType {
             AddressType::P2wpkh => "p2wpkh",
             AddressType::P2wsh => "p2wsh",
             AddressType::P2tr => "p2tr",
+            AddressType::P2a => "p2a",
         })
     }
 }
@@ -114,6 +117,7 @@ impl FromStr for AddressType {
             "p2wpkh" => Ok(AddressType::P2wpkh),
             "p2wsh" => Ok(AddressType::P2wsh),
             "p2tr" => Ok(AddressType::P2tr),
+            "p2a" => Ok(AddressType::P2a),
             _ => Err(UnknownAddressTypeError(s.to_owned())),
         }
     }
@@ -572,6 +576,8 @@ impl Address {
                     Some(AddressType::P2wsh)
                 } else if program.is_p2tr() {
                     Some(AddressType::P2tr)
+                } else if program.is_p2a() {
+                    Some(AddressType::P2a)
                 } else {
                     None
                 },
@@ -1526,4 +1532,23 @@ mod tests {
         assert_eq!(&rinsed.address, foo_checked.address.as_unchecked());
         assert_eq!(rinsed, foo_unchecked);
     }
+
+
+    #[test]
+    fn pay_to_anchor_address_regtest() {
+        // Verify that p2a uses the expected address for regtest.
+        // This test-vector is borrowed from the bitcoin source code.
+        let address_str = "bcrt1pfeesnyr2tx";
+
+        let script = ScriptBuf::new_p2a();
+        let address_unchecked = address_str.parse().unwrap();
+        let address = Address::from_script(&script, Network::Regtest).unwrap();
+        assert_eq!(address.as_unchecked(), &address_unchecked);
+        assert_eq!(address.to_string(), address_str);
+
+        // Verify that the address is considered standard
+        // and that the output type is P2a
+        assert!(address.is_spend_standard());
+        assert_eq!(address.address_type(), Some(AddressType::P2a));
+    }
 }

bitcoin/src/address/script_pubkey.rs

@@ -12,6 +12,7 @@ use crate::key::{
 use crate::opcodes::all::*;
 use crate::script::witness_program::WitnessProgram;
 use crate::script::witness_version::WitnessVersion;
+use crate::script::witness_program::P2A_PROGRAM;
 use crate::script::{
     self, Builder, PushBytes, RedeemScriptSizeError, Script, ScriptBuf, ScriptExt as _, ScriptHash,
     WScriptHash, WitnessScriptSizeError,
@@ -170,6 +171,11 @@ define_extension_trait! {
             new_witness_program_unchecked(WitnessVersion::V1, output_key.serialize())
         }
 
+        /// Generates pay to anchor output.
+        fn new_p2a() -> Self {
+            new_witness_program_unchecked(WitnessVersion::V1, P2A_PROGRAM)
+        }
+
         /// Generates P2WSH-type of scriptPubkey with a given [`WitnessProgram`].
         fn new_witness_program(witness_program: &WitnessProgram) -> Self {
             Builder::new()
@@ -183,14 +189,14 @@ define_extension_trait! {
 /// Generates P2WSH-type of scriptPubkey with a given [`WitnessVersion`] and the program bytes.
 /// Does not do any checks on version or program length.
 ///
-/// Convenience method used by `new_p2wpkh`, `new_p2wsh`, `new_p2tr`, and `new_p2tr_tweaked`.
+/// Convenience method used by `new_p2a`, `new_p2wpkh`, `new_p2wsh`, `new_p2tr`, and `new_p2tr_tweaked`.
 pub(super) fn new_witness_program_unchecked<T: AsRef<PushBytes>>(
     version: WitnessVersion,
     program: T,
 ) -> ScriptBuf {
     let program = program.as_ref();
     debug_assert!(program.len() >= 2 && program.len() <= 40);
-    // In SegWit v0, the program must be 20 or 32 bytes long.
+    // In SegWit v0, the program must be either 20 (P2WPKH) bytes or 32 (P2WSH) bytes long
     debug_assert!(version != WitnessVersion::V0 || program.len() == 20 || program.len() == 32);
     Builder::new().push_opcode(version.into()).push_slice(program).into_script()
 }

bitcoin/src/blockdata/script/witness_program.rs

@@ -25,6 +25,9 @@ pub const MIN_SIZE: usize = 2;
 /// The maximum byte size of a segregated witness program.
 pub const MAX_SIZE: usize = 40;
 
+/// The P2A program which is given by 0x4e73.
+pub(crate) const P2A_PROGRAM: [u8;2] = [78, 115];
+
 /// The segregated witness program.
 ///
 /// The segregated witness program is technically only the program bytes _excluding_ the witness
@@ -105,6 +108,11 @@ impl WitnessProgram {
         WitnessProgram::new_p2tr(pubkey)
     }
 
+    /// Constructs a new pay to anchor address
+    pub const fn p2a() -> Self {
+        WitnessProgram { version: WitnessVersion::V1, program: ArrayVec::from_slice(&P2A_PROGRAM)}
+    }
+
     /// Returns the witness program version.
     pub fn version(&self) -> WitnessVersion { self.version }
 
@@ -128,6 +136,11 @@ impl WitnessProgram {
 
     /// Returns true if this witness program is for a P2TR output.
     pub fn is_p2tr(&self) -> bool { self.version == WitnessVersion::V1 && self.program.len() == 32 }
+
+    /// Returns true if this is a pay to anchor output.
+    pub fn is_p2a(&self) -> bool {
+        self.version == WitnessVersion::V1 && self.program == P2A_PROGRAM
+    }
 }
 
 /// Witness program error.