Add segwit API

The bips are a little bit hard to use correctly, add a `segwit` API with
the aim that "typical" modern bitcoin usage is easy and correct.

src/lib.rs

@@ -43,6 +43,7 @@ pub use crate::primitives::{Bech32, Bech32m};
 
 mod error;
 pub mod primitives;
+pub mod segwit;
 
 #[cfg(feature = "arrayvec")]
 use arrayvec::{ArrayVec, CapacityError};

src/segwit.rs

@@ -0,0 +1,170 @@
+// SPDX-License-Identifier: MIT
+
+//! Segregated Witness API - enabling typical usage for encoding and decoding segwit addresses.
+//!
+//! The bips contain some complexity, this module should allow you to create modern bitcoin
+//! addresses, and parse existing addresses from the Bitcoin blockchain, correctly and easily.
+//!
+//! You should not need to intimately know [BIP-173] and [BIP-350] in order to correctly use this
+//! module. If you are doing unusual things, consider using the `primitives` submodules directly.
+//!
+//! Note, we do implement the bips to spec, however this is done in the `primitives` submodules, to
+//! convince yourself, and to see the nitty gritty, you can look at the test vector code in
+//! [`bip_173_test_vectors.rs`] and [`bip_350_test_vectors.rs`].
+//!
+//! [BIP-173]: <https://github.com/bitcoin/bips/blob/master/bip-0173.mediawiki>
+//! [BIP-350]: <https://github.com/bitcoin/bips/blob/master/bip-0350.mediawiki>
+//! [`bip_173_test_vectors.rs`]: <https://github.com/rust-bitcoin/rust-bech32/blob/master/tests/bip_173_test_vectors.rs>
+//! [`bip_350_test_vectors.rs`]: <https://github.com/rust-bitcoin/rust-bech32/blob/master/tests/bip_350_test_vectors.rs>
+
+use core::fmt;
+
+use crate::primitives::decode::{SegwitHrpstring, SegwitHrpstringError};
+use crate::primitives::gf32::Fe32;
+// TODO: Add ergonomic re-exports of types used in this modules public API, ether to `lib.rs` or here.
+use crate::primitives::hrp::{self, Hrp};
+use crate::primitives::iter::{ByteIterExt, Fe32IterExt};
+use crate::primitives::{Bech32, Bech32m};
+
+/// Decodes a bech32 address returning the witness version and encode data.
+///
+/// Handles segwit v0 and v1 addresses with the respective checksum algorithm.
+#[cfg(feature = "alloc")]
+pub fn decode(s: &str) -> Result<(Fe32, Vec<u8>), SegwitHrpstringError> {
+    let segwit = SegwitHrpstring::new(s)?;
+    let version = segwit.witness_version();
+    let data = segwit.byte_iter().collect::<Vec<u8>>();
+    Ok((version, data))
+}
+
+/// Encodes a witness program as a bech32 address.
+///
+/// Uses segwit v1 and the bech32m checksum algorithm in line with [BIP-350]
+///
+/// [BIP-350]: <https://github.com/bitcoin/bips/blob/master/bip-0350.mediawiki>
+#[cfg(feature = "alloc")]
+pub fn encode(program: &[u8]) -> String { encode_program_as_segwit_v1_mainnet_address(program) }
+
+/// Encodes a witness program as a segwit version 0 address suitable for use on mainnet.
+#[cfg(feature = "alloc")]
+pub fn encode_program_as_segwit_v0_mainnet_address(program: &[u8]) -> String {
+    let hrp = hrp::BC;
+    let version = Fe32::Q;
+    encode_program(&hrp, version, program)
+}
+
+/// Encodes a witness program as a segwit version 1 address suitable for use on mainnet.
+#[cfg(feature = "alloc")]
+pub fn encode_program_as_segwit_v1_mainnet_address(program: &[u8]) -> String {
+    let hrp = hrp::BC;
+    let version = Fe32::P;
+    encode_program(&hrp, version, program)
+}
+
+/// Encodes a witness program as a segwit version 0 address suitable for use on testnet.
+#[cfg(feature = "alloc")]
+pub fn encode_program_as_segwit_v0_testnet_address(program: &[u8]) -> String {
+    let hrp = hrp::TB;
+    let version = Fe32::Q;
+    encode_program(&hrp, version, program)
+}
+
+/// Encodes a witness program as a segwit version 1 address suitable for use on testnet.
+#[cfg(feature = "alloc")]
+pub fn encode_program_as_segwit_v1_testnet_address(program: &[u8]) -> String {
+    let hrp = hrp::TB;
+    let version = Fe32::P;
+    encode_program(&hrp, version, program)
+}
+
+/// Encodes a witness program as a bech32 address string using the given `hrp` and `version`.
+#[cfg(feature = "alloc")]
+pub fn encode_program(hrp: &Hrp, version: Fe32, program: &[u8]) -> String {
+    // Possibly faster to use `collect` instead of writing char by char?
+    // (Counter argument: "Early optimization is the root of all evil.")
+    let mut buf = String::new();
+    encode_program_to_fmt(&mut buf, hrp, version, program).expect("TODO: Handle errors");
+    buf
+}
+
+/// Encodes a witness program to a writer ([`fmt::Write`]).
+///
+/// Prefixes with the appropriate witness version byte and appends the appropriate checksum.
+/// Currently no checks done on the validity of the `hrp`, `version`, or `program`.
+pub fn encode_program_to_fmt(
+    fmt: &mut dyn fmt::Write,
+    hrp: &Hrp,
+    version: Fe32,
+    program: &[u8],
+) -> fmt::Result {
+    match version {
+        Fe32::Q => {
+            for c in program
+                .iter()
+                .copied()
+                .bytes_to_fes()
+                .with_checksum::<Bech32>(hrp)
+                .with_witness_version(Fe32::Q)
+                .chars()
+            {
+                fmt.write_char(c)?;
+            }
+        }
+        witver => {
+            for c in program
+                .iter()
+                .copied()
+                .bytes_to_fes()
+                .with_checksum::<Bech32m>(hrp)
+                .with_witness_version(witver)
+                .chars()
+            {
+                fmt.write_char(c)?;
+            }
+        }
+    }
+    Ok(())
+}
+
+#[cfg(all(test, feature = "alloc"))]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn parse_valid_mainnet_addresses() {
+        // A few recent addresses from mainnet (Block 801266).
+        let addresses = vec![
+            "bc1q2s3rjwvam9dt2ftt4sqxqjf3twav0gdx0k0q2etxflx38c3x8tnssdmnjq", // Segwit v0
+            "bc1py3m7vwnghyne9gnvcjw82j7gqt2rafgdmlmwmqnn3hvcmdm09rjqcgrtxs", // Segwit v1
+        ];
+
+        for address in addresses {
+            // Just shows we handle both v0 and v1 addresses, for complete test
+            // coverage see primitives submodules and test vectors.
+            assert!(decode(address).is_ok());
+        }
+    }
+
+    #[test]
+    fn roundtrip_valid_v0_mainnet_address() {
+        let address = "bc1qwqdg6squsna38e46795at95yu9atm8azzmyvckulcc7kytlcckxswvvzej";
+        let (_version, data) = decode(address).expect("failed to decode address");
+        let encoded = encode_program_as_segwit_v0_mainnet_address(&data);
+        assert_eq!(encoded, address);
+    }
+
+    #[test]
+    fn roundtrip_valid_v1_mainnet_address() {
+        let address = "bc1pguzvu9c7d6qc9pwgu93vqmwzsr6e3kpxewjk93wkprn4suhz8w3qp3yxsd";
+        let (_version, data) = decode(address).expect("failed to decode address");
+
+        let explicit = encode_program_as_segwit_v1_mainnet_address(&data);
+        let implicit = encode(&data);
+
+        // Ensure `encode` implicitly uses v1.
+        assert_eq!(implicit, explicit);
+
+        // Ensure it roundtrips.
+        assert_eq!(implicit, address);
+    }
+}