use crate::error::{Context, Error, bail, ensure};
use crate::{
container,
format::{PublicRecord, RecordKind, Urma},
multipart::{Geometry, MultipartRecord},
};
use bitcoin::{
Script, ScriptBuf, Transaction, TxOut, Witness, XOnlyPublicKey,
hashes::Hash,
opcodes::all::{OP_CHECKSIG, OP_ENDIF, OP_IF},
script::{Builder, Instruction, PushBytesBuf},
secp256k1::{Keypair, Message, Secp256k1},
sighash::{Prevouts, SighashCache, TapSighashType},
taproot::{ControlBlock, LeafVersion, TapLeafHash, TaprootBuilder, TaprootSpendInfo},
transaction::Version,
};
pub struct ParsedEnvelope {
pub author: XOnlyPublicKey,
pub record: Vec<u8>,
pub script: ScriptBuf,
pub control: ControlBlock,
}
fn validate_record(record: &[u8]) -> Result<(), Error> {
match RecordKind::parse(record)? {
RecordKind::Private => {
container::inspect_header(record)?;
}
RecordKind::DataPart | RecordKind::LeafManifest | RecordKind::RootManifest => {
MultipartRecord::decode(record)?;
}
RecordKind::Container => bail!("offline container cannot be published as a record"),
RecordKind::Post
| RecordKind::Reply
| RecordKind::Profile
| RecordKind::Avatar
| RecordKind::WirePost
| RecordKind::WireReply
| RecordKind::ProfileRecord => {
PublicRecord::decode(record)?;
}
}
Ok(())
}
fn record_script(record: &[u8], author: XOnlyPublicKey) -> Result<ScriptBuf, Error> {
let mut builder = Builder::new()
.push_x_only_key(&author)
.push_opcode(OP_CHECKSIG)
.push_int(0)
.push_opcode(OP_IF)
.push_slice(Urma::MAGIC);
for part in record.chunks(520) {
builder = match part {
[value @ 1..=16] => builder.push_int(i64::from(*value)),
[0x81] => builder.push_int(-1),
bytes => builder.push_slice(PushBytesBuf::try_from(bytes.to_vec())?),
};
}
Ok(builder.push_opcode(OP_ENDIF).into_script())
}
pub fn build(record: &[u8], signer: &Keypair) -> Result<(ScriptBuf, TaprootSpendInfo), Error> {
build_for_author(record, signer.x_only_public_key().0)
}
pub fn build_for_author(
record: &[u8],
author: XOnlyPublicKey,
) -> Result<(ScriptBuf, TaprootSpendInfo), Error> {
validate_record(record)?;
let script = record_script(record, author)?;
let info = TaprootBuilder::new()
.add_leaf(0, script.clone())?
.finalize(&Secp256k1::new(), author)
.map_err(|tree| Error::Invalid(format!("invalid single-leaf Taproot tree: {tree:?}")))?;
Ok((script, info))
}
pub fn witness(
signature: &[u8],
script: &ScriptBuf,
info: &TaprootSpendInfo,
) -> Result<Witness, Error> {
ensure!(
signature.len() == 64,
"URMA requires implicit SIGHASH_DEFAULT"
);
let control = info
.control_block(&(script.clone(), LeafVersion::TapScript))
.context("script missing from Taproot tree")?
.serialize();
ensure!(control.len() == 33, "URMA requires one leaf");
Ok(Witness::from_slice(&[
signature,
script.as_bytes(),
&control,
]))
}
pub fn is_candidate(witness: &Witness) -> bool {
if witness.len() != 3 {
return false;
}
let Some(script) = witness.iter().nth(1) else {
return false;
};
script.len() >= 41 && script[34..41] == [0, 99, 4, b'U', b'R', b'M', b'A']
}
pub fn extract(witness: &Witness) -> Result<ParsedEnvelope, Error> {
let parsed = extract_envelope(witness)?;
validate_record(&parsed.record)?;
Ok(parsed)
}
fn extract_envelope(witness: &Witness) -> Result<ParsedEnvelope, Error> {
ensure!(witness.len() == 3, "invalid witness item count");
let items: Vec<_> = witness.iter().collect();
ensure!(
items[0].len() == 64 && items[2].len() == 33,
"invalid signature or control length"
);
ensure!(
items[1].len() >= 42
&& items[1].len()
<= Geometry::RECORD_BYTES + 3 * Geometry::RECORD_BYTES.div_ceil(520) + 42,
"script size out of bounds"
);
let script = ScriptBuf::from_bytes(items[1].to_vec());
let author = XOnlyPublicKey::from_slice(&items[1][1..33])?;
let control = ControlBlock::decode(items[2])?;
ensure!(
control.leaf_version == LeafVersion::TapScript && control.internal_key == author,
"invalid author/internal-key commitment"
);
let mut ops = script.instructions_minimal().skip(5);
let mut record = Vec::new();
loop {
let instruction = ops.next().context("missing envelope end")??;
match instruction {
Instruction::PushBytes(part) => {
ensure!(
!part.is_empty() && part.len() <= 520,
"invalid record segment"
);
record.extend_from_slice(part.as_bytes());
}
Instruction::Op(opcode) if opcode == OP_ENDIF => {
let Some(instruction) = ops.next() else { break };
bail!("trailing script instruction: {instruction:?}");
}
Instruction::Op(opcode) if (0x51..=0x60).contains(&opcode.to_u8()) => {
record.push(opcode.to_u8() - 0x50)
}
Instruction::Op(opcode) if opcode.to_u8() == 0x4f => record.push(0x81),
instruction => bail!("invalid envelope instruction {instruction:?}"),
}
ensure!(record.len() <= Geometry::RECORD_BYTES, "record too large");
}
ensure!(
record_script(&record, author)? == script,
"noncanonical envelope or segmentation"
);
Ok(ParsedEnvelope {
author,
record,
script,
control,
})
}
pub fn verify_reveal(reveal: &Transaction, commit: &Transaction) -> Result<ParsedEnvelope, Error> {
let parsed = verify_record_proof(reveal, commit)?;
validate_record(&parsed.record)?;
Ok(parsed)
}
pub(crate) fn verify_record_proof(
reveal: &Transaction,
commit: &Transaction,
) -> Result<ParsedEnvelope, Error> {
ensure!(reveal.input.len() == 1, "reveal must have one input");
let source = reveal.input[0].previous_output;
ensure!(
source.txid == commit.compute_txid(),
"reveal does not spend the supplied commit"
);
let prevout = commit
.output
.get(usize::try_from(source.vout)?)
.context("commit outpoint absent")?;
verify_prevout_proof(reveal, prevout)
}
pub fn verify_prevout(reveal: &Transaction, prevout: &TxOut) -> Result<ParsedEnvelope, Error> {
let parsed = verify_prevout_proof(reveal, prevout)?;
validate_record(&parsed.record)?;
Ok(parsed)
}
fn verify_prevout_proof(reveal: &Transaction, prevout: &TxOut) -> Result<ParsedEnvelope, Error> {
let parsed = extract_reveal_envelope(reveal)?;
ensure!(
reveal.output[0].value <= prevout.value,
"reveal spends more than prevout"
);
ensure!(
prevout.script_pubkey.is_p2tr(),
"commit output must be P2TR"
);
let secp = Secp256k1::verification_only();
let output_key = XOnlyPublicKey::from_slice(&prevout.script_pubkey.as_bytes()[2..34])?;
ensure!(
parsed
.control
.verify_taproot_commitment(&secp, output_key, &parsed.script),
"invalid Taproot commitment"
);
let signature = bitcoin::secp256k1::schnorr::Signature::from_slice(
reveal.input[0]
.witness
.iter()
.next()
.context("signature absent")?,
)?;
let hash = SighashCache::new(reveal).taproot_script_spend_signature_hash(
0,
&Prevouts::All(std::slice::from_ref(prevout)),
TapLeafHash::from_script(&parsed.script, LeafVersion::TapScript),
TapSighashType::Default,
)?;
secp.verify_schnorr(
&signature,
&Message::from_digest(hash.to_byte_array()),
&parsed.author,
)
.context("invalid author signature")?;
Ok(parsed)
}
pub fn extract_reveal(reveal: &Transaction) -> Result<ParsedEnvelope, Error> {
let parsed = extract_reveal_envelope(reveal)?;
validate_record(&parsed.record)?;
Ok(parsed)
}
fn extract_reveal_envelope(reveal: &Transaction) -> Result<ParsedEnvelope, Error> {
validate_reveal_shape(reveal.version.0, reveal.input.len(), reveal.output.len())?;
validate_reveal_scripts(&reveal.input[0].script_sig, &reveal.output[0].script_pubkey)?;
extract_envelope(&reveal.input[0].witness)
}
pub fn validate_reveal_shape(version: i32, inputs: usize, outputs: usize) -> Result<(), Error> {
ensure!(
version == Version::TWO.0 && inputs == 1 && outputs == 1,
"invalid reveal transaction shape"
);
Ok(())
}
pub fn validate_reveal_scripts(script_sig: &Script, return_script: &Script) -> Result<(), Error> {
ensure!(script_sig.is_empty(), "reveal scriptSig must be empty");
ensure!(
return_script.is_p2wpkh() || return_script.is_p2tr(),
"invalid reveal return output"
);
Ok(())
}