primitives: reject transactions with 0 outputs
What the developer wrote
Authored by jrakibi
primitives: reject transactions with 0 outputs
Transactions must have at least one output.
This is another syntactic check that doesn't depend on any context,
and the last one on this list https://github.com/rust-bitcoin/rust-bitcoin/issues/5383#issuecomment-3646014920.
We add validation to reject transactions with empty outputs during decoding.
Two existing tests that created transactions with no outputs are ignored
and will be fixed in the next commit.
What changed, and why it matters
This commit adds a rule to reject Bitcoin transactions that have no outputs when they are decoded. In Bitcoin, every valid transaction must send bitcoin somewhere, so a transaction with zero outputs is invalid. The change prevents the library from accepting or processing such malformed transactions, which could otherwise lead to inconsistent behavior compared to Bitcoin Core and other nodes.
Review the ignored tests to ensure they are fixed promptly and do not leave coverage gaps. Verify that the NoOutputs check is applied consistently across all transaction construction and deserialization paths, not only the streaming decoder.
Security signals we found
New validation rejects zero-output transactions during decoding
Adds error variant TransactionDecoderErrorInner::NoOutputs
Regression test references Bitcoin Core tx_invalid.json 'No outputs' vector
Existing invalid tests ignored rather than fixed in same commit
Evidence from the diff
The patch introduces a new syntactic validation check in the TransactionDecoder’s Done state: if tx.outputs.is_empty(), decoding fails with a new NoOutputs error variant. It also adds a regression test using a vector from Bitcoin Core’s tx_invalid.json. Two existing tests that created zero-output transactions are marked #[ignore] pending a follow-up fix. This aligns rust-bitcoin’s transaction decoding with consensus-compatible syntactic checks.
Changed components
primitives/src/transaction.rs TransactionDecoderprimitives/src/block.rs testsInspect captured patch +25 / −0
diff --git a/primitives/src/block.rs b/primitives/src/block.rs
index 3a24052b..5190efad 100644
--- a/primitives/src/block.rs
+++ b/primitives/src/block.rs
@@ -1284,6 +1284,7 @@ mod tests {
}
#[test]
+ #[ignore] // bad test; will be fixed in next commit
#[cfg(feature = "alloc")]
fn block_decode() {
// Make a simple block, encode then decode. Verify equivalence.
diff --git a/primitives/src/transaction.rs b/primitives/src/transaction.rs
index 2e74e3d8..07dc18b6 100644
--- a/primitives/src/transaction.rs
+++ b/primitives/src/transaction.rs
@@ -588,6 +588,10 @@ impl Decoder for TransactionDecoder {
State::Witnesses(..) => Err(E(Inner::EarlyEnd("witnesses"))),
State::LockTime(..) => Err(E(Inner::EarlyEnd("locktime"))),
State::Done(tx) => {
+ // Reject transactions with no outputs
+ if tx.outputs.is_empty() {
+ return Err(E(Inner::NoOutputs));
+ }
// check for null prevout in non-coinbase txs
if tx.inputs.len() > 1 {
for (index, input) in tx.inputs.iter().enumerate() {
@@ -737,6 +741,8 @@ enum TransactionDecoderErrorInner {
DuplicateInput(OutPoint),
/// Sum of output values exceeds `MAX_MONEY`
OutputValueSumTooLarge(u64),
+ /// Transaction has no outputs.
+ NoOutputs,
}
#[cfg(feature = "alloc")]
@@ -799,6 +805,7 @@ impl fmt::Display for TransactionDecoderError {
write!(f, "duplicate input: {:?}:{}", outpoint.txid, outpoint.vout),
E::OutputValueSumTooLarge(val) =>
write!(f, "sum of output values {} satoshis exceeds MAX_MONEY", val),
+ E::NoOutputs => write!(f, "transaction has no outputs"),
}
}
}
@@ -823,6 +830,7 @@ impl std::error::Error for TransactionDecoderError {
E::CoinbaseScriptSigTooLarge(_) => None,
E::DuplicateInput(_) => None,
E::OutputValueSumTooLarge(_) => None,
+ E::NoOutputs => None,
}
}
}
@@ -2389,6 +2397,7 @@ mod tests {
}
#[test]
+ #[ignore] // bad test; will be fixed in next commit
#[cfg(feature = "alloc")]
fn decode_zero_inputs() {
// Test empty transaction with no inputs or outputs.
@@ -2566,4 +2575,19 @@ mod tests {
let result = decoder.push_bytes(&mut slice);
assert!(result.is_err(), "output value > MAX_MONEY should be rejected during decoding");
}
+
+ #[test]
+ #[cfg(all(feature = "alloc", feature = "hex"))]
+ fn reject_transaction_with_no_outputs() {
+ // Test vector taken from Bitcoin Core tx_invalid.json
+ // https://github.com/bitcoin/bitcoin/blob/master/src/test/data/tx_invalid.json#L36
+ // "No outputs"
+ let tx_bytes = hex!("01000000010001000000000000000000000000000000000000000000000000000000000000000000006d483045022100f16703104aab4e4088317c862daec83440242411b039d14280e03dd33b487ab802201318a7be236672c5c56083eb7a5a195bc57a40af7923ff8545016cd3b571e2a601232103c40e5d339df3f30bf753e7e04450ae4ef76c9e45587d1d993bdc4cd06f0651c7acffffffff0000000000");
+
+ let mut decoder = Transaction::decoder();
+ let mut slice = tx_bytes.as_slice();
+ decoder.push_bytes(&mut slice).unwrap();
+ let err = decoder.end().unwrap_err();
+ assert_eq!(err, TransactionDecoderError(TransactionDecoderErrorInner::NoOutputs));
+ }
}
Why this scored 47/100
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