Add Transaction::receipts_root_offset (#136)

The receipts root will be updated at runtime in the vm. Hence, its
offset must be known for script transactions.

This function is checking for the correct variant of
`Transaction::Script` so it won't be misused for transactions that
doesn't contain receipts root offsets.

fuel-tx/src/transaction/offset.rs

@@ -2,7 +2,7 @@ use super::{TRANSACTION_CREATE_FIXED_SIZE, TRANSACTION_SCRIPT_FIXED_SIZE};
 use crate::{Input, Metadata, StorageSlot, Transaction};
 
 use fuel_types::bytes::{self, SizedBytes};
-use fuel_types::ContractId;
+use fuel_types::{Bytes32, ContractId};
 
 impl Transaction {
  /// For a serialized transaction of type `Script`, return the bytes offset
@@ -195,4 +195,13 @@ impl Transaction {
  + offset
  })
  }
+
+ /// For a serialized transaction of type `Script`, return the bytes offset
+ /// of the receipts root
+ pub const fn receipts_root_offset(&self) -> Option<usize> {
+ match self {
+ Self::Script { .. } => Some(TRANSACTION_SCRIPT_FIXED_SIZE - Bytes32::LEN),
+ Self::Create { .. } => None,
+ }
+ }
 }

fuel-tx/tests/bytes.rs

@@ -1,5 +1,4 @@
 use fuel_asm::Opcode;
-use fuel_crypto::Hasher;
 use fuel_tx::{default_parameters::*, *};
 use fuel_tx_test_helpers::{generate_bytes, generate_nonempty_bytes};
 use fuel_types::{bytes, ContractId, Immediate24};

fuel-tx/tests/offset.rs

@@ -1,9 +1,12 @@
 use fuel_tx::*;
 use fuel_tx_test_helpers::TransactionFactory;
 use fuel_types::bytes::{Deserializable, SerializableVec};
+use rand::{rngs::StdRng, Rng, SeedableRng};
 
 #[test]
 fn iow_offset() {
+ let rng = &mut StdRng::seed_from_u64(8586);
+
  TransactionFactory::from_seed(3493)
  .take(100)
  .for_each(|(mut tx, _)| {
@@ -44,5 +47,16 @@ fn iow_offset() {
  assert_eq!(w, &witness);
  assert_eq!(offset, offset_p);
  });
+
+ tx.receipts_root_offset().map(|offset| {
+ let receipts_root = rng.gen();
+
+ tx.set_receipts_root(receipts_root);
+
+ let bytes = tx.to_bytes();
+ let receipts_root_p = &bytes[offset..offset + Bytes32::LEN];
+
+ assert_eq!(&receipts_root[..], receipts_root_p);
+ });
  });
 }