txid implementation

src/state.cairo

@@ -107,16 +107,6 @@ pub struct Transaction {
     pub lock_time: u32,
 }
 
-/// Output of a transaction.
-/// https://learnmeabitcoin.com/technical/transaction/output/
-#[derive(Drop, Copy)]
-pub struct TxOut {
-    /// The value of the output in satoshis.
-    pub value: i64,
-    /// The spending script (aka locking code) for this output.
-    pub pk_script: @ByteArray,
-}
-
 /// Input of a transaction.
 /// https://learnmeabitcoin.com/technical/transaction/input/
 ///
@@ -131,3 +121,13 @@ pub struct TxIn {
     /// The index of output in the utreexo set (meta field).
     pub txo_index: u64,
 }
+
+/// Output of a transaction.
+/// https://learnmeabitcoin.com/technical/transaction/output/
+#[derive(Drop, Copy)]
+pub struct TxOut {
+    /// The value of the output in satoshis.
+    pub value: i64,
+    /// The spending script (aka locking code) for this output.
+    pub pk_script: @ByteArray,
+}

src/validation.cairo

@@ -1,4 +1,7 @@
-use super::state::{Block, ChainState, Transaction, UtreexoState};
+use core::sha256::compute_sha256_byte_array;
+use core::to_byte_array::FormatAsByteArray;
+use core::num::traits::{Zero, One, BitSize};
+use super::state::{Block, ChainState, Transaction, UtreexoState, TxIn, TxOut};
 use super::utils::{shl, shr};
 
 const MAX_TARGET: u256 = 0x00000000FFFF0000000000000000000000000000000000000000000000000000;
@@ -37,10 +40,50 @@ impl BlockValidatorImpl of BlockValidator {
 
 #[generate_trait]
 impl TransactionValidatorImpl of TransactionValidator {
+    // marker, flag, and witness fields in segwit transactions are not included
+    // this means txid computation is the same for legacy and segwit tx
     fn txid(self: @Transaction) -> u256 {
-        // TODO: implement
-        0
+        let version: ByteArray = (*self.version).format_as_byte_array(10);
+        let inputs: Span<TxIn> = *self.inputs;
+        let outputs: Span<TxOut> = *self.outputs;
+        let locktime: ByteArray = (*self.lock_time).format_as_byte_array(10);
+
+        let mut sha256_input: ByteArray = "";
+        sha256_input.append(@version);
+
+        let mut i = 0;
+        while i < inputs.len() {
+            sha256_input.append(*inputs.at(i).script);
+            sha256_input.append(@(*inputs.at(i).sequence).format_as_byte_array(10));
+            sha256_input.append(@(*inputs.at(i).txo_index).format_as_byte_array(10));
+
+            i += 1;
+        };
+
+        let mut i = 0;
+        while i < outputs.len() {
+            let value: felt252 = (*outputs.at(i).value).into();
+            sha256_input.append(@value.format_as_byte_array(10));
+
+            i += 1;
+        };
+
+        sha256_input.append(@locktime);
+
+        let txid = compute_sha256_byte_array(@sha256_input).span();
+
+        let mut result: u256 = 0;
+        let mut i: u32 = 0;
+        while i != 8 {
+            let byte: u256 = (*txid[i]).into();
+            result += shl(byte, (8 * i).into());
+
+            i += 1;
+        };
+
+        result
     }
+
     fn fee(self: @Transaction) -> u256 {
         // TODO: implement
         0