lang: Add InstructionData::write_to implementation (#2733)

Co-authored-by: acheron <98934430+acheroncrypto@users.noreply.github.com>
Co-authored-by: acheron <acheroncrypto@gmail.com>

CHANGELOG.md

@@ -15,6 +15,7 @@ The minor version will be incremented upon a breaking change and the patch versi
 - cli: Allow force `init` and `new` ([#2698](https://github.com/coral-xyz/anchor/pull/2698)).
 - cli: Add verifiable option when `deploy` ([#2705](https://github.com/coral-xyz/anchor/pull/2705)).
 - cli: Add support for passing arguments to the underlying `solana program deploy` command with `anchor deploy` ([#2709](https://github.com/coral-xyz/anchor/pull/2709)).
+- lang: Add `InstructionData::write_to` implementation ([#2733](https://github.com/coral-xyz/anchor/pull/2733)).
 
 ### Fixes
 

lang/src/lib.rs

@@ -271,6 +271,16 @@ pub trait InstructionData: Discriminator + AnchorSerialize {
  self.serialize(&mut data).unwrap();
  data
  }
+
+ /// Clears `data` and writes instruction data to it.
+ ///
+ /// We use a `Vec<u8>`` here because of the additional flexibility of re-allocation (only if
+ /// necessary), and because the data field in `Instruction` expects a `Vec<u8>`.
+ fn write_to(&self, mut data: &mut Vec<u8>) {
+ data.clear();
+ data.extend_from_slice(&Self::DISCRIMINATOR);
+ self.serialize(&mut data).unwrap()
+ }
 }
 
 /// An event that can be emitted via a Solana log. See [`emit!`](crate::prelude::emit) for an example.

lang/tests/serialization.rs

@@ -0,0 +1,36 @@
+use anchor_lang::{AnchorDeserialize, AnchorSerialize, Discriminator, InstructionData};
+
+#[test]
+fn test_instruction_data() {
+ // Define some test type and implement ser/de, discriminator, and ix data
+ #[derive(Default, AnchorSerialize, AnchorDeserialize, PartialEq, Eq)]
+ struct MyType {
+ foo: [u8; 8],
+ bar: String,
+ }
+ impl Discriminator for MyType {
+ const DISCRIMINATOR: [u8; 8] = [1, 2, 3, 4, 5, 6, 7, 8];
+ }
+ impl InstructionData for MyType {}
+
+ // Initialize some instance of the type
+ let instance = MyType {
+ foo: [0, 2, 4, 6, 8, 10, 12, 14],
+ bar: "sharding sucks".into(),
+ };
+
+ // Serialize using both methods
+ let data = instance.data();
+ let mut write = vec![];
+ instance.write_to(&mut write);
+
+ // Check that one is correct and that they are equal (implies other is correct)
+ let correct_disc = data[0..8] == MyType::DISCRIMINATOR;
+ let correct_data = MyType::deserialize(&mut &data[8..]).is_ok_and(|result| result == instance);
+ let correct_serialization = correct_disc & correct_data;
+ assert!(correct_serialization, "serialization was not correct");
+ assert_eq!(
+ &data, &write,
+ "the different methods produced different serialized representations"
+ );
+}