I have the following struct defined in the Solana anchor program

pub struct Parent {
    pub field1: String,
    pub data_arr: Vec<Data>,

#[derive(Debug, Clone, AnchorSerialize, AnchorDeserialize)]
pub struct Data {
    pub field1: String,
    pub field2: f64,
    pub field3: u8,

And I have this function that pushes the given data into the data_arr Vector

pub push_data(ctx: Context<AddData>, data: Vec<Data>)  -> Result<()> {


I am trying to call this instruction using Solana web3js library by creating a transaction instruction and passing the data buffer. It works for data types like String, u8, f64, etc. But I am getting the following error when trying to send this custom struct data,

Error: 'Program log: AnchorError occurred. Error Code: InstructionDidNotDeserialize. Error Number: 102. Error Message: The program could not deserialize the given instruction.',

I followed this method: How to serialize instruction buffer for an Anchor program


// data that actually needs to be serialized
// const data = [{ field1: 'str1', field2: 22.12, field3: 2 }, { field1: 'str2', field2: 29.21, field3: 8 }];

// serializing a string parameter
const data = 'sample data';

const string_u8vec = new TextEncoder().encode(data)
const string_u8vec_length = Buffer.from(new Uint8Array(new BN(string_u8vec.length).toArray("le", 4)));

const instructionBuffer = Buffer.concat([
   ixBuffer,            // namespace+method_name
   string_u8vec_length, // the length of the string
   string_u8vec         // the string itself


The above approach works if the data is a string. How to generate the data buffer if we need to pass other data types like PubKey, and Custom structs like the above one. Please help. Thanks.

1 Answer 1


For your custom struct, you'll follow a similar process, but one more layer of indirection since it's a Vec<Data>, meaning:

const data = [{ field1: '0', field2: '0'}, { field1: '1', field2: '1'}];

// serializing the data length
const data_length = Buffer.allocUnsafe(4);
data_length.writeUInt32LE(data.length, 0);

// serializing field 1
const field1 = data[0].field1;
const field1_buf = new TextEncoder().encode(field1)
const field1_length = Buffer.allocUnsafe(4);
field1_length.writeUInt32LE(field1_buf.length, 0);

// serializing field 2
const field2 = data[0].field2;
const field2_buf = new TextEncoder().encode(field2)
const field2_length = Buffer.allocUnsafe(4);
field2_length.writeUInt32LE(field2_buf.length, 0);

const instructionBuffer = Buffer.concat([
   ixBuffer,            // namespace+method_name

And then redoing the field1 and field2 parts for every element in the array.

  • how to serialize fields with integer or float values?
    – Vivek
    Commented Sep 19, 2022 at 6:25
  • It would be better to ask a separate question on exactly what you need help with
    – Jon C
    Commented Sep 19, 2022 at 10:48

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