I see what you’re getting at. Here’s an article with some guidance on how to deal with a “data size error” when using “sol_invoke_signed_c” in Rust:

Error Handling: Solana Data Size Error

When building a custom Rust library for Solana smart contracts, one common issue is a “data size error” when calling “sol_invoke_signed_c”. This error is caused by Solana’s signature verification requirements.

Understanding the Error

A “data size error” is usually caused by incorrect encoding or decoding of data. In this context, this is because Rust’s “Vec” and other data structures do not support arbitrary precision integers like those used in Solana.

Solution: Use the correct data structure

To resolve this issue, you need to use a data structure that can store large integers, such as “u64” or “u128”. You can create a custom type that wraps u64 and provides methods for arithmetic operations.

Here is an example of how you might define such a type:

use std::convert::{From, To};
struct SignedData(u64);
impl SignedData {
fn new(value: u64) -> Self {
SignedData (value)
}
fn get_value(&self) -> u64 {
self.0
}
}
impl From for SignedData {
fn from(value: u64) -> Self {
SignedData (value)
}
}

Usage example

You can now create an instance of SignedData and use it with sol_invoke_signed_c:

use solana_program::{
account_info::{next_account_info, AccountInfo},
entrypoint,
program_error::ProgramError,
pubkey::Pubkey,
};
entrypoint!(process_instruction);
fn process_instruction(
_account_info: account_info,
Instruction_data: &[u8],
_signing_key_id: &Pubkey,
) -> Result<_, Programerror> {
let signed_data = SignedData::new(1);
println!("Signed data value: {}", signed_data.get_value());
// Call sol_invoke_signed_c with the signed data
let (result, result_signer_id) = sol_invoke_signed_c(
Instruction_data,
&signed_data,
next_account_info(),
_signing_key_id,
);
OK(())
}

Best Practices

When working with sol_invoke_signed_c, keep the following best practices in mind:

• Always use the correct data structure when storing and manipulating large integers.

• Use the From property to convert between u64 and SignedData.

• When creating a SignedData instance, ensure that it is properly initialized to avoid problems.

By following these guidelines and using the correct data structures, you should be able to successfully resolve the “data size error” when working with sol_invoke_signed_c in a custom Rust library for Solana smart contracts.