Day 26: Working with Bytes

In Solana, public keys are 32-byte arrays. Let's build a simplified Pubkey type!

Solana's Pubkey

// Actual Solana SDK
pub struct Pubkey([u8; 32]);

Every account, program, and wallet in Solana is identified by a 32-byte public key. Understanding byte manipulation is essential!

Fixed-Size Byte Arrays

// Creating arrays
let zeros = [0u8; 32];           // All zeros
let ones = [1u8; 32];            // All ones
let mixed = [1, 2, 3, 0, 0, ...]; // Specific values

// Comparing arrays
zeros == [0u8; 32]  // true
zeros != ones       // true

Newtype Pattern

Wrap a type for type safety:

#[derive(Debug, Clone, Copy, PartialEq)]
struct Pubkey([u8; 32]);

impl Pubkey {
    const fn new(bytes: [u8; 32]) -> Self {
        Pubkey(bytes)
    }
}

Common Operations

impl Pubkey {
    // Check if all zeros
    fn is_zero(&self) -> bool {
        self.0 == [0u8; 32]
    }
    
    // Get as slice
    fn as_bytes(&self) -> &[u8] {
        &self.0
    }
    
    // Get first n bytes
    fn first_bytes<const N: usize>(&self) -> [u8; N] {
        self.0[..N].try_into().unwrap()
    }
}

The "System Program" Pattern

impl Pubkey {
    // Constant pubkey (like system program)
    const SYSTEM_PROGRAM: Pubkey = Pubkey([0u8; 32]);
    
    fn is_system_program(&self) -> bool {
        *self == Self::SYSTEM_PROGRAM
    }
}

The Task

Implement for Pubkey:

default() - returns a pubkey with all zeros
is_zero() - checks if all bytes are zero
as_bytes() - returns the bytes as a slice

Requirements

Pubkey::default().is_zero() → true
Pubkey::new([1u8; 32]).is_zero() → false
Pubkey::new([1u8; 32]).as_bytes()[0] → 1

Hints

fn default() -> Self {
    Pubkey([0u8; 32])
}

fn is_zero(&self) -> bool {
    self.0 == [0u8; 32]
}

fn as_bytes(&self) -> &[u8] {
    &self.0
}