Trait Writer

Source

pub trait Writer {
    // Required methods
    fn write_byte(&mut self, byte: u8) -> Result<(), SerializeError>;
    fn write_bytes(&mut self, bytes: &[u8]) -> Result<(), SerializeError>;
}

Expand description

A trait for writing bytes during serialization with error handling.

This trait enables custom serialization targets that can report errors, such as buffer overflow. It’s designed to support use cases like buffer pooling where you need to detect when a fixed-size buffer is too small.

§Example

use facet_format_postcard::{Writer, SerializeError};

struct PooledWriter {
    buf: Vec<u8>,  // In practice, this would be from a buffer pool
    overflow: Option<Vec<u8>>,
}

impl Writer for PooledWriter {
    fn write_byte(&mut self, byte: u8) -> Result<(), SerializeError> {
        // Try pooled buffer first, fall back to Vec on overflow
        if let Some(ref mut overflow) = self.overflow {
            overflow.push(byte);
        } else if self.buf.len() < self.buf.capacity() {
            self.buf.push(byte);
        } else {
            // Overflow - allocate Vec and transfer contents
            let mut overflow = Vec::new();
            overflow.extend_from_slice(&self.buf);
            overflow.push(byte);
            self.overflow = Some(overflow);
        }
        Ok(())
    }

    fn write_bytes(&mut self, bytes: &[u8]) -> Result<(), SerializeError> {
        if let Some(ref mut overflow) = self.overflow {
            overflow.extend_from_slice(bytes);
        } else if self.buf.len() + bytes.len() <= self.buf.capacity() {
            self.buf.extend_from_slice(bytes);
        } else {
            // Overflow - allocate Vec and transfer contents
            let mut overflow = Vec::new();
            overflow.extend_from_slice(&self.buf);
            overflow.extend_from_slice(bytes);
            self.overflow = Some(overflow);
        }
        Ok(())
    }
}