Sans I/O compression

Use a session when your application owns the input/output buffers and decides when more bytes are available. Sessions perform no I/O. This works in a blocking loop, an async task, or a custom event loop without an I/O adapter.

For transport integration, see Read / Write I/O. For the inverse operation, see Sans I/O decompression.

Drive a raw encoder

Supply chunks with Operation::Process. After the last chunk, call Finish until EncoderStatus::Finished. An empty input passed with Process is not EOF. The deliberately small output buffer below forces repeated output drains.

use mbrotli::{
    Compressor, Decompressor, EncoderConfig, EncoderStatus, InputSize, Operation, Quality,
};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let input = b"incremental encoding with tiny buffers\n".repeat(100);
    let config = EncoderConfig::default().with_quality(Quality::Q5);
    let mut encoder = Compressor::new(config)?;
    let mut compressed = Vec::new();
    let mut output = [0; 11];
    {
        let mut session = encoder.start(InputSize::Exact(input.len() as u64).into())?;
        for chunk in input.chunks(7) {
            let mut remaining = chunk;
            loop {
                let progress = session.process(remaining, &mut output, Operation::Process)?;
                remaining = &remaining[progress.consumed..];
                compressed.extend_from_slice(&output[..progress.produced]);
                if progress.status == EncoderStatus::NeedsInput {
                    assert!(remaining.is_empty());
                    break;
                }
            }
        }
        loop {
            let progress = session.process(&[], &mut output, Operation::Finish)?;
            compressed.extend_from_slice(&output[..progress.produced]);
            if progress.status == EncoderStatus::Finished {
                break;
            }
        }
    }
    // Exact input size, offset zero, and no flushes preserve one-shot bytes.
    assert_eq!(compressed, encoder.compress(&input)?);
    let mut decoder = Decompressor::new(Default::default())?;
    assert_eq!(decoder.decompress(&compressed)?, input);
    Ok(())
}

Always advance input by consumed and publish only output[..produced] before handling status. NeedsOutput requires output space and the unconsumed input suffix; reaching the end of the current input slice alone does not finish the stream.

Flush and finish are different

Operation::Flush makes accepted bytes decodable without ending the stream. Drain it to NeedsInput before changing operation or supplying new input. Flush boundaries can change output size and bytes. Finish ends the stream; while retrying it, keep the same operation and exact unconsumed input suffix.

Use InputSize::Exact when the total input size is known. Otherwise use the default unknown size; the encoder infers its size hint when it first encodes. See stream scheduling and identity.

Drive parallel input

ParallelCompressor::start(window) returns (session, queue). Keep workers running the queue while you feed input and drain output. The session’s process does not block: ParallelEncoderStatus::Pending means progress depends on tasks. Call session.wait() with independently runnable workers, or execute queued tasks yourself before waiting on a single thread.

The complete Sans I/O parallel example handles all statuses and source chunks. Its window bounds queued, running, and not-yet-delivered segments. Without flushes, output matches a batch over the same input and segment configuration. See parallel session mechanics.

Drive a framed encoder

Enable experimental. Container process takes an output buffer and a FramedEncodeOperation; resource process takes payload, output, and an ordinary Operation. Finish the resource before finishing the container.

use mbrotli::framing::{
    FramedCompressor, FramedDecompressor, FramedEncodeConfig,
    FramedEncodeOperation, FramedEncoderStatus, FramingConfig,
};
use mbrotli::{EncoderConfig, Operation, Quality};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let input = b"framed incremental payload\n".repeat(20);
    let config = FramedEncodeConfig::default()
        .with_encoder_config(EncoderConfig::default().with_quality(Quality::Q5))
        .with_framing_config(FramingConfig { chunk_bytes: 32, ..Default::default() });
    let mut encoder = FramedCompressor::new(config)?;
    let mut session = encoder.start(Default::default())?;
    let mut buffer = [0; 13];
    let mut container = Vec::new();
    // Drain the main header before accepting a resource command.
    loop {
        let progress = session.process(&mut buffer, FramedEncodeOperation::Process)?;
        container.extend_from_slice(&buffer[..progress.produced]);
        if progress.status == FramedEncoderStatus::NeedsInput {
            break;
        }
    }
    {
        let mut resource = session.resource(Default::default(), Default::default())?;
        let mut chunks = input.chunks(9).peekable();
        while let Some(chunk) = chunks.next() {
            let operation = if chunks.peek().is_none() {
                Operation::Finish
            } else {
                Operation::Process
            };
            let mut remaining = chunk;
            loop {
                let progress = resource.process(remaining, &mut buffer, operation)?;
                remaining = &remaining[progress.consumed..];
                container.extend_from_slice(&buffer[..progress.produced]);
                if progress.status == FramedEncoderStatus::Finished
                    || progress.status == FramedEncoderStatus::NeedsInput
                {
                    assert!(remaining.is_empty());
                    break;
                }
            }
        }
        assert!(resource.is_finished());
    }
    loop {
        let progress = session.process(&mut buffer, FramedEncodeOperation::Finish)?;
        container.extend_from_slice(&buffer[..progress.produced]);
        if progress.status == FramedEncoderStatus::Finished {
            break;
        }
    }
    let mut decoder = FramedDecompressor::new(Default::default())?;
    assert_eq!(decoder.decompress(&container)?.resources[0].data, input);
    Ok(())
}

The example marks the last nonempty chunk with Finish; for an empty resource, drive resource.process(&[], output, Operation::Finish) to Finished too. Metadata and new resource commands require previous container output to be drained; otherwise they return OutputPending without committing the command. See resource lifecycles and metadata.

Ownership and cancellation

Borrowed sessions exclusively borrow their codec owner. Dropping an unfinished session cancels it; dropping an unfinished framed resource abandons its container. Forgetting a session requires owner recovery. No drop performs transport I/O. Owned session variants move the codec into the session when a lifetime-free holder fits your application better. See owned sessions.