A small and idiomatic bzip2 compressor and decompressor library for go.

API: compress with NewWriter, decompress with NewReader. Compression is implemented here; NewReader uses the standard library reader so the wire format matches NewWriter.

The compressor streams output to the underlying io.Writer per block and on Close; always check errors from Write and Close. See API.md for lifecycle and release checks.

Performance: The default build uses a pure Go encoder with an O(n log n) block sorter (counting-sort passes) and is suitable for portability. For maximum throughput matching the reference C implementation, build with -tags libbzip2 (requires CGO, libbz2 headers, and -lbz2). NewReader is unchanged and always uses the standard library.

Recent benchmark snapshots (Go 1.26.2, tests/bench_test.go):

• Pure Go BenchmarkWriterMultiBlock: about 116-119 MB/s, about 4.47 MB/op, 15 allocs/op (new Writer each iteration).
• Pure Go BenchmarkWriterMultiBlockReuseDiscard: about 148-153 MB/s, 0 B/op, 0 allocs/op (reuse one Writer via Reset after warmup).
• Pure Go BenchmarkWriteBlockPrepared (internal/enc): about 469-471 MB/s, 0 B/op, 0 allocs/op (prepared block encoder hot path).
• -tags libbzip2 BenchmarkWriterMultiBlock: about 149-166 MB/s, about 192 B/op, 3 allocs/op.
• -tags libbzip2 BenchmarkWriterMultiBlockReuseDiscard: about 147-155 MB/s, 0 B/op, 0 allocs/op.

0 allocs/op is expected in steady-state reuse paths (Writer.Reset + warm buffers). Creating a new Writer per stream still allocates.

Build / test with the libbz2-backed compressor:

CGO_ENABLED=1 go build -tags libbzip2 ./...
CGO_ENABLED=1 go test -tags libbzip2 ./...

On Linux, install the bzip2 development package (libbz2-dev, bzip2-devel, or your distro’s equivalent) so bzlib.h and -lbz2 resolve.

go get github.com/Quad4-Software/bzip2@latest

import (
	"bytes"
	"io"

	"github.com/Quad4-Software/bzip2/pkg/bzip2"
)

func Example() {
	var buf bytes.Buffer
	w, err := bzip2.NewWriter(&buf, 9)
	if err != nil {
		panic(err)
	}
	if _, err := io.Copy(w, bytes.NewReader([]byte("hello"))); err != nil {
		panic(err)
	}
	if err := w.Close(); err != nil {
		panic(err)
	}
	out, err := io.ReadAll(bzip2.NewReader(&buf))
	_ = out
}

See API.md for details.

0BSD. See LICENSE.