Artifact [dc7b90e535]

Artifact dc7b90e535b7654ac49fb41f71291ca647c8898520bc41440454e1024c56d53b:

• File internal/blob/compress.go — part of check-in [f5744359d3] at 2026-04-19 16:30:54 on branch trunk — Initial open source release

  libfossil is a pure-Go implementation of the Fossil SCM, reading and writing the same .fossil SQLite repository format as upstream Fossil.

  This is the first public release of code that previously lived in a private repository. The module path is github.com/danmestas/libfossil and the binary is named libfossil to avoid $PATH collisions with upstream fossil.

  Included: - Repo lifecycle (create, clone), checkout/checkin, timeline, merge, diff, annotate, shun, tag, branch, bisect, stash, undo/redo - Sync-over-HTTP protocol (client and handler) - Two SQLite drivers: modernc (pure Go, default) and ncruces (wasm-capable) - Observer interfaces (SyncObserver, CheckoutObserver) with an optional OpenTelemetry implementation in observer/otel (separate submodule) - Deterministic simulation testing harness with BUGGIFY fault injection - Kong-based embeddable CLI under cli/ and a standalone binary under cmd/libfossil/ (user: [email protected], size: 2030) [annotate] [blame] [check-ins using]

package blob

import (
	"bytes"
	"compress/zlib"
	"encoding/binary"
	"fmt"
	"io"

	"github.com/danmestas/libfossil/simio"
)

// Compress produces Fossil-compatible compressed blob content:
// [4-byte big-endian uncompressed size][zlib-compressed data].
// This matches Fossil's blob_compress() in src/blob.c.
func Compress(data []byte) (result []byte, err error) {
	if data == nil {
		panic("blob.Compress: data must not be nil")
	}
	defer func() {
		if err == nil && len(result) == 0 {
			panic("blob.Compress: postcondition violated: result is empty with no error")
		}
	}()

	var buf bytes.Buffer
	// 4-byte big-endian uncompressed size prefix.
	if err := binary.Write(&buf, binary.BigEndian, uint32(len(data))); err != nil {
		return nil, fmt.Errorf("write size prefix: %w", err)
	}
	w := zlib.NewWriter(&buf)
	if _, err := w.Write(data); err != nil {
		return nil, fmt.Errorf("zlib compress: %w", err)
	}
	if err := w.Close(); err != nil {
		return nil, fmt.Errorf("zlib close: %w", err)
	}
	return buf.Bytes(), nil
}

// Decompress handles Fossil's compressed blob format:
// [4-byte big-endian uncompressed size][zlib-compressed data].
// The 4-byte prefix is skipped before decompressing.
func Decompress(data []byte) (result []byte, err error) {
	if data == nil {
		panic("blob.Decompress: data must not be nil")
	}
	defer func() {
		if err == nil && result == nil {
			panic("blob.Decompress: postcondition violated: result is nil with no error")
		}
	}()

	if len(data) < 5 {
		return nil, fmt.Errorf("zlib decompress: data too short (%d bytes)", len(data))
	}
	// Skip the 4-byte size prefix.
	zlibData := data[4:]
	r, err := zlib.NewReader(bytes.NewReader(zlibData))
	if err != nil {
		return nil, fmt.Errorf("zlib decompress: %w", err)
	}
	defer r.Close()
	out, err := io.ReadAll(r)
	if err != nil {
		return nil, fmt.Errorf("zlib read: %w", err)
	}
	// BUGGIFY: truncate decompressed output to exercise partial-read handling.
	if simio.Buggify(0.02) && len(out) > 1 {
		out = out[:len(out)/2]
	}
	return out, nil
}