Line data    Source code

       1             : // Copyright 2021 The LevelDB-Go and Pebble Authors. All rights reserved. Use
       2             : // of this source code is governed by a BSD-style license that can be found in
       3             : // the LICENSE file.
       4             : 
       5             : //go:build cgo
       6             : // +build cgo
       7             : 
       8             : package block
       9             : 
      10             : import (
      11             :         "bytes"
      12             : 
      13             :         "github.com/DataDog/zstd"
      14             : )
      15             : 
      16             : // UseStandardZstdLib indicates whether the zstd implementation is a port of the
      17             : // official one in the facebook/zstd repository.
      18             : //
      19             : // This constant is only used in tests. Some tests rely on reproducibility of
      20             : // SST files, but a custom implementation of zstd will produce different
      21             : // compression result. So those tests have to be disabled in such cases.
      22             : //
      23             : // We cannot always use the official facebook/zstd implementation since it
      24             : // relies on CGo.
      25             : const UseStandardZstdLib = true
      26             : 
      27             : // decodeZstd decompresses src with the Zstandard algorithm. The destination
      28             : // buffer must already be sufficiently sized, otherwise decodeZstd may error.
      29           1 : func decodeZstd(dst, src []byte) ([]byte, error) {
      30           1 :         n, err := zstd.DecompressInto(dst, src)
      31           1 :         // NB: zstd.DecompressInto may return n < 0 if err != nil.
      32           1 :         if err != nil {
      33           1 :                 return nil, err
      34           1 :         }
      35           1 :         return dst[:n], nil
      36             : }
      37             : 
      38             : // encodeZstd compresses b with the Zstandard algorithm at default compression
      39             : // level (level 3). It reuses the preallocated capacity of compressedBuf if it
      40             : // is sufficient. The subslice `compressedBuf[:varIntLen]` should already encode
      41             : // the length of `b` before calling encodeZstd. It returns the encoded byte
      42             : // slice, including the `compressedBuf[:varIntLen]` prefix.
      43           1 : func encodeZstd(compressedBuf []byte, varIntLen int, b []byte) []byte {
      44           1 :         buf := bytes.NewBuffer(compressedBuf[:varIntLen])
      45           1 :         writer := zstd.NewWriterLevel(buf, 3)
      46           1 :         writer.Write(b)
      47           1 :         writer.Close()
      48           1 :         return buf.Bytes()
      49           1 : }