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package zstd_test
import (
"bytes"
"fmt"
"github.com/klauspost/compress/zstd"
)
func ExampleWithEncoderDictRaw() {
// "Raw" dictionaries can be used for compressed delta encoding.
source := []byte(`
This is the source file. Compression of the target file with
the source file as the dictionary will produce a compressed
delta encoding of the target file.`)
target := []byte(`
This is the target file. Decompression of the delta encoding with
the source file as the dictionary will produce this file.`)
// The dictionary id is arbitrary. We use zero for compatibility
// with zstd --patch-from, but applications can use any id
// not in the range [32768, 1<<31).
const id = 0
bestLevel := zstd.WithEncoderLevel(zstd.SpeedBestCompression)
w, _ := zstd.NewWriter(nil, bestLevel,
zstd.WithEncoderDictRaw(id, source))
delta := w.EncodeAll(target, nil)
r, _ := zstd.NewReader(nil, zstd.WithDecoderDictRaw(id, source))
out, err := r.DecodeAll(delta, nil)
if err != nil || !bytes.Equal(out, target) {
panic("decoding error")
}
// Ordinary compression, for reference.
w, _ = zstd.NewWriter(nil, bestLevel)
compressed := w.EncodeAll(target, nil)
// Check that the delta is at most half as big as the compressed file.
fmt.Println(len(delta) < len(compressed)/2)
// Output:
// true
}
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