Using compress/flate (Dictionary) in Go

package main

import (
	"bytes"
	"compress/flate"
	"fmt"
	"io"
	"log"
	"os"
	"strings"
)

func main() {
	// The dictionary is a string of bytes. When compressing some input data,
	// the compressor will attempt to substitute substrings with matches found
	// in the dictionary. As such, the dictionary should only contain substrings
	// that are expected to be found in the actual data stream.
	const dict = `<?xml version="1.0"?>` + `<book>` + `<data>` + `<meta name="` + `" content="`

	// The data to compress should (but is not required to) contain frequent
	// substrings that match those in the dictionary.
	const data = `<?xml version="1.0"?>
<book>
	<meta name="title" content="The Go Programming Language"/>
	<meta name="authors" content="Alan Donovan and Brian Kernighan"/>
	<meta name="published" content="2015-10-26"/>
	<meta name="isbn" content="978-0134190440"/>
	<data>...</data>
</book>
`

	var b bytes.Buffer

	// Compress the data using the specially crafted dictionary.
	zw, err := flate.NewWriterDict(&b, flate.DefaultCompression, []byte(dict))
	if err != nil {
		log.Fatal(err)
	}
	if _, err := io.Copy(zw, strings.NewReader(data)); err != nil {
		log.Fatal(err)
	}
	if err := zw.Close(); err != nil {
		log.Fatal(err)
	}

	// The decompressor must use the same dictionary as the compressor.
	// Otherwise, the input may appear as corrupted.
	fmt.Println("Decompressed output using the dictionary:")
	zr := flate.NewReaderDict(bytes.NewReader(b.Bytes()), []byte(dict))
	if _, err := io.Copy(os.Stdout, zr); err != nil {
		log.Fatal(err)
	}
	if err := zr.Close(); err != nil {
		log.Fatal(err)
	}

	fmt.Println()

	// Substitute all of the bytes in the dictionary with a '#' to visually
	// demonstrate the approximate effectiveness of using a preset dictionary.
	fmt.Println("Substrings matched by the dictionary are marked with #:")
	hashDict := []byte(dict)
	for i := range hashDict {
		hashDict[i] = '#'
	}
	zr = flate.NewReaderDict(&b, hashDict)
	if _, err := io.Copy(os.Stdout, zr); err != nil {
		log.Fatal(err)
	}
	if err := zr.Close(); err != nil {
		log.Fatal(err)
	}
}