internal/pkg: decompress xz streams

This uses a port of the public domain xz implementation.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/xz/example_test.go

@@ -0,0 +1,95 @@
+/*
+ * Package xz examples
+ *
+ * Author: Michael Cross <https://github.com/xi2>
+ *
+ * This file has been put into the public domain.
+ * You can do whatever you want with this file.
+ */
+
+package xz_test
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+	"path/filepath"
+
+	"hakurei.app/internal/xz"
+)
+
+func ExampleNewReader() {
+	// load some XZ data into memory
+	data, err := ioutil.ReadFile(
+		filepath.Join("testdata", "xz-utils", "good-1-check-sha256.xz"))
+	if err != nil {
+		log.Fatal(err)
+	}
+	// create an xz.Reader to decompress the data
+	r, err := xz.NewReader(bytes.NewReader(data), 0)
+	if err != nil {
+		log.Fatal(err)
+	}
+	// write the decompressed data to os.Stdout
+	_, err = io.Copy(os.Stdout, r)
+	if err != nil {
+		log.Fatal(err)
+	}
+	// Output:
+	// Hello
+	// World!
+}
+
+func ExampleReader_Multistream() {
+	// load some XZ data into memory
+	data, err := ioutil.ReadFile(
+		filepath.Join("testdata", "xz-utils", "good-1-check-sha256.xz"))
+	if err != nil {
+		log.Fatal(err)
+	}
+	// create a MultiReader that will read the data twice
+	mr := io.MultiReader(bytes.NewReader(data), bytes.NewReader(data))
+	// create an xz.Reader from the MultiReader
+	r, err := xz.NewReader(mr, 0)
+	if err != nil {
+		log.Fatal(err)
+	}
+	// set Multistream mode to false
+	r.Multistream(false)
+	// decompress the first stream
+	_, err = io.Copy(os.Stdout, r)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println("Read first stream")
+	// reset the XZ reader so it is ready to read the second stream
+	err = r.Reset(nil)
+	if err != nil {
+		log.Fatal(err)
+	}
+	// set Multistream mode to false again
+	r.Multistream(false)
+	// decompress the second stream
+	_, err = io.Copy(os.Stdout, r)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println("Read second stream")
+	// reset the XZ reader so it is ready to read further streams
+	err = r.Reset(nil)
+	// confirm that the second stream was the last one
+	if err == io.EOF {
+		fmt.Println("No more streams")
+	}
+	// Output:
+	// Hello
+	// World!
+	// Read first stream
+	// Hello
+	// World!
+	// Read second stream
+	// No more streams
+}