tarutil: new package for working with tar archives

Will be used by the coordinator and gomote in future changes.

Change-Id: I57c8f268e60848c212831d14ba8b12b74a8f7a22
Reviewed-on: https://go-review.googlesource.com/3419
Reviewed-by: Andrew Gerrand <adg@golang.org>

tarutil/tarutil.go

@@ -0,0 +1,93 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package tarutil contains utilities for working with tar archives.
+package tarutil
+
+import (
+	"archive/tar"
+	"compress/gzip"
+	"errors"
+	"io"
+)
+
+// FileList is a list of entries in a tar archive which acts
+// as a template to make .tar.gz io.Readers as needed.
+//
+// The zero value is a valid empty list.
+//
+// All entries must be added before calling OpenTarGz.
+type FileList struct {
+	files []headerContent
+}
+
+type headerContent struct {
+	header *tar.Header
+
+	// For regularf files:
+	size    int64
+	content io.ReaderAt
+}
+
+// Add adds a non-regular file to the FileList.
+func (fl *FileList) Add(h *tar.Header) {
+	fl.files = append(fl.files, headerContent{header: h})
+}
+
+// AddRegular adds a regular file to the FileList.
+func (fl *FileList) AddRegular(h *tar.Header, size int64, content io.ReaderAt) {
+	fl.files = append(fl.files, headerContent{
+		header:  h,
+		size:    size,
+		content: content,
+	})
+}
+
+// OpenTarGz returns an io.Reader of a gzip-compressed tar file
+// containing the contents of the FileList.
+// All Add calls must happen before OpenTarGz is called.
+// Callers must call Close on the returned ReadCloser to release
+// resources.
+func (fl *FileList) OpenTarGz() io.ReadCloser {
+	pr, pw := io.Pipe()
+	go func() {
+		err := fl.writeTarGz(pw)
+		pw.CloseWithError(err)
+	}()
+	return struct {
+		io.Reader
+		io.Closer
+	}{
+		pr,
+		funcCloser(func() error {
+			pw.CloseWithError(errors.New("tarutil: .tar.gz generation aborted with Close"))
+			return nil
+		}),
+	}
+}
+
+func (fl *FileList) writeTarGz(w *io.PipeWriter) error {
+	zw := gzip.NewWriter(w)
+	tw := tar.NewWriter(zw)
+	for _, f := range fl.files {
+		if err := tw.WriteHeader(f.header); err != nil {
+			return err
+		}
+		if f.content != nil {
+			if _, err := io.CopyN(tw, io.NewSectionReader(f.content, 0, f.size), f.size); err != nil {
+				return err
+			}
+		}
+	}
+
+	if err := tw.Close(); err != nil {
+		return err
+	}
+	return zw.Close()
+}
+
+// funcCloser implements io.Closer with a function.
+type funcCloser func() error
+
+func (fn funcCloser) Close() error { return fn() }

tarutil/tarutil_test.go

@@ -0,0 +1,83 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tarutil
+
+import (
+	"archive/tar"
+	"compress/gzip"
+	"io"
+	"io/ioutil"
+	"os"
+	"path"
+	"strings"
+	"testing"
+	"time"
+)
+
+// fileInfo is an os.FileInfo implementation for tarHeader.
+type fileInfo struct {
+	name   string
+	mode   os.FileMode
+	size   int64
+	target string // if symlink
+}
+
+func (fi fileInfo) IsDir() bool        { return fi.mode.IsDir() }
+func (fi fileInfo) ModTime() time.Time { return time.Time{} }
+func (fi fileInfo) Mode() os.FileMode  { return fi.mode }
+func (fi fileInfo) Name() string       { return path.Base(fi.name) }
+func (fi fileInfo) Size() int64        { return fi.size }
+func (fi fileInfo) Sys() interface{}   { return nil }
+
+func tarHeader(t *testing.T, fi fileInfo) *tar.Header {
+	h, err := tar.FileInfoHeader(fi, fi.target)
+	if err != nil {
+		t.Fatalf("tarHeader: %v", err)
+	}
+	h.Name = fi.name // see docs on tar.FileInfoHeader
+	return h
+}
+
+func TestFileList(t *testing.T) {
+	fl := new(FileList)
+
+	fl.Add(tarHeader(t, fileInfo{name: "symlink-file", target: "link-target", mode: 0644 | os.ModeSymlink}))
+	fl.AddRegular(tarHeader(t, fileInfo{name: "regular.txt", mode: 0644, size: 7}), 7, strings.NewReader("foo bar"))
+
+	tgz := fl.OpenTarGz()
+	defer tgz.Close()
+	zr, err := gzip.NewReader(tgz)
+	if err != nil {
+		t.Fatalf("gzip.NewReader: %v", err)
+	}
+	tr := tar.NewReader(zr)
+	saw := 0
+	for {
+		h, err := tr.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			t.Fatalf("tar.Reader.Next: %v", err)
+		}
+		saw++
+		switch h.Name {
+		case "symlink-file":
+		case "regular.txt":
+			all, err := ioutil.ReadAll(tr)
+			if err != nil {
+				t.Fatalf("Reading regular.txt: %v", err)
+			}
+			if string(all) != "foo bar" {
+				t.Errorf("regular.txt = %q; want \"foo bar\"", all)
+			}
+		default:
+			t.Fatalf("unknown name %q", h.Name)
+		}
+	}
+	if saw != 2 {
+		t.Errorf("number of entries = %d; want 2", saw)
+	}
+}