archive/tar: add FileInfoHeader function

Fixes #3295

R=adg, rsc, mike.rosset
CC=golang-dev
https://golang.org/cl/5796073

api/next.txt

+pkg archive/tar, func FileInfoHeader(os.FileInfo, string) (*Header, error)
 pkg crypto/tls, const TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA uint16
 pkg crypto/tls, const TLS_RSA_WITH_AES_256_CBC_SHA uint16
 pkg crypto/x509, const ECDSA PublicKeyAlgorithm

src/pkg/archive/tar/common.go

@@ -11,7 +11,12 @@
 //   http://www.gnu.org/software/tar/manual/html_node/Standard.html
 package tar
 
-import "time"
+import (
+	"errors"
+	"fmt"
+	"os"
+	"time"
+)
 
 const (
 	blockSize = 512
@@ -49,6 +54,62 @@ type Header struct {
 	ChangeTime time.Time // status change time
 }
 
+// sysStat, if non-nil, populates h from system-dependent fields of fi.
+var sysStat func(fi os.FileInfo, h *Header) error
+
+// Mode constants from the tar spec.
+const (
+	c_ISDIR  = 040000
+	c_ISFIFO = 010000
+	c_ISREG  = 0100000
+	c_ISLNK  = 0120000
+	c_ISBLK  = 060000
+	c_ISCHR  = 020000
+	c_ISSOCK = 0140000
+)
+
+// FileInfoHeader creates a partially-populated Header from fi.
+// If fi describes a symlink, FileInfoHeader records link as the link target.
+func FileInfoHeader(fi os.FileInfo, link string) (*Header, error) {
+	if fi == nil {
+		return nil, errors.New("tar: FileInfo is nil")
+	}
+	h := &Header{
+		Name:    fi.Name(),
+		ModTime: fi.ModTime(),
+		Mode:    int64(fi.Mode().Perm()), // or'd with c_IS* constants later
+	}
+	switch {
+	case fi.Mode()&os.ModeType == 0:
+		h.Mode |= c_ISREG
+		h.Typeflag = TypeReg
+		h.Size = fi.Size()
+	case fi.IsDir():
+		h.Typeflag = TypeDir
+		h.Mode |= c_ISDIR
+	case fi.Mode()&os.ModeSymlink != 0:
+		h.Typeflag = TypeSymlink
+		h.Mode |= c_ISLNK
+		h.Linkname = link
+	case fi.Mode()&os.ModeDevice != 0:
+		if fi.Mode()&os.ModeCharDevice != 0 {
+			h.Mode |= c_ISCHR
+			h.Typeflag = TypeChar
+		} else {
+			h.Mode |= c_ISBLK
+			h.Typeflag = TypeBlock
+		}
+	case fi.Mode()&os.ModeSocket != 0:
+		h.Mode |= c_ISSOCK
+	default:
+		return nil, fmt.Errorf("archive/tar: unknown file mode %v", fi.Mode())
+	}
+	if sysStat != nil {
+		return h, sysStat(fi, h)
+	}
+	return h, nil
+}
+
 var zeroBlock = make([]byte, blockSize)
 
 // POSIX specifies a sum of the unsigned byte values, but the Sun tar uses signed byte values.

src/pkg/archive/tar/stat_atim.go

+// Copyright 2012 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.
+
+// +build linux openbsd
+
+package tar
+
+import (
+	"syscall"
+	"time"
+)
+
+func statAtime(st *syscall.Stat_t) time.Time {
+	return time.Unix(st.Atim.Unix())
+}
+
+func statCtime(st *syscall.Stat_t) time.Time {
+	return time.Unix(st.Ctim.Unix())
+}

src/pkg/archive/tar/stat_atimespec.go

+// Copyright 2012 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.
+
+// +build darwin freebsd netbsd
+
+package tar
+
+import (
+	"syscall"
+	"time"
+)
+
+func statAtime(st *syscall.Stat_t) time.Time {
+	return time.Unix(st.Atimespec.Unix())
+}
+
+func statCtime(st *syscall.Stat_t) time.Time {
+	return time.Unix(st.Ctimespec.Unix())
+}

src/pkg/archive/tar/stat_unix.go

+// Copyright 2012 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.
+
+// +build linux darwin freebsd openbsd netbsd
+
+package tar
+
+import (
+	"os"
+	"syscall"
+)
+
+func init() {
+	sysStat = statUnix
+}
+
+func statUnix(fi os.FileInfo, h *Header) error {
+	sys, ok := fi.Sys().(*syscall.Stat_t)
+	if !ok {
+		return nil
+	}
+	h.Uid = int(sys.Uid)
+	h.Gid = int(sys.Gid)
+	// TODO(bradfitz): populate username & group.  os/user
+	// doesn't cache LookupId lookups, and lacks group
+	// lookup functions.
+	h.AccessTime = statAtime(sys)
+	h.ChangeTime = statCtime(sys)
+	// TODO(bradfitz): major/minor device numbers?
+	return nil
+}

src/pkg/archive/tar/tar_test.go

+// Copyright 2012 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 tar
+
+import (
+	"os"
+	"testing"
+	"time"
+)
+
+func TestFileInfoHeader(t *testing.T) {
+	fi, err := os.Lstat("testdata/small.txt")
+	if err != nil {
+		t.Fatal(err)
+	}
+	h, err := FileInfoHeader(fi, "")
+	if err != nil {
+		t.Fatalf("on small.txt: %v", err)
+	}
+	if g, e := h.Name, "small.txt"; g != e {
+		t.Errorf("Name = %q; want %q", g, e)
+	}
+	if g, e := h.Mode, int64(0644|c_ISREG); g != e {
+		t.Errorf("Mode = %#o; want %#o", g, e)
+	}
+	if g, e := h.Size, int64(5); g != e {
+		t.Errorf("Size = %v; want %v", g, e)
+	}
+	if g, e := h.ModTime, fi.ModTime(); !g.Equal(e) {
+		t.Errorf("ModTime = %v; want %v", g, e)
+	}
+}
+
+func TestFileInfoHeaderSymlink(t *testing.T) {
+	h, err := FileInfoHeader(symlink{}, "some-target")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if g, e := h.Name, "some-symlink"; g != e {
+		t.Errorf("Name = %q; want %q", g, e)
+	}
+	if g, e := h.Linkname, "some-target"; g != e {
+		t.Errorf("Linkname = %q; want %q", g, e)
+	}
+}
+
+type symlink struct{}
+
+func (symlink) Name() string       { return "some-symlink" }
+func (symlink) Size() int64        { return 0 }
+func (symlink) Mode() os.FileMode  { return os.ModeSymlink }
+func (symlink) ModTime() time.Time { return time.Time{} }
+func (symlink) IsDir() bool        { return false }
+func (symlink) Sys() interface{}   { return nil }

src/pkg/go/build/deps_test.go

@@ -177,7 +177,7 @@ var pkgDeps = map[string][]string{
 	},
 
 	// One of a kind.
-	"archive/tar":         {"L4", "OS"},
+	"archive/tar":         {"L4", "OS", "syscall"},
 	"archive/zip":         {"L4", "OS", "compress/flate"},
 	"compress/bzip2":      {"L4"},
 	"compress/flate":      {"L4"},