archive/zip: add functions to convert between os.FileInfo & FileHeader

Fixes #2186

R=golang-dev, gri, adg
CC=golang-dev
https://golang.org/cl/5579044

src/pkg/archive/zip/reader_test.go

@@ -250,13 +250,9 @@ func readTestFile(t *testing.T, ft ZipTestFile, f *File) {
 }
 
 func testFileMode(t *testing.T, f *File, want os.FileMode) {
-	mode, err := f.Mode()
+	mode := f.Mode()
 	if want == 0 {
-		if err == nil {
-			t.Errorf("%s mode: got %v, want none", f.Name, mode)
-		}
-	} else if err != nil {
-		t.Errorf("%s mode: %s", f.Name, err)
+		t.Errorf("%s mode: got %v, want none", f.Name, mode)
 	} else if mode != want {
 		t.Errorf("%s mode: want %v, got %v", f.Name, want, mode)
 	}

src/pkg/archive/zip/struct.go

@@ -12,6 +12,7 @@ This package does not support ZIP64 or disk spanning.
 package zip
 
 import (
+	"errors"
 	"os"
 	"time"
 )
@@ -55,6 +56,38 @@ type FileHeader struct {
 	Comment          string
 }
 
+// FileInfo returns an os.FileInfo for the FileHeader.
+func (fh *FileHeader) FileInfo() os.FileInfo {
+	return headerFileInfo{fh}
+}
+
+// headerFileInfo implements os.FileInfo.
+type headerFileInfo struct {
+	fh *FileHeader
+}
+
+func (fi headerFileInfo) Name() string       { return fi.fh.Name }
+func (fi headerFileInfo) Size() int64        { return int64(fi.fh.UncompressedSize) }
+func (fi headerFileInfo) IsDir() bool        { return fi.Mode().IsDir() }
+func (fi headerFileInfo) ModTime() time.Time { return fi.fh.ModTime() }
+func (fi headerFileInfo) Mode() os.FileMode  { return fi.fh.Mode() }
+
+// FileInfoHeader creates a partially-populated FileHeader from an
+// os.FileInfo.
+func FileInfoHeader(fi os.FileInfo) (*FileHeader, error) {
+	size := fi.Size()
+	if size > (1<<32 - 1) {
+		return nil, errors.New("zip: file over 4GB")
+	}
+	fh := &FileHeader{
+		Name:             fi.Name(),
+		UncompressedSize: uint32(size),
+	}
+	fh.SetModTime(fi.ModTime())
+	fh.SetMode(fi.Mode())
+	return fh, nil
+}
+
 type directoryEnd struct {
 	diskNbr            uint16 // unused
 	dirDiskNbr         uint16 // unused
@@ -131,8 +164,7 @@ const (
 )
 
 // Mode returns the permission and mode bits for the FileHeader.
-// An error is returned in case the information is not available.
-func (h *FileHeader) Mode() (mode os.FileMode, err error) {
+func (h *FileHeader) Mode() (mode os.FileMode) {
 	switch h.CreatorVersion >> 8 {
 	case creatorUnix, creatorMacOSX:
 		mode = unixModeToFileMode(h.ExternalAttrs >> 16)
@@ -142,7 +174,7 @@ func (h *FileHeader) Mode() (mode os.FileMode, err error) {
 	if len(h.Name) > 0 && h.Name[len(h.Name)-1] == '/' {
 		mode |= os.ModeDir
 	}
-	return mode, nil
+	return mode
 }
 
 // SetMode changes the permission and mode bits for the FileHeader.

src/pkg/archive/zip/zip_test.go

@@ -10,6 +10,7 @@ import (
 	"bytes"
 	"fmt"
 	"io"
+	"reflect"
 	"testing"
 	"time"
 )
@@ -66,3 +67,22 @@ func TestModTime(t *testing.T) {
 		t.Errorf("times don't match: got %s, want %s", outTime, testTime)
 	}
 }
+
+func TestFileHeaderRoundTrip(t *testing.T) {
+	fh := &FileHeader{
+		Name:             "foo.txt",
+		UncompressedSize: 987654321,
+		ModifiedTime:     1234,
+		ModifiedDate:     5678,
+	}
+	fi := fh.FileInfo()
+	fh2, err := FileInfoHeader(fi)
+
+	// Ignore these fields:
+	fh2.CreatorVersion = 0
+	fh2.ExternalAttrs = 0
+
+	if !reflect.DeepEqual(fh, fh2) {
+		t.Errorf("mismatch\n input=%#v\noutput=%#v\nerr=%v", fh, fh2, err)
+	}
+}