internal/fs: clone symlinks on Windows and fall back to file copying

Signed-off-by: Ibrahim AshShohail <ibra.sho@gmail.com>

internal/fs/fs.go

@@ -9,7 +9,9 @@ import (
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"runtime"
 	"strings"
+	"syscall"
 	"unicode"
 
 	"github.com/pkg/errors"
@@ -270,9 +272,25 @@ func CopyDir(src, dst string) error {
 // the copied data is synced/flushed to stable storage.
 func copyFile(src, dst string) (err error) {
 	if sym, err := IsSymlink(src); err != nil {
-		return err
+		return errors.Wrap(err, "symlink check failed")
 	} else if sym {
-		return cloneSymlink(src, dst)
+		if err := cloneSymlink(src, dst); err != nil {
+			if runtime.GOOS == "windows" {
+				// If cloning the symlink fails on Windows because the user
+				// does not have the required privileges, ignore the error and
+				// fall back to copying the file contents.
+				//
+				// ERROR_PRIVILEGE_NOT_HELD is 1314 (0x522):
+				// https://msdn.microsoft.com/en-us/library/windows/desktop/ms681385(v=vs.85).aspx
+				if lerr, ok := err.(*os.LinkError); ok && lerr.Err != syscall.Errno(1314) {
+					return err
+				}
+			} else {
+				return err
+			}
+		} else {
+			return nil
+		}
 	}
 
 	in, err := os.Open(src)
@@ -285,30 +303,22 @@ func copyFile(src, dst string) (err error) {
 	if err != nil {
 		return
 	}
-	defer func() {
-		if e := out.Close(); e != nil {
-			err = e
-		}
-	}()
+	defer out.Close()
 
-	_, err = io.Copy(out, in)
-	if err != nil {
+	if _, err = io.Copy(out, in); err != nil {
 		return
 	}
 
-	err = out.Sync()
-	if err != nil {
+	if err = out.Sync(); err != nil {
 		return
 	}
 
 	si, err := os.Stat(src)
 	if err != nil {
 		return
 	}
+
 	err = os.Chmod(dst, si.Mode())
-	if err != nil {
-		return
-	}
 
 	return
 }
@@ -318,15 +328,10 @@ func copyFile(src, dst string) (err error) {
 func cloneSymlink(sl, dst string) error {
 	resolved, err := os.Readlink(sl)
 	if err != nil {
-		return errors.Wrap(err, "failed to resolve symlink")
-	}
-
-	err = os.Symlink(resolved, dst)
-	if err != nil {
-		return errors.Wrapf(err, "failed to create symlink %s to %s", dst, resolved)
+		return err
 	}
 
-	return nil
+	return os.Symlink(resolved, dst)
 }
 
 // IsDir determines is the path given is a directory or not.

internal/fs/fs_test.go

@@ -504,43 +504,46 @@ func TestCopyFileSymlink(t *testing.T) {
 	h.TempDir(".")
 
 	testcases := map[string]string{
-		filepath.Join("./testdata/symlinks/file-symlink"):    filepath.Join(h.Path("."), "dst-file"),
-		filepath.Join("./testdata/symlinks/dir-symlink"):     filepath.Join(h.Path("."), "dst-dir"),
-		filepath.Join("./testdata/symlinks/invalid-symlink"): filepath.Join(h.Path("."), "invalid-symlink"),
+		filepath.Join("./testdata/symlinks/file-symlink"):         filepath.Join(h.Path("."), "dst-file"),
+		filepath.Join("./testdata/symlinks/windows-file-symlink"): filepath.Join(h.Path("."), "windows-dst-file"),
+		filepath.Join("./testdata/symlinks/dir-symlink"):          filepath.Join(h.Path("."), "dst-dir"),
+		filepath.Join("./testdata/symlinks/invalid-symlink"):      filepath.Join(h.Path("."), "invalid-symlink"),
 	}
 
 	for symlink, dst := range testcases {
-		var err error
-		if err = copyFile(symlink, dst); err != nil {
-			t.Fatalf("failed to copy symlink: %s", err)
-		}
-
-		var want, got string
-
-		if runtime.GOOS == "windows" {
-			// Creating symlinks on Windows require an additional permission
-			// regular users aren't granted usually. So we copy the file
-			// content as a fall back instead of creating a real symlink.
-			srcb, err := ioutil.ReadFile(symlink)
-			h.Must(err)
-			dstb, err := ioutil.ReadFile(dst)
-			h.Must(err)
-
-			want = string(srcb)
-			got = string(dstb)
-		} else {
-			want, err = os.Readlink(symlink)
-			h.Must(err)
+		t.Run(symlink, func(t *testing.T) {
+			var err error
+			if err = copyFile(symlink, dst); err != nil {
+				t.Fatalf("failed to copy symlink: %s", err)
+			}
 
-			got, err = os.Readlink(dst)
-			if err != nil {
-				t.Fatalf("could not resolve symlink: %s", err)
+			var want, got string
+
+			if runtime.GOOS == "windows" {
+				// Creating symlinks on Windows require an additional permission
+				// regular users aren't granted usually. So we copy the file
+				// content as a fall back instead of creating a real symlink.
+				srcb, err := ioutil.ReadFile(symlink)
+				h.Must(err)
+				dstb, err := ioutil.ReadFile(dst)
+				h.Must(err)
+
+				want = string(srcb)
+				got = string(dstb)
+			} else {
+				want, err = os.Readlink(symlink)
+				h.Must(err)
+
+				got, err = os.Readlink(dst)
+				if err != nil {
+					t.Fatalf("could not resolve symlink: %s", err)
+				}
 			}
-		}
 
-		if want != got {
-			t.Fatalf("resolved path is incorrect. expected %s, got %s", want, got)
-		}
+			if want != got {
+				t.Fatalf("resolved path is incorrect. expected %s, got %s", want, got)
+			}
+		})
 	}
 }
 
@@ -791,13 +794,6 @@ func TestIsNonEmptyDir(t *testing.T) {
 }
 
 func TestIsSymlink(t *testing.T) {
-	if runtime.GOOS == "windows" {
-		// XXX: creating symlinks is not supported in Go on
-		// Microsoft Windows. Skipping this this until a solution
-		// for creating symlinks is is provided.
-		t.Skip("skipping on windows")
-	}
-
 	dir, err := ioutil.TempDir("", "dep")
 	if err != nil {
 		t.Fatal(err)
@@ -818,6 +814,7 @@ func TestIsSymlink(t *testing.T) {
 
 	dirSymlink := filepath.Join(dir, "dirSymlink")
 	fileSymlink := filepath.Join(dir, "fileSymlink")
+
 	if err = os.Symlink(dirPath, dirSymlink); err != nil {
 		t.Fatal(err)
 	}

internal/fs/testdata/symlinks/windows-file-symlink

@@ -0,0 +1 @@
+C:/Users/ibrahim/go/src/github.com/golang/dep/internal/fs/testdata/test.file