os synlink use related path

Author: izouxv

basepath.go

@@ -216,7 +216,11 @@ func (b *BasePathFs) ReadlinkIfPossible(name string) (string, error) {
 		return "", &os.PathError{Op: "readlink", Path: name, Err: err}
 	}
 	if reader, ok := b.source.(LinkReader); ok {
-		return reader.ReadlinkIfPossible(name)
+		srcPath, err := reader.ReadlinkIfPossible(name)
+		if err != nil {
+			return "", err
+		}
+		return strings.TrimPrefix(srcPath, filepath.Clean(b.path)), nil
 	}
 	return "", &os.PathError{Op: "readlink", Path: name, Err: ErrNoReadlink}
 }

os.go

@@ -16,6 +16,7 @@ package afero
 
 import (
 	"os"
+	"path/filepath"
 	"time"
 )
 
@@ -105,9 +106,18 @@ func (OsFs) LstatIfPossible(name string) (os.FileInfo, bool, error) {
 }
 
 func (OsFs) SymlinkIfPossible(oldname, newname string) error {
-	return os.Symlink(oldname, newname)
+	relpath, err := filepath.Rel(newname, oldname)
+	if err != nil {
+		return &os.LinkError{Op: "symlink", Old: oldname, New: newname, Err: err}
+	}
+	return os.Symlink(relpath, newname)
 }
 
 func (OsFs) ReadlinkIfPossible(name string) (string, error) {
-	return os.Readlink(name)
+	path, err := os.Readlink(name)
+	if err != nil {
+		return "", err
+	}
+	pathAbs := filepath.Clean(filepath.Join(name, path))
+	return pathAbs, nil
 }

symlink_test.go

@@ -132,14 +132,15 @@ func TestReadlinkIfPossible(t *testing.T) {
 	}
 
 	testRead := func(r LinkReader, name string, output *string) {
-		_, err := r.ReadlinkIfPossible(name)
+		str, err := r.ReadlinkIfPossible(name)
 		if (err != nil) && (output == nil) {
 			t.Fatalf("Error reading link, expected success, got error: %v", err)
 		} else if (err == nil) && (output != nil) {
 			t.Fatalf("Error reading link, succeeded when expecting error: %v", *output)
 		} else if err != nil && err.Error() != *output && !strings.HasSuffix(err.Error(), *output) {
 			t.Fatalf("Error reading link, expected error '%v', instead received '%v'", *output, err)
 		}
+		t.Logf("str: %v", str)
 	}
 
 	notSupported := ErrNoReadlink.Error()