Make the merge func in UnionFile configureable

cacheOnReadFs.go

@@ -205,7 +205,7 @@ func (u *CacheOnReadFs) OpenFile(name string, flag int, perm os.FileMode) (File,
 			bfi.Close() // oops, what if O_TRUNC was set and file opening in the layer failed...?
 			return nil, err
 		}
-		return &UnionFile{base: bfi, layer: lfi}, nil
+		return &UnionFile{Base: bfi, Layer: lfi}, nil
 	}
 	return u.layer.OpenFile(name, flag, perm)
 }
@@ -251,7 +251,7 @@ func (u *CacheOnReadFs) Open(name string) (File, error) {
 	if err != nil && bfile == nil {
 		return nil, err
 	}
-	return &UnionFile{base: bfile, layer: lfile}, nil
+	return &UnionFile{Base: bfile, Layer: lfile}, nil
 }
 
 func (u *CacheOnReadFs) Mkdir(name string, perm os.FileMode) error {
@@ -286,5 +286,5 @@ func (u *CacheOnReadFs) Create(name string) (File, error) {
 		bfh.Close()
 		return nil, err
 	}
-	return &UnionFile{base: bfh, layer: lfh}, nil
+	return &UnionFile{Base: bfh, Layer: lfh}, nil
 }

composite_test.go

@@ -51,7 +51,6 @@ func CleanupTempDirs(t *testing.T) {
 func TestUnionCreateExisting(t *testing.T) {
 	base := &MemMapFs{}
 	roBase := &ReadOnlyFs{source: base}
-
 	ufs := NewCopyOnWriteFs(roBase, &MemMapFs{})
 
 	base.MkdirAll("/home/test", 0777)

copyOnWriteFs.go

@@ -258,7 +258,7 @@ func (u *CopyOnWriteFs) Open(name string) (File, error) {
 		return nil, fmt.Errorf("BaseErr: %v\nOverlayErr: %v", bErr, lErr)
 	}
 
-	return &UnionFile{base: bfile, layer: lfile}, nil
+	return &UnionFile{Base: bfile, Layer: lfile}, nil
 }
 
 func (u *CopyOnWriteFs) Mkdir(name string, perm os.FileMode) error {

copyOnWriteFs_test.go

@@ -8,6 +8,7 @@ func TestCopyOnWrite(t *testing.T) {
 	base := NewOsFs()
 	roBase := NewReadOnlyFs(base)
 	ufs := NewCopyOnWriteFs(roBase, NewMemMapFs())
+
 	fs = ufs
 	err = fs.MkdirAll("nonexistent/directory/", 0744)
 	if err != nil {

unionFile.go

@@ -21,32 +21,33 @@ import (
 // successful read in the overlay will move the cursor position in the base layer
 // by the number of bytes read.
 type UnionFile struct {
-	base  File
-	layer File
-	off   int
-	files []os.FileInfo
+	Base   File
+	Layer  File
+	Merger DirsMerger
+	off    int
+	files  []os.FileInfo
 }
 
 func (f *UnionFile) Close() error {
 	// first close base, so we have a newer timestamp in the overlay. If we'd close
 	// the overlay first, we'd get a cacheStale the next time we access this file
 	// -> cache would be useless ;-)
-	if f.base != nil {
-		f.base.Close()
+	if f.Base != nil {
+		f.Base.Close()
 	}
-	if f.layer != nil {
-		return f.layer.Close()
+	if f.Layer != nil {
+		return f.Layer.Close()
 	}
 	return BADFD
 }
 
 func (f *UnionFile) Read(s []byte) (int, error) {
-	if f.layer != nil {
-		n, err := f.layer.Read(s)
-		if (err == nil || err == io.EOF) && f.base != nil {
+	if f.Layer != nil {
+		n, err := f.Layer.Read(s)
+		if (err == nil || err == io.EOF) && f.Base != nil {
 			// advance the file position also in the base file, the next
 			// call may be a write at this position (or a seek with SEEK_CUR)
-			if _, seekErr := f.base.Seek(int64(n), os.SEEK_CUR); seekErr != nil {
+			if _, seekErr := f.Base.Seek(int64(n), os.SEEK_CUR); seekErr != nil {
 				// only overwrite err in case the seek fails: we need to
 				// report an eventual io.EOF to the caller
 				err = seekErr
@@ -54,123 +55,135 @@ func (f *UnionFile) Read(s []byte) (int, error) {
 		}
 		return n, err
 	}
-	if f.base != nil {
-		return f.base.Read(s)
+	if f.Base != nil {
+		return f.Base.Read(s)
 	}
 	return 0, BADFD
 }
 
 func (f *UnionFile) ReadAt(s []byte, o int64) (int, error) {
-	if f.layer != nil {
-		n, err := f.layer.ReadAt(s, o)
-		if (err == nil || err == io.EOF) && f.base != nil {
-			_, err = f.base.Seek(o+int64(n), os.SEEK_SET)
+	if f.Layer != nil {
+		n, err := f.Layer.ReadAt(s, o)
+		if (err == nil || err == io.EOF) && f.Base != nil {
+			_, err = f.Base.Seek(o+int64(n), os.SEEK_SET)
 		}
 		return n, err
 	}
-	if f.base != nil {
-		return f.base.ReadAt(s, o)
+	if f.Base != nil {
+		return f.Base.ReadAt(s, o)
 	}
 	return 0, BADFD
 }
 
 func (f *UnionFile) Seek(o int64, w int) (pos int64, err error) {
-	if f.layer != nil {
-		pos, err = f.layer.Seek(o, w)
-		if (err == nil || err == io.EOF) && f.base != nil {
-			_, err = f.base.Seek(o, w)
+	if f.Layer != nil {
+		pos, err = f.Layer.Seek(o, w)
+		if (err == nil || err == io.EOF) && f.Base != nil {
+			_, err = f.Base.Seek(o, w)
 		}
 		return pos, err
 	}
-	if f.base != nil {
-		return f.base.Seek(o, w)
+	if f.Base != nil {
+		return f.Base.Seek(o, w)
 	}
 	return 0, BADFD
 }
 
 func (f *UnionFile) Write(s []byte) (n int, err error) {
-	if f.layer != nil {
-		n, err = f.layer.Write(s)
-		if err == nil && f.base != nil { // hmm, do we have fixed size files where a write may hit the EOF mark?
-			_, err = f.base.Write(s)
+	if f.Layer != nil {
+		n, err = f.Layer.Write(s)
+		if err == nil && f.Base != nil { // hmm, do we have fixed size files where a write may hit the EOF mark?
+			_, err = f.Base.Write(s)
 		}
 		return n, err
 	}
-	if f.base != nil {
-		return f.base.Write(s)
+	if f.Base != nil {
+		return f.Base.Write(s)
 	}
 	return 0, BADFD
 }
 
 func (f *UnionFile) WriteAt(s []byte, o int64) (n int, err error) {
-	if f.layer != nil {
-		n, err = f.layer.WriteAt(s, o)
-		if err == nil && f.base != nil {
-			_, err = f.base.WriteAt(s, o)
+	if f.Layer != nil {
+		n, err = f.Layer.WriteAt(s, o)
+		if err == nil && f.Base != nil {
+			_, err = f.Base.WriteAt(s, o)
 		}
 		return n, err
 	}
-	if f.base != nil {
-		return f.base.WriteAt(s, o)
+	if f.Base != nil {
+		return f.Base.WriteAt(s, o)
 	}
 	return 0, BADFD
 }
 
 func (f *UnionFile) Name() string {
-	if f.layer != nil {
-		return f.layer.Name()
+	if f.Layer != nil {
+		return f.Layer.Name()
 	}
-	return f.base.Name()
+	return f.Base.Name()
 }
 
-// UnionKey can be implemented to use an alternate key than FileInfo.Name when
-// weaving the two directories together. The use case(s) are uncommon and special,
-// but this will allow a union file system with multiple files with the same filename.
-// This needs to be implemented by your own implementation of os.FileInfo as
-// returned in Readdir.
-type UnionKey interface {
-	AferoUnionKey() string
-}
+// DirsMerger is how UnionFile weaves two directories together.
+// It takes the FileInfo slices from the layer and the base and returns a
+// single view.
+type DirsMerger func(lofi, bofi []os.FileInfo) ([]os.FileInfo, error)
 
-func (f *UnionFile) key(ofi os.FileInfo) string {
-	switch tp := ofi.(type) {
-	case UnionKey:
-		return tp.AferoUnionKey()
-	default:
-		return tp.Name()
+var defaultUnionMergeDirsFn = func(lofi, bofi []os.FileInfo) ([]os.FileInfo, error) {
+	var files = make(map[string]os.FileInfo)
+
+	for _, fi := range lofi {
+		files[fi.Name()] = fi
 	}
+
+	for _, fi := range bofi {
+		if _, exists := files[fi.Name()]; !exists {
+			files[fi.Name()] = fi
+		}
+	}
+
+	rfi := make([]os.FileInfo, len(files))
+
+	i := 0
+	for _, fi := range files {
+		rfi[i] = fi
+		i++
+	}
+
+	return rfi, nil
+
 }
 
 // Readdir will weave the two directories together and
 // return a single view of the overlayed directories
 func (f *UnionFile) Readdir(c int) (ofi []os.FileInfo, err error) {
+	var merge DirsMerger = f.Merger
+	if merge == nil {
+		merge = defaultUnionMergeDirsFn
+	}
+
 	if f.off == 0 {
-		var files = make(map[string]os.FileInfo)
-		var rfi []os.FileInfo
-		if f.layer != nil {
-			rfi, err = f.layer.Readdir(-1)
+		var lfi []os.FileInfo
+		if f.Layer != nil {
+			lfi, err = f.Layer.Readdir(-1)
 			if err != nil {
 				return nil, err
 			}
-			for _, fi := range rfi {
-				files[f.key(fi)] = fi
-			}
 		}
 
-		if f.base != nil {
-			rfi, err = f.base.Readdir(-1)
+		var bfi []os.FileInfo
+		if f.Base != nil {
+			bfi, err = f.Base.Readdir(-1)
 			if err != nil {
 				return nil, err
 			}
-			for _, fi := range rfi {
-				if _, exists := files[fi.Name()]; !exists {
-					files[f.key(fi)] = fi
-				}
-			}
+
 		}
-		for _, fi := range files {
-			f.files = append(f.files, fi)
+		merged, err := merge(lfi, bfi)
+		if err != nil {
+			return nil, err
 		}
+		f.files = append(f.files, merged...)
 	}
 	if c == -1 {
 		return f.files[f.off:], nil
@@ -192,53 +205,53 @@ func (f *UnionFile) Readdirnames(c int) ([]string, error) {
 }
 
 func (f *UnionFile) Stat() (os.FileInfo, error) {
-	if f.layer != nil {
-		return f.layer.Stat()
+	if f.Layer != nil {
+		return f.Layer.Stat()
 	}
-	if f.base != nil {
-		return f.base.Stat()
+	if f.Base != nil {
+		return f.Base.Stat()
 	}
 	return nil, BADFD
 }
 
 func (f *UnionFile) Sync() (err error) {
-	if f.layer != nil {
-		err = f.layer.Sync()
-		if err == nil && f.base != nil {
-			err = f.base.Sync()
+	if f.Layer != nil {
+		err = f.Layer.Sync()
+		if err == nil && f.Base != nil {
+			err = f.Base.Sync()
 		}
 		return err
 	}
-	if f.base != nil {
-		return f.base.Sync()
+	if f.Base != nil {
+		return f.Base.Sync()
 	}
 	return BADFD
 }
 
 func (f *UnionFile) Truncate(s int64) (err error) {
-	if f.layer != nil {
-		err = f.layer.Truncate(s)
-		if err == nil && f.base != nil {
-			err = f.base.Truncate(s)
+	if f.Layer != nil {
+		err = f.Layer.Truncate(s)
+		if err == nil && f.Base != nil {
+			err = f.Base.Truncate(s)
 		}
 		return err
 	}
-	if f.base != nil {
-		return f.base.Truncate(s)
+	if f.Base != nil {
+		return f.Base.Truncate(s)
 	}
 	return BADFD
 }
 
 func (f *UnionFile) WriteString(s string) (n int, err error) {
-	if f.layer != nil {
-		n, err = f.layer.WriteString(s)
-		if err == nil && f.base != nil {
-			_, err = f.base.WriteString(s)
+	if f.Layer != nil {
+		n, err = f.Layer.WriteString(s)
+		if err == nil && f.Base != nil {
+			_, err = f.Base.WriteString(s)
 		}
 		return n, err
 	}
-	if f.base != nil {
-		return f.base.WriteString(s)
+	if f.Base != nil {
+		return f.Base.WriteString(s)
 	}
 	return 0, BADFD
 }