Merge pull request #65 from nalind/diffoptions

Make Diff() methods take an optional *DiffOptions

cmd/containers-storage/diff.go

@@ -14,6 +14,7 @@ import (
 var (
 	applyDiffFile    = ""
 	diffFile         = ""
+	diffUncompressed = false
 	diffGzip         = false
 	diffBzip2        = false
 	diffXz           = false
@@ -71,28 +72,27 @@ func diff(flags *mflag.FlagSet, action string, m storage.Store, args []string) i
 		diffStream = f
 		defer f.Close()
 	}
-	reader, err := m.Diff(from, to)
-	if err != nil {
-		fmt.Fprintf(os.Stderr, "%v\n", err)
-		return 1
-	}
-	if diffGzip || diffBzip2 || diffXz {
-		compression := archive.Uncompressed
+
+	options := storage.DiffOptions{}
+	if diffUncompressed || diffGzip || diffBzip2 || diffXz {
+		c := archive.Uncompressed
 		if diffGzip {
-			compression = archive.Gzip
-		} else if diffBzip2 {
-			compression = archive.Bzip2
-		} else if diffXz {
-			compression = archive.Xz
+			c = archive.Gzip
 		}
-		compressor, err := archive.CompressStream(diffStream, compression)
+		if diffBzip2 {
+			c = archive.Bzip2
+		}
+		if diffXz {
+			c = archive.Xz
+		}
+		options.Compression = &c
+	}
+
+	reader, err := m.Diff(from, to, &options)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "%v\n", err)
 		return 1
 	}
-		diffStream = compressor
-		defer compressor.Close()
-	}
 	_, err = io.Copy(diffStream, reader)
 	reader.Close()
 	if err != nil {
@@ -171,9 +171,10 @@ func init() {
 		action:      diff,
 		addFlags: func(flags *mflag.FlagSet, cmd *command) {
 			flags.StringVar(&diffFile, []string{"-file", "f"}, "", "Write to file instead of stdout")
+			flags.BoolVar(&diffUncompressed, []string{"-uncompressed", "u"}, diffUncompressed, "Use no compression")
 			flags.BoolVar(&diffGzip, []string{"-gzip", "c"}, diffGzip, "Compress using gzip")
-			flags.BoolVar(&diffBzip2, []string{"-bzip2", "-bz2", "b"}, diffBzip2, "Compress using bzip2")
-			flags.BoolVar(&diffXz, []string{"-xz", "x"}, diffXz, "Compress using xz")
+			flags.BoolVar(&diffBzip2, []string{"-bzip2", "-bz2", "b"}, diffBzip2, "Compress using bzip2 (not currently supported)")
+			flags.BoolVar(&diffXz, []string{"-xz", "x"}, diffXz, "Compress using xz (not currently supported)")
 		},
 	})
 	commands = append(commands, command{

docs/containers-storage-diff.md

@@ -19,9 +19,14 @@ Write the diff to the specified file instead of stdout.
 
 **-c | --gzip**
 
-Compress the diff using gzip compression.  If the layer was populated by a
-layer diff, and that layer diff was compressed, this will be done
-automatically.
+Force the diff to be compressed using gzip compression.  If the layer was
+populated by a layer diff, and that layer diff was compressed, this will be
+done automatically.
+
+**-u | --uncompressed**
+
+Force the diff to be uncompressed.  If the layer was populated by a layer diff,
+and that layer diff was compressed, it will be decompressed for output.
 
 ## EXAMPLE
 **oci-storage diff my-base-layer**

layers.go

@@ -81,6 +81,12 @@ type layerMountPoint struct {
 	MountCount int    `json:"count"`
 }
 
+// DiffOptions override the default behavior of Diff() methods.
+type DiffOptions struct {
+	// Compression, if set overrides the default compressor when generating a diff.
+	Compression *archive.Compression
+}
+
 // ROLayerStore wraps a graph driver, adding the ability to refer to layers by
 // name, and keeping track of parent-child relationships, along with a list of
 // all known layers.
@@ -107,8 +113,9 @@ type ROLayerStore interface {
 	// Diff produces a tarstream which can be applied to a layer with the contents
 	// of the first layer to produce a layer with the contents of the second layer.
 	// By default, the parent of the second layer is used as the first
-	// layer, so it need not be specified.
-	Diff(from, to string) (io.ReadCloser, error)
+	// layer, so it need not be specified.  Options can be used to override
+	// default behavior, but are also not required.
+	Diff(from, to string, options *DiffOptions) (io.ReadCloser, error)
 
 	// DiffSize produces an estimate of the length of the tarstream which would be
 	// produced by Diff.
@@ -741,13 +748,15 @@ func (r *layerStore) newFileGetter(id string) (drivers.FileGetCloser, error) {
 	}, nil
 }
 
-func (r *layerStore) Diff(from, to string) (io.ReadCloser, error) {
+func (r *layerStore) Diff(from, to string, options *DiffOptions) (io.ReadCloser, error) {
 	var metadata storage.Unpacker
 
 	from, to, toLayer, err := r.findParentAndLayer(from, to)
 	if err != nil {
 		return nil, ErrLayerUnknown
 	}
+	// Default to applying the type of encryption that we noted was used
+	// for the layerdiff when it was applied.
 	compression := archive.Uncompressed
 	if cflag, ok := toLayer.Flags[compressionFlag]; ok {
 		if ctype, ok := cflag.(float64); ok {
@@ -756,6 +765,11 @@ func (r *layerStore) Diff(from, to string) (io.ReadCloser, error) {
 			compression = archive.Compression(ctype)
 		}
 	}
+	// If a particular compression type (or no compression) was selected,
+	// use that instead.
+	if options != nil && options.Compression != nil {
+		compression = *options.Compression
+	}
 	if from != toLayer.Parent {
 		diff, err := r.driver.Diff(to, from)
 		if err == nil && (compression != archive.Uncompressed) {

store.go

@@ -298,8 +298,8 @@ type Store interface {
 	DiffSize(from, to string) (int64, error)
 
 	// Diff returns the tarstream which would specify the changes returned by
-	// Changes.
-	Diff(from, to string) (io.ReadCloser, error)
+	// Changes.  If options are passed in, they can override default behaviors.
+	Diff(from, to string, options *DiffOptions) (io.ReadCloser, error)
 
 	// ApplyDiff applies a tarstream to a layer.  Information about the tarstream
 	// is cached with the layer.  Typically, a layer which is populated using a
@@ -1747,7 +1747,7 @@ func (s *store) DiffSize(from, to string) (int64, error) {
 	return -1, ErrLayerUnknown
 }
 
-func (s *store) Diff(from, to string) (io.ReadCloser, error) {
+func (s *store) Diff(from, to string, options *DiffOptions) (io.ReadCloser, error) {
 	rlstore, err := s.LayerStore()
 	if err != nil {
 		return nil, err
@@ -1764,7 +1764,7 @@ func (s *store) Diff(from, to string) (io.ReadCloser, error) {
 			rlstore.Load()
 		}
 		if rlstore.Exists(to) {
-			return rlstore.Diff(from, to)
+			return rlstore.Diff(from, to, options)
 		}
 	}
 	return nil, ErrLayerUnknown