Merge pull request #716 from mtrmac/compression-types

Don’t drag in compression implementations into c/image/types

pkg/compression/compression.go

@@ -7,43 +7,35 @@ import (
 	"io"
 	"io/ioutil"
 
+	"github.com/containers/image/pkg/compression/internal"
+	"github.com/containers/image/pkg/compression/types"
 	"github.com/klauspost/pgzip"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 	"github.com/ulikunitz/xz"
 )
 
 // Algorithm is a compression algorithm that can be used for CompressStream.
-type Algorithm struct {
-	name         string
-	prefix       []byte
-	decompressor DecompressorFunc
-	compressor   compressorFunc
-}
+type Algorithm = types.Algorithm
 
 var (
 	// Gzip compression.
-	Gzip = Algorithm{"gzip", []byte{0x1F, 0x8B, 0x08}, GzipDecompressor, gzipCompressor}
+	Gzip = internal.NewAlgorithm("gzip", []byte{0x1F, 0x8B, 0x08}, GzipDecompressor, gzipCompressor)
 	// Bzip2 compression.
-	Bzip2 = Algorithm{"bzip2", []byte{0x42, 0x5A, 0x68}, Bzip2Decompressor, bzip2Compressor}
+	Bzip2 = internal.NewAlgorithm("bzip2", []byte{0x42, 0x5A, 0x68}, Bzip2Decompressor, bzip2Compressor)
 	// Xz compression.
-	Xz = Algorithm{"Xz", []byte{0xFD, 0x37, 0x7A, 0x58, 0x5A, 0x00}, XzDecompressor, xzCompressor}
+	Xz = internal.NewAlgorithm("Xz", []byte{0xFD, 0x37, 0x7A, 0x58, 0x5A, 0x00}, XzDecompressor, xzCompressor)
 	// Zstd compression.
-	Zstd = Algorithm{"zstd", []byte{0x28, 0xb5, 0x2f, 0xfd}, ZstdDecompressor, zstdCompressor}
+	Zstd = internal.NewAlgorithm("zstd", []byte{0x28, 0xb5, 0x2f, 0xfd}, ZstdDecompressor, zstdCompressor)
 
 	compressionAlgorithms = map[string]Algorithm{
-		Gzip.name:  Gzip,
-		Bzip2.name: Bzip2,
-		Xz.name:    Xz,
-		Zstd.name:  Zstd,
+		Gzip.Name():  Gzip,
+		Bzip2.Name(): Bzip2,
+		Xz.Name():    Xz,
+		Zstd.Name():  Zstd,
 	}
 )
 
-// Name returns the name for the compression algorithm.
-func (c Algorithm) Name() string {
-	return c.name
-}
-
 // AlgorithmByName returns the compressor by its name
 func AlgorithmByName(name string) (Algorithm, error) {
 	algorithm, ok := compressionAlgorithms[name]
@@ -55,7 +47,7 @@ func AlgorithmByName(name string) (Algorithm, error) {
 
 // DecompressorFunc returns the decompressed stream, given a compressed stream.
 // The caller must call Close() on the decompressed stream (even if the compressed input stream does not need closing!).
-type DecompressorFunc func(io.Reader) (io.ReadCloser, error)
+type DecompressorFunc = internal.DecompressorFunc
 
 // GzipDecompressor is a DecompressorFunc for the gzip compression algorithm.
 func GzipDecompressor(r io.Reader) (io.ReadCloser, error) {
@@ -76,10 +68,6 @@ func XzDecompressor(r io.Reader) (io.ReadCloser, error) {
 	return ioutil.NopCloser(r), nil
 }
 
-// compressorFunc writes the compressed stream to the given writer using the specified compression level.
-// The caller must call Close() on the stream (even if the input stream does not need closing!).
-type compressorFunc func(io.Writer, *int) (io.WriteCloser, error)
-
 // gzipCompressor is a CompressorFunc for the gzip compression algorithm.
 func gzipCompressor(r io.Writer, level *int) (io.WriteCloser, error) {
 	if level != nil {
@@ -100,7 +88,7 @@ func xzCompressor(r io.Writer, level *int) (io.WriteCloser, error) {
 
 // CompressStream returns the compressor by its name
 func CompressStream(dest io.Writer, algo Algorithm, level *int) (io.WriteCloser, error) {
-	return algo.compressor(dest, level)
+	return internal.AlgorithmCompressor(algo)(dest, level)
 }
 
 // DetectCompressionFormat returns a DecompressorFunc if the input is recognized as a compressed format, nil otherwise.
@@ -118,10 +106,10 @@ func DetectCompressionFormat(input io.Reader) (Algorithm, DecompressorFunc, io.R
 	var retAlgo Algorithm
 	var decompressor DecompressorFunc
 	for _, algo := range compressionAlgorithms {
-		if bytes.HasPrefix(buffer[:n], algo.prefix) {
-			logrus.Debugf("Detected compression format %s", algo.name)
+		if bytes.HasPrefix(buffer[:n], internal.AlgorithmPrefix(algo)) {
+			logrus.Debugf("Detected compression format %s", algo.Name())
 			retAlgo = algo
-			decompressor = algo.decompressor
+			decompressor = internal.AlgorithmDecompressor(algo)
 			break
 		}
 	}

pkg/compression/internal/types.go

@@ -0,0 +1,57 @@
+package internal
+
+import "io"
+
+// CompressorFunc writes the compressed stream to the given writer using the specified compression level.
+// The caller must call Close() on the stream (even if the input stream does not need closing!).
+type CompressorFunc func(io.Writer, *int) (io.WriteCloser, error)
+
+// DecompressorFunc returns the decompressed stream, given a compressed stream.
+// The caller must call Close() on the decompressed stream (even if the compressed input stream does not need closing!).
+type DecompressorFunc func(io.Reader) (io.ReadCloser, error)
+
+// Algorithm is a compression algorithm that can be used for CompressStream.
+type Algorithm struct {
+	name         string
+	prefix       []byte
+	decompressor DecompressorFunc
+	compressor   CompressorFunc
+}
+
+// NewAlgorithm creates an Algorithm instance.
+// This function exists so that Algorithm instances can only be created by code that
+// is allowed to import this internal subpackage.
+func NewAlgorithm(name string, prefix []byte, decompressor DecompressorFunc, compressor CompressorFunc) Algorithm {
+	return Algorithm{
+		name:         name,
+		prefix:       prefix,
+		decompressor: decompressor,
+		compressor:   compressor,
+	}
+}
+
+// Name returns the name for the compression algorithm.
+func (c Algorithm) Name() string {
+	return c.name
+}
+
+// AlgorithmCompressor returns the compressor field of algo.
+// This is a function instead of a public method so that it is only callable from by code
+// that is allowed to import this internal subpackage.
+func AlgorithmCompressor(algo Algorithm) CompressorFunc {
+	return algo.compressor
+}
+
+// AlgorithmDecompressor returns the decompressor field of algo.
+// This is a function instead of a public method so that it is only callable from by code
+// that is allowed to import this internal subpackage.
+func AlgorithmDecompressor(algo Algorithm) DecompressorFunc {
+	return algo.decompressor
+}
+
+// AlgorithmPrefix returns the prefix field of algo.
+// This is a function instead of a public method so that it is only callable from by code
+// that is allowed to import this internal subpackage.
+func AlgorithmPrefix(algo Algorithm) []byte {
+	return algo.prefix
+}

pkg/compression/types/types.go

@@ -0,0 +1,13 @@
+package types
+
+import (
+	"github.com/containers/image/pkg/compression/internal"
+)
+
+// DecompressorFunc returns the decompressed stream, given a compressed stream.
+// The caller must call Close() on the decompressed stream (even if the compressed input stream does not need closing!).
+type DecompressorFunc = internal.DecompressorFunc
+
+// Algorithm is a compression algorithm provided and supported by pkg/compression.
+// It can’t be supplied from the outside.
+type Algorithm = internal.Algorithm

types/types.go

@@ -6,8 +6,8 @@ import (
 	"time"
 
 	"github.com/containers/image/docker/reference"
-	"github.com/containers/image/pkg/compression"
-	"github.com/opencontainers/go-digest"
+	compression "github.com/containers/image/pkg/compression/types"
+	digest "github.com/opencontainers/go-digest"
 	v1 "github.com/opencontainers/image-spec/specs-go/v1"
 )