compression: let algorithms register a MIME type

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

manifest/common.go

@@ -68,7 +68,7 @@ func compressionVariantMIMEType(variantTable []compressionMIMETypeSet, mimeType
 			if mt == mimeType { // Found the variant
 				name := mtsUncompressed
 				if algorithm != nil {
-					name = algorithm.Name()
+					name = algorithm.MIME()
 				}
 				if res, ok := variants[name]; ok {
 					if res != mtsUnsupportedMIMEType {

pkg/compression/compression.go

@@ -20,13 +20,13 @@ type Algorithm = types.Algorithm
 
 var (
 	// Gzip compression.
-	Gzip = internal.NewAlgorithm("gzip", []byte{0x1F, 0x8B, 0x08}, GzipDecompressor, gzipCompressor)
+	Gzip = internal.NewAlgorithm("gzip", "gzip", []byte{0x1F, 0x8B, 0x08}, GzipDecompressor, gzipCompressor)
 	// Bzip2 compression.
-	Bzip2 = internal.NewAlgorithm("bzip2", []byte{0x42, 0x5A, 0x68}, Bzip2Decompressor, bzip2Compressor)
+	Bzip2 = internal.NewAlgorithm("bzip2", "bzip2", []byte{0x42, 0x5A, 0x68}, Bzip2Decompressor, bzip2Compressor)
 	// Xz compression.
-	Xz = internal.NewAlgorithm("Xz", []byte{0xFD, 0x37, 0x7A, 0x58, 0x5A, 0x00}, XzDecompressor, xzCompressor)
+	Xz = internal.NewAlgorithm("Xz", "xz", []byte{0xFD, 0x37, 0x7A, 0x58, 0x5A, 0x00}, XzDecompressor, xzCompressor)
 	// Zstd compression.
-	Zstd = internal.NewAlgorithm("zstd", []byte{0x28, 0xb5, 0x2f, 0xfd}, ZstdDecompressor, zstdCompressor)
+	Zstd = internal.NewAlgorithm("zstd", "zstd", []byte{0x28, 0xb5, 0x2f, 0xfd}, ZstdDecompressor, zstdCompressor)
 
 	compressionAlgorithms = map[string]Algorithm{
 		Gzip.Name():  Gzip,

pkg/compression/internal/types.go

@@ -13,6 +13,7 @@ type DecompressorFunc func(io.Reader) (io.ReadCloser, error)
 // Algorithm is a compression algorithm that can be used for CompressStream.
 type Algorithm struct {
 	name         string
+	mime         string
 	prefix       []byte
 	decompressor DecompressorFunc
 	compressor   CompressorFunc
@@ -21,9 +22,10 @@ type Algorithm struct {
 // 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 {
+func NewAlgorithm(name, mime string, prefix []byte, decompressor DecompressorFunc, compressor CompressorFunc) Algorithm {
 	return Algorithm{
 		name:         name,
+		mime:         mime,
 		prefix:       prefix,
 		decompressor: decompressor,
 		compressor:   compressor,
@@ -35,6 +37,11 @@ func (c Algorithm) Name() string {
 	return c.name
 }
 
+// Name returns the MIME type to use for the compression algorithm.
+func (c Algorithm) MIME() string {
+	return c.mime
+}
+
 // 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.