Add support for zstd compressed layers

dive/image/docker/image_archive.go

@@ -11,6 +11,8 @@ import (
 	"path"
 	"strings"
 
+	"github.com/klauspost/compress/zstd"
+
 	"github.com/wagoodman/dive/dive/filetree"
 	"github.com/wagoodman/dive/dive/image"
 )
@@ -77,6 +79,26 @@ func NewImageArchive(tarFile io.ReadCloser) (*ImageArchive, error) {
 					return img, err
 				}
 
+				// add the layer to the image
+				img.layerMap[tree.Name] = tree
+			} else if strings.HasSuffix(name, ".tar.zst") || strings.HasSuffix(name, ".zst") {
+				currentLayer++
+
+				// Add zstd reader
+				zst, err := zstd.NewReader(tarReader)
+				if err != nil {
+					return img, err
+				}
+
+				// Add tar reader
+				layerReader := tar.NewReader(zst)
+
+				// Process layer
+				tree, err := processLayerTar(name, layerReader)
+				if err != nil {
+					return img, err
+				}
+
 				// add the layer to the image
 				img.layerMap[tree.Name] = tree
 			} else if strings.HasSuffix(name, ".json") || strings.HasPrefix(name, "sha256:") {
@@ -89,36 +111,47 @@ func NewImageArchive(tarFile io.ReadCloser) (*ImageArchive, error) {
 				// For the OCI-compatible image format (used since Docker 25), use mime sniffing
 				// but limit this to only the blobs/ (containing the config, and the layers)
 
-				// The idea here is that we try various formats in turn, and those tries should
-				// never consume more bytes than this buffer contains so we can start again.
+				// The idea here is that we read the first few bytes of the file to determine if
+				// it's encrypted with gzip or zstd. If it is, we'll decompress it first.
+
+				// There is one edge case to consider: if the tar file's first file's name begins
+				// with 0x1f8b or 0x28b52ffd, the file will be erronously decompressed. This is
+				// very unlikely: filenames usually are not binary, but it's worth mentioning.
 
-				// 512 bytes ought to be enough (as that's the size of a TAR entry header),
-				// but play it safe with 1024 bytes. This should also include very small layers
-				// (unless they've also been gzipped, but Docker does not appear to do it)
 				buffer := make([]byte, 1024)
 				n, err := io.ReadFull(tarReader, buffer)
+
 				if err != nil && err != io.ErrUnexpectedEOF {
 					return img, err
 				}
 
-				// Only try reading a TAR if file is "big enough"
-				if n == cap(buffer) {
-					var unwrappedReader io.Reader
+				var unwrappedReader io.Reader
+
+				if n >= 2 && buffer[0] == 0x1f && buffer[1] == 0x8b {
+					// This is a gzipped file
 					unwrappedReader, err = gzip.NewReader(io.MultiReader(bytes.NewReader(buffer[:n]), tarReader))
 					if err != nil {
-						// Not a gzipped entry
-						unwrappedReader = io.MultiReader(bytes.NewReader(buffer[:n]), tarReader)
+						return img, err
 					}
-
-					// Try reading a TAR
-					layerReader := tar.NewReader(unwrappedReader)
-					tree, err := processLayerTar(name, layerReader)
-					if err == nil {
-						currentLayer++
-						// add the layer to the image
-						img.layerMap[tree.Name] = tree
-						continue
+				} else if n >= 4 && buffer[0] == 0x28 && buffer[1] == 0xb5 && buffer[2] == 0x2f && buffer[3] == 0xfd {
+					// This is a zstd file
+					unwrappedReader, err = zstd.NewReader(io.MultiReader(bytes.NewReader(buffer[:n]), tarReader))
+					if err != nil {
+						return img, err
 					}
+				} else {
+					// This is not a compressed file
+					unwrappedReader = io.MultiReader(bytes.NewReader(buffer[:n]), tarReader)
+				}
+
+				// Try reading a TAR
+				layerReader := tar.NewReader(unwrappedReader)
+				tree, err := processLayerTar(name, layerReader)
+				if err == nil {
+					currentLayer++
+					// add the layer to the image
+					img.layerMap[tree.Name] = tree
+					continue
 				}
 
 				// Not a TAR (or smaller than our buffer), might be a JSON file

go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/dustin/go-humanize v1.0.0
 	github.com/fatih/color v1.7.0
 	github.com/google/uuid v1.1.1
+	github.com/klauspost/compress v1.17.6
 	github.com/logrusorgru/aurora v0.0.0-20190803045625-94edacc10f9b
 	github.com/lunixbochs/vtclean v1.0.0
 	github.com/mitchellh/go-homedir v1.1.0

go.sum

@@ -85,6 +85,8 @@ github.com/julienschmidt/httprouter v1.2.0/go.mod h1:SYymIcj16QtmaHHD7aYtjjsJG7V
 github.com/kisielk/errcheck v1.1.0/go.mod h1:EZBBE59ingxPouuu3KfxchcWSUPOHkagtvWXihfKN4Q=
 github.com/kisielk/errcheck v1.5.0/go.mod h1:pFxgyoBC7bSaBwPgfKdkLd5X25qrDl4LWUI2bnpBCr8=
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
+github.com/klauspost/compress v1.17.6 h1:60eq2E/jlfwQXtvZEeBUYADs+BwKBWURIY+Gj2eRGjI=
+github.com/klauspost/compress v1.17.6/go.mod h1:/dCuZOvVtNoHsyb+cuJD3itjs3NbnF6KH9zAO4BDxPM=
 github.com/konsorten/go-windows-terminal-sequences v1.0.1/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
 github.com/konsorten/go-windows-terminal-sequences v1.0.2 h1:DB17ag19krx9CFsz4o3enTrPXyIXCl+2iCXH/aMAp9s=
 github.com/konsorten/go-windows-terminal-sequences v1.0.2/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=