build: handle at symbols in an oci-layout path

The buildx command line will now handle `@` symbols in the
`oci-layout://` path when used with named contexts. Instead of
assuming the `@` symbol is part of the reference digest, it will first
check that it is a valid reference digest. Otherwise, it will assume
it's part of the file path.

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

build/opt.go

@@ -558,12 +558,8 @@ func loadInputs(ctx context.Context, d *driver.DriverHandle, inp *Inputs, pw pro
 
 		// handle OCI layout
 		if localPath, ok := strings.CutPrefix(v.Path, "oci-layout://"); ok {
-			localPath, dig, hasDigest := strings.Cut(localPath, "@")
-			localPath, tag, hasTag := strings.Cut(localPath, ":")
-			if !hasTag {
-				tag = "latest"
-			}
-			if !hasDigest {
+			localPath, dig, tag := parseOCILayoutPath(localPath)
+			if dig == "" {
 				dig, err = resolveDigest(localPath, tag)
 				if err != nil {
 					return nil, errors.Wrapf(err, "oci-layout reference %q could not be resolved", v.Path)
@@ -899,7 +895,7 @@ type lazyFileWriter struct {
 
 func (w *lazyFileWriter) Write(p []byte) (int, error) {
 	if w.file == nil {
-		if err := os.MkdirAll(filepath.Dir(w.path), 0755); err != nil {
+		if err := os.MkdirAll(filepath.Dir(w.path), 0o755); err != nil {
 			return 0, err
 		}
 		f, err := os.Create(w.path)
@@ -1017,3 +1013,35 @@ func isActive(ce *client.CacheOptionsEntry) bool {
 	}
 	return ce.Attrs["token"] != "" && (ce.Attrs["url"] != "" || ce.Attrs["url_v2"] != "")
 }
+
+// parseOCILayoutPath handles the oci-layout url accepted by buildx.
+func parseOCILayoutPath(s string) (localPath, dgst, tag string) {
+	localPath = s
+
+	// Look for the digest reference. There might be multiple @ symbols
+	// in the path and the @ symbol may be part of the path or part of
+	// the digest. If we find the @ symbol, verify that it's a valid
+	// digest reference instead of just assuming it is because it
+	// might be part of the file path.
+	if i := strings.LastIndex(localPath, "@"); i >= 0 {
+		after := localPath[i+1:]
+		if reference.DigestRegexp.MatchString(after) {
+			localPath, dgst = localPath[:i], after
+		}
+	}
+
+	// Do the same with the tag. This isn't as necessary since colons
+	// aren't valid as file paths on Linux/Unix systems, but they are valid
+	// on Windows systems so we might as well just be safe.
+	if i := strings.LastIndex(localPath, ":"); i >= 0 {
+		after := localPath[i+1:]
+		if reference.TagRegexp.MatchString(after) {
+			localPath, tag = localPath[:i], after
+		}
+	}
+
+	if tag == "" {
+		tag = "latest"
+	}
+	return
+}

build/opt_test.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/docker/buildx/util/buildflags"
 	"github.com/moby/buildkit/client"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -38,3 +39,45 @@ func TestCacheOptions_DerivedVars(t *testing.T) {
 		},
 	}, CreateCaches(cacheFrom))
 }
+
+func TestParseOCILayoutPath(t *testing.T) {
+	for _, tt := range []struct {
+		s    string
+		path string
+		dgst string
+		tag  string
+	}{
+		{
+			s:    "/path/to/oci/layout",
+			path: "/path/to/oci/layout",
+			tag:  "latest",
+		},
+		{
+			s:    "/path/to/oci/layout:1.3",
+			path: "/path/to/oci/layout",
+			tag:  "1.3",
+		},
+		{
+			s:    "/path/to/oci/layout@sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+			path: "/path/to/oci/layout",
+			dgst: "sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+			tag:  "latest",
+		},
+		{
+			s:    "/path/to/oci/@/layout@sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+			path: "/path/to/oci/@/layout",
+			dgst: "sha256:aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+			tag:  "latest",
+		},
+		{
+			s:    "/path/to/oci/@/layout",
+			path: "/path/to/oci/@/layout",
+			tag:  "latest",
+		},
+	} {
+		path, dgst, tag := parseOCILayoutPath(tt.s)
+		assert.Equal(t, tt.path, path, "comparing path: %s", tt.s)
+		assert.Equal(t, tt.dgst, dgst, "comparing digest: %s", tt.s)
+		assert.Equal(t, tt.tag, tag, "comparing tag: %s", tt.s)
+	}
+}