Add optional digest suffix to template locator

The suffix is "@digest" which may include an optional algorithm
(defaults to "sha256"). The encoded digest must be at least 7
characters long.

Examples:
- template://my@sha256:60a87371451eabcd211c929759db61746a7c6a1c068f59d868db6aa8dca637bd
- template://my@sha256:60a87371451
- template://my@60a8737

Signed-off-by: Jan Dubois <[email protected]>

pkg/limatmpl/locator.go

@@ -14,6 +14,7 @@ import (
 	"github.com/containerd/containerd/identifiers"
 	"github.com/lima-vm/lima/pkg/ioutilx"
 	"github.com/lima-vm/lima/pkg/templatestore"
+	"github.com/opencontainers/go-digest"
 	"github.com/sirupsen/logrus"
 )
 
@@ -33,12 +34,33 @@ func Read(ctx context.Context, name, locator string) (*Template, error) {
 		Locator: locator,
 	}
 
-	isTemplateURL, templateURL := SeemsTemplateURL(locator)
+	algorithm := digest.SHA256
+	expectedDigest := ""
+
+	// Split off optional digest suffix
+	index := strings.LastIndex(locator, "@")
+	if index > strings.LastIndex(locator, "/") {
+		tmpl.Locator = locator[:index]
+		expectedDigest = locator[index+1:]
+		index = strings.LastIndex(expectedDigest, ":")
+		if index != -1 {
+			algorithm = digest.Algorithm(expectedDigest[:index])
+			expectedDigest = expectedDigest[index+1:]
+			if !algorithm.Available() {
+				return nil, fmt.Errorf("locator %q digest algorithm is not available", locator)
+			}
+		}
+		if len(expectedDigest) < 7 {
+			return nil, fmt.Errorf("locator %q expected digest length less than 7 characters", locator)
+		}
+	}
+
+	isTemplateURL, templateURL := SeemsTemplateURL(tmpl.Locator)
 	switch {
 	case isTemplateURL:
 		// No need to use SecureJoin here. https://github.com/lima-vm/lima/pull/805#discussion_r853411702
 		templateName := filepath.Join(templateURL.Host, templateURL.Path)
-		logrus.Debugf("interpreting argument %q as a template name %q", locator, templateName)
+		logrus.Debugf("interpreting argument %q as a template name %q", tmpl.Locator, templateName)
 		if tmpl.Name == "" {
 			// e.g., templateName = "deprecated/centos-7" , tmpl.Name = "centos-7"
 			tmpl.Name = filepath.Base(templateName)
@@ -47,15 +69,15 @@ func Read(ctx context.Context, name, locator string) (*Template, error) {
 		if err != nil {
 			return nil, err
 		}
-	case SeemsHTTPURL(locator):
+	case SeemsHTTPURL(tmpl.Locator):
 		if tmpl.Name == "" {
-			tmpl.Name, err = InstNameFromURL(locator)
+			tmpl.Name, err = InstNameFromURL(tmpl.Locator)
 			if err != nil {
 				return nil, err
 			}
 		}
-		logrus.Debugf("interpreting argument %q as a http url for instance %q", locator, tmpl.Name)
-		req, err := http.NewRequestWithContext(ctx, http.MethodGet, locator, http.NoBody)
+		logrus.Debugf("interpreting argument %q as a http url for instance %q", tmpl.Locator, tmpl.Name)
+		req, err := http.NewRequestWithContext(ctx, http.MethodGet, tmpl.Locator, http.NoBody)
 		if err != nil {
 			return nil, err
 		}
@@ -68,15 +90,15 @@ func Read(ctx context.Context, name, locator string) (*Template, error) {
 		if err != nil {
 			return nil, err
 		}
-	case SeemsFileURL(locator):
+	case SeemsFileURL(tmpl.Locator):
 		if tmpl.Name == "" {
-			tmpl.Name, err = InstNameFromURL(locator)
+			tmpl.Name, err = InstNameFromURL(tmpl.Locator)
 			if err != nil {
 				return nil, err
 			}
 		}
-		logrus.Debugf("interpreting argument %q as a file url for instance %q", locator, tmpl.Name)
-		r, err := os.Open(strings.TrimPrefix(locator, "file://"))
+		logrus.Debugf("interpreting argument %q as a file url for instance %q", tmpl.Locator, tmpl.Name)
+		r, err := os.Open(strings.TrimPrefix(tmpl.Locator, "file://"))
 		if err != nil {
 			return nil, err
 		}
@@ -85,15 +107,15 @@ func Read(ctx context.Context, name, locator string) (*Template, error) {
 		if err != nil {
 			return nil, err
 		}
-	case SeemsYAMLPath(locator):
+	case SeemsYAMLPath(tmpl.Locator):
 		if tmpl.Name == "" {
-			tmpl.Name, err = InstNameFromYAMLPath(locator)
+			tmpl.Name, err = InstNameFromYAMLPath(tmpl.Locator)
 			if err != nil {
 				return nil, err
 			}
 		}
-		logrus.Debugf("interpreting argument %q as a file path for instance %q", locator, tmpl.Name)
-		r, err := os.Open(locator)
+		logrus.Debugf("interpreting argument %q as a file path for instance %q", tmpl.Locator, tmpl.Name)
+		r, err := os.Open(tmpl.Locator)
 		if err != nil {
 			return nil, err
 		}
@@ -102,12 +124,22 @@ func Read(ctx context.Context, name, locator string) (*Template, error) {
 		if err != nil {
 			return nil, err
 		}
-	case locator == "-":
+	case tmpl.Locator == "-":
 		tmpl.Bytes, err = io.ReadAll(os.Stdin)
 		if err != nil {
 			return nil, fmt.Errorf("unexpected error reading stdin: %w", err)
 		}
 	}
+
+	if expectedDigest != "" {
+		actualDigest := algorithm.FromBytes(tmpl.Bytes).Encoded()
+		if len(expectedDigest) < len(actualDigest) {
+			actualDigest = actualDigest[:len(expectedDigest)]
+		}
+		if actualDigest != expectedDigest {
+			return nil, fmt.Errorf("locator %q digest doesn't match content digest %q", locator, actualDigest)
+		}
+	}
 	return tmpl, nil
 }