add semver tagging semantics

check_test.go

@@ -571,6 +571,66 @@ var _ = DescribeTable("tracking semver tags",
 			Versions: []string{"1", "2", "3"},
 		},
 	),
+	Entry("variants",
+		SemverTagExample{
+			Variant: "foo",
+
+			Tags: map[string]string{
+				"latest":    "random-1",
+				"1.0.0":     "random-1",
+				"0.9.0":     "random-2",
+				"foo":       "random-3",
+				"1.0.0-foo": "random-3",
+				"0.9.0-foo": "random-4",
+				"bar":       "random-5",
+				"1.0.0-bar": "random-5",
+				"0.9.0-bar": "random-6",
+			},
+
+			Versions: []string{"0.9.0-foo", "1.0.0-foo"},
+		},
+	),
+	Entry("distinguishing additional variants from prereleases",
+		SemverTagExample{
+			Variant: "foo",
+
+			Tags: map[string]string{
+				"1.0.0-foo":             "random-1",
+				"1.0.0-rc.1-foo":        "random-2",
+				"1.0.0-alpha.1-foo":     "random-3",
+				"1.0.0-beta.1-foo":      "random-4",
+				"1.0.0-bar-foo":         "random-5",
+				"1.0.0-rc.1-bar-foo":    "random-6",
+				"1.0.0-alpha.1-bar-foo": "random-7",
+				"1.0.0-beta.1-bar-foo":  "random-8",
+			},
+
+			Versions: []string{
+				"1.0.0-alpha.1-foo",
+				"1.0.0-beta.1-foo",
+				"1.0.0-rc.1-foo",
+				"1.0.0-foo",
+			},
+		},
+	),
+	Entry("variant with bare variant tag pointing to unique digest",
+		SemverTagExample{
+			Variant: "foo",
+
+			Tags: map[string]string{
+				"latest":    "random-1",
+				"1.0.0":     "random-1",
+				"0.9.0":     "random-2",
+				"foo":       "random-3",
+				"0.8.0-foo": "random-4",
+				"bar":       "random-5",
+				"1.0.0-bar": "random-5",
+				"0.9.0-bar": "random-6",
+			},
+
+			Versions: []string{"0.8.0-foo", "foo"},
+		},
+	),
 )
 
 type SemverTagExample struct {
@@ -602,6 +662,7 @@ func (example SemverTagExample) Run() {
 	req := resource.CheckRequest{
 		Source: resource.Source{
 			Repository: repo.Name(),
+			Variant:    example.Variant,
 		},
 	}
 

cmd/check/main.go

@@ -98,7 +98,7 @@ func main() {
 
 			repo.Registry = mirror
 
-			response, err = checkRepositoryWithRetry(req.Source.RegistryMirror.BasicCredentials, req.Version, repo)
+			response, err = checkRepositoryWithRetry(req.Source.RegistryMirror.BasicCredentials, req.Source.Variant, req.Version, repo)
 			if err != nil {
 				logrus.Warnf("checking mirror %s failed: %s", mirror.RegistryStr(), err)
 			} else if len(response) == 0 {
@@ -109,7 +109,7 @@ func main() {
 		}
 
 		if len(response) == 0 {
-			response, err = checkRepositoryWithRetry(req.Source.BasicCredentials, req.Version, repo)
+			response, err = checkRepositoryWithRetry(req.Source.BasicCredentials, req.Source.Variant, req.Version, repo)
 			if err != nil {
 				logrus.Errorf("checking origin failed: %s", err)
 				os.Exit(1)
@@ -121,11 +121,11 @@ func main() {
 	json.NewEncoder(os.Stdout).Encode(response)
 }
 
-func checkRepositoryWithRetry(principal resource.BasicCredentials, version *resource.Version, ref name.Repository) (resource.CheckResponse, error) {
+func checkRepositoryWithRetry(principal resource.BasicCredentials, variant string, version *resource.Version, ref name.Repository) (resource.CheckResponse, error) {
 	var response resource.CheckResponse
 	err := resource.RetryOnRateLimit(func() error {
 		var err error
-		response, err = checkRepository(principal, version, ref)
+		response, err = checkRepository(principal, variant, version, ref)
 		return err
 	})
 	return response, err
@@ -141,7 +141,7 @@ func checkTagWithRetry(principal resource.BasicCredentials, version *resource.Ve
 	return response, err
 }
 
-func checkRepository(principal resource.BasicCredentials, version *resource.Version, ref name.Repository) (resource.CheckResponse, error) {
+func checkRepository(principal resource.BasicCredentials, variant string, version *resource.Version, ref name.Repository) (resource.CheckResponse, error) {
 	auth := &authn.Basic{
 		Username: principal.Username,
 		Password: principal.Password,
@@ -158,6 +158,11 @@ func checkRepository(principal resource.BasicCredentials, version *resource.Vers
 		return resource.CheckResponse{}, fmt.Errorf("list repository tags: %w", err)
 	}
 
+	bareTag := "latest"
+	if variant != "" {
+		bareTag = variant
+	}
+
 	var latestTag string
 
 	versions := []*semver.Version{}
@@ -166,16 +171,38 @@ func checkRepository(principal resource.BasicCredentials, version *resource.Vers
 	digestVersions := map[string]*semver.Version{}
 	for _, identifier := range tags {
 		var ver *semver.Version
-		if identifier == "latest" {
-			// TODO: handle variants, e.g. 'alpine' is latest for
-			// 'x.x.x-alpine'
+		if identifier == bareTag {
 			latestTag = identifier
 		} else {
-			ver, err = semver.NewVersion(identifier)
+			verStr := identifier
+			if variant != "" {
+				if !strings.HasSuffix(identifier, "-"+variant) {
+					continue
+				}
+
+				verStr = strings.TrimSuffix(identifier, "-"+variant)
+			}
+
+			ver, err = semver.NewVersion(verStr)
 			if err != nil {
 				// not a version
 				continue
 			}
+
+			pre := ver.Prerelease()
+			if pre != "" {
+				// contains additional variant
+				if strings.Contains(pre, "-") {
+					continue
+				}
+
+				if !strings.HasPrefix(pre, "alpha.") &&
+					!strings.HasPrefix(pre, "beta.") &&
+					!strings.HasPrefix(pre, "rc.") {
+					// additional variant, not a prerelease segment
+					continue
+				}
+			}
 		}
 
 		tagRef := ref.Tag(identifier)

types.go

@@ -46,6 +46,7 @@ type RegistryMirror struct {
 
 type Source struct {
 	Repository string `json:"repository"`
+	Variant    string `json:"variant,omitempty"`
 	Tag        Tag    `json:"tag,omitempty"`
 
 	BasicCredentials