Adding --select-alpha and --extract to create image policy

.github/workflows/e2e.yaml

@@ -171,7 +171,13 @@ jobs:
           ./bin/flux create image policy podinfo \
             --image-ref=podinfo \
             --interval=1m \
-            --semver=5.0.x
+            --select-semver=5.0.x
+      - name: flux create image policy podinfo-select-alpha
+        run: |
+          ./bin/flux create image policy podinfo-alpha \
+            --image-ref=podinfo \
+            --interval=1m \
+            --select-alpha=desc
       - name: flux get image policy
         run: |
           ./bin/flux get image policy podinfo | grep '5.0.3'

cmd/flux/create_image_policy.go

@@ -18,6 +18,10 @@ package main
 
 import (
 	"fmt"
+	"regexp/syntax"
+	"strings"
+	"unicode"
+	"unicode/utf8"
 
 	"github.com/spf13/cobra"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -39,18 +43,22 @@ the status of the object.`,
 	RunE: createImagePolicyRun}
 
 type imagePolicyFlags struct {
-	imageRef    string
-	semver      string
-	filterRegex string
+	imageRef      string
+	semver        string
+	alpha         string
+	filterRegex   string
+	filterExtract string
 }
 
 var imagePolicyArgs = imagePolicyFlags{}
 
 func init() {
 	flags := createImagePolicyCmd.Flags()
 	flags.StringVar(&imagePolicyArgs.imageRef, "image-ref", "", "the name of an image repository object")
-	flags.StringVar(&imagePolicyArgs.semver, "semver", "", "a semver range to apply to tags; e.g., '1.x'")
-	flags.StringVar(&imagePolicyArgs.filterRegex, "filter-regex", "", " regular expression pattern used to filter the image tags")
+	flags.StringVar(&imagePolicyArgs.semver, "select-semver", "", "a semver range to apply to tags; e.g., '1.x'")
+	flags.StringVar(&imagePolicyArgs.alpha, "select-alpha", "", "use alphabetical sorting to select image; either \"asc\" meaning select the last, or \"desc\" meaning select the first")
+	flags.StringVar(&imagePolicyArgs.filterRegex, "filter-regex", "", "regular expression pattern used to filter the image tags")
+	flags.StringVar(&imagePolicyArgs.filterExtract, "filter-extract", "", "replacement pattern (using capture groups from --filter-regex) to use for sorting")
 
 	createImageCmd.AddCommand(createImagePolicyCmd)
 }
@@ -90,18 +98,40 @@ func createImagePolicyRun(cmd *cobra.Command, args []string) error {
 	}
 
 	switch {
+	case imagePolicyArgs.semver != "" && imagePolicyArgs.alpha != "":
+		return fmt.Errorf("policy cannot be specified with both --select-semver and --select-alpha")
 	case imagePolicyArgs.semver != "":
 		policy.Spec.Policy.SemVer = &imagev1.SemVerPolicy{
 			Range: imagePolicyArgs.semver,
 		}
+	case imagePolicyArgs.alpha != "":
+		if imagePolicyArgs.alpha != "desc" && imagePolicyArgs.alpha != "asc" {
+			return fmt.Errorf("--select-alpha must be one of [\"asc\", \"desc\"]")
+		}
+		policy.Spec.Policy.Alphabetical = &imagev1.AlphabeticalPolicy{
+			Order: imagePolicyArgs.alpha,
+		}
 	default:
-		return fmt.Errorf("a policy must be provided with --semver")
+		return fmt.Errorf("a policy must be provided with either --select-semver or --select-alpha")
 	}
 
 	if imagePolicyArgs.filterRegex != "" {
+		exp, err := syntax.Parse(imagePolicyArgs.filterRegex, syntax.Perl)
+		if err != nil {
+			return fmt.Errorf("--filter-regex is an invalid regex pattern")
+		}
 		policy.Spec.FilterTags = &imagev1.TagFilter{
 			Pattern: imagePolicyArgs.filterRegex,
 		}
+
+		if imagePolicyArgs.filterExtract != "" {
+			if err := validateExtractStr(imagePolicyArgs.filterExtract, exp.CapNames()); err != nil {
+				return err
+			}
+			policy.Spec.FilterTags.Extract = imagePolicyArgs.filterExtract
+		}
+	} else if imagePolicyArgs.filterExtract != "" {
+		return fmt.Errorf("cannot specify --filter-extract without specifying --filter-regex")
 	}
 
 	if createArgs.export {
@@ -117,3 +147,94 @@ func createImagePolicyRun(cmd *cobra.Command, args []string) error {
 	})
 	return err
 }
+
+// Performs a dry-run of the extract function in Regexp to validate the template
+func validateExtractStr(template string, capNames []string) error {
+	for len(template) > 0 {
+		i := strings.Index(template, "$")
+		if i < 0 {
+			return nil
+		}
+		template = template[i:]
+		if len(template) > 1 && template[1] == '$' {
+			template = template[2:]
+			continue
+		}
+		name, num, rest, ok := extract(template)
+		if !ok {
+			// Malformed extract string, assume user didn't want this
+			template = template[1:]
+			return fmt.Errorf("--filter-extract is malformed")
+		}
+		template = rest
+		if num >= 0 {
+			// we won't worry about numbers as we can't validate these
+			continue
+		} else {
+			found := false
+			for _, capName := range capNames {
+				if name == capName {
+					found = true
+				}
+			}
+			if !found {
+				return fmt.Errorf("capture group $%s used in --filter-extract not found in --filter-regex", name)
+			}
+		}
+
+	}
+	return nil
+}
+
+// extract method from the regexp package
+// returns the name or number of the value prepended by $
+func extract(str string) (name string, num int, rest string, ok bool) {
+	if len(str) < 2 || str[0] != '$' {
+		return
+	}
+	brace := false
+	if str[1] == '{' {
+		brace = true
+		str = str[2:]
+	} else {
+		str = str[1:]
+	}
+	i := 0
+	for i < len(str) {
+		rune, size := utf8.DecodeRuneInString(str[i:])
+		if !unicode.IsLetter(rune) && !unicode.IsDigit(rune) && rune != '_' {
+			break
+		}
+		i += size
+	}
+	if i == 0 {
+		// empty name is not okay
+		return
+	}
+	name = str[:i]
+	if brace {
+		if i >= len(str) || str[i] != '}' {
+			// missing closing brace
+			return
+		}
+		i++
+	}
+
+	// Parse number.
+	num = 0
+	for i := 0; i < len(name); i++ {
+		if name[i] < '0' || '9' < name[i] || num >= 1e8 {
+			num = -1
+			break
+		}
+		num = num*10 + int(name[i]) - '0'
+	}
+	// Disallow leading zeros.
+	if name[0] == '0' && len(name) > 1 {
+		num = -1
+	}
+
+	rest = str[i:]
+	ok = true
+	return
+}

docs/cmd/flux_create_image_policy.md

@@ -18,10 +18,12 @@ flux create image policy <name> [flags]
 ### Options
 
 ```
-      --filter-regex string    regular expression pattern used to filter the image tags
-  -h, --help                  help for policy
-      --image-ref string      the name of an image repository object
-      --semver string         a semver range to apply to tags; e.g., '1.x'
+      --filter-extract string   replacement pattern (using capture groups from --filter-regex) to use for sorting
+      --filter-regex string     regular expression pattern used to filter the image tags
+  -h, --help                    help for policy
+      --image-ref string        the name of an image repository object
+      --select-alpha string     use alphabetical sorting to select image; either "asc" meaning select the last, or "desc" meaning select the first
+      --select-semver string    a semver range to apply to tags; e.g., '1.x'
 ```
 
 ### Options inherited from parent commands