Adding extract pattern validation

Signed-off-by: Jonathan Innis <jonathan.innis.ji@gmail.com>

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"
@@ -94,6 +98,8 @@ 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,
@@ -110,11 +116,18 @@ func createImagePolicyRun(cmd *cobra.Command, args []string) error {
 	}
 
 	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 != "" {
@@ -134,3 +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
+}