Add string translation to CEL interceptor.

This adds a new "translate" function to the CEL interceptor library that
allows using a regular expression to translate replacement characters to
specified strings.

docs/cel_expressions.md

@@ -470,7 +470,21 @@ which can be accessed by indexing.
      <pre>[1, 2, 3, 4, 5].last() == 5</pre>
     </td>
   </tr>
-
+  <tr>
+    <th>
+     translate()
+    </th>
+    <td>
+     <pre>&lt;string&gt;.translatet(string, string) -> &lt;string&gt;</pre>
+    </td>
+    <td>
+     Uses a regular expression to replace characters from the source string with characters from the replacements.
+    </td>
+    <td>
+     <pre>"This is $an Invalid5String ".translate("[^a-z0-9]+", "") == "hisisannvalid5tring"</pre><br />
+     <pre>"This is $an Invalid5String ".translate("[^a-z0-9]+", "ABC") == "ABChisABCisABCanABCnvalid5ABCtring"</pre>
+    </td>
+  </tr>
 </table>
 
 ## Troubleshooting CEL expressions

pkg/interceptors/cel/cel_test.go

@@ -215,6 +215,19 @@ func TestInterceptor_Process(t *testing.T) {
 			"two":   "default",
 			"three": "default",
 		},
+	}, {
+		name: "string replacement with regexp",
+		CEL: &InterceptorParams{
+			Overlays: []Overlay{
+				{Key: "replaced1", Expression: `body.value.lowerAscii().translate("[^a-z0-9]+", "")`},
+				{Key: "replaced2", Expression: `body.value.lowerAscii().translate("[^a-z0-9]+", "ABC")`},
+			},
+		},
+		body: json.RawMessage(`{"value":"This is $an Invalid5String"}`),
+		wantExtensions: map[string]interface{}{
+			"replaced1": "thisisaninvalid5string",
+			"replaced2": "thisABCisABCanABCinvalid5string",
+		},
 	}, {
 		name: "filters and overlays can access passed in extensions",
 		CEL: &InterceptorParams{
@@ -278,7 +291,7 @@ func TestInterceptor_Process(t *testing.T) {
 			if tt.wantExtensions != nil {
 				got := res.Extensions
 				if diff := cmp.Diff(tt.wantExtensions, got); diff != "" {
-					rt.Fatalf("cel.Process() did return correct extensions (-wantMsg+got): %v", diff)
+					rt.Fatalf("cel.Process() did rnot eturn correct extensions (-wantMsg+got): %v", diff)
 				}
 			}
 		})
@@ -343,6 +356,16 @@ func TestInterceptor_Process_Error(t *testing.T) {
 		body:     []byte(`{"value":"test"}`),
 		wantCode: codes.InvalidArgument,
 		wantMsg:  `expression "test.value" check failed: ERROR:.*undeclared reference to 'test'`,
+	}, {
+		name: "unable to parse regexp in translate",
+		CEL: &InterceptorParams{
+			Overlays: []Overlay{
+				{Key: "converted", Expression: `body.value.translate("[^a-z0-9+", "")`},
+			},
+		},
+		body:     []byte(`{"value":"testing"}`),
+		wantCode: codes.InvalidArgument,
+		wantMsg:  "failed to parse regular expression for translation: error parsing regexp: missing closing ]",
 	},
 	}
 	for _, tt := range tests {

pkg/interceptors/cel/triggers.go

@@ -22,6 +22,7 @@ import (
 	"net/http"
 	"net/url"
 	"reflect"
+	"regexp"
 	"strings"
 
 	"github.com/google/cel-go/cel"
@@ -145,6 +146,16 @@ import (
 //
 // 		body.jsonObjectOrList.marshalJSON()
 
+// translate
+//
+// translate returns a copy of src, replacing matches of the with the replacement string repl. Inside repl, $ signs are interpreted as in Expand, so for instance $1 represents the text of the first submatch.
+//
+// 		<string>.translate(string, string) -> <string>
+//
+// Examples:
+//
+// 		"this is $aN INvalid5string ".replace("[^a-z0-9]+", "") == "thisisaninvalid5string"
+
 // Triggers creates and returns a new cel.Lib with the triggers extensions.
 func Triggers(ctx context.Context, ns string, sg interceptors.SecretGetter) cel.EnvOption {
 	return cel.Lib(triggersLib{ctx: ctx, defaultNS: ns, secretGetter: sg})
@@ -194,6 +205,9 @@ func (t triggersLib) CompileOptions() []cel.EnvOption {
 		cel.Function("first",
 			cel.MemberOverload("first_list", []*cel.Type{listStrDyn}, cel.DynType,
 				cel.UnaryBinding(listFirst))),
+		cel.Function("translate",
+			cel.MemberOverload("translate_string_string", []*cel.Type{cel.StringType, cel.StringType, cel.StringType}, cel.StringType,
+				cel.FunctionBinding(translateString))),
 	}
 }
 
@@ -276,6 +290,7 @@ func parseJSONString(val ref.Val) ref.Val {
 	if err != nil {
 		return types.NewErr("failed to create a new registry in parseJSON: %w", err)
 	}
+
 	return types.NewDynamicMap(r, decodedVal)
 }
 
@@ -353,6 +368,30 @@ func listFirst(val ref.Val) ref.Val {
 	return l.Get(types.Int(0))
 }
 
+func translateString(vals ...ref.Val) ref.Val {
+	regstr, ok := vals[1].(types.String)
+	if !ok {
+		return types.ValOrErr(regstr, "unexpected type '%v' used in translate", vals[1].Type())
+	}
+
+	src, ok := vals[0].(types.String)
+	if !ok {
+		return types.ValOrErr(src, "unexpected type '%v' used in translate", vals[0].Type())
+	}
+
+	repl, ok := vals[2].(types.String)
+	if !ok {
+		return types.ValOrErr(repl, "unexpected type '%v' used in translate", vals[2].Type())
+	}
+
+	re, err := regexp.Compile(string(regstr))
+	if err != nil {
+		return types.NewErr("failed to parse regular expression for translation: %w", err)
+	}
+
+	return types.String(re.ReplaceAllString(string(src), string(repl)))
+}
+
 func max(x, y types.Int) types.Int {
 	switch x.Compare(y) {
 	case types.IntNegOne: