topdown: Add base64.is_valid builtin

Adds a builtin to check if a string is valid base64

Fixes: #2690

Signed-off-by: Calle Pettersson <calle@cape.nu>

ast/builtins.go

@@ -130,6 +130,7 @@ var DefaultBuiltins = [...]*Builtin{
 	JSONUnmarshal,
 	Base64Encode,
 	Base64Decode,
+	Base64IsValid,
 	Base64UrlEncode,
 	Base64UrlDecode,
 	URLQueryDecode,
@@ -1231,6 +1232,15 @@ var Base64Decode = &Builtin{
 	),
 }
 
+// Base64IsValid verifies the input string is base64 encoded.
+var Base64IsValid = &Builtin{
+	Name: "base64.is_valid",
+	Decl: types.NewFunction(
+		types.Args(types.S),
+		types.B,
+	),
+}
+
 // Base64UrlEncode serializes the input string into base64url encoding.
 var Base64UrlEncode = &Builtin{
 	Name: "base64url.encode",

capabilities.json

@@ -195,6 +195,20 @@
         "type": "function"
       }
     },
+    {
+      "name": "base64.is_valid",
+      "decl": {
+        "args": [
+          {
+            "type": "string"
+          }
+        ],
+        "result": {
+          "type": "boolean"
+        },
+        "type": "function"
+      }
+    },
     {
       "name": "base64url.decode",
       "decl": {

test/cases/testdata/base64builtins/test-base64builtins-0935.yaml

@@ -0,0 +1,25 @@
+cases:
+- data: {}
+  modules:
+  - |
+    package generated
+
+    p = x {
+      base64.is_valid("aGVsbG8=", x)
+    }
+  note: base64builtins/is_valid-true
+  query: data.generated.p = x
+  want_result:
+  - x: true
+- data: {}
+  modules:
+  - |
+    package generated
+
+    p = x {
+      base64.is_valid("{'not':'base64'}", x)
+    }
+  note: base64builtins/is_valid-false
+  query: data.generated.p = x
+  want_result:
+  - x: false

topdown/encoding.go

@@ -69,6 +69,16 @@ func builtinBase64Decode(a ast.Value) (ast.Value, error) {
 	return ast.String(result), err
 }
 
+func builtinBase64IsValid(a ast.Value) (ast.Value, error) {
+	str, err := builtins.StringOperand(a, 1)
+	if err != nil {
+		return nil, err
+	}
+
+	_, err = base64.StdEncoding.DecodeString(string(str))
+	return ast.Boolean(err == nil), nil
+}
+
 func builtinBase64UrlEncode(a ast.Value) (ast.Value, error) {
 	str, err := builtins.StringOperand(a, 1)
 	if err != nil {
@@ -230,6 +240,7 @@ func init() {
 	RegisterFunctionalBuiltin1(ast.JSONUnmarshal.Name, builtinJSONUnmarshal)
 	RegisterFunctionalBuiltin1(ast.Base64Encode.Name, builtinBase64Encode)
 	RegisterFunctionalBuiltin1(ast.Base64Decode.Name, builtinBase64Decode)
+	RegisterFunctionalBuiltin1(ast.Base64IsValid.Name, builtinBase64IsValid)
 	RegisterFunctionalBuiltin1(ast.Base64UrlEncode.Name, builtinBase64UrlEncode)
 	RegisterFunctionalBuiltin1(ast.Base64UrlDecode.Name, builtinBase64UrlDecode)
 	RegisterFunctionalBuiltin1(ast.URLQueryDecode.Name, builtinURLQueryDecode)