Revert to cel-as-matcher approach

xds/type/matcher/v3/cel.proto

@@ -0,0 +1,60 @@
+syntax = "proto3";
+
+package xds.type.matcher.v3;
+
+import "xds/annotations/v3/status.proto";
+import "xds/type/v3/cel.proto";
+
+import "google/protobuf/wrappers.proto";
+
+import "validate/validate.proto";
+
+option java_package = "com.github.xds.type.matcher.v3";
+option java_outer_classname = "CelMatcherProto";
+option java_multiple_files = true;
+option go_package = "github.com/cncf/xds/go/xds/type/matcher/v3";
+
+option (xds.annotations.v3.file_status).work_in_progress = true;
+
+// [#protodoc-title: Common Expression Language (CEL) matchers]
+
+// Performs a match by evaluating a `Common Expression Language
+// <https://github.com/google/cel-spec>`_ (CEL) expression against the standardized set of
+// :ref:`HTTP attributes <arch_overview_attributes>` specified via ``HttpAttributesCelMatchInput``.
+//
+// .. attention::
+//
+//   The match is ``true``, iff the result of the evaluation is a bool AND true.
+//   In all other cases, the match is ``false``, including but not limited to: non-bool types,
+//   ``false``, ``null``,`` int(1)``, etc.
+//   In case CEL expression raises an error, the result of the evaluation is interpreted "no match".
+//
+// Refer to :ref:`Unified Matcher API <envoy_v3_api_msg_.xds.type.matcher.v3.Matcher>` documentation
+// for usage details.
+//
+// [#comment:TODO(sergiitk): Link HttpAttributesMatchInput + usage example.]
+// [#comment:TODO(sergiitk): Add extension category.]
+message CelBoolMatcher {
+  // Either parsed or checked representation of the CEL program.
+  type.v3.CelExpression expr_match = 1 [(validate.rules).message = {required: true}];
+}
+
+// Extracts a string by evaluating a `Common Expression Language
+// <https://github.com/google/cel-spec>`_ (CEL) expression against the standardized set of
+// :ref:`HTTP attributes <arch_overview_attributes>`.
+//
+// .. attention::
+//
+//   Besides CEL evaluation raising an error explicitly, CEL program returning a type other than
+//   the ``string``, or not returning anything, are considered an error as well.
+//
+// [#comment:TODO(sergiitk): Add extension category.]
+message CelExtractString {
+  // The CEL expression used to extract a string from the CEL environment.
+  // the "subject string") that should be replaced.
+  type.v3.CelExpression expr_extract = 1 [(validate.rules).message = {required: true}];
+
+  // If CEL expression evaluates to an error, this value is be returned to the caller.
+  // If not set, the error is propagated to the caller.
+  google.protobuf.StringValue default_value = 2;
+}

xds/type/matcher/v3/http_inputs.proto

@@ -3,7 +3,6 @@ syntax = "proto3";
 package xds.type.matcher.v3;
 
 import "xds/annotations/v3/status.proto";
-import "xds/type/v3/cel.proto";
 
 import "validate/validate.proto";
 
@@ -14,38 +13,17 @@ option go_package = "github.com/cncf/xds/go/xds/type/matcher/v3";
 
 option (xds.annotations.v3.file_status).work_in_progress = true;
 
-
 // [#protodoc-title: Common HTTP Inputs]
 
-// Specifies that matching will be performed on the set of :ref:`HTTP attributes
-// <arch_overview_attributes>` using `Common Expression Language
-// <https://github.com/google/cel-spec>`_ (CEL) expression.
-//
-// The resulting input is the result of evaluating the CEL program. The result should be one of the
-// supported types. Refer to the following table for the supported CEL result types, and known
-// compatible matchers.
-//
-// .. list-table::
-//   :widths: 25 75
-//   :header-rows: 1
+// Specifies that matching should be performed on the set of :ref:`HTTP attributes
+// <arch_overview_attributes>`.
 //
-//   * - CEL result type
-//     - Compatible Matchers
-//   * - ``string``
-//     - :ref:`StringMatcher <envoy_v3_api_msg_.xds.type.matcher.v3.StringMatcher>`
-//   * - ``bool``
-//     - TBD
+// The attributes will be exposed via `Common Expression Language
+// <https://github.com/google/cel-spec>`_ runtime to associated CEL matcher.
 //
 // Refer to :ref:`Unified Matcher API <envoy_v3_api_msg_.xds.type.matcher.v3.Matcher>` documentation
 // for usage details.
 //
-// .. attention::
-//
-//   In case CEL expression raises an error, the result of the evaluation is interpreted
-//   short-circuited "no match". Associated Matcher is not evaluated.
-//
 // [#extension: envoy.matching.inputs.http_attributes]
 message HttpAttributesCelMatchInput {
-  // CEL expression to evaluate.
-  type.v3.CelExpression expr = 1 [(validate.rules).message = {required: true}];
 }