WiP: Local reply mapper

api/envoy/config/filter/accesslog/v2/accesslog.proto

@@ -45,6 +45,8 @@ message AccessLog {
   }
 }
 
+// [#next-major-version: In the v3 API, we should consider renaming
+// it to more generic filter]
 message AccessLogFilter {
   oneof filter_specifier {
     option (validate.required) = true;

api/envoy/config/filter/accesslog/v3alpha/accesslog.proto

@@ -45,6 +45,8 @@ message AccessLog {
   }
 }
 
+// [#next-major-version: In the v3 API, we should consider renaming
+// it to more generic filter]
 message AccessLogFilter {
   oneof filter_specifier {
     option (validate.required) = true;

api/envoy/config/filter/network/http_connection_manager/v2/http_connection_manager.proto

@@ -11,6 +11,7 @@ import "envoy/api/v2/core/protocol.proto";
 import "envoy/api/v2/rds.proto";
 import "envoy/api/v2/srds.proto";
 import "envoy/config/filter/accesslog/v2/accesslog.proto";
+import "envoy/type/format.proto";
 import "envoy/type/percent.proto";
 
 import "google/protobuf/any.proto";
@@ -23,7 +24,7 @@ import "validate/validate.proto";
 // [#protodoc-title: HTTP connection manager]
 // HTTP connection manager :ref:`configuration overview <config_http_conn_man>`.
 
-// [#comment:next free field: 36]
+// [#comment:next free field: 37]
 message HttpConnectionManager {
   enum CodecType {
     // For every new connection, the connection manager will determine which
@@ -461,6 +462,36 @@ message HttpConnectionManager {
   // with `prefix` match set to `/dir`. Defaults to `false`. Note that slash merging is not part of
   // `HTTP spec <https://tools.ietf.org/html/rfc3986>` and is provided for convenience.
   bool merge_slashes = 33;
+
+  // [#not-implemented-hide:]
+  // Configuration of local reply returned by Envoy. Allows to specify mappings and format of
+  // response.
+  LocalReplyConfig local_reply_config = 36;
+}
+
+message LocalReplyConfig {
+  // Configuration of list of mappers which allows to filter and change local response.
+  // The client will iterate through mappers until first match.
+  repeated ResponseMapper mapper = 1;
+
+  // Allows to define custom format of local reply.
+  // It is allowed to use :ref:`command operators <config_access_log_command_operators>`
+  // which will be resolved to actual data.
+  type.StringOrJson format = 2;
+}
+
+message ResponseMapper {
+  // Filter is used to determine if the response should be changed.
+  accesslog.v2.AccessLogFilter filter = 1 [(validate.rules).message = {required: true}];
+
+  // Rewriter defines which values in local reply should be changed.
+  ResponseRewriter rewriter = 2 [(validate.rules).message = {required: true}];
+}
+
+// Configuration of new value for matched local response.
+message ResponseRewriter {
+  // Status code for matched response.
+  google.protobuf.UInt32Value status_code = 1;
 }
 
 message Rds {

api/envoy/config/filter/network/http_connection_manager/v3alpha/http_connection_manager.proto

@@ -12,6 +12,7 @@ import "envoy/api/v3alpha/rds.proto";
 import "envoy/api/v3alpha/srds.proto";
 import "envoy/config/filter/accesslog/v3alpha/accesslog.proto";
 import "envoy/config/filter/network/http_connection_manager/v2/http_connection_manager.proto";
+import "envoy/type/v3alpha/format.proto";
 import "envoy/type/v3alpha/percent.proto";
 
 import "google/protobuf/any.proto";
@@ -24,7 +25,7 @@ import "validate/validate.proto";
 // [#protodoc-title: HTTP connection manager]
 // HTTP connection manager :ref:`configuration overview <config_http_conn_man>`.
 
-// [#comment:next free field: 36]
+// [#comment:next free field: 37]
 message HttpConnectionManager {
   enum CodecType {
     // For every new connection, the connection manager will determine which
@@ -449,6 +450,36 @@ message HttpConnectionManager {
   // with `prefix` match set to `/dir`. Defaults to `false`. Note that slash merging is not part of
   // `HTTP spec <https://tools.ietf.org/html/rfc3986>` and is provided for convenience.
   bool merge_slashes = 33;
+
+  // [#not-implemented-hide:]
+  // Configuration of local reply returned by Envoy. Allows to specify mappings and format of
+  // response.
+  LocalReplyConfig local_reply_config = 36;
+}
+
+message LocalReplyConfig {
+  // Configuration of list of mappers which allows to filter and change local response.
+  // The client will iterate through mappers until first match.
+  repeated ResponseMapper mapper = 1;
+
+  // Allows to define custom format of local reply.
+  // It is allowed to use :ref:`command operators <config_access_log_command_operators>`
+  // which will be resolved to actual data.
+  type.v3alpha.StringOrJson format = 2;
+}
+
+message ResponseMapper {
+  // Filter is used to determine if the response should be changed.
+  accesslog.v3alpha.AccessLogFilter filter = 1 [(validate.rules).message = {required: true}];
+
+  // Rewriter defines which values in local reply should be changed.
+  ResponseRewriter rewriter = 2 [(validate.rules).message = {required: true}];
+}
+
+// Configuration of new value for matched local response.
+message ResponseRewriter {
+  // Status code for matched response.
+  google.protobuf.UInt32Value status_code = 1;
 }
 
 message Rds {

api/envoy/type/format.proto

@@ -0,0 +1,43 @@
+syntax = "proto3";
+
+package envoy.type;
+
+option java_outer_classname = "FormatProto";
+option java_multiple_files = true;
+option java_package = "io.envoyproxy.envoy.type";
+
+import "google/protobuf/struct.proto";
+
+// [#protodoc-title: Format]
+
+// Allows to define one of format: flat plain text or structured json.
+message StringOrJson {
+  oneof format {
+    // Allows to specify flat plain text format.
+    //
+    // .. code-block:: yaml
+    //
+    //   string_format: "My custom message"
+    //
+    string string_format = 1;
+
+    // Allows to specify structured data as json.
+    //
+    // .. code-block:: yaml
+    //
+    //  json_format:
+    //    protocol: "HTTP/1.1"
+    //    message: "My message"
+    //
+    // The following JSON object would be created:
+    //
+    // .. code-block:: json
+    //
+    //  {
+    //    "protocol": "HTTP/1.1",
+    //    "message": "My message"
+    //  }
+    //
+    google.protobuf.Struct json_format = 2;
+  }
+}

api/envoy/type/v3alpha/format.proto

@@ -0,0 +1,43 @@
+syntax = "proto3";
+
+package envoy.type.v3alpha;
+
+option java_outer_classname = "FormatProto";
+option java_multiple_files = true;
+option java_package = "io.envoyproxy.envoy.type.v3alpha";
+
+import "google/protobuf/struct.proto";
+
+// [#protodoc-title: Format]
+
+// Allows to define one of format: flat plain text or structured json.
+message StringOrJson {
+  oneof format {
+    // Allows to specify flat plain text format.
+    //
+    // .. code-block:: yaml
+    //
+    //   string_format: "My custom message"
+    //
+    string string_format = 1;
+
+    // Allows to specify structured data as json.
+    //
+    // .. code-block:: yaml
+    //
+    //  json_format:
+    //    protocol: "HTTP/1.1"
+    //    message: "My message"
+    //
+    // The following JSON object would be created:
+    //
+    // .. code-block:: json
+    //
+    //  {
+    //    "protocol": "HTTP/1.1",
+    //    "message": "My message"
+    //  }
+    //
+    google.protobuf.Struct json_format = 2;
+  }
+}

docs/root/api-v2/types/types.rst

@@ -5,6 +5,7 @@ Types
   :glob:
   :maxdepth: 2
 
+  ../type/format.proto
   ../type/http_status.proto
   ../type/percent.proto
   ../type/range.proto

docs/root/configuration/observability/access_log.rst

@@ -91,6 +91,8 @@ Format dictionaries have the following restrictions:
 
 * The dictionary must map strings to strings (specifically, strings to command operators). Nesting is not currently supported.
 
+.. _config_access_log_command_operators:
+
 Command Operators
 -----------------
 

tools/spelling_dictionary.txt

@@ -718,6 +718,7 @@ resolvers
 resync
 ret
 retriable
+rewriter
 rpcs
 rq
 rtrim