// Copyright 2025 Envoy Project Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// 
//     http://www.apache.org/licenses/LICENSE-2.0
// 
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

syntax = "proto3";

package envoy.extensions.http.stateful_session.header.v3;

import "udpa/annotations/status.proto";
import "validate/validate.proto";

option java_package = "io.envoyproxy.envoy.extensions.http.stateful_session.header.v3";
option java_outer_classname = "HeaderProto";
option java_multiple_files = true;
option go_package = "github.com/envoyproxy/go-control-plane/envoy/extensions/http/stateful_session/header/v3;headerv3";
option (udpa.annotations.file_status).package_version_status = ACTIVE;

// [#protodoc-title: Header based stateful session extension]

// This extension allows the session state to be tracked via request headers.
//
// This extension encodes the address of the upstream host selected by the load balancer
// into a response header with the :ref:`header configuration
// <envoy_v3_api_msg_extensions.http.stateful_session.header.v3.HeaderBasedSessionState>`.
// When new requests are incoming, this extension will try to parse the specific upstream host
// address by header name. If the address parsed from the header corresponds to a valid
// upstream host, this upstream host will be selected first. See :ref:`stateful session filter
// <envoy_v3_api_msg_extensions.filters.http.stateful_session.v3.StatefulSession>`.
//
// For example, if the header name is set to ``session-header``, Envoy will prefer ``1.2.3.4:80``
// as the upstream host when the request contains the following header:
//
// .. code-block:: none
//
//     session-header: "MS4yLjMuNDo4MA=="
//
// When processing the upstream response, if ``1.2.3.4:80`` is indeed the final choice the extension
// does nothing. If ``1.2.3.4:80`` is not the final choice, the new selected host will be set to
// response headers (via the ``session-header`` response header).
//
// [#extension: envoy.http.stateful_session.header]
message HeaderBasedSessionState {
  // The name that will be used to obtain header value from downstream HTTP request or generate
  // new header for downstream.
  string name = 1 [(validate.rules).string = {min_len: 1}];
}
