api: mark internal listener as implemented and change internal listener binding (#22274)

Signed-off-by: Kuat Yessenov <kuat@google.com>

Commit Message: Expose internal listener functionality. Marks the fields as implemented. Adds the following functional changes prior to publishing:
* do not use the `address` field per https://github.com/envoyproxy/envoy/pull/21132, and instead use the listener `name` field as originally expected.
* add an `endpoint_id` field to upstream address to fix https://github.com/envoyproxy/envoy/pull/22420; it's not possible to have multiple internal addresses to the same listener in a single pool without some extra identifier beyond the listener name, because pools identify addresses using `asString()`.
* fixes https://github.com/envoyproxy/envoy/issues/20665 by using stat prefix `listener.envoy_internal_<listener_name>`.

Adds a few sample configs (and fixes https://github.com/envoyproxy/envoy/issues/20335):
* minimal two chained `tcp_proxy` listeners;
* encap HTTP in HTTP CONNECT;
* decap HTTP in HTTP CONNECT;

Risk Level: low, hidden prior
Testing: yes
Docs Changes: yes
Release Notes: yes

Mirrored from https://github.com/envoyproxy/envoy @ 02489bbf8990faddb6be1f2e0f22851b64c3fc85

envoy/config/core/v3/address.proto

@@ -32,15 +32,20 @@ message Pipe {
 }
 
 // The address represents an envoy internal listener.
-// [#comment: TODO(lambdai): Make this address available for listener and endpoint.
-// TODO(asraa): When address available, remove workaround from test/server/server_fuzz_test.cc:30.]
+// [#comment: TODO(asraa): When address available, remove workaround from test/server/server_fuzz_test.cc:30.]
 message EnvoyInternalAddress {
   oneof address_name_specifier {
     option (validate.required) = true;
 
-    // [#not-implemented-hide:] The :ref:`listener name <envoy_v3_api_field_config.listener.v3.Listener.name>` of the destination internal listener.
+    // Specifies the :ref:`name <envoy_v3_api_field_config.listener.v3.Listener.name>` of the
+    // internal listener.
     string server_listener_name = 1;
   }
+
+  // Specifies an endpoint identifier to distinguish between multiple endpoints for the same internal listener in a
+  // single upstream pool. Only used in the upstream addresses for tracking changes to individual endpoints. This, for
+  // example, may be set to the final destination IP for the target internal listener.
+  string endpoint_id = 2;
 }
 
 // [#next-free-field: 7]
@@ -143,7 +148,8 @@ message Address {
 
     Pipe pipe = 2;
 
-    // [#not-implemented-hide:]
+    // Specifies a user-space address handled by :ref:`internal listeners
+    // <envoy_v3_api_field_config.listener.v3.Listener.internal_listener>`.
     EnvoyInternalAddress envoy_internal_address = 3;
   }
 }

envoy/config/listener/v3/listener.proto

@@ -103,7 +103,6 @@ message Listener {
   }
 
   // Configuration for envoy internal listener. All the future internal listener features should be added here.
-  // [#not-implemented-hide:]
   message InternalListenerConfig {
   }
 
@@ -333,24 +332,21 @@ message Listener {
   google.protobuf.BoolValue bind_to_port = 26;
 
   // The exclusive listener type and the corresponding config.
-  // TODO(lambdai): https://github.com/envoyproxy/envoy/issues/15372
-  // Will create and add TcpListenerConfig. Will add UdpListenerConfig and ApiListener.
-  // [#not-implemented-hide:]
   oneof listener_specifier {
     // Used to represent an internal listener which does not listen on OSI L4 address but can be used by the
     // :ref:`envoy cluster <envoy_v3_api_msg_config.cluster.v3.Cluster>` to create a user space connection to.
-    // The internal listener acts as a tcp listener. It supports listener filters and network filter chains.
-    // The internal listener require :ref:`address <envoy_v3_api_field_config.listener.v3.Listener.address>` has
-    // field `envoy_internal_address`.
+    // The internal listener acts as a TCP listener. It supports listener filters and network filter chains.
+    // Upstream clusters refer to the internal listeners by their :ref:`name
+    // <envoy_v3_api_field_config.listener.v3.Listener.name>`. :ref:`Address
+    // <envoy_v3_api_field_config.listener.v3.Listener.address>` must not be set on the internal listeners.
     //
-    // There are some limitations are derived from the implementation. The known limitations include
+    // There are some limitations that are derived from the implementation. The known limitations include:
     //
     // * :ref:`ConnectionBalanceConfig <envoy_v3_api_msg_config.listener.v3.Listener.ConnectionBalanceConfig>` is not
-    //   allowed because both cluster connection and listener connection must be owned by the same dispatcher.
+    //   allowed because both the cluster connection and the listener connection must be owned by the same dispatcher.
     // * :ref:`tcp_backlog_size <envoy_v3_api_field_config.listener.v3.Listener.tcp_backlog_size>`
     // * :ref:`freebind <envoy_v3_api_field_config.listener.v3.Listener.freebind>`
     // * :ref:`transparent <envoy_v3_api_field_config.listener.v3.Listener.transparent>`
-    // [#not-implemented-hide:]
     InternalListenerConfig internal_listener = 27;
   }