rewrite buffer implementation to eliminate evbuffer dependency (#5441)

Signed-off-by: Brian Pane <[email protected]>

docs/root/intro/version_history.rst

@@ -39,6 +39,7 @@ Version history
 * mysql: added a MySQL proxy filter that is capable of parsing SQL queries over MySQL wire protocol. Refer to ::ref:`MySQL proxy<config_network_filters_mysql_proxy>` for more details.
 * http: added :ref:`max request headers size <envoy_api_field_config.filter.network.http_connection_manager.v2.HttpConnectionManager.max_request_headers_kb>`. The default behaviour is unchanged.
 * http: added modifyDecodingBuffer/modifyEncodingBuffer to allow modifying the buffered request/response data.
+* performance: new buffer implementation (disabled by default; to test it, add "--use-libevent-buffers 0" to the command-line arguments when starting Envoy).
 * http: added encodeComplete/decodeComplete. These are invoked at the end of the stream, after all data has been encoded/decoded respectively. Default implementation is a no-op.
 * redis: added :ref:`hashtagging <envoy_api_field_config.filter.network.redis_proxy.v2.RedisProxy.ConnPoolSettings.enable_hashtagging>` to guarantee a given key's upstream.
 * redis: added :ref:`latency stats <config_network_filters_redis_proxy_per_command_stats>` for commands.

include/envoy/server/options.h

@@ -174,6 +174,11 @@ class Options {
    */
   virtual bool mutexTracingEnabled() const PURE;
 
+  /**
+   * @return whether to use the old libevent evbuffer-based Buffer implementation.
+   */
+  virtual bool libeventBufferEnabled() const PURE;
+
   /**
    * @return bool indicating whether cpuset size should determine the number of worker threads.
    */