Telnet: (optional) buffered output for AsyncTcp server (#1929)

* telnet: buffered output for async server

* telnet: make async buffer an option

* just use the queue containers directly

* try with simpler list

* exhaust buffers as much as possible in a single try

* don't forget to destroy the client object

* naming

* kill the connection earlier

* fix merge issues

code/espurna/config/all.h

@@ -19,6 +19,8 @@
 
 */
 
+#include <core_version.h>
+
 #ifdef USE_CUSTOM_H
 #include "custom.h"
 #endif

code/espurna/config/dependencies.h

@@ -86,3 +86,8 @@
 #undef MDNS_CLIENT_SUPPORT
 #define MDNS_CLIENT_SUPPORT         0          // default resolver already handles this
 #endif
+
+#if not defined(ARDUINO_ESP8266_RELEASE_2_3_0)
+#undef TELNET_SERVER_ASYNC_BUFFERED
+#define TELNET_SERVER_ASYNC_BUFFERED 1         // enable buffered telnet by default on latest Cores
+#endif

code/espurna/config/general.h

@@ -130,6 +130,11 @@
 #define TELNET_SERVER           TELNET_SERVER_ASYNC // Can be either TELNET_SERVER_ASYNC (using ESPAsyncTCP) or TELNET_SERVER_WIFISERVER (using WiFiServer)
 #endif
 
+#ifndef TELNET_SERVER_ASYNC_BUFFERED
+#define TELNET_SERVER_ASYNC_BUFFERED         0  // Enable buffered output for telnet server (+1Kb)
+                                                // Helps to avoid lost data with lwip2 TCP_MSS=536 option
+#endif
+
 // Enable this flag to add support for reverse telnet (+800 bytes)
 // This is useful to telnet to a device behind a NAT or firewall
 // To use this feature, start a listen server on a publicly reachable host with e.g. "ncat -vlp <port>" and use the MQTT reverse telnet command to connect

code/espurna/config/prototypes.h

@@ -3,7 +3,6 @@
 #include <functional>
 #include <vector>
 #include <memory>
-#include <core_version.h>
 
 extern "C" {
     #include "user_interface.h"
@@ -32,6 +31,12 @@ extern "C" {
   #include <lwip/init.h> // LWIP_VERSION_MAJOR
 }
 
+// ref: https://github.com/me-no-dev/ESPAsyncTCP/pull/115/files#diff-e2e636049095cc1ff920c1bfabf6dcacR8
+// This is missing with Core 2.3.0 and is sometimes missing from the build flags. Assume HIGH_BANDWIDTH version.
+#ifndef TCP_MSS
+#define TCP_MSS (1460)
+#endif
+
 uint32_t systemResetReason();
 uint8_t systemStabilityCounter();
 void systemStabilityCounter(uint8_t);