Implement 'banner' option

README.md

@@ -31,6 +31,20 @@ stream_server:
    port: 1234
 ```
 
+Welcome/MOTD Message
+--------------------
+
+The optional 'banner' property allows to specify a string text to be always sent to client upon connecting.
+This is very useful for things like always forcing telnet client into character mode.
+Example: 
+
+```yaml
+stream_server:
+  banner: "\xFF\xFB\x01\xFF\xFB\x03\xFF\xFC\x34\r\nWelcome to my console"
+```
+
+The example above sends a special sequence to telnet that disables local echo and enables character mode.
+
 Sensors
 -------
 The server provides a binary sensor that signals whether there currently is a client connected:

components/stream_server/__init__.py

@@ -6,6 +6,7 @@
 # ESPHome doesn't know the Stream abstraction yet, so hardcode to use a UART for now.
 
 AUTO_LOAD = ["socket"]
+CONF_BANNER = "banner"
 
 DEPENDENCIES = ["uart", "network"]
 
@@ -30,6 +31,9 @@ def validate_buffer_size(buffer_size):
             cv.Optional(CONF_BUFFER_SIZE, default=128): cv.All(
                 cv.positive_int, validate_buffer_size
             ),
+            cv.Optional(CONF_BANNER): cv.All(
+                cv.string
+            )
         }
     )
     .extend(cv.COMPONENT_SCHEMA)
@@ -41,6 +45,7 @@ async def to_code(config):
     var = cg.new_Pvariable(config[CONF_ID])
     cg.add(var.set_port(config[CONF_PORT]))
     cg.add(var.set_buffer_size(config[CONF_BUFFER_SIZE]))
-
+    if CONF_BANNER in config:
+        cg.add(var.set_banner(config[CONF_BANNER]))
     await cg.register_component(var, config)
     await uart.register_uart_device(var, config)

components/stream_server/stream_server.cpp

@@ -75,7 +75,12 @@ void StreamServerComponent::accept() {
     if (!socket)
         return;
 
+    if (banner_ && strlen(banner_)) {
+        socket->write(banner_, strlen(banner_));
+    }
+
     socket->setblocking(false);
+
     std::string identifier = socket->getpeername();
     this->clients_.emplace_back(std::move(socket), identifier, this->buf_head_);
     ESP_LOGD(TAG, "New client connected from %s", identifier.c_str());

components/stream_server/stream_server.h

@@ -29,6 +29,8 @@ class StreamServerComponent : public esphome::Component {
     void set_connection_count_sensor(esphome::sensor::Sensor *connection_count) { this->connection_count_sensor_ = connection_count; }
 #endif
 
+    void set_banner(const char *banner) { this->banner_ = banner; };
+
     void setup() override;
     void loop() override;
     void dump_config() override;
@@ -63,6 +65,7 @@ class StreamServerComponent : public esphome::Component {
     esphome::uart::UARTComponent *stream_{nullptr};
     uint16_t port_;
     size_t buf_size_;
+    const char *banner_ = NULL;
 
 #ifdef USE_BINARY_SENSOR
     esphome::binary_sensor::BinarySensor *connected_sensor_;