LineServer is a custom ESPHome component based on @oxan’s stream_server. It acts as a transparent UART-to-TCP line-oriented bridge, with extended support for line terminators, timeouts, and directional buffers. This makes it ideal for RS-232-based command protocols like RIO (Russound), which use line-based communication patterns.

The component listens on a configurable TCP port and forwards lines between UART and TCP clients, flushing on a terminator or idle timeout.

• Bi-directional UART–TCP communication
• Independent ring buffers for UART and TCP
• Configurable line terminators for each direction
• Idle flush timeout to handle incomplete lines
• Optional lambda handlers for custom processing of incomplete lines
• TCP client tracking with optional sensors
• Multiple UARTs supported
• Compatible with Wi-Fi and Ethernet

• ESPHome version 2022.3.0 or newer

external_components:
  - source: github://gstos/esphome-line-server
    components: [line_server]

uart:
  id: uart_bus
  tx_pin: GPIO17
  rx_pin: GPIO16
  baud_rate: 9600

line_server:
  uart_id: uart_bus

uart:
  id: uart_bus
  tx_pin: GPIO17
  rx_pin: GPIO16
  baud_rate: 9600

line_server:
  uart_id: uart_bus
  port: 7000                        # TCP port (default: 6638)
  uart_buffer_size: 512            # Must be power of 2
  tcp_buffer_size: 512             # Must be power of 2
  uart_terminator: "\r\n"          # Flush UART buffer on this sequence
  tcp_terminator: "\r"             # Flush TCP buffer on this sequence
  uart_timeout: 500ms              # Flush UART partial line after idle
  tcp_timeout: 300ms               # Flush TCP partial line after idle

  uart_timeout_lambda: |-
    return "[UART TIMEOUT]";       # Optional: override stale UART line

  tcp_timeout_lambda: |-
    return "[TCP TIMEOUT]";        # Optional: override stale TCP line

You can use a lambda to process, modify, or preserve partial messages that timeout without a terminator.

line_server:
  uart_id: uart_bus
  uart_timeout_lambda: |-
    return partial;  # Just forward the partial line

line_server:
  uart_id: uart_bus
  uart_timeout_lambda: |-
    return partial + " [incomplete]";

line_server:
  uart_id: uart_bus
  uart_timeout_lambda: |-
    if (partial.length() < 5) return "";  // discard
    return partial;

binary_sensor:
  - platform: line_server
    connected:
      name: TCP Client Connected

sensor:
  - platform: line_server
    connections:
      name: TCP Client Count

You can use multiple UARTs with separate line servers:

uart:
  - id: uart1
    rx_pin: GPIO16
    tx_pin: GPIO17
    baud_rate: 9600

  - id: uart2
    rx_pin: GPIO25
    tx_pin: GPIO26
    baud_rate: 19200

line_server:
  - uart_id: uart1
    port: 7001

  - uart_id: uart2
    port: 7002

• Buffer sizes must be powers of two.
• Terminators must be ≤ 4 bytes, UTF-8 encoded.
• The *_timeout_lambda allows customizing what is sent when an incomplete line is flushed. Returning an empty string means the data is discarded.
• All data is treated as raw — no Telnet, RFC2217, or control sequences.
• Notice that the UART buffer size implements an additional buffer on top of the ESPHome RX buffer.
• For now, it is up for the consumer of the TCP API to handle "request -> response" cycles correctly. In the future, we may implement some sort of state handling to properly manage "request -> response" cycles correctly. Have that in mind, specially if you are sending requests from multiple clients to the same UART.
• Notice that the default behaviour is to flush the buffers on a timeout. Consider this behaviour for protocols that expect a response to a command.
• Originally based on esphome-stream-server by @oxan.