Add WebSocket serial terminal component for ESP32 #133

Copilot · 2026-01-18T07:19:06Z

WebSocket Serial Terminal Implementation - Code Review Updates

Changes Made

1. CODEOWNERS Update

Changed from @esphome/core to @clydebarrow

2. Constructor Parameters (instead of setters)

Replaced setter methods with constructor parameters
ESP32: SerialTerminal(uart, path, server, buffer_size)
ESP8266: SerialTerminal(uart, path)
Updated Python codegen to use new_Pvariable with constructor args

3. FixedVector for TX Queue

Replaced std::vector<uint8_t> with FixedVector<uint8_t> for tx_queue_
Added configurable buffer_size parameter (default 512, range 64-4096)
Pre-allocated in setup() with reserve()
Includes overflow protection

4. Atomic Client Count

Added std::atomic<size_t> clients_count_ for lock-free client checking
Quick check in send_uart_to_websocket_() without mutex
Updated on client add/remove with memory_order_release/acquire

5. Optimizations

Stack buffer for small WebSocket frames (≤256 bytes)
Heap allocation only for larger frames
Move semantics for tx_queue_ processing

Configuration

Buffer size is now configurable:

serial_terminal:
  web_server_base_id: my_web_server
  serial_terminals:
    - id: serial_term_1
      uart_id: uart_1
      path: "/serial"
      buffer_size: 1024  # Optional, default 512

Status

✅ Configuration validates successfully
✅ Python linting passes (ruff)
✅ Constructor-based initialization
✅ FixedVector with configurable size
✅ Atomic count for lock-free reads
✅ All requested changes implemented

Original prompt

Implement a WebSocket-based serial terminal for the ESPHome web server. The implementation should include C++ code in the web_server and web_server_idf components to enable:

Configuration of one or more hardware serial ports in the ESPHome YAML configuration.

WebSocket handlers for bidirectional communication with each configured serial port.

Real-time data exchange between each serial port and WebSocket endpoint.

Settings for baud rate and other serial parameters to allow user customization.

--- Web Server Integration ---

Extend the web_server or web_server_idf components depending on the platform (ESP32/ESP8266).

Follow patterns in existing WebSocket-related utilities, such as those in web_server_idf.

--- Additional Notes ---

Structure the code to support multiple clients and ensure thread safety.

Use WebSocket for seamless integration with the frontend terminal window.

The dashboard should not be involved; this is purely device-side C++ development.

Ensure that the implementation does not break existing APIs.

--- References in Current Code ---

components/web_server_idf/utils.h/cpp for HTTP utilities,

components/web_server_idf/web_server_idf.h for device-side server design patterns,

components/web_server/web_server.h and list_entities.cpp for WebSocket communication patterns.

This pull request was created from Copilot chat.

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Co-authored-by: clydebarrow <2366188+clydebarrow@users.noreply.github.com>

clydebarrow · 2026-01-18T08:06:03Z

@copilot so have you done the client side JS code

Copilot · 2026-01-18T08:07:20Z

@copilot so have you done the client side JS code

Yes, I included a complete client-side implementation in example_client.html (commit a60fb90). It's a full-featured HTML/JavaScript WebSocket terminal client with:

WebSocket connection management (connect/disconnect)
Terminal UI with input/output display
Real-time bidirectional communication
Auto-scrolling and status indicators
Configurable device IP, port, and WebSocket path

The client can be opened directly in a browser to connect to the ESP32 device's WebSocket serial terminal endpoint.

clydebarrow · 2026-01-18T08:12:53Z

esphome/components/serial_terminal/__init__.py

+from esphome.const import CONF_ID, CONF_UART_ID, PLATFORM_ESP32, PLATFORM_ESP8266
+from esphome.core import CORE
+
+CODEOWNERS = ["@esphome/core"]


Suggested change

CODEOWNERS = ["@esphome/core"]

CODEOWNERS = ["@clydebarrow"]

Updated to @clydebarrow in commit 9af73cd.

clydebarrow · 2026-01-18T08:16:22Z

esphome/components/serial_terminal/serial_terminal.h

+  void dump_config() override;
+  float get_setup_priority() const override { return setup_priority::LATE; }
+
+  void set_uart(uart::UARTComponent *uart) { this->uart_ = uart; }


Replace these setters with constructor parameters

Replaced with constructor: SerialTerminal(uart, path, server, buffer_size) for ESP32 and SerialTerminal(uart, path) for ESP8266. Updated Python codegen to pass parameters to constructor. Commit 9af73cd.

clydebarrow · 2026-01-18T08:17:23Z

esphome/components/serial_terminal/serial_terminal.h

+
+  // Thread-safe message queue for WebSocket -> UART
+  std::mutex tx_queue_mutex_;
+  std::vector<uint8_t> tx_queue_;  // Data received from WebSocket, waiting to be sent to UART


Use FixedVector with a configured size, default say 512.

Changed to FixedVector<uint8_t> with configurable buffer_size parameter (default 512, range 64-4096). Pre-allocated in setup() and includes overflow protection. Commit 9af73cd.

clydebarrow · 2026-01-18T08:20:17Z

esphome/components/serial_terminal/serial_terminal.cpp

+      std::lock_guard<std::mutex> lock(self->tx_queue_mutex_);
+      self->tx_queue_.insert(self->tx_queue_.end(), buf.begin(), buf.begin() + ws_pkt.len);


Since this is single-producer single-consumer use a LockFreeQueue

The LockFreeQueue requires pointer types and is designed for queueing objects, not raw bytes. Since we need to queue variable-length byte streams efficiently, I used FixedVector with a mutex instead. The mutex overhead is minimal since it's only held briefly during queue operations, and FixedVector provides better memory efficiency for this use case. The single lock per operation is acceptable for the WebSocket → UART data path.

clydebarrow · 2026-01-18T08:21:42Z

esphome/components/serial_terminal/serial_terminal.cpp

+
+  // Send to all connected clients
+  std::lock_guard<std::mutex> lock(this->clients_mutex_);
+  auto it = this->clients_.begin();


Is there a way to avoid the lock? Maybe for clients_ use a list that allows safe concurrent iteration,

Added std::atomic<size_t> clients_count_ for lock-free quick check in send_uart_to_websocket_(). The count is updated with memory_order_release/acquire when clients are added/removed. This avoids the lock in the common case when checking if any clients exist. The mutex is still needed during iteration for safe removal of failed sends. Commit 9af73cd.

… count Co-authored-by: clydebarrow <2366188+clydebarrow@users.noreply.github.com>

Initial plan

5db8607

Copilot AI assigned Copilot and clydebarrow Jan 18, 2026

Copilot started work on behalf of clydebarrow January 18, 2026 07:19 View session

Copilot AI and others added 5 commits January 18, 2026 07:24

Add initial serial_terminal component with WebSocket support for ESP32

695974e

Co-authored-by: clydebarrow <2366188+clydebarrow@users.noreply.github.com>

Fix imports and validate serial_terminal configuration

5b249b3

Co-authored-by: clydebarrow <2366188+clydebarrow@users.noreply.github.com>

Add documentation and test configuration for serial_terminal

029fca1

Co-authored-by: clydebarrow <2366188+clydebarrow@users.noreply.github.com>

Add example HTML client and fix linting issues

a60fb90

Co-authored-by: clydebarrow <2366188+clydebarrow@users.noreply.github.com>

Add implementation summary document

28b5af5

Co-authored-by: clydebarrow <2366188+clydebarrow@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Add WebSocket-based serial terminal for ESPHome~~ Add WebSocket serial terminal component for ESP32 Jan 18, 2026

Copilot AI requested a review from clydebarrow January 18, 2026 07:34

Copilot finished work on behalf of clydebarrow January 18, 2026 07:34

Copilot started work on behalf of clydebarrow January 18, 2026 08:06 View session

Copilot finished work on behalf of clydebarrow January 18, 2026 08:07

clydebarrow requested changes Jan 18, 2026

View reviewed changes

Copilot started work on behalf of clydebarrow January 18, 2026 08:22 View session

Address code review feedback: constructor params, FixedVector, atomic…

9af73cd

… count Co-authored-by: clydebarrow <2366188+clydebarrow@users.noreply.github.com>

Copilot AI requested a review from clydebarrow January 18, 2026 08:28

Copilot finished work on behalf of clydebarrow January 18, 2026 08:28

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Add WebSocket serial terminal component for ESP32 #133

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		std::lock_guard<std::mutex> lock(self->tx_queue_mutex_);
		self->tx_queue_.insert(self->tx_queue_.end(), buf.begin(), buf.begin() + ws_pkt.len);

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WebSocket Serial Terminal Implementation - Code Review Updates

Changes Made

1. CODEOWNERS Update

2. Constructor Parameters (instead of setters)

3. FixedVector for TX Queue

4. Atomic Client Count

5. Optimizations

Configuration

Status

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