keybridged

keybridged is a Go HTTP daemon that sends key events to hardware bridges over UART or USB CDC. It is the companion backend for bridge firmwares:

• PicoUSBKeyBridge (UART -> USB HID keyboard)
• NordicBTKeyBridge (USB CDC -> BLE HID keyboard)

If you’re deciding which bridge to use:

• Need a wired USB keyboard presented to the target host → PicoUSBKeyBridge
• Need a Bluetooth LE keyboard presented to the target host → NordicBTKeyBridge

What it does

• Keeps a persistent connection to the bridge’s serial transport (USB CDC or a USB-to-UART adapter).
• Retries forever and logs device output to stdout.
• Exposes a small HTTP API for sending key events.

Build and run

go run github.com/2opremio/keybridged/cmd/keybridged@latest

macOS deployment:

./scripts/deploy_macos.sh

Flags:

• -host (default: localhost)
• -port (default: 9876)
• -send-timeout (default: 2) seconds to wait when queueing an event
• -vid (default: 0x1915) USB VID for the serial transport device
• -pid (default: 0x520F) USB PID for the serial transport device

Note: these flags do not refer to the HID keyboard identity (USB HID VID/PID or BLE PnP ID). They are only used to locate the serial device that keybridged talks to.

Examples:

• NordicBTKeyBridge (nRF52840 USB CDC, default):

./keybridged -vid 0x1915 -pid 0x520F

• PicoUSBKeyBridge using an FT232 USB-to-UART adapter (example hardware):

./keybridged -vid 0x0403 -pid 0x6001

HTTP API

POST /pressandrelease sends a single event (press + release). If type is omitted, it defaults to keyboard.

Request body:

{
  "type": <string> ("keyboard"|"consumer"),
  "code": <uint16>,
  "modifiers": {
    "left_ctrl": <bool>,
    "left_shift": <bool>,
    "left_alt": <bool>,
    "left_gui": <bool>,
    "right_ctrl": <bool>,
    "right_shift": <bool>,
    "right_alt": <bool>,
    "right_gui": <bool>,
    "apple_fn": <bool>
  }
}

• type:
  • "keyboard": standard key presses (letters, numbers, modifiers, function keys).
  • "consumer": media/system controls (volume, play/pause, keyboard layout toggle).
• code is a HID usage ID. See the on-wire details and code references in the serial protocol docs: PicoUSBKeyBridge#serial-protocol.
  • keyboard: USB HID Keyboard/Keypad keycode (8-bit; the JSON field is uint16 for convenience). code: 0 means "modifier-only" (no key pressed).
  • consumer: USB HID Consumer Page (0x0C) usage (16-bit).
• Keyboard modifiers (optional, macOS symbols/Apple names):
  • left_ctrl (⌃ Ctrl), left_shift (⇧ Shift), left_alt (⌥ Option), left_gui (⌘ Command)
  • right_ctrl (⌃ Ctrl), right_shift (⇧ Shift), right_alt (⌥ Option), right_gui (⌘ Command)
  • apple_fn (Fn) sets the Apple Fn bit in the keyboard report

If there’s demand, we can add a WebSocket API for more efficient key-event streaming than one HTTP request per key, and for real-time device log streaming.

Examples

Send letter A (a (HID code 4) + Shift):

curl -X POST "http://localhost:9876/pressandrelease" \
  -H "Content-Type: application/json" \
  -d '{"type":"keyboard","code":4,"modifiers":{"left_shift":true}}'

Hide/show iPad keyboard (AL Keyboard Layout / consumer usage 0x01AE):

curl -X POST "http://localhost:9876/pressandrelease" \
  -H "Content-Type: application/json" \
  -d '{"type":"consumer","code":430}'

Play/Pause (consumer usage 0x00CD):

curl -X POST "http://localhost:9876/pressandrelease" \
  -H "Content-Type: application/json" \
  -d '{"type":"consumer","code":205}'

Send only Apple Fn (modifier-only, no key):

curl -X POST "http://localhost:9876/pressandrelease" \
  -H "Content-Type: application/json" \
  -d '{"type":"keyboard","code":0,"modifiers":{"apple_fn":true}}'

Client library

There is a small Go client in client/ for calling the HTTP API.

package main

import "github.com/2opremio/keybridged/client"

kbClient := client.New(client.Config{
	Host: "localhost:9876",
})
err := kbClient.SendPressAndRelease(ctx, client.PressAndReleaseRequest{
	Type: "keyboard",
	Code: 0x04,
	Modifiers: &client.PressAndReleaseModifiers{
		LeftShift: true,
	},
}) // A with Shift

Serial protocol details

Serial protocol documentation lives in PicoUSBKeyBridge#serial-protocol.