I built a self-hosted remote terminal that survives app kills, network switches, and phone sleep — runs on Web, iOS, Android, and HarmonyOS

Two months ago I was SSH'd into a server from my phone on a train. Switched to another app for 10 seconds, came back — tab killed, session gone.

Every mobile terminal app has the same problem: none can actually keep a connection alive. The OS kills background processes, switches networks, or puts the radio to sleep.

I flipped the model: what if the shell keeps running on a remote agent, and your phone is just the display?

Architecture

• Worker — lightweight agent on any machine. Manages PTY sessions that keep running with zero connected clients.


• Gateway — .NET 10 middleware. Auth, routing, session coordination.


• Client — Web (React + xterm.js), iOS, Android, HarmonyOS. Pure rendering with scrollback replay on reconnect.
  

Client (Browser / iOS / Android / HarmonyOS)

         ↕  SignalR

     Gateway (.NET 10)

         ↕  SignalR

     Worker (.NET 10 + PTY)

The Hard Part: Hand-Rolling SignalR for HarmonyOS

On iOS/Android/Web, there's a Microsoft SDK. On HarmonyOS? Nothing.

1091 lines of ArkTS later, I had a full SignalR client:

• Negotiate handshake — HTTP POST, extract connection token


• WebSocket transport — exponential backoff reconnection


• Hub protocol — 5 message types (Invocation, StreamItem, Completion, Ping, Close), 0x1E record-separated


• Keepalive — 15s ping, cyclic reconnect (official SDK gives up after 5; mine does 15)
  

switch (message.type) {

  case 1: this.invokeHandler(invocation.target, invocation.arguments); break;

  case 2: pending.resolve(streamItem.item); break;

  case 3: completion.error ? pending.reject(err) : pending.resolve(result); break;

  case 6: break; // Ping

  case 7: this.handleCloseMessage(close); break;

}

Virtual Keyboard on Mobile

No physical keyboard means no Ctrl+C. My solution: sticky modifier keys. Tap Ctrl once to latch it, tap C to send SIGINT:

const ch = 'c'.toLowerCase().charCodeAt(0);  // 99

this.sendInput(String.fromCharCode(ch - 96)); // x03 = SIGINT

ArkTS Constraints

Every one caused a compile error: no as const, no untyped object literals, no destructuring, throw only accepts Error.

Numbers

425 commits, 53 days, 1 person, 5 platforms. HarmonyOS: 8645 lines ArkTS, 1091 lines SignalR.

Try It

docker run -d -p 5045:5045 ghcr.io/monster-echo/corterm-gateway:latest

GitHub: github.com/monster-echo/CortexTerminal2

App Store · Google Play · Huawei AppGallery

Questions about SignalR, PTY lifecycle, or cross-platform CI? Ask below.