Find a free port for PyOCD telnet semihosting

Author: thegecko

src/abstract-server.ts

@@ -48,8 +48,10 @@ export abstract class AbstractServer extends EventEmitter {
 
             try {
                 this.timer = setTimeout(() => this.onSpawnError(new Error('Timeout waiting for gdb server to start')), TIMEOUT);
+
                 const command = args.gdbServer || 'gdb-server';
-                this.process = spawn(command, args.gdbServerArguments, {
+                const serverArguments = await this.resolveServerArguments(args.gdbServerArguments);
+                this.process = spawn(command, serverArguments, {
                     cwd: dirname(command),
                 });
 
@@ -78,6 +80,10 @@ export abstract class AbstractServer extends EventEmitter {
         }
     }
 
+    protected async resolveServerArguments(serverArguments?: string[]): Promise<string[]> {
+        return serverArguments || [];
+    }
+
     protected onExit(code: number, signal: string) {
         this.emit('exit', code, signal);
 

src/pyocd-server.ts

@@ -24,14 +24,35 @@
 */
 
 import { AbstractServer } from './abstract-server';
+import { PortScanner } from './port-scanner';
 
 const LAUNCH_REGEX = /GDB server started/;
 const ERROR_REGEX = /:ERROR:gdbserver:/;
 const PERCENT_MULTIPLIER = 100 / 40; // pyOCD outputs 40 markers for progress
 
 export class PyocdServer extends AbstractServer {
+
+    protected portScanner = new PortScanner();
     protected progress = 0;
 
+    protected async resolveServerArguments(serverArguments?: string[]): Promise<string[]> {
+        if (!serverArguments) {
+            serverArguments = [];
+        }
+
+        const telnetPort = await this.portScanner.findFreePort(4444);
+
+        if (!telnetPort) {
+            return serverArguments;
+        }
+
+        return [
+            ...serverArguments,
+            '--telnet-port',
+            telnetPort.toString()
+        ];
+    }
+
     protected onStdout(chunk: string | Buffer) {
         super.onStdout(chunk);
         const buffer = typeof chunk === 'string' ? chunk : chunk.toString('utf8');