Tunnel ADB connections to the proxy, as a fallback route

Author: pimterry

custom-typings/adbkit.d.ts

@@ -38,6 +38,7 @@ declare module '@devicefarmer/adbkit' {
         shell(id: string, cmd: string | string[]): Promise<stream.Readable>;
         root(id: string): Promise<true>;
         on(type: 'error', handler: (error: Error) => void): void;
+        reverse(id: string, remote: string, local: string): Promise<true>;
     }
 
     export function createClient(options?: {

src/interceptors/android/android-adb-interceptor.ts

@@ -100,10 +100,13 @@ export class AndroidAdbInterceptor implements Interceptor {
                 )
             ),
             port: proxyPort,
+            localTunnelPort: proxyPort,
             certFingerprint: generateSPKIFingerprint(this.config.https.certContent)
         };
         const intentData = urlSafeBase64(JSON.stringify(setupParams));
 
+        await this.adbClient.reverse(options.deviceId, 'tcp:' + proxyPort, 'tcp:' + proxyPort).catch(() => {});
+
         // Use ADB to launch the app with the proxy details
         await this.adbClient.startActivity(options.deviceId, {
             wait: true,
@@ -112,7 +115,40 @@ export class AndroidAdbInterceptor implements Interceptor {
         });
 
         this.deviceProxyMapping[proxyPort] = this.deviceProxyMapping[proxyPort] || [];
-        this.deviceProxyMapping[proxyPort].push(options.deviceId);
+
+        if (!this.deviceProxyMapping[proxyPort].includes(options.deviceId)) {
+            this.deviceProxyMapping[proxyPort].push(options.deviceId);
+
+            let tunnelConnectFailures = 0;
+
+            // The reverse tunnel can break when connecting/disconnecting from the VPN. This is a problem! It can
+            // also break in other cases, e.g. when ADB is restarted for some reason. To handle this, we constantly
+            // reinforce the tunnel while HTTP Toolkit is running & the device is connected.
+            const tunnelCheckInterval = setInterval(async () => {
+                if (this.deviceProxyMapping[proxyPort].includes(options.deviceId)) {
+                    try {
+                        await this.adbClient.reverse(options.deviceId, 'tcp:' + proxyPort, 'tcp:' + proxyPort)
+                        tunnelConnectFailures = 0;
+                    } catch (e) {
+                        tunnelConnectFailures += 1;
+                        console.log(`${options.deviceId} ADB tunnel failed`, e);
+
+                        if (tunnelConnectFailures >= 5) {
+                            // After 10 seconds disconnected, give up
+                            console.log(`${options.deviceId} disconnected, dropping the ADB tunnel`);
+                            this.deviceProxyMapping[proxyPort] = this.deviceProxyMapping[proxyPort]
+                                .filter(id => id !== options.deviceId);
+                            clearInterval(tunnelCheckInterval);
+                        }
+                    }
+                } else {
+                    // Deactivation at shutdown will clear the proxy data, and so clear this interval
+                    // will automatically shut down.
+                    clearInterval(tunnelCheckInterval);
+                }
+            }, 2000);
+            tunnelCheckInterval.unref(); // Don't let this block shutdown
+        }
     }
 
     async deactivate(port: number | string): Promise<void | {}> {