When launching a Flutter Android App, it launches in the Android emulator, however Flutter listens to some extra ports for debugging. These ports are random like 59044. Currently since I did not whitelist any, it does not launch my app, it gets stuck in the flutter logo waiting for debugging connection.

I'm behind some very unusual firewall and I need to allow all the ports needed for this project. Is there a way to set this flutter debugging port to a fixed one?

I tried on Android Studio configurations this extra argument for flutter attach:

--host-vmservice-port=50300

but it still tries random ports like 63398. I also tried --device-vmservice-port even though I don't understand what is the difference

Also it launches that https inspection tool on another random port, and I needed that one as well

When launching a Flutter Android App, it launches in the Android emulator, however Flutter listens to some extra ports for debugging. These ports are random like 59044. Currently since I did not whitelist any, it does not launch my app, it gets stuck in the flutter logo waiting for debugging connection.

I'm behind some very unusual firewall and I need to allow all the ports needed for this project. Is there a way to set this flutter debugging port to a fixed one?

I tried on Android Studio configurations this extra argument for flutter attach:

--host-vmservice-port=50300

but it still tries random ports like 63398. I also tried --device-vmservice-port even though I don't understand what is the difference

Also it launches that https inspection tool on another random port, and I needed that one as well

• android
• flutter

• You can set a fixed debugging port in Flutter by using --host-vmservice-port=50300 and --device-vmservice-port=50300 together, but for full control, configure your firewall to allow a range of ports (e.g., 50000–60000) to cover Flutter's dynamic allocation. – Manish Commented Feb 28 at 12:50
• @bob Im using SSH reverse forwarding, theres no way to allow a range of ports. Is there a way to prevent these allocations? – Poperton Commented Feb 28 at 17:39

4 Answers 4

Simply put, you can set Flask debugging port by running the following command:

flutter run --observatory-port=50300 --host-vmservice-port=50300 --device-vmservice-port=50300

Make sure to enable these ports in your firewall.

• Observatory Port: where the debugging happens, with Dart VM
• Host VM Service Port: sets the port on your host machine
• Device VM Service Port: essentially just forcing the emulator to use the same port as the host.

As for my understanding the flags you tried (--host-vmservice-port and --device-vmservice-port) are related but used for different purposses:

• --host-vmservice-port is for the port on your development machine
• --device-vmservice-port is for the port on the target device/emulator

Check out Fig docs for more info.

but if you need to run your flutter app in a specific port you should use this flag when you run your flutter app:

• --vm-service-port=50300

Use it like that from the terminal:

flutter run --vm-service-port=50300

Or configure your run configuration in Android Studio with these argument.

Or in your launch.json file if you use vscode:

{
  "configurations": [
    {
      "name": "Flutter",
      "request": "launch",
      "type": "dart",
      "args": [
        "--vm-service-port=50300",
      ]
    }
  ]
}

PS:

• the devtools will use the same port.
• if you run the web version of your app it will run on (8080) default port.

Check this part of the code where flutter is trying to retrieve the hostVmservicePort.

    ...
    // If DDS is enabled and no explicit DDS port is provided, use the
    // host-vmservice-port for DDS instead and bind the VM service to a random
    // port.
    if (enableDds && argResults?.wasParsed('dds-port') != true) {
      return null;
    }
    ...

If Dart Development Service (DDS) is enabled (which is enabled by default) and no explicit DDS port is provided, then host-vmservice-port is used for DDS and a random port is assigned to the host-vmservice-port.

So along with --host-vmservice-port also set the --dds-port to a custom available port.

Android emulator runs behind a "virtual router" that isolates it from your development machine network.

Depending on you use case and machine network configuration, you could try using network redirection: https://developer.android/studio/run/emulator-networking