Sending messages from server (HL2) to client (PC)

[anjelomerte]

Hey, yet another question:) Thanks for being so active on your issues!

Is there a way to send messages from the server to the client? I see that e.g. when remotely creating scenes in Unity from the client, a result array is "pulled", so there seems to be some communication in this direction implemented.

In particular, I would like to start and stop the streaming from the server side. For that, the transmission of a simple timestamp would be sufficient. Is this possible without modification of the underlying C++ plugin?

Edit: Just read that TCP port 3816 seems to be dedicated to that purpose and 4byte integers can be transmitted

[jdibenes]

Hi, There's no support for sending messages from HL2 to the PC in the same format as they are sent from PC to HL2. You can try using the HL2->PC 4-byte message queue by itself but maybe it would be simpler to create a new command to poll the server every few milliseconds and determine whether to stop/start the stream or do nothing. In either case, no modification of the C++ plugin is necessary, just need to change the RemoteUnityScene C# script and hl2ss_rus.py.

[anjelomerte]

Hey jdibenes,

thanks for the reply and sorry for my late reply, sth got inbetween. Anyways, your suggestion with polling the server seemed very reasonable which is what I'm currently digging into. I have managed to implement some custom commands for now to test behavior. The client can send some stuff (e.g. text) to the server (confirmed). However, I am struggling to read the response e.g. in the follwing setting:

# Create command buffer and append command(s)
buffer = command_buffer() 
buffer.tell_connect_success()

 # Send command(s) in buffer to the Unity app and receive response (4 byte unsigned integer per command)
client.push(buffer)
response = client.pull(buffer)

# Evaluate response
print(response[0])

In line response = client.pull(buffer) the program simply freezes. Why could that be? How can I read the uint response by the server? I need to be able to read the response to e.g. pack a timestamp as an integer. Thanks a lot!

[jdibenes]

That code looks OK. How are you implementing the tell_connect_success method?

[anjelomerte]

I tried to follow your code examples. In the module we would have a class command_buffer(hl2ss.umq_command_buffer) like so:

# Custom command buffer -------------------------------------------------------
class command_buffer(hl2ss.umq_command_buffer):
    # Command structure
    # id:     u32 (4 bytes)
    # size:   u32 (4 bytes)
    # params: size bytes

    # Indicate successful connection
    def connect_success(self):
        # Command id: 0xFFFFFFFD
        # Command params: empty byte data (id enough to indicate purpose)
        self.add(0xFFFFFFFD, b"") 

Then we define some methods to call like so:

# Message functions -----------------------------------------------------------
# Inform server about succuessful connect
def inform_connect():
    # Create command buffer and append command(s)
    buffer = command_buffer() 
    buffer.connect_success()

     # Send command(s) in buffer to the Unity app and receive response (4 byte unsigned integer per command)
    client.push(buffer)
    # response = client.pull(buffer)

    # Evaluate response
    # print("Received response:")
    # print(response[0])

[anjelomerte]

It simply was a problem of my network. For some reason it allowed messages from client to server but not the other way around. On another network it worked. Thanks a lot for your input!

[anjelomerte]

Hey jdibenes! In a more longterm perspective, communication from server to client will be pretty much necessary for me personally. Basically, I would like to control the whole streamin process from HoloLens side. Could you elaborate on how one could implement communication in that direction e.g. like you mentioned in your intial reply, utilizing the message queue? Thank you!