sockets | C code for working with sockets in both UNIX and Internet | Runtime Evironment library

I have an app that communicates with a bluetooth device, and I'm trying to replace that app with some code.

I tried using C# InTheHand nuget, Microsoft's Bluetooth LE Explorer, python's sockets and others to send data and see what happens.

But there's something I still don't understand - in each way using different libraries I saw in wireshark a different protocol: ATT, RFCOMM, L2CAP...

When I sniffed my bluetooth traffic from my phone using the app mentioned before, I saw mostly HCI_CMD protocol traffic.

How can I choose the protocol I want to send? Is there a simple package for that? something to read?

Do I need to build the packet myself? including headers and such?

Thank you!

Update: Using Microsoft's Bluetooth LE Explorer I was able to send a packet that lit up my lamp, starting with 02010e10000c00040012(data)
Using bleak I was able to send a packet starting with 02010e10000c00040052(data)
the difference makes the lamp not ligh up and I'm not sure if I can change it via bleak as it's not part of the data I send

First time using IO Completion Ports. I'm having an issue where the GetQueuedCompletionStatus returns a Null for the Completion Key, which I am using to pass a data struct with handles for other portions of the code. The GetQueuedCompletionStatus seems to be triggering off messages received just fine otherwise.

I tried to include just the code involving the IO Completion ports:

The Data Structs:

I have a C# Winform application trying to launch a node server.

However the code for this is written in a different cs file, Class1.cs rather than in Form.cs itself. I need to keep this separated in different files. Below is my Class1.cs file:

I am trying to get my robot to communicate with my PC via sockets by using local IP addresses on my own home network (not devices outside my network). The robot is acting as the server and my own PC is acting as the client/host. I don't really know what ports are open on my robot but I do definitely know that port 22 on the robot is open (which is the SSH port). The robot is a lego EV3 robot apart from it has had some ev3python software put onto it. When I run my program I am getting the following error on the server (my robot):

I'm trying to deploy my Laravel Websockets application as part of my Laravel 8 API project. Everything works locally, but after deploying I'm unable to connect to port 6001 on my website's domain, which is a sub-domain.

I'm using a Cent OS 8 server with Apache and already have port 80 open to my website on https://api.example.com/, and in order for my site on https://site.example.com/ I've gone ahead and created a sub-domain called https://api-socket.example.com/ and need to proxy this through to port 6001.

The config for a Nginx server I've tried to replace as a virtual host but when I restart httpd I get a 521 error with Cloudflare, my config is:

/etc/httpd/sites-available/api-socket.example.com.conf

I am new to Objective-c. I am using swiftui to make my app. But need to implant objective-c code for BLE. all work until I get this code

in .h file

I created a TCP server for receiving information from some devices, and I wanted to created an API out from this server, and I exported two variables in order to use them in the API. When I do that, my server starts in my other process, making that they execute at the same time, I don't know why this happens

I'm trying trying to send data from a c file using winsock2 compiled with Visual Studio to a WebSocket server in Javascript. But I didn't succeed in making them communicate on windows. As I'm not a c visual studio and socket expert, I don't understand why the C client does not send any data to my JS WebSocket server.

Here are the two following "code" that I'm using. If you have some tips or a good ideas. Feel free to answer.

C code

I am writing a small TCP sockets "library", and I ran into much trouble.

When something happens to the socket that causes it to be instantly closed and freed (regardless of background lingering, talking about user space here), which is only done within a locked mutex since the application I'm writing is multi-threaded, I need a way to tell all the other (potentially) waiting threads (on the same mutex) that want to do something with the socket: "I'm terribly sorry, but the socket has been destroyed and you cannot access it" so that they don't cause any segmentation fault or such.

The idea I had was: the mutex was part of the socket (socket = a structure that contains multiple things, including a mutex and a file descriptor) so I couldn't quite free the socket if other threads were waiting for it (undefined behavior), so the possible solution is to allocate the mutex, free the socket but not the mutex, set some flag (in the allocated memory) saying that the socket has been closed, and a counter so that the last thread waking up and getting notified that it cannot use the socket unlocks and destroys the mutex and frees the memory allocated. The mutex can still be accessed without segfault if we just store its pointer before acquiring the mutex (and the pointer won't ever change).

This solution has a fundamental problem though - what if between unlocking the mutex and freeing it by the last holder, the thread gets preempted and another one locks the mutex again (since you NEED to check socket-related stuff after you acquire the lock, so no way of knowing it got destroyed, unless you maybe use an atomic variable but then again, checking the atomic variable and locking the mutex as a whole are not an atomic operation). Or if you try to access the mutex on the already-freed socket. Undefined behavior emerges.

Any ideas how to solve this problem? I.e. how to destroy a socket so that other threads know about it to quit safely, and there are no race conditions? By quitting I mean aborting the socket function they were in, not cancelling or stopping the threads themselves.