uWebSockets | Simple , secure & standards compliant web server | HTTP library

By default a lambda's call operator is const-qualified.

Inside the lambda's body the this pointer to the lambda is therefore also const-qualified and so is the member wrapper. std::packaged_task does not have a const-qualified operator(), so it cannot be called.

You can make the lambda's operator() non-const-qualified by adding the mutable keyword:

Let's take this step by step. Let's start with the very definition of what std::async does. It:

runs the function f asynchronously (potentially in a separate thread

The word "potentially" is a distraction here, but the point is that a different execution thread is going to be involved here. For all practical reasons, the function getting std::async-ed can, and on modern C++ implementations, it will run in a new execution thread.

The very reason for having different execution threads, in the first place, is that they are completely independent of their parent execution thread. Different execution threads must properly implement sequencing operations in order to mutually exchange information between themselves, in some form or fashion.

According to the documentation, the remote address is an attribute of the response. Ergo:

You can "front-load" the type inference into a type alias.

As @DazWilkin mentioned, WebSockets can be used with App Engine Flexible environment and with Cloud Run.

App Engine standard environment doesn't support this.

It is because the compiler cannot convert 'brace-enclosed initializer list' to T&&. It can be solved by declaring the struct and converting it to Rvalue reference.

Is there any linking sequence problem? I see that usockets links behind libuv, maybe we can try swap the sequence: to link usockets first.

You are using static linkage, and usockets depends on libuv, so swap the sequence will fix the problem.

Related questions:

Why does the order in which libraries are linked sometimes cause errors in GCC?

The thing is, that you have to set the path to the library file as the target_link_libraries argument.

According to the documentation, if you want to link the library, each argument of target_link_libraries can be:

• A library target name
• A full path to a library file (e.g. /usr/lib/foo.so)
• A plain library name (e.g. foo)

In your case I suggest you to add the complete path to the library.

I don't have all the code of your project, so I suggest you consider this minimal example:

Answering my own question, not entirely but will post what worked for me. Ultimately I could not figure out what was wrong with the code above, I suspect somewhere I was not doing something right with the initialization or requests.

Some of the files are from above and have not been modified, but I'll post them anyways. Also, I had used this article as a starting point.

CustomPeerConnection.java