Add winpty_get_console_process_list

[the-ress]

For a better implementation of microsoft/vscode#30152 and microsoft/vscode#29926 we need a list of processes attached to the console (instead of using a full process tree).

GetConsoleProcessList needs to be called from a process attached to the console. Since winpty-agent is already attached to it, it seems to be a good place to call it from.

[rprichard]

I'll try to get to this in a week or two.

[Tyriar]

@rprichard friendly ping 😃

[rprichard]

Looking at this code:

    auto processCount = GetConsoleProcessList(&processList[0], processList.size());
    if (processList.size() < processCount) {
        processList.resize(processCount);
        processCount = GetConsoleProcessList(&processList[0], processList.size());
    }

The process list can change while we're trying to read it, so I'd prefer that
the code loop while the processList vector was too small. Maybe on each time
through the loop, resize the vector to something like, "the greater of processCount * 2
and processCount". Multiplying by two caps the number of loop iterations. processCount * 2 could overflow, and if it does, then using
processCount will ensure that std::bad_alloc is raised (and turned into an
out-of-memory error at the winpty C API).

Otherwise, I'm happy with the PR.

[the-ress]

Thanks, I didn't think of that. It should be fixed now.

[rprichard]

If this code were to overflow, processList.size() would be 0x40000000, and newSize would be -0x80000000 (i.e. INT_MIN). newSize would be greater than processList.size() because it would be converted from int to size_t for the comparison.

I'd prefer to replace "const int newSize = ... ; ... if { ... }" with:

const auto newSize = std::max<DWORD>(processList.size() * 2, processCount);

If you do, also add #include <algorithm> to the top.

Overflow shouldn't ever happen. If it somehow does, then there is one code path handling it -- std::vector::resize throws std::bad_alloc.

[the-ress]

I used std::max as you said...

[rprichard]

ok, thanks!

[Tyriar]

🎉