Don't check if the listening socket is valid #23601

This is a piece of #21878, chopped off to ease review.

Listening sockets in CConnman::vhListenSocket are always valid (underlying file descriptor is not INVALID_SOCKET).

Code-review ACK 6c9ee92ffe390064881ef5bf47e38e345d78a2a1 🔌

Verified that it's currently not possible that CConnman::vhListenSocket ever contains invalid sockets. The only place where an element gets added to the vector is in the method CConnman::BindListenPort:

https://github.com/bitcoin/bitcoin/blob/111c3e06b35b7867f2e0f740e988f648ac6c325d/src/net.cpp#L2394

which would already return earlier (directly after CreateSock(...)) if the socket contained in the sock wrapper was not valid. Also built and ran unit tests locally with success.

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #21879 (Wrap accept() and extend usage of Sock by vasild)
• #21878 (Make all networking code mockable by vasild)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

utACK.

If INVALID_SOCKET can get into recv_set, we have UB earlier anyway. Therefore, .count should always be 0 even if somehow listen_socket.socket were INVALID_SOCKET.

If this is safe, is there a reason why it can't be removed here as well?

src/net.cpp=void CConnman::StopNodes()
src/net.cpp-{
...
src/net.cpp-
src/net.cpp-    // Close listening sockets.
src/net.cpp:    for (ListenSocket& hListenSocket : vhListenSocket) {
src/net.cpp-        if (hListenSocket.socket != INVALID_SOCKET) {

@MarcoFalke, that's right - can be removed from here too and should have been part of this PR, I missed it.

I missed it because in #21878 that "close listening sockets" code becomes unnecessary and is removed:

-    // Close listening sockets.
-    for (ListenSocket& hListenSocket : vhListenSocket) {
-        if (hListenSocket.socket != INVALID_SOCKET) {
-            if (!CloseSocket(hListenSocket.socket)) {
-                LogPrintf("CloseSocket(hListenSocket) failed with error %s\n", NetworkErrorString(WSAG
-            }
-        }
-    }

This removal is also in #21879 which is chopped off from the big #21878 to ease review.

I will leave it as is to avoid further conflicts, hoping that #21879 will eventually make it in.