Plug errno in TCPSocket::Connect()

[krytarowski]

Summary

Reset errno to 0 for error branches.

Without this, debugging real issues in LLDB is harder
as we don't know what and when caused the errno
to be set.

Sponsored by <The NetBSD Foundation>

[labath]

This seems weird. I have never seen anyone resetting errno *after* a call. Wouldn't it be better to log strerror(errno) somewhere, or make sure that the Status object reflects the actual error?

[clayborg]

Yeah, never seen that before. Are you sure CreateSocket is doing the right thing and checking for the correct return value? That is the only way I can see this causing issues.

[krytarowski]

This just helps debugging connectivity issues in other unrelated code-parts (I'm debugging why select(2) / recv(2) don't receive a packet of type qHostInfo).

Floating errno is annoying.

TCPSocket::Connect() has no bugs at least I'm not aware of them.

[krytarowski]

https://github.com/search?l=C&q=save_errno&ref=opensearch&type=Code

Here is an approach with save_errno, useful in libraries when we preserve errno for public functions in the API of a library as-is, and not leaking it from the internals to unrelated code.

Right now I don't volunteer to perform this for LLDB, but it would be nice to not propagate it.

[labath]

Yes, but that's why we have the Error objects, so we don't have to do the errno save-restore dance.

If this is just a debugging aid, then maybe you should keep it as such (locally). There are plenty of places that will leave a stray errno around and I don't think we want to do this resetting on all of them.

[krytarowski]

This is considered to be a local patch.

source/Host/common/TCPSocket.cpp

Status TCPSocket::Connect(llvm::StringRef name) {
   int32_t port = INT32_MIN;
   if (!DecodeHostAndPort(name, host_str, port_str, port, &error))
     return error;
 
   auto addresses = lldb_private::SocketAddress::GetAddressInfo(
       host_str.c_str(), NULL, AF_UNSPEC, SOCK_STREAM, IPPROTO_TCP);
   for (auto address : addresses) {
     error = CreateSocket(address.GetFamily());
-    if (error.Fail())
+    if (error.Fail()) {
+      errno = 0;
       continue;
+    }
 
     address.SetPort(port);
 
     if (-1 == ::connect(GetNativeSocket(), &address.sockaddr(),
                         address.GetLength())) {
       CLOSE_SOCKET(GetNativeSocket());
+      errno = 0;
       continue;
     }
 
     SetOptionNoDelay();
 
     error.Clear();
     return error;
   }