Do not save ResolutionError if resolution succeeds for any address family (#12678)

* Do not save ResolutionError if resolution succeeds for any address family

Socket with Happy Eyeballs Version 2 performs connection attempts and name resolution in parallel.

In the existing implementation, if a connection attempt failed for one address family while name resolution was still in progress for the other, and that name resolution later failed, the method would terminate with a name resolution error.
This behavior was intended to ensure that the final error reflected the most recent failure, potentially overriding an earlier error.

However, [Bug #21088](https://bugs.ruby-lang.org/issues/21088) made me realize that terminating with a name resolution error is unnatural when name resolution succeeded for at least one address family.

This PR modifies the behavior so that if name resolution succeeds for one address family, any name resolution error from the other is not saved.

This PR includes the following changes:

* Do not display select(2) as the system call that caused the raised error, as it is for internal processing

* Fix bug: Get errno with Socket::SO_ERROR in Windows environment with a workaround for tests not passing

2 files changed, 26 insertions, 16 deletions

diff --git a/ext/socket/ipsocket.c b/ext/socket/ipsocket.c
index ff35682486..bd73f49ece 100644
--- a/ext/socket/ipsocket.c
+++ b/ext/socket/ipsocket.c
@@ -892,7 +892,6 @@ init_fast_fallback_inetsock_internal(VALUE v)
         }
 
         status = rb_thread_fd_select(nfds, &arg->readfds, &arg->writefds, NULL, delay_p);
-        syscall = "select(2)";
 
         now = current_clocktime_ts();
         if (is_timeout_tv(resolution_delay_expires_at, now)) {
@@ -998,9 +997,11 @@ init_fast_fallback_inetsock_internal(VALUE v)
 
                             if (arg->getaddrinfo_entries[IPV6_ENTRY_POS]->err &&
                                 arg->getaddrinfo_entries[IPV6_ENTRY_POS]->err != EAI_ADDRFAMILY) {
-                                last_error.type = RESOLUTION_ERROR;
-                                last_error.ecode = arg->getaddrinfo_entries[IPV6_ENTRY_POS]->err;
-                                syscall = "getaddrinfo(3)";
+                                if (!resolution_store.v4.finished || resolution_store.v4.has_error) {
+                                    last_error.type = RESOLUTION_ERROR;
+                                    last_error.ecode = arg->getaddrinfo_entries[IPV6_ENTRY_POS]->err;
+                                    syscall = "getaddrinfo(3)";
+                                }
                                 resolution_store.v6.has_error = true;
                             } else {
                                 resolution_store.v6.ai = arg->getaddrinfo_entries[IPV6_ENTRY_POS]->ai;
@@ -1015,9 +1016,11 @@ init_fast_fallback_inetsock_internal(VALUE v)
                             resolution_store.v4.finished = true;
 
                             if (arg->getaddrinfo_entries[IPV4_ENTRY_POS]->err) {
-                                last_error.type = RESOLUTION_ERROR;
-                                last_error.ecode = arg->getaddrinfo_entries[IPV4_ENTRY_POS]->err;
-                                syscall = "getaddrinfo(3)";
+                                if (!resolution_store.v6.finished || resolution_store.v6.has_error) {
+                                    last_error.type = RESOLUTION_ERROR;
+                                    last_error.ecode = arg->getaddrinfo_entries[IPV4_ENTRY_POS]->err;
+                                    syscall = "getaddrinfo(3)";
+                                }
                                 resolution_store.v4.has_error = true;
                             } else {
                                 resolution_store.v4.ai = arg->getaddrinfo_entries[IPV4_ENTRY_POS]->ai;
@@ -1057,9 +1060,11 @@ init_fast_fallback_inetsock_internal(VALUE v)
                 resolution_store.v6.finished = true;
 
                 if (arg->getaddrinfo_entries[IPV6_ENTRY_POS]->err) {
-                    last_error.type = RESOLUTION_ERROR;
-                    last_error.ecode = arg->getaddrinfo_entries[IPV6_ENTRY_POS]->err;
-                    syscall = "getaddrinfo(3)";
+                    if (!resolution_store.v4.finished || resolution_store.v4.has_error) {
+                        last_error.type = RESOLUTION_ERROR;
+                        last_error.ecode = arg->getaddrinfo_entries[IPV6_ENTRY_POS]->err;
+                        syscall = "getaddrinfo(3)";
+                    }
                     resolution_store.v6.has_error = true;
                 } else {
                     resolution_store.v6.ai = arg->getaddrinfo_entries[IPV6_ENTRY_POS]->ai;
@@ -1075,9 +1080,11 @@ init_fast_fallback_inetsock_internal(VALUE v)
                 resolution_store.v4.finished = true;
 
                 if (arg->getaddrinfo_entries[IPV4_ENTRY_POS]->err) {
-                    last_error.type = RESOLUTION_ERROR;
-                    last_error.ecode = arg->getaddrinfo_entries[IPV4_ENTRY_POS]->err;
-                    syscall = "getaddrinfo(3)";
+                    if (!resolution_store.v6.finished || resolution_store.v6.has_error) {
+                        last_error.type = RESOLUTION_ERROR;
+                        last_error.ecode = arg->getaddrinfo_entries[IPV4_ENTRY_POS]->err;
+                        syscall = "getaddrinfo(3)";
+                    }
                     resolution_store.v4.has_error = true;
                 } else {
                     resolution_store.v4.ai = arg->getaddrinfo_entries[IPV4_ENTRY_POS]->ai;
diff --git a/ext/socket/lib/socket.rb b/ext/socket/lib/socket.rb
index 46879c19c2..4ebc437a99 100644
--- a/ext/socket/lib/socket.rb
+++ b/ext/socket/lib/socket.rb
@@ -833,7 +833,7 @@ class Socket < BasicSocket
       if except_sockets&.any?
         except_sockets.each do |except_socket|
           failed_ai = connecting_sockets.delete except_socket
-          sockopt = except_socket.getsockopt(Socket::SOL_SOCKET, Socket::SO_CONNECT_TIME)
+          sockopt = except_socket.getsockopt(Socket::SOL_SOCKET, Socket::SO_ERROR)
           except_socket.close
           ip_address = failed_ai.ipv6? ? "[#{failed_ai.ip_address}]" : failed_ai.ip_address
           last_error = SystemCallError.new("connect(2) for #{ip_address}:#{failed_ai.ip_port}", sockopt.int)
@@ -862,7 +862,10 @@ class Socket < BasicSocket
             unless (Socket.const_defined?(:EAI_ADDRFAMILY)) &&
               (result.is_a?(Socket::ResolutionError)) &&
               (result.error_code == Socket::EAI_ADDRFAMILY)
-              last_error = result
+              other = family_name == :ipv6 ? :ipv4 : :ipv6
+              if !resolution_store.resolved?(other) || !resolution_store.resolved_successfully?(other)
+                last_error = result
+              end
             end
           else
             resolution_store.add_resolved(family_name, result)
@@ -1068,7 +1071,7 @@ class Socket < BasicSocket
     end
 
     def resolved_successfully?(family)
-      resolved?(family) && !!@error_dict[family]
+      resolved?(family) && !@error_dict[family]
     end
 
     def resolved_all_families?