Fix gai_strerror() thread-safety on Windows.

Commit 5579388d removed code that supplied a fallback implementation of
getaddrinfo(), which was dead code on modern systems.  One tiny piece of
the removed code was still doing something useful on Windows, though:
that OS's own gai_strerror()/gai_strerrorA() function returns a pointer
to a static buffer that it overwrites each time, so it's not
thread-safe.  In rare circumstances, a multi-threaded client program
could get an incorrect or corrupted error message.

Restore the replacement gai_strerror() function, though now that it's
only for Windows we can put it into a win32-specific file and cut it
down to the errors that Windows documents.  The error messages here are
taken from FreeBSD, because Windows' own messages seemed too verbose.

Back-patch to 16.

Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/CA%2BhUKGKz%2BF9d2PTiXwfYV7qJw%2BWg2jzACgSDgPizUw7UG%3Di58A%40mail.gmail.com

1 files changed, 45 insertions, 0 deletions

diff --git a/src/port/win32gai_strerror.c b/src/port/win32gai_strerror.c
new file mode 100644
index 00000000000..5b47d1722df
--- /dev/null
+++ b/src/port/win32gai_strerror.c
@@ -0,0 +1,45 @@
+/*-------------------------------------------------------------------------
+ *
+ * win32gai_strerror.c
+ *	  Thread-safe gai_strerror() for Windows.
+ *
+ * Portions Copyright (c) 2024, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *    src/port/win32gai_strerror.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include <sys/socket.h>
+
+/*
+ * Windows has gai_strerrorA(), but it is not thread-safe so we avoid it.
+ *
+ * https://learn.microsoft.com/en-us/windows/win32/api/ws2tcpip/nf-ws2tcpip-gai_strerrora
+ */
+const char *
+gai_strerror(int errcode)
+{
+	switch (errcode)
+	{
+		case EAI_AGAIN:
+			return "Temporary failure in name resolution";
+		case EAI_BADFLAGS:
+			return "Bad value for ai_flags";
+		case EAI_FAIL:
+			return "Non-recoverable failure in name resolution";
+		case EAI_FAMILY:
+			return "ai_family not supported";
+		case EAI_MEMORY:
+			return "Memory allocation failure";
+		case EAI_NONAME:
+			return "Name or service not known";
+		case EAI_SERVICE:
+			return "Servname not supported for ai_socktype";
+		case EAI_SOCKTYPE:
+			return "ai_socktype not supported";
+		default:
+			return "Unknown server error";
+	}
+}