mingw: make sure errno is set correctly when socket operations fail

The winsock2 library provides functions that work on different data
types than file descriptors, therefore we wrap them.

But that is not the only difference: they also do not set `errno` but
expect the callers to enquire about errors via `WSAGetLastError()`.

Let's translate that into appropriate `errno` values whenever the socket
operations fail so that Git's code base does not have to change its
expectations.

This closes #2404

Helped-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

compat/mingw.c

@@ -2089,26 +2089,158 @@ static void ensure_socket_initialization(void)
 	initialized = 1;
 }
 
+static int winsock_error_to_errno(DWORD err)
+{
+	switch (err) {
+	case WSAEINTR: return EINTR;
+	case WSAEBADF: return EBADF;
+	case WSAEACCES: return EACCES;
+	case WSAEFAULT: return EFAULT;
+	case WSAEINVAL: return EINVAL;
+	case WSAEMFILE: return EMFILE;
+	case WSAEWOULDBLOCK: return EWOULDBLOCK;
+	case WSAEINPROGRESS: return EINPROGRESS;
+	case WSAEALREADY: return EALREADY;
+	case WSAENOTSOCK: return ENOTSOCK;
+	case WSAEDESTADDRREQ: return EDESTADDRREQ;
+	case WSAEMSGSIZE: return EMSGSIZE;
+	case WSAEPROTOTYPE: return EPROTOTYPE;
+	case WSAENOPROTOOPT: return ENOPROTOOPT;
+	case WSAEPROTONOSUPPORT: return EPROTONOSUPPORT;
+	case WSAEOPNOTSUPP: return EOPNOTSUPP;
+	case WSAEAFNOSUPPORT: return EAFNOSUPPORT;
+	case WSAEADDRINUSE: return EADDRINUSE;
+	case WSAEADDRNOTAVAIL: return EADDRNOTAVAIL;
+	case WSAENETDOWN: return ENETDOWN;
+	case WSAENETUNREACH: return ENETUNREACH;
+	case WSAENETRESET: return ENETRESET;
+	case WSAECONNABORTED: return ECONNABORTED;
+	case WSAECONNRESET: return ECONNRESET;
+	case WSAENOBUFS: return ENOBUFS;
+	case WSAEISCONN: return EISCONN;
+	case WSAENOTCONN: return ENOTCONN;
+	case WSAETIMEDOUT: return ETIMEDOUT;
+	case WSAECONNREFUSED: return ECONNREFUSED;
+	case WSAELOOP: return ELOOP;
+	case WSAENAMETOOLONG: return ENAMETOOLONG;
+	case WSAEHOSTUNREACH: return EHOSTUNREACH;
+	case WSAENOTEMPTY: return ENOTEMPTY;
+	/* No errno equivalent; default to EIO */
+	case WSAESOCKTNOSUPPORT:
+	case WSAEPFNOSUPPORT:
+	case WSAESHUTDOWN:
+	case WSAETOOMANYREFS:
+	case WSAEHOSTDOWN:
+	case WSAEPROCLIM:
+	case WSAEUSERS:
+	case WSAEDQUOT:
+	case WSAESTALE:
+	case WSAEREMOTE:
+	case WSASYSNOTREADY:
+	case WSAVERNOTSUPPORTED:
+	case WSANOTINITIALISED:
+	case WSAEDISCON:
+	case WSAENOMORE:
+	case WSAECANCELLED:
+	case WSAEINVALIDPROCTABLE:
+	case WSAEINVALIDPROVIDER:
+	case WSAEPROVIDERFAILEDINIT:
+	case WSASYSCALLFAILURE:
+	case WSASERVICE_NOT_FOUND:
+	case WSATYPE_NOT_FOUND:
+	case WSA_E_NO_MORE:
+	case WSA_E_CANCELLED:
+	case WSAEREFUSED:
+	case WSAHOST_NOT_FOUND:
+	case WSATRY_AGAIN:
+	case WSANO_RECOVERY:
+	case WSANO_DATA:
+	case WSA_QOS_RECEIVERS:
+	case WSA_QOS_SENDERS:
+	case WSA_QOS_NO_SENDERS:
+	case WSA_QOS_NO_RECEIVERS:
+	case WSA_QOS_REQUEST_CONFIRMED:
+	case WSA_QOS_ADMISSION_FAILURE:
+	case WSA_QOS_POLICY_FAILURE:
+	case WSA_QOS_BAD_STYLE:
+	case WSA_QOS_BAD_OBJECT:
+	case WSA_QOS_TRAFFIC_CTRL_ERROR:
+	case WSA_QOS_GENERIC_ERROR:
+	case WSA_QOS_ESERVICETYPE:
+	case WSA_QOS_EFLOWSPEC:
+	case WSA_QOS_EPROVSPECBUF:
+	case WSA_QOS_EFILTERSTYLE:
+	case WSA_QOS_EFILTERTYPE:
+	case WSA_QOS_EFILTERCOUNT:
+	case WSA_QOS_EOBJLENGTH:
+	case WSA_QOS_EFLOWCOUNT:
+#ifndef _MSC_VER
+	case WSA_QOS_EUNKNOWNPSOBJ:
+#endif
+	case WSA_QOS_EPOLICYOBJ:
+	case WSA_QOS_EFLOWDESC:
+	case WSA_QOS_EPSFLOWSPEC:
+	case WSA_QOS_EPSFILTERSPEC:
+	case WSA_QOS_ESDMODEOBJ:
+	case WSA_QOS_ESHAPERATEOBJ:
+	case WSA_QOS_RESERVED_PETYPE:
+	default: return EIO;
+	}
+}
+
+/*
+ * On Windows, `errno` is a global macro to a function call.
+ * This makes it difficult to debug and single-step our mappings.
+ */
+static inline void set_wsa_errno(void)
+{
+	DWORD wsa = WSAGetLastError();
+	int e = winsock_error_to_errno(wsa);
+	errno = e;
+
+#ifdef DEBUG_WSA_ERRNO
+	fprintf(stderr, "winsock error: %d -> %d\n", wsa, e);
+	fflush(stderr);
+#endif
+}
+
+static inline int winsock_return(int ret)
+{
+	if (ret < 0)
+		set_wsa_errno();
+
+	return ret;
+}
+
+#define WINSOCK_RETURN(x) do { return winsock_return(x); } while (0)
+
 #undef gethostname
 int mingw_gethostname(char *name, int namelen)
 {
-    ensure_socket_initialization();
-    return gethostname(name, namelen);
+	ensure_socket_initialization();
+	WINSOCK_RETURN(gethostname(name, namelen));
 }
 
 #undef gethostbyname
 struct hostent *mingw_gethostbyname(const char *host)
 {
+	struct hostent *ret;
+
 	ensure_socket_initialization();
-	return gethostbyname(host);
+
+	ret = gethostbyname(host);
+	if (!ret)
+		set_wsa_errno();
+
+	return ret;
 }
 
 #undef getaddrinfo
 int mingw_getaddrinfo(const char *node, const char *service,
 		      const struct addrinfo *hints, struct addrinfo **res)
 {
 	ensure_socket_initialization();
-	return getaddrinfo(node, service, hints, res);
+	WINSOCK_RETURN(getaddrinfo(node, service, hints, res));
 }
 
 int mingw_socket(int domain, int type, int protocol)
@@ -2128,7 +2260,7 @@ int mingw_socket(int domain, int type, int protocol)
 		 * in errno so that _if_ someone looks up the code somewhere,
 		 * then it is at least the number that are usually listed.
 		 */
-		errno = WSAGetLastError();
+		set_wsa_errno();
 		return -1;
 	}
 	/* convert into a file descriptor */
@@ -2144,35 +2276,35 @@ int mingw_socket(int domain, int type, int protocol)
 int mingw_connect(int sockfd, struct sockaddr *sa, size_t sz)
 {
 	SOCKET s = (SOCKET)_get_osfhandle(sockfd);
-	return connect(s, sa, sz);
+	WINSOCK_RETURN(connect(s, sa, sz));
 }
 
 #undef bind
 int mingw_bind(int sockfd, struct sockaddr *sa, size_t sz)
 {
 	SOCKET s = (SOCKET)_get_osfhandle(sockfd);
-	return bind(s, sa, sz);
+	WINSOCK_RETURN(bind(s, sa, sz));
 }
 
 #undef setsockopt
 int mingw_setsockopt(int sockfd, int lvl, int optname, void *optval, int optlen)
 {
 	SOCKET s = (SOCKET)_get_osfhandle(sockfd);
-	return setsockopt(s, lvl, optname, (const char*)optval, optlen);
+	WINSOCK_RETURN(setsockopt(s, lvl, optname, (const char*)optval, optlen));
 }
 
 #undef shutdown
 int mingw_shutdown(int sockfd, int how)
 {
 	SOCKET s = (SOCKET)_get_osfhandle(sockfd);
-	return shutdown(s, how);
+	WINSOCK_RETURN(shutdown(s, how));
 }
 
 #undef listen
 int mingw_listen(int sockfd, int backlog)
 {
 	SOCKET s = (SOCKET)_get_osfhandle(sockfd);
-	return listen(s, backlog);
+	WINSOCK_RETURN(listen(s, backlog));
 }
 
 #undef accept
@@ -2183,6 +2315,11 @@ int mingw_accept(int sockfd1, struct sockaddr *sa, socklen_t *sz)
 	SOCKET s1 = (SOCKET)_get_osfhandle(sockfd1);
 	SOCKET s2 = accept(s1, sa, sz);
 
+	if (s2 == INVALID_SOCKET) {
+		set_wsa_errno();
+		return -1;
+	}
+
 	/* convert into a file descriptor */
 	if ((sockfd2 = _open_osfhandle(s2, O_RDWR|O_BINARY)) < 0) {
 		int err = errno;