compat/mingw: handle WSA errors in strerror

We map WSAGetLastError() errors to errno errors in winsock_error_to_errno(),
but the MSVC strerror() implementation only produces "Unknown error" for
most of them. Produce some more meaningful error messages in these
cases.

Our builds for ARM64 link against the newer UCRT strerror() that does know
these errors, so we won't change the strerror() used there.

The wording of the messages is copied from glibc strerror() messages.

Reported-by: M Hickford <mirth.hickford@gmail.com>
Signed-off-by: Matthias Aßhauer <mha1993@live.de>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Makefile

@@ -1351,6 +1351,7 @@ THIRD_PARTY_SOURCES += $(UNIT_TEST_DIR)/clar/clar/%
 
 CLAR_TEST_SUITES += u-ctype
 CLAR_TEST_SUITES += u-strvec
+CLAR_TEST_SUITES += u-mingw
 CLAR_TEST_PROG = $(UNIT_TEST_BIN)/unit-tests$(X)
 CLAR_TEST_OBJS = $(patsubst %,$(UNIT_TEST_DIR)/%.o,$(CLAR_TEST_SUITES))
 CLAR_TEST_OBJS += $(UNIT_TEST_DIR)/clar/clar.o

compat/mingw.c

@@ -2673,6 +2673,91 @@ static inline int winsock_return(int ret)
 
 #define WINSOCK_RETURN(x) do { return winsock_return(x); } while (0)
 
+#undef strerror
+char *mingw_strerror(int errnum)
+{
+	static char buf[41] ="";
+	switch (errnum) {
+		case EWOULDBLOCK:
+			xsnprintf(buf, 41, "%s", "Operation would block");
+			break;
+		case EINPROGRESS:
+			xsnprintf(buf, 41, "%s", "Operation now in progress");
+			break;
+		case EALREADY:
+			xsnprintf(buf, 41, "%s", "Operation already in progress");
+			break;
+		case ENOTSOCK:
+			xsnprintf(buf, 41, "%s", "Socket operation on non-socket");
+			break;
+		case EDESTADDRREQ:
+			xsnprintf(buf, 41, "%s", "Destination address required");
+			break;
+		case EMSGSIZE:
+			xsnprintf(buf, 41, "%s", "Message too long");
+			break;
+		case EPROTOTYPE:
+			xsnprintf(buf, 41, "%s", "Protocol wrong type for socket");
+			break;
+		case ENOPROTOOPT:
+			xsnprintf(buf, 41, "%s", "Protocol not available");
+			break;
+		case EPROTONOSUPPORT:
+			xsnprintf(buf, 41, "%s", "Protocol not supported");
+			break;
+		case EOPNOTSUPP:
+			xsnprintf(buf, 41, "%s", "Operation not supported");
+			break;
+		case EAFNOSUPPORT:
+			xsnprintf(buf, 41, "%s", "Address family not supported by protocol");
+			break;
+		case EADDRINUSE:
+			xsnprintf(buf, 41, "%s", "Address already in use");
+			break;
+		case EADDRNOTAVAIL:
+			xsnprintf(buf, 41, "%s", "Cannot assign requested address");
+			break;
+		case ENETDOWN:
+			xsnprintf(buf, 41, "%s", "Network is down");
+			break;
+		case ENETUNREACH:
+			xsnprintf(buf, 41, "%s", "Network is unreachable");
+			break;
+		case ENETRESET:
+			xsnprintf(buf, 41, "%s", "Network dropped connection on reset");
+			break;
+		case ECONNABORTED:
+			xsnprintf(buf, 41, "%s", "Software caused connection abort");
+			break;
+		case ECONNRESET:
+			xsnprintf(buf, 41, "%s", "Connection reset by peer");
+			break;
+		case ENOBUFS:
+			xsnprintf(buf, 41, "%s", "No buffer space available");
+			break;
+		case EISCONN:
+			xsnprintf(buf, 41, "%s", "Transport endpoint is already connected");
+			break;
+		case ENOTCONN:
+			xsnprintf(buf, 41, "%s", "Transport endpoint is not connected");
+			break;
+		case ETIMEDOUT:
+			xsnprintf(buf, 41, "%s", "Connection timed out");
+			break;
+		case ECONNREFUSED:
+			xsnprintf(buf, 41, "%s", "Connection refused");
+			break;
+		case ELOOP:
+			xsnprintf(buf, 41, "%s", "Too many levels of symbolic links");
+			break;
+		case EHOSTUNREACH:
+			xsnprintf(buf, 41, "%s", "No route to host");
+			break;
+		default: return strerror(errnum);
+	}
+	return buf;
+}
+
 #undef gethostname
 int mingw_gethostname(char *name, int namelen)
 {

compat/mingw.h

@@ -314,6 +314,11 @@ int mingw_socket(int domain, int type, int protocol);
 int mingw_connect(int sockfd, struct sockaddr *sa, size_t sz);
 #define connect mingw_connect
 
+char *mingw_strerror(int errnum);
+#ifndef _UCRT
+#define strerror mingw_strerror
+#endif
+
 int mingw_bind(int sockfd, struct sockaddr *sa, size_t sz);
 #define bind mingw_bind
 

t/meson.build

@@ -1,5 +1,6 @@
 clar_test_suites = [
   'unit-tests/u-ctype.c',
+  'unit-tests/u-mingw.c',
   'unit-tests/u-strvec.c',
 ]
 

t/unit-tests/u-mingw.c

@@ -0,0 +1,72 @@
+#include "unit-test.h"
+
+#if defined(GIT_WINDOWS_NATIVE) && !defined(_UCRT)
+#undef strerror
+int errnos_contains(int);
+static int errnos [53]={
+    /* errnos in err_win_to_posix */
+    EACCES, EBUSY, EEXIST, ERANGE, EIO, ENODEV, ENXIO, ENOEXEC, EINVAL, ENOENT,
+    EPIPE, ENAMETOOLONG, ENOSYS, ENOTEMPTY, ENOSPC, EFAULT, EBADF, EPERM, EINTR,
+    E2BIG, ESPIPE, ENOMEM, EXDEV, EAGAIN, ENFILE, EMFILE, ECHILD, EROFS,
+    /* errnos only in winsock_error_to_errno */
+    EWOULDBLOCK, EINPROGRESS, EALREADY, ENOTSOCK, EDESTADDRREQ, EMSGSIZE,
+    EPROTOTYPE, ENOPROTOOPT, EPROTONOSUPPORT, EOPNOTSUPP, EAFNOSUPPORT,
+    EADDRINUSE, EADDRNOTAVAIL, ENETDOWN, ENETUNREACH, ENETRESET, ECONNABORTED,
+    ECONNRESET, ENOBUFS, EISCONN, ENOTCONN, ETIMEDOUT, ECONNREFUSED, ELOOP,
+    EHOSTUNREACH
+    };
+
+int errnos_contains(int errnum)
+{
+    for(int i=0;i<53;i++)
+	if(errnos[i]==errnum)
+	    return 1;
+    return 0;
+}
+#endif
+
+void test_mingw__no_strerror_shim_on_ucrt(void)
+{
+#if defined(GIT_WINDOWS_NATIVE) && defined(_UCRT)
+    cl_assert_(strerror != mingw_strerror,
+	"mingw_strerror is unnescessary when building against UCRT");
+#else
+    cl_skip();
+#endif
+}
+
+void test_mingw__strerror(void)
+{
+#if defined(GIT_WINDOWS_NATIVE) && !defined(_UCRT)
+    for(int i=0;i<53;i++)
+    {
+	char *crt;
+	char *mingw;
+	mingw = mingw_strerror(errnos[i]);
+	crt = strerror(errnos[i]);
+	cl_assert_(!strcasestr(mingw, "unknown error"),
+	    "mingw_strerror should know all errno values we care about");
+	if(!strcasestr(crt, "unknown error"))
+	    cl_assert_equal_s(crt,mingw);
+    }
+#else
+    cl_skip();
+#endif
+}
+
+void test_mingw__errno_translation(void)
+{
+#if defined(GIT_WINDOWS_NATIVE) && !defined(_UCRT)
+    /* GetLastError() return values are currently defined from 0 to 15841,
+    testing up to 20000 covers some room for future expansion */
+    for (int i=0;i<20000;i++)
+    {
+	if(i!=ERROR_SUCCESS)
+	    cl_assert_(errnos_contains(err_win_to_posix(i)),
+		"all err_win_to_posix return values should be tested against mingw_strerror");
+	/* ideally we'd test the same for winsock_error_to_errno, but it's static */
+    }
+#else
+    cl_skip();
+#endif
+}