WIN32 compatibility for setsockopt() in modbus-tcp.c

[desteemy]

UNIX systems <sys/socket.h> require const void *, while Windows <winsock2.h> const char *. Previous version without type casting did not build on Windows, resulting in:

CC modbus-tcp.lo
modbus-tcp.c: In function '_modbus_tcp_set_ipv4_options':
modbus-tcp.c:239:50: error: passing argument 4 of 'setsockopt' from incompatible pointer type [-Wincompatible-pointer-types]
239 | rc = setsockopt(s, IPPROTO_TCP, TCP_NODELAY, &option, sizeof(int));
| ^~~~~~~
| |
| int *
In file included from modbus-tcp.c:31:
C:/msys64/mingw64/include/winsock2.h:1035:88: note: expected 'const char *' but argument is of type 'int *'
1035 | WINSOCK_API_LINKAGE int WSAAPI setsockopt(SOCKET s,int level,int optname,const char *optval,int optlen);
| ~~~~~~~~~~~~^~~~~~
modbus-tcp.c: In function 'modbus_tcp_listen':
modbus-tcp.c:566:53: error: passing argument 4 of 'setsockopt' from incompatible pointer type [-Wincompatible-pointer-types]
566 | if (setsockopt(new_s, SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(enable)) == -1) {
| ^~~~~~~
| |
| int *
C:/msys64/mingw64/include/winsock2.h:1035:88: note: expected 'const char *' but argument is of type 'int *'
1035 | WINSOCK_API_LINKAGE int WSAAPI setsockopt(SOCKET s,int level,int optname,const char *optval,int optlen);
| ~~~~~~~~~~~~^~~~~~
modbus-tcp.c: In function 'modbus_tcp_pi_listen':
modbus-tcp.c:683:58: error: passing argument 4 of 'setsockopt' from incompatible pointer type [-Wincompatible-pointer-types]
683 | rc = setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(enable));
| ^~~~~~~
| |
| int *
C:/msys64/mingw64/include/winsock2.h:1035:88: note: expected 'const char *' but argument is of type 'int *'
1035 | WINSOCK_API_LINKAGE int WSAAPI setsockopt(SOCKET s,int level,int optname,const char *optval,int optlen);
| ~~~~~~~~~~~~^~~~~~
make[2]: *** [Makefile:486: modbus-tcp.lo] Error 1
make[1]: *** [Makefile:505: all-recursive] Error 1
make: *** [Makefile:391: all] Error 2

#721

[cla-bot]

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[desteemy]

We require contributors to sign our Contributor License Agreement. In order for us to review and merge your code, please fill https://forms.gle/5635zjphDo5JEJQSA to get added. Your document will be manually checked by the maintainer. Be patient...

I have just sent it. Waiting for verification. My guess is that this is not the best option to verify that the person who sends the form is actually the person who commits the code :)