From: Erik Faye-Lund <kusmabite@gmail.com>
Date: Sun, 10 Oct 2010 20:20:58 GMT
Subject: Re: [PATCH v3 01/14] mingw: add network-wrappers for daemon
Message-ID: <AANLkTinP7RKOhLFZs71P5dpmA1p1OsjikSmVv5WkkL1z@mail.gmail.com>
In-Reply-To: <4CB216C2.1060608@gmail.com>

On Sun, Oct 10, 2010 at 9:40 PM, Eric Sunshine <ericsunshine@gmail.com> wrote:
> On 10/10/2010 9:20 AM, Erik Faye-Lund wrote:
>>
>> From: Mike Pape<dotzenlabs@gmail.com>
>>
>> git-daemon requires some socket-functionality that is not yet
>> supported in the Windows-port. This patch adds said functionality,
>> and makes sure WSAStartup gets called by socket(), since it is the
>> first network-call in git-daemon. In addition, a check is added to
>> prevent WSAStartup (and WSACleanup, though atexit) from being
>> called more than once, since git-daemon calls both socket() and
>> gethostbyname().
>>
>> Signed-off-by: Mike Pape<dotzenlabs@gmail.com>
>> Signed-off-by: Erik Faye-Lund<kusmabite@gmail.com>
>> ---
>> diff --git a/compat/mingw.c b/compat/mingw.c
>> index 6590f33..563ef1f 100644
>> --- a/compat/mingw.c
>> +++ b/compat/mingw.c
>> +#undef accept
>> +int mingw_accept(int sockfd1, struct sockaddr *sa, socklen_t *sz)
>> +{
>> +       int sockfd2;
>> +
>> +       SOCKET s1 = (SOCKET)_get_osfhandle(sockfd1);
>> +       SOCKET s2 = accept(s1, sa, sz);
>> +
>> +       /* convert into a file descriptor */
>> +       if ((sockfd2 = _open_osfhandle(s2, O_RDWR|O_BINARY))<  0) {
>> +               closesocket(s2);
>> +               return error("unable to make a socket file descriptor:
>> %s",
>> +                       strerror(errno));
>
> Is 'errno' from _open_osfhandle() still valid when handed to strerror() or
> has it been clobbered by closesocket()?
>
> Corollary: Does _open_osfhandle() indeed set 'errno', or is it more
> appropriate to call WSAGetLastError()? (The documentation I read for
> _open_osfhandle() did not say anything about how to determine the reason for
> failure.)
>

_open_osfhandle seems to set both errno and the winsock-error.
closesocket() sets the winsock-error but not the CRT. I've just tested
with a very simple application:

---8<---
#include <winsock2.h>
#include <io.h>
#include <fcntl.h>
#include <stdio.h>

const char *win32_strerror(DWORD dw)
{
	static char tmp[4096];
	FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, NULL, dw,
	    MAKELANGID(LANG_NEUTRAL, SUBLANG_NEUTRAL),
	    tmp, sizeof(tmp), NULL);
	return tmp;
}

int main()
{
	WSADATA wsa = {0};

	WSAStartup(MAKEWORD(2, 0), &wsa);
	printf("errno: '%s'\nWSAGetLastError: '%s'\n",
	    strerror(errno), win32_strerror(WSAGetLastError()));
	errno = 0;

	_open_osfhandle(-1, O_RDWR | O_BINARY);
	printf("errno: '%s'\nWSAGetLastError: '%s'\n",
	    strerror(errno), win32_strerror(WSAGetLastError()));
	errno = 0;

	closesocket(-1);
	printf("errno: '%s'\nWSAGetLastError: '%s'\n",
	    strerror(errno), win32_strerror(WSAGetLastError()));

	return 0;
}

---8<---

The output is:

---8<---
errno: 'Result too large'
WSAGetLastError: 'The operation completed successfully.
'
errno: 'Bad file descriptor'
WSAGetLastError: 'The handle is invalid.
'
errno: 'No error'
WSAGetLastError: 'An operation was attempted on something that is not a socket.
'
---8<---

So, it seems that WSAGetLastError() gets clobbered by closesocket(),
but not errno.