MinGW: Make git native protocol work.

As it turns out, the things returned by Winsock2's socket() are handles
that can be passed to ReadFile()/WriteFile() - almost. The way this works
is by wrapping those handles into file descriptors with _open_osfhandle().
But it turns out that the sockets created by the plain socket() function
are prepared for "overlapped" I/O, which confuses ReadFile()/WriteFile().
Therefore, a reimplementation is provided that uses WSASocket() to
explicitly asks for non-overlapped sockets.

Special thanks got to H. Peter Anvin, who provided the necessary clues.

README.MinGW

@@ -50,14 +50,14 @@ This works:
 - All the plumbings.
 - Many porcelains, in particular, checkout, add, rm, commit, diff,
   branch, merge, rebase, log, show, bisect, grep...
-- pull, clone, fetch, push via ssh.
+- pull, clone, fetch, push via native git protocal as well as ssh.
 - Local pull, clone, fetch, push.
 - gitk, if invoked as "wish84 <prefix>\bin\gitk", but there are
-  artefacts in its layout.
+  artefacts in its layout. A workaround by Mark Levedahl is in
+  branch 'devel'.
 
 This does not work:
 
-- pull, clone, fetch, push via native GIT protocol.
 - daemon, svn, *import, cvs*
 - and certainly a lot more that I never have found a need to look at.
 

compat/mingw.c

@@ -293,3 +293,22 @@ void mingw_execve(const char *cmd, const char **argv, const char **env)
 			exit(ret);
 	}
 }
+
+int mingw_socket(int domain, int type, int protocol)
+{
+	SOCKET s = WSASocket(domain, type, protocol, NULL, 0, 0);
+	if (s == INVALID_SOCKET) {
+		/*
+		 * WSAGetLastError() values are regular BSD error codes
+		 * biased by WSABASEERR.
+		 * However, strerror() does not know about networking
+		 * specific errors, which are values beginning at 38 or so.
+		 * Therefore, we choose to leave the biased error code
+		 * in errno so that _if_ someone looks up the code somewhere,
+		 * then it is at least the number that are usually listed.
+		 */
+		errno = WSAGetLastError();
+		return -1;
+	}
+	return s;
+}

connect.c

@@ -527,7 +527,23 @@ static int git_tcp_connect_sock(char *host)
 
 static void git_tcp_connect(int fd[2], char *host)
 {
+#ifndef __MINGW32__
 	int sockfd = git_tcp_connect_sock(host);
+#else
+	int sockfd;
+	WSADATA wsa;
+
+	if (WSAStartup(MAKEWORD(2,2), &wsa))
+		die("unable to initialize winsock subsystem, error %d",
+			WSAGetLastError());
+	atexit((void(*)(void)) WSACleanup);
+
+	sockfd = git_tcp_connect_sock(host);
+	/* convert into a file descriptor */
+	if ((sockfd = _open_osfhandle(sockfd, O_RDWR|O_BINARY)) < 0)
+		die("unable to make a socket file descriptor: %s",
+			strerror(errno));
+#endif
 
 	fd[0] = sockfd;
 	fd[1] = dup(sockfd);

git-compat-util.h

@@ -374,6 +374,9 @@ struct tm *localtime_r(const time_t *timep, struct tm *result);
 char *mingw_getcwd(char *pointer, int len);
 #define getcwd mingw_getcwd
 
+int mingw_socket(int domain, int type, int protocol);
+#define socket mingw_socket
+
 #define setlinebuf(x)
 #define fsync(x)