Add umask and rename compatibility wrappers for Windows

umask() doesn't exist on Windows and is thus a no-op.

rename() only works if the destination doesn't already exist,
so we must unlink before renaming.

commands.cpp

@@ -765,7 +765,7 @@ int migrate_key (int argc, char** argv)
 				return 1;
 			}
 
-			if (rename(new_key_file_name.c_str(), key_file_name) == -1) {
+			if (util_rename(new_key_file_name.c_str(), key_file_name) == -1) {
 				std::clog << "Error: " << key_file_name << ": " << strerror(errno) << std::endl;
 				unlink(new_key_file_name.c_str());
 				return 1;

key.cpp

@@ -134,9 +134,9 @@ bool		Key_file::load_from_file (const char* key_file_name)
 
 bool		Key_file::store_to_file (const char* key_file_name) const
 {
-	mode_t		old_umask = umask(0077); // make sure key file is protected (TODO: Windows compat)
+	mode_t		old_umask = util_umask(0077); // make sure key file is protected
 	std::ofstream	key_file_out(key_file_name, std::fstream::binary);
-	umask(old_umask);
+	util_umask(old_umask);
 	if (!key_file_out) {
 		return false;
 	}

util-unix.cpp

@@ -69,14 +69,14 @@ void	temp_fstream::open (std::ios_base::openmode mode)
 	char*			path = &path_buffer[0];
 	std::strcpy(path, tmpdir);
 	std::strcpy(path + tmpdir_len, "/git-crypt.XXXXXX");
-	mode_t			old_umask = umask(0077);
+	mode_t			old_umask = util_umask(0077);
 	int			fd = mkstemp(path);
 	if (fd == -1) {
 		int		mkstemp_errno = errno;
-		umask(old_umask);
+		util_umask(old_umask);
 		throw System_error("mkstemp", "", mkstemp_errno);
 	}
-	umask(old_umask);
+	util_umask(old_umask);
 	std::fstream::open(path, mode);
 	if (!std::fstream::is_open()) {
 		unlink(path);
@@ -277,3 +277,13 @@ bool successful_exit (int status)
 static void	init_std_streams_platform ()
 {
 }
+
+mode_t util_umask (mode_t mode)
+{
+	return umask(mode);
+}
+
+int util_rename (const char* from, const char* to)
+{
+	return rename(from, to);
+}

util-win32.cpp

@@ -325,3 +325,16 @@ static void	init_std_streams_platform ()
 	_setmode(_fileno(stdin), _O_BINARY);
 	_setmode(_fileno(stdout), _O_BINARY);
 }
+
+mode_t util_umask (mode_t mode)
+{
+	// Not available in Windows and function not always defined in Win32 environments
+	return 0;
+}
+
+int util_rename (const char* from, const char* to)
+{
+	// On Windows OS, it is necessary to ensure target file doesn't exist
+	unlink(to);
+	return rename(from, to);
+}

util.hpp

@@ -35,6 +35,7 @@
 #include <ios>
 #include <iosfwd>
 #include <stdint.h>
+#include <sys/types.h>
 #include <fstream>
 #include <vector>
 
@@ -69,6 +70,8 @@ void		store_be32 (unsigned char*, uint32_t);
 bool		read_be32 (std::istream& in, uint32_t&);
 void		write_be32 (std::ostream& out, uint32_t);
 void		init_std_streams ();
+mode_t		util_umask (mode_t);
+int		util_rename (const char*, const char*);
 
 #endif