Add file modes for opening a file write only

runtime/bin/file_macos.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include "bin/file.h"
 
 #include <errno.h>  // NOLINT
@@ skipping 141 matching lines @@
   struct stat st;
   if (NO_RETRY_EXPECTED(stat(name, &st)) == 0) {
     // Only accept regular files and character devices.
     if (!S_ISREG(st.st_mode) && !S_ISCHR(st.st_mode)) {
       errno = (S_ISDIR(st.st_mode)) ? EISDIR : ENOENT;
       return NULL;
     }
   }
   int flags = O_RDONLY;
   if ((mode & kWrite) != 0) {
+    ASSERT((mode & kWriteOnly) == 0);
     flags = (O_RDWR | O_CREAT);
   }
+  if ((mode & kWriteOnly) != 0) {
+    ASSERT((mode & kWrite) == 0);
+    flags = (O_WRONLY | O_CREAT);
+  }
   if ((mode & kTruncate) != 0) {
     flags = flags | O_TRUNC;
   }
   int fd = TEMP_FAILURE_RETRY(open(name, flags, 0666));
   if (fd < 0) {
     return NULL;
   }
   FDUtils::SetCloseOnExec(fd);
-  if (((mode & kWrite) != 0) && ((mode & kTruncate) == 0)) {
+  if ((((mode & kWrite) != 0) && ((mode & kTruncate) == 0)) ||
+      (((mode & kWriteOnly) != 0) && ((mode & kTruncate) == 0))) {
     int64_t position = lseek(fd, 0, SEEK_END);
     if (position < 0) {
       return NULL;
     }
   }
   return new File(new FileHandle(fd));
 }
 
 
 File* File::OpenStdio(int fd) {
@@ skipping 242 matching lines @@
   return (file_1_info.st_ino == file_2_info.st_ino &&
           file_1_info.st_dev == file_2_info.st_dev) ?
       File::kIdentical :
       File::kDifferent;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)