Support fchmod and include the correct portability headers for FileUtil

Summary: `FileUtil.cpp` uses `fchmod`, which Windows doesn't have, so implement it and also include the correct portability headers for the use of `mkstemp` and now `fchmod` as well.

Reviewed By: yfeldblum

Differential Revision: D4360650

fbshipit-source-id: 300163689c54574548e7bf274a56264714d216ed

folly/FileUtil.cpp

@@ -22,7 +22,9 @@
 #include <folly/detail/FileUtilDetail.h>
 #include <folly/portability/Fcntl.h>
 #include <folly/portability/Sockets.h>
+#include <folly/portability/Stdlib.h>
 #include <folly/portability/SysFile.h>
+#include <folly/portability/SysStat.h>
 
 namespace folly {
 

folly/portability/SysStat.cpp

@@ -22,6 +22,32 @@
 extern "C" {
 int chmod(char const* fn, int am) { return _chmod(fn, am); }
 
+int fchmod(int fd, mode_t mode) {
+  HANDLE h = (HANDLE)_get_osfhandle(fd);
+  if (h == INVALID_HANDLE_VALUE) {
+    return -1;
+  }
+
+  FILE_ATTRIBUTE_TAG_INFO attr{};
+  if (!GetFileInformationByHandleEx(
+          h, FileAttributeTagInfo, &attr, sizeof(attr))) {
+    return -1;
+  }
+
+  if (mode & _S_IWRITE) {
+    attr.FileAttributes &= ~FILE_ATTRIBUTE_READONLY;
+  } else {
+    attr.FileAttributes |= FILE_ATTRIBUTE_READONLY;
+  }
+
+  if (!SetFileInformationByHandle(
+          h, FileAttributeTagInfo, &attr, sizeof(attr))) {
+    return -1;
+  }
+
+  return 0;
+}
+
 // Just return the result of a normal stat for now
 int lstat(const char* path, struct stat* st) { return stat(path, st); }
 

folly/portability/SysStat.h

@@ -19,6 +19,8 @@
 #include <sys/stat.h>
 
 #ifdef _WIN32
+#include <folly/portability/SysTypes.h>
+
 // Windows gives weird names to these.
 #define S_IXUSR 0
 #define S_IWUSR _S_IWRITE
@@ -38,6 +40,7 @@
 
 extern "C" {
 int chmod(char const* fn, int am);
+int fchmod(int fd, mode_t mode);
 int lstat(const char* path, struct stat* st);
 int mkdir(const char* fn, int mode);
 int umask(int md);