io: fix dispatch_io_create_with_path() on Windows

This function assumes POSIX-style paths. Add Windows-specific checks for absolute paths and separators. Additionally, `_dispatch_fd_entry_guarded_open()` does not handle the open flags correctly. `O_RDONLY` is 0, so we need to use a switch statement to check for it. `O_EXCL` is not handled at all. `O_TRUNC`'s behavior needs to change depending on whether `O_CREAT` is specified. Finally, we must open files with maximum sharing to match the semantics of other platforms. (The dispatch_io test already has a handle open when it calls `dispatch_io_create_with_path()`.)

Author: adierking

src/CMakeLists.txt

@@ -244,6 +244,7 @@ target_link_libraries(dispatch
 if(CMAKE_SYSTEM_NAME STREQUAL Windows)
  target_link_libraries(dispatch
  PRIVATE
+ ShLwApi
  WS2_32
  WinMM
  synchronization)

src/io.c

@@ -406,15 +406,29 @@ dispatch_io_create_f(dispatch_io_type_t type, dispatch_fd_t fd,
 ^(int error){ cleanup_handler(context, error); });
 }
 
+#if defined(_WIN32)
+#define _is_separator(ch) ((ch) == '/' || (ch) == '\\')
+#else
+#define _is_separator(ch) ((ch) == '/')
+#endif
+
 dispatch_io_t
 dispatch_io_create_with_path(dispatch_io_type_t type, const char *path,
 int oflag, mode_t mode, dispatch_queue_t queue,
 void (^cleanup_handler)(int error))
 {
-if ((type != DISPATCH_IO_STREAM && type != DISPATCH_IO_RANDOM) ||
-!(*path == '/')) {
+if (type != DISPATCH_IO_STREAM && type != DISPATCH_IO_RANDOM) {
+return DISPATCH_BAD_INPUT;
+}
+#if defined(_WIN32)
+if (PathIsRelativeA(path)) {
+return DISPATCH_BAD_INPUT;
+}
+#else
+if (!_is_separator(*path)) {
 return DISPATCH_BAD_INPUT;
 }
+#endif
 size_t pathlen = strlen(path);
 dispatch_io_path_data_t path_data = malloc(sizeof(*path_data) + pathlen+1);
 if (!path_data) {
@@ -449,9 +463,15 @@ dispatch_io_create_with_path(dispatch_io_type_t type, const char *path,
 break;
 default:
 if ((path_data->oflag & O_CREAT) &&
-(*(path_data->path + path_data->pathlen - 1) != '/')) {
+!_is_separator(*(path_data->path + path_data->pathlen - 1))) {
 // Check parent directory
-char *c = strrchr(path_data->path, '/');
+char *c = NULL;
+for (ssize_t i = (ssize_t)path_data->pathlen - 1; i >= 0; i--) {
+if (_is_separator(path_data->path[i])) {
+c = &path_data->path[i];
+break;
+}
+}
 dispatch_assert(c);
 *c = 0;
 int perr;
@@ -465,7 +485,11 @@ dispatch_io_create_with_path(dispatch_io_type_t type, const char *path,
 err = 0;
 break;
 );
+#if defined(_WIN32)
+*c = '\\';
+#else
 *c = '/';
+#endif
 }
 break;
 );
@@ -1287,18 +1311,31 @@ _dispatch_fd_entry_guarded_open(dispatch_fd_entry_t fd_entry, const char *path,
 #if defined(_WIN32)
 (void)mode;
 DWORD dwDesiredAccess = 0;
-if (oflag & _O_RDWR)
-dwDesiredAccess = GENERIC_READ | GENERIC_WRITE;
-else if (oflag & _O_RDONLY)
-dwDesiredAccess = GENERIC_READ;
-else if (oflag & _O_WRONLY)
-dwDesiredAccess = GENERIC_WRITE;
+switch (oflag & (_O_RDONLY | _O_WRONLY | _O_RDWR)) {
+case _O_RDONLY:
+dwDesiredAccess = GENERIC_READ;
+break;
+case _O_WRONLY:
+dwDesiredAccess = GENERIC_WRITE;
+break;
+case _O_RDWR:
+dwDesiredAccess = GENERIC_READ | GENERIC_WRITE;
+break;
+}
 DWORD dwCreationDisposition = OPEN_EXISTING;
-if (oflag & _O_CREAT)
+if (oflag & _O_CREAT) {
 dwCreationDisposition = OPEN_ALWAYS;
-if (oflag & _O_TRUNC)
-dwCreationDisposition = CREATE_ALWAYS;
-return (dispatch_fd_t)CreateFile(path, dwDesiredAccess, 0, NULL, dwCreationDisposition, 0, NULL);
+if (oflag & _O_EXCL) {
+dwCreationDisposition = CREATE_NEW;
+} else if (oflag & _O_TRUNC) {
+dwCreationDisposition = CREATE_ALWAYS;
+}
+} else if (oflag & _O_TRUNC) {
+dwCreationDisposition = TRUNCATE_EXISTING;
+}
+return (dispatch_fd_t)CreateFile(path, dwDesiredAccess,
+FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
+dwCreationDisposition, 0, NULL);
 #else
 return open(path, oflag, mode);
 #endif

src/shims/generic_win_stubs.h

@@ -6,6 +6,7 @@
 
 #include <Windows.h>
 #include <crtdbg.h>
+#include <Shlwapi.h>
 
 #include <io.h>
 #include <process.h>