frame: use a more Win32 friendly version of reading a file in memory

It's only used when the file cannot be mapped in memory.

This was not a real implementation of pread. As the comment suggests, the
original offset was not respected. But we don't care in this case as we want to
read the whole file from start to end.

It is now a cancelation point. We can't cancel during the duration of the
ReadFile call, but at least we cancel when it's done even if the whole file is
not read.

src/misc/frame.c

@@ -385,27 +385,6 @@ vlc_frame_t *vlc_frame_shm_Alloc (void *addr, size_t length)
 #endif
 
 
-#ifdef _WIN32
-# include <io.h>
-
-static
-ssize_t pread (int fd, void *buf, size_t count, off_t offset)
-{
-    HANDLE handle = (HANDLE)(intptr_t)_get_osfhandle (fd);
-    if (handle == INVALID_HANDLE_VALUE)
-        return -1;
-
-    OVERLAPPED olap = {.Offset = offset, .OffsetHigh = (offset >> 32)};
-    DWORD written;
-    /* This braindead API will override the file pointer even if we specify
-     * an explicit read offset... So do not expect this to mix well with
-     * regular read() calls. */
-    if (ReadFile (handle, buf, count, &written, &olap))
-        return written;
-    return -1;
-}
-#endif
-
 vlc_frame_t *vlc_frame_File(int fd, bool write)
 {
     size_t length;
@@ -451,9 +430,10 @@ vlc_frame_t *vlc_frame_File(int fd, bool write)
             return vlc_frame_mmap_Alloc (addr, length);
     }
 #elif defined(_WIN32)
+    HANDLE handle = INVALID_HANDLE_VALUE;
     if (length > 0)
     {
-        HANDLE handle = (HANDLE)(intptr_t)_get_osfhandle (fd);
+        handle = (HANDLE)(intptr_t)_get_osfhandle (fd);
         if (handle != INVALID_HANDLE_VALUE)
         {
             void *addr = NULL;
@@ -465,7 +445,9 @@ vlc_frame_t *vlc_frame_File(int fd, bool write)
             if (hMap != INVALID_HANDLE_VALUE)
                 addr = MapViewOfFileFromApp(hMap, access, 0, length);
 #else
-            hMap = CreateFileMapping(handle, NULL, prot, 0, length, NULL);
+            DWORD hLength = (DWORD)(length >> 32);
+            DWORD lLength = (DWORD)(length & 0xFFFFFFFF);
+            hMap = CreateFileMapping(handle, NULL, prot, hLength, lLength, NULL);
             if (hMap != INVALID_HANDLE_VALUE)
                 addr = MapViewOfFile(hMap, access, 0, 0, length);
 #endif
@@ -475,6 +457,12 @@ vlc_frame_t *vlc_frame_File(int fd, bool write)
 
             CloseHandle(hMap);
         }
+        else
+        {
+            // fail early
+            errno = EBADF;
+            return NULL;
+        }
     }
 #else
     (void) write;
@@ -486,6 +474,48 @@ vlc_frame_t *vlc_frame_File(int fd, bool write)
         return NULL;
     vlc_frame_cleanup_push (frame);
 
+#if defined(_WIN32)
+    LARGE_INTEGER srcPointer = { 0 };
+    if (unlikely(!SetFilePointerEx(handle, srcPointer, &srcPointer, FILE_CURRENT)))
+    {
+        vlc_frame_Release (frame);
+        frame = NULL;
+        errno = EIO;
+        goto done;
+    }
+    LARGE_INTEGER startPointer = { 0 };
+    if (unlikely(!SetFilePointerEx(handle, startPointer, NULL, FILE_BEGIN)))
+    {
+        vlc_frame_Release (frame);
+        frame = NULL;
+        errno = EIO;
+        goto done;
+    }
+    for (size_t i = 0; i < length;)
+    {
+        DWORD hOffset = (DWORD)(i >> 32);
+        DWORD lOffset = (DWORD)(i & 0xFFFFFFFF);
+        OVERLAPPED olap = {.Offset = hOffset, .OffsetHigh = lOffset};
+        DWORD lLength = (length - i) > ULONG_MAX ? ULONG_MAX : (DWORD)(length - i);
+        DWORD len;
+        if (!ReadFile(handle, frame->p_buffer + i, lLength, &len, &olap))
+        {
+            vlc_frame_Release (frame);
+            frame = NULL;
+            errno = EIO;
+            break;
+        }
+        vlc_testcancel();
+        i += len;
+    }
+    if (unlikely(!SetFilePointerEx(handle, srcPointer, NULL, FILE_BEGIN)))
+    {
+        vlc_frame_Release (frame);
+        frame = NULL;
+        errno = EIO;
+        goto done;
+    }
+#else // !_WIN32
     for (size_t i = 0; i < length;)
     {
         ssize_t len = pread (fd, frame->p_buffer + i, length - i, i);
@@ -497,6 +527,8 @@ vlc_frame_t *vlc_frame_File(int fd, bool write)
         }
         i += len;
     }
+#endif // !_WIN32
+done:
     vlc_cleanup_pop ();
     return frame;
 }