rustdesk/rustdesk · error

Invalid mask cursor buffer size, got {} bytes, expected {}

Error message

Invalid mask cursor buffer size, got {} bytes, expected {}

What it means

Post-copy sanity check: the number of mask bytes actually retrieved does not match the expected bmWidthBytes × bmHeight buffer size. This indicates the OS delivered a different mask layout than the BITMAP header advertised (stale handle or unusual driver), so the buffer is unusable for building valid cursor data.

Source

Thrown at src/platform/windows.rs:285

        let mut height = if ii.is_color() {
            bm_mask.bmHeight
        } else {
            bm_mask.bmHeight / 2
        };
        let cbits_size = width * height * 4;
        if cbits_size < 16 {
            bail!("Invalid icon: too small"); // solve some crash
        }
        let mut cbits: Vec<u8> = Vec::new();
        cbits.resize(cbits_size as _, 0);
        let mut mbits: Vec<u8> = Vec::new();
        mbits.resize((bm_mask.bmWidthBytes * bm_mask.bmHeight) as _, 0);
        let r = GetBitmapBits(ii.0.hbmMask, mbits.len() as _, mbits.as_mut_ptr() as _);
        if r == 0 {
            bail!("Failed to copy bitmap data");
        }
        if r != (mbits.len() as i32) {
            bail!(
                "Invalid mask cursor buffer size, got {} bytes, expected {}",
                r,
                mbits.len()
            );
        }
        let do_outline;
        if ii.is_color() {
            get_rich_cursor_data(ii.0.hbmColor, width, height, &mut cbits)?;
            do_outline = fix_cursor_mask(
                &mut mbits,
                &mut cbits,
                width as _,
                height as _,
                bm_mask.bmWidthBytes as _,
            );
        } else {
            do_outline = handleMask(
                cbits.as_mut_ptr(),

View on GitHub (pinned to 91c9fccbb0)

Solutions

1. Discard this cursor frame and retry capture, since the mismatch usually stems from a cursor being replaced concurrently
2. Validate the BITMAP header dimensions immediately before the copy and re-query GetObjectA if the cursor handle may be stale
3. Skip serializing this cursor and keep the previously captured shape

When it happens

Trigger: Thrown at src/platform/windows.rs:285 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of rustdesk/rustdesk@91c9fccbb0 (2026-09-10). Data as JSON: /api/errors/5735c8894686a942. Report an issue: GitHub.