clipboard: fix a bug when pasting image to LibreOffice

[metalefty]

While here, embed correct file size in BMP file header.

Fixes: #3102
Sponsored by: Krämer Pferdesport GmbH & Co KG

[metalefty]

Rebased onto #3088 to fix FreeBSD CI.

[metalefty]

@matt335672 Can you have a look at this area especially? I'm not sure if this is a good way to embed file size in BMP file header.

[matt335672]

Yes, that could do with tidying up.

Personally, I'd use the stream functions we already have. They've been well-tested, an xrdp developer should be familiar with them, and a lot of magic numbers can be avoided. Something like this maybe (compiles, but not tested):-

    /* Assemble bmp header */
    /* See https://en.wikipedia.org/wiki/BMP_file_format#Bitmap_file_header */
    make_stream(hdr_s);
    if (hdr_s == 0)
    {
        g_free(g_clip_c2s.data);
        g_clip_c2s.total_bytes = 0;
        return 0;
    }
    init_stream(hdr_s, BMPFILEHEADER_LEN);
    out_uint8(hdr_s, 'B');
    out_uint8(hdr_s, 'M');
    out_uint32_le(hdr_s, g_clip_c2s.total_bytes);
    out_uint16_le(hdr_s, 0);
    out_uint16_le(hdr_s, 0);
    out_uint32_le(hdr_s, BMPFILEHEADER_LEN + 40);

    /* Copy header and data to output stream */
    g_memcpy(g_clip_c2s.data, hdr_s->data, BMPFILEHEADER_LEN);
    in_uint8a(s, g_clip_c2s.data + BMPFILEHEADER_LEN, len);
    free_stream(hdr_s);

You can remove g_bmp_image_header, and simply define BMPFILEHEADER_LEN as 14.

It's not as efficient, but that probably doesn't matter. It's not being called that often to need to optimise it.

[metalefty]

Thanks, it worked and applied tidy-up. I also replaced the magic number 40 with BMPINFOHEADER_LEN.

[matt335672]

LGTM

Also needs to go into devel