Document portal: Writing causes error

[Unrud]

Exporting a document and writing to it from within the sandbox causes xdg-document-portal to stop working.

Test:

APP="..."

tmp="$(mktemp)"
sandbox_tmp="$(flatpak document-export --app="$APP" --unique --transient --allow-write "$tmp")"
flatpak run --command=dd "$APP" if=/dev/zero of="$sandbox_tmp" ibs=1M count=100 obs=1
flatpak document-unexport "$sandbox_tmp"
rm "$tmp"

Output:

dd: writing to ‘/run/user/1000/doc/7a021286/tmp.xxP9AopWEd’: Software caused connection abort
1+0 records in
16097+0 records out
16097 bytes (16 kB) copied, 0,202229 s, 79,6 kB/s
Error: GDBus.Error:org.gtk.GDBus.UnmappedGError.Quark._g_2dio_2derror_2dquark.Code1: No such file or directory

...
XDP: xdp_fuse_lookup 5/7a021286 -> 
XDP: xdp_fuse_lookup <- inode 4
XDP: xdp_fuse_lookup 4/tmp.xxP9AopWEd -> 
XDP: xdp_fuse_lookup <- inode 6
XDP: xdp_fuse_open 6 flags 100001
XDP: Created temp file .xdp_tmp.xxP9AopWEd.X66SVY
XDP: xdp_fuse_setattr 6 8 (nil)
XDP: xdp_fuse_write_buf 6 0
XDP: xdp_fuse_write_buf 6 1
...
XDP: xdp_fuse_write_buf 6 16095
XDP: xdp_fuse_write_buf 6 16096
fuse: copy from pipe: short read

[Unrud]

Workaround: Removing the fuse argument splice_read seems to fix the problem.

[alexlarsson]

Yeah, i can reproduce this too. I wonder if its a fuse issue. Lemme dig into it.

[alexlarsson]

This seems related to buffer sizes. I can't seem to reproduce with:

while true; do flatpak run --command=dd org.gnome.gedit if=/dev/zero of="$sandbox_tmp" ibs=100k count=1 obs=4096; done

But with:

while true; do flatpak run --command=dd org.gnome.gedit if=/dev/zero of="$sandbox_tmp" ibs=100k count=1 obs=4095; done

It reproduces pretty quickly.

[alexlarsson]

I was able to reproduce it with a 4096 size too. This seems completely busted, i think we'll just disable spice_read.