xsel silently fails to set selection to file contents if over ~4000 bytes

[skierpage]

xsel version 1.2.0 (Fedora package xsel-1.2.0-24.fc30.src.rpm)
Fedora 30 KDE Spin
X.Org X Server 1.20.5. (xorg-x11-server 1.20.5-4.fc30).

After writing all the below this sounds like closed bugs #13 and #14, but I think I'm running latest version 1.20 ??!

I've used xsel -b for years, thanks! Today I tried to set the clipboard selection to the contents of a 9 kB file with xsel -b < MYFILE and after 10 minutes of WTF I realized the command was failing and setting the clipboard contents to empty, even though its exit status $? is 0. When it fails it appends xsel: BadWindow (invalid Window parameter): Resource temporarily unavailable to ~/.xsel.log.

I reduced and increased the file size until I determined that xsel -b < SOMEFILE succeeds with a 4075-byte file and fails with 4076 bytes... but now 4075 is failing too! So the limit varies. I can use Ctrl-C in GUI apps to set the clipboard selection to much bigger files.

I ran strace on the failure vs/ successful xsel of another file, and the contents are essentially the same, then I realized there's a child process ;-) ; with -ff the child process gets some errors from recvmsg(3, {msg_namelen=0}, 0) = -1 EAGAIN (Resource temporarily unavailable) but seems to keep going and writes bits of the file until it opens /usr/share/X11/XErrorDB and reports errors. I can upload the strace if it will help.

I'll file a separate bug that when the child process fails with exit_group(1), the error isn't reported to the parent.

[skierpage]

I built latest xsel from source and still have this problem. Sometimes the child process that xsel forks times out with BadWindow and sometimes doesn't. When I first ran xsel -b --nodetach < MY_4k_FILE, it took many seconds before printing out

/tmp/xsel_build/bin/xsel: BadWindow (invalid Window parameter): Resource temporarily unavailable

and exit, but if I repeat the command it fails quickly with the same error... and then other times it works, waiting for someone to request the selection and providing it correctly.

[amerlyq]

Maybe this commit from fork will fix it?
On input, dont exit parent (returning to invoker) until either select… · mckellyln/xsel@b7d8442⠀
https://github.com/mckellyln/xsel/commit/b7d8442d9f661550ef78a4f1bd164bf7304f70db

However, neovim simply started preferring xclip due to xsel codebase being neglected...
nvim xsel not working properly? · Issue #5853 · neovim/neovim
neovim/neovim#5853