Write file from stdin and exit

[manix]

Hello,

I have a rather unique case where I'd like to write a file to the Pico without first saving it on my local filesystem.

For this purpose I added a fairly simple new command wstdinf, which reads stdin and writes it to a file on the Pico, supposedly:

class Shell(cmd.Cmd):
    ...

    def do_wstdinf(self, line):
        [ filename ] = self.line_to_args(line)
        src_file = io.StringIO("")
        filesize = 0
        for line in sys.stdin:
           src_file.write(line)
           filesize += len(line)
    
        dst_dev, dst_dev_filename = get_dev_and_path(filename)
    
        # Copying from host to remote
        dst_dev.remote(recv_file_from_host, src_file, dst_dev_filename,
                              filesize, xfer_func=send_file_to_remote)
    
    ...

I test it with the following command

$ echo -e "wstdinf /pyboard/print.py\nprint('test')\n" | rshell 
Connecting to /dev/ttyACM0 (buffer-size 512)...
Trying to connect to REPL  connected
Retrieving sysname ... rp2
Testing if sys.stdin.buffer exists ... Y
Retrieving root directories ... /test.py/
Setting time ... Aug 20, 2022 13:42:15
Evaluating board_name ... pyboard
Retrieving time epoch ... Jan 01, 1970
Welcome to rshell. Use Control-D (or the exit command) to exit rshell.
/home/xxx> /dev/ttyACM0 closed
/home/xxx> 

After which any subsequent executions of rshell are unsuccessful:

$ rshell 
Connecting to /dev/ttyACM0 (buffer-size 512)...
Trying to connect to REPL 

If I unplug and plug in the usb again, I see that the file is created, but is empty:

/home/xxx> ls -la /pyboard/
     0 Jan  1 1970  print.py
  7293 Aug 20 02:30 test.py

It's probably something small that I'm missing but I've spent upwards of a few hours on this already and I'd really appreciate any help.