Using the content write interface

[Benjamin M Romer]

Hi,

I'm experimenting with snaps and would like to use the content interface 
to share files with another snap. I couldn't find documentation for it, 
so I figured I'd ask.

Since there's a "write:" option for the content interface, and the snap 
itself is read-only, it seemed likely that there is a way to expose 
files in $SNAP_DATA or $SNAP_COMMON so that the consuming snap could see 
and modify them.

I tried using $SNAP_DATA for the path, but that doesn't work:

cannot mount /snap/supplier/x1/$SNAP_DATA at /snap/consumer/x1/data with 
options bind. errmsg: No such file or directory

The mount point exists, so I believe it was using "$SNAP_DATA" 
literally, and not doing any substitution. What's the right way to point 
it at the right directory (assuming it's possible)?

If write is not possible, is there a way to expose $SNAP_DATA with the 
"read:" option?

Thanks in advance. :)

-- Ben