Why /zip is read-only?

[franalbani]

For some reason, I was confident that it was possible for a cosmo binary to write inside /zip (and even persist the changes in the file itself).

But after failing to do it with cosmo's python:

$ ./python -c "open('/zip/memories.txt', 'w').write('memory')"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
OSError: [Errno 30] Read-only file system: '/zip/memories.txt'

and then verifying with a simple C example, I started git greping the repo searching for something to prove myself I was wrong.

This is the only thing I found:

// zipos being a read-only filesystem, ...

I would like to understand why it is so and if there is another way to achieve the same result.

Thanks!

[metaist]

cosmofy is a tool I wrote that has some lower-level tools that let you ls/cat/add/rm on a cosmo python file.

I have run this tool on itself, so, yes, it is possible for a cosmo file to write to itself. You just have to remember to use zipfile.ZipFile instead of open() because you're technically modifying a zip file, not just writing bytes to disk.

[franalbani]

Nice!

I ignored that.

I leave this for future readers:

$ wget https://cosmo.zip/pub/cosmos/v/4.0.2/bin/python
$ chmod +x python
$ ./python -c 'from zipfile import ZipFile; ZipFile("python", "a").open("example.txt", "w").write(b"something")'
$ ./python -c 'print(open("/zip/example.txt").read())'
something

[couleurm]

what would the C equivalent look like?