Don't use exec() for file

[erkyrath]

Note: This PR is built on top of #41 ! Merge that first.

I've written a little utility to pipe the output of unzip/untar into file.

This uses the Node event-driven file-stream API. All the output of unzip -p xxx.zip file goes through the unbox process. But we don't store it all, not even in memory. It's just passed along chunk by chunk.

(The stdout/stderr output of file does get accumulated in memory. But that's tiny.)

Now, the bad news: this doesn't fix the problems that I originally thought it would fix. In #39 , I mentioned two files causing errors:

• /if-archive/infocom/compilers/inform6/library/contributions/platypus.zip (see Icon^M etc)
• /if-archive/games/mini-comps/adrift/onehourcomp4.zip (see agent_4F[1].A.taf)

Turns out these are not shell bugs. They are mismatches between what unzip reports in its file list and what it accepts as a filename. Oh well!

(I recognize the Icon^M thing. It's a MacOS Classic convention where a folder icon appeared in the filesystem with that filename, yes, with a ctrl-M in it. Everybody hated that.)

Anyhow, this spurred me into cleaning up the exec() situation, and I'm very happy about that. I think my implementation is correct. It's possible I missed something; I still haven't spent a lot of time in async-node-land.

[erkyrath]

I see the lint error but I don't know what the idiom is to make it go away.

[curiousdannii]

Arrow functions with no arguments have the syntax of () => {}. Or function() {} works too ;).

[erkyrath]

Thanks -- I knew it had to be something obvious.