overwriting fs streams will cause fd leaks

[jonathanong]

this is really only a case when you do this.status = 304, but i'm opening an issue here since koa may want to handle it better. i can't think of a good way to, though.

basically, every time you do fs.createReadStream(), it'll open a descriptor every time. if you unset the body as this.status = 304, then you won't ever "close" the fd.

example: https://gist.github.com/jonathanong/8186604

not sure what to do. the only solution right now other than have node fix their shit is to have conditional-get middleware handle this or have send include 304 handling

[jonathanong]

okay two solutions:

• FDs should only open once a file stream is being consumed nodejs/node-v0.x-archive#6782 (comment), which i think i'm leaning towards. if we do this, then we should explicitly tell people to use send for files
• this really stupid utility i just made: https://github.com/stream-utils/dethroy/blob/master/index.js for when this.body = null. this will support all streams, not just file streams, and will only work on the last body value, but i think it's fine.

[jonathanong]

this will be handled by #255

[jonathanong]

#255