Attempting to save an image-rich presentation causes an error from Mongo

[banksJeremy]

The error that shows up in Mongo's log is vague...

Assertion: 10334:Invalid BSONObj size: 21942433

... but it looks like Mongo has a maximum document size the defaults to 16MB and I might be hitting due to having a lot of embedded images.

Butter keeps waiting for a response from Mongo that never comes, so it never closes the connection to the browser, causing a silent failure from the user's perspective.

[banksJeremy]

Inside the handler for app.post('/api/project/:id?', ...) in butter/cornfield/app.js I replaced

doc.save();
res.json({ error: 'okay', project: proj });

with

doc.save(function (err) {
  if ( !err ) {
    res.json({ error: 'okay', project: proj });
  } else {
    res.json( {error: 'internal db error' }, 500 );
  }
});

to fail better. (banksJeremy/butter@4eececb)

This works, and now I'm confused why the failure left a connection open. I'd think that .save() would be async and return instantly, so res.json(...) would be called and close the connection in either case. Maybe it's not async? Weird.

[banksJeremy]

Filed upstream: t1603