I held off on adding...

func Errors(ctx context.Context) chan<- error {
    v := ctx.Value(ipfsContextErrorLog)
    ch, ok := v.(chan<- error)
    if !ok {
        return nil
    }
    return ch
}

One concern with this is that it leaks the implementation of the error logging. If the parent context was created using context.Background(), then callers may push errors to a nil channel.

@jbenet

@perfmode yep, good point. i guess this is why WithCancel only gives you the cancel func once. LGTM

@whyrusleeping ?

Other than an impressively long test name, LGTM

wooo. unlike this: