don't set header when respond=false and header sent

[dead-horse]

many people using next.js or migrate there app from express will set respond=false, but lots of koa's middleware will set header like:

async (ctx, next) => {
    await next();
    ctx.set('foo', 'bar');
}

it will cause Can't set headers after they are sent error if we already sent response body before. Maybe we can make ctx.set() invalid when respond=false and header sent. (We can log something when NODE_ENV is develop to hint developer this unexpected behavior)

related issues:

• Support ctx.respond = false session#95
• Setting session before login throws Error: Can’t set headers after they are sent session#89

Any thoughts?

[nordsimon]

I just saw your reference @dead-horse. From my point of view, respond.false is very useful and sometimes neccessary in specific implementations. I would go for logging a warning in develop (or via debug) module mode but still allow and fix the behaviour. Maybe add some more info what side effects respond false has ?

[nordsimon]

And yes, I see that this should actually live in koa and not in koa-session, I will close my PR in order to find a solution here

[dead-horse]

this is already fixed in #1137