Response code auto set to 204 after being previously set to 200 with undefined or null body.

[austin-rausch]

Koa version 2.12.0

Running this snippet and sending a request will return a 204 response code despite the status code being explicitly set to 200, it does return a 200 if you reverse the two lines:

const koa = require('koa');
const app = new koa();
app.use(ctx => {
  ctx.status = 200;
  ctx.body = undefined;
});
app.listen(3000);

This contradicts the documentation and I believe it is caused by not checking for _explicitStatus on this line.

I'm happy to fix the issue by adding the check there, I just want to confirm this is un-intended behavior or if its a mistake in the documentation. As far as I can tell the HTTP spec doesn't specifically mandate that a body be included on a 200 response, only that a 204 MUST NOT include a message-body.

[ejose19]

Yes, there are some cases one wants to reply with "no body" for other status codes as well, that's why I submitted #1447 which is already on latest version (2.12.0)

To obtain the result you want use as this

// This must be always set first before status, since null | undefined 
// body automatically sets the status to 204
  ctx.body = null;
// Now we override the 204 status with the desired one
  ctx.status = 200; 

notice the server won't respond with "null" value, it will be no response like it does for 204

[austin-rausch]

I can't say I agree with the behavior, if a response code is set explicitly, then a body is set after it shouldn't change the response code. Thats a strange side effect that I don't think many people will expect.

If I set a status code, I would expect that status code to be what is returned assuming it is valid for the body given.

If the response code and body are invalid together I would expect an error to be thrown.

At the very least this side effect needs documented correctly. Again, offering to do it just looking for some confirmation or consensus.

[miwnwski]

A docs PR for response.body= seems sane 👍