Response Object

server['response'] is basically an instantiation of HTTPResponse class.

Here are some of available methods:

set_content_type(content_type=b'text/html; charset=utf-8')
set_cookie(name, value='', expires=0, path='/', domain=None, secure=False, httponly=False, samesite=None)
set_header(name, value='')
set_status(status=200, message=b'OK')

You can use the write() or end() method instead of yield / return to send the HTTP response body. Although the latter is preferred.

You can imagine that write() is like yield, it can be called more than once. Whereas end() is like return, which is only allowed to be called once.

Whether yield, return, write(), or end() will implicitly send the HTTP header once. Normally, You don’t need to set anything except a few things like response status, Content-Type, Set-Cookie by using the set_* method above (should be called earlier).

If you need to send RAW responses, consider using the send() method. This will not implicitly send the HTTP header. The set_* method call will be meaningless.

Here’s a summary of the comparison:

Methods	Implicit HTTP Header	Info
yield b’Hello’	Yes
return ‘Hello’	Yes
await response.write(b’Hello’)	Yes
await response.write(b’’)	Yes	May send as `b'0\r\n\r\n'` if chunked is enabled
await response.write(None)	Yes	Send the prepared HTTP header then call `send(None)`
await response.end(b’Hello’)	Yes
await response.end()	Yes	Same as calling `write(b'')` then `send(None)`
await response.send(b’HTTP/1.1 …’)	No	Send RAW responses, Non-HTTP is possible
await response.send(None)	No	Same as `response.close(keepalive=True)`
response.close(keepalive=True)	No	Mark the end of response. Connection will be closed, but respect HTTP keep-alive
response.close()	No	Just close the connection. Called automatically in handlers when `None` is returned