Response sent in chunked transfer encoding and indicating errors happening after some data has already been sent

Question

I am sending large amount of data in my response to the client in chunked transfer encoding format.

How should I be dealing with any errors that occur midway during writing of the response?

I would like to know if there is any HTTP Spec recommended practice regarding this for clients to know that indeed the response is not a successful one but that the server ran into some issue.

Answer 1

Once you have started sending the HTTP headers to the client, you can't send anything else. You have to finish sending the response you intended to send, ie the chunked data and associated headers. If an error occurs midway through that, there is no way to report that error to the client. All you can do is close the connection. Either the client does not receive all of the headers, or it does not receive the terminating 0-length chunk at the end of the response. Either way is enough for the client to know that the server encountered an error during sending.

Answer 2

Chunked responses can use trailer header with some integrity check or post-processing status. This may be better than closing the connection as described in accepted answer because you can have custom error message. However, you only benefit from that if you have control of both server and client.