Write HTTP trailer headers manually - http

Question

This question was motivated by the answers here:
What to do with errors when streaming the body of an Http request
In this case, I have already written a HTTP 200 OK header, then I need to amend this if there is an error, by writing a trail header that says there was an error after writing a success header.
I have this Node.js code:
const writeResponse = function(file: string, socket: Socket){
socket.write([
'HTTP/1.1 200 OK',
'Content-Type: text/javascript; charset=UTF-8',
'Content-Encoding: UTF-8',
'Accept-Ranges: bytes',
'Connection: keep-alive',
].join('\n') + '\n\n');
getStream(file)
.pipe(socket)
.once('error', function (e: any) {
// there was an error
// how can I write trail headers here ?
s.write('some bad shit happened\n')
});
}
how do I write a useful trail header to the response that can be displayed well by the browser?
I think this is the relevant spec for trail headers:
https://www.rfc-editor.org/rfc/rfc2616#section-14.40
I think they should be called "trailing headers", but whatever.

Answer 1

Firstly:
I think this is the relevant spec for trail headers: https://www.rfc-editor.org/rfc/rfc2616#section-14.40
RFC 2616 has been obsoleted by RFC 7230. The current spec for trailers is RFC 7230 § 4.1.2.
Secondly:
].join('\n') + '\n\n'
Lines in HTTP message framing are terminated with \r\n, not \n.
Thirdly:
Content-Encoding: UTF-8
Content-Encoding is for content codings (like gzip), not charsets (like UTF-8). You probably don’t need to indicate charset separately from Content-Type.
And lastly:
how do I write a useful trail header to the response that can be displayed well by the browser?
You don’t. Mainstream Web browsers do not care about trailers.
See also (by the same user?): How to write malformed HTTP response to “guarantee” something akin to HTTP 500