Additional content-type parameters are thrown away

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Bug Report

Restify Version

6.3.4

Node.js Version

8.9.1

Expected behaviour

Given the following code, I would expect the content-type string I set to be used.

res.contentType = "text/plain; version=0.0.4; charset=utf-8"
res.send(...)

Should produce:

Content-Type: text/plain; version=0.0.4; charset=utf-8

For context, the content-type I'm using comes from: Prometheus client, Prometheus docs

Actual behaviour

Only the contents of the string before the first ; are used, resulting in:

Content-Type: text/plain

Repro case

var restify = require('restify');

const server = restify.createServer({
  name: 'myapp',
  version: '1.0.0'
});

server.get('/test', function (req, res, next) {
  res.contentType = "text/plain; version=0.0.4; charset=utf-8"
  res.send(200, "some text")
  return next();
});

server.listen(8080, function () {
  console.log('%s listening at %s', server.name, server.url);
});

Cause

The string is split here, throwing away the rest:

https://github.com/restify/node-restify/blob/74e0cf55fc452931215280741516d30555d76f7a/lib/response.js#L466

Are you willing and able to fix this?

Maybe 😄

Assuming there isn't some reason this is intended behaviour, I can have a look at fixing.

Start in lib/response.js at the content-type handling around line 466 and run the provided Restify reproduction. Preserve the complete content-type value, including parameters, and verify that the response emits text/plain; version=0.0.4; charset=utf-8 rather than only text/plain.