How to prevent Deno's fetch implementation from sending default headers?

[jsejcksn]

I noticed that Deno adds default headers to every fetch request. They are even included as expected values in this unit test.

Here is an example:

{
  "accept": "*/*",
  "user-agent": "Deno/1.7.2",
  "accept-encoding": "gzip, br",
  "host": "localhost:8000"
}

How can I prevent this so that a fetch request can be sent with no header values?

[kitsonk]

There are certain headers that are required to be sent by the user agent and certain ones which cannot be controlled by the user. It is all rather extensive but documented in the standard: https://fetch.spec.whatwg.org/#terminology-headers

[jsejcksn]

Hi @kitsonk thanks for replying. Thanks for the link as well.

I just read through the entire section "2.2.2. Headers".

I did read the section about forbidden headers (controlled by the user agent), which I am familiar with, but I did not see anything mentioned about required headers. Can you elaborate on that?

[jsejcksn]

I did not see anything mentioned about required headers. Can you elaborate on that?

@kitsonk I've searched more about this and still am not finding anything. Will you please provide more information?

[kitsonk]

A forbidden header name is a header name that is a byte-case-insensitive match for one of

Accept-Charset
Accept-Encoding
Access-Control-Request-Headers
Access-Control-Request-Method
Connection
Content-Length
Cookie
Cookie2
Date
DNT
Expect
Host
Keep-Alive
Origin
Referer
TE
Trailer
Transfer-Encoding
Upgrade
Via
or a header name that starts with a byte-case-insensitive match for Proxy- or Sec- (including being a byte-case-insensitive match for just Proxy- or Sec-).

These are forbidden so the user agent remains in full control over them. Names starting with Sec- are reserved to allow new headers to be minted that are safe from APIs using fetch that allow control over headers by developers, such as XMLHttpRequest. [XHR]

So this means that Deno get to choose to set those and that API consumers cannot control them.

§ 4.8 specifies that when Accept isn't set, it is to be set to */* and § 4.6.11 indicates that if the user agent is not set that a default value is set. So while you can change the values of those two headers, you cannot omit them.

[jsejcksn]

Ok, so if I want to send a network request without any headers using Deno, how would I do it? Does Deno.createHttpClient allow me to do this?