| -------------------| ------------------------------------------------------|

|`Accept-Encoding`|`gzip, deflate, br` (when`options.compress === true`)|

|`Connection`|`close`_(when no`options.agent` is present)_|

|`Content-Length`|_(automatically calculated, if possible)_|

|`Host`|_(host and port information from the target URI)_|

|`Transfer-Encoding`|`chunked`_(when`req.body` is a stream)_|

See[`http.Agent`](https://nodejs.org/api/http.html#http_new_agent_options) for more information.

If no agent is specified, the default agent provided by Node.js is used. Note that[this changed in Node.js 19](https://github.com/nodejs/node/blob/4267b92604ad78584244488e7f7508a690cb80d0/lib/_http_agent.js#L564) to have`keepalive` true by default. If you wish to enable`keepalive` in an earlier version of Node.js, you can override the agent as per the following code sample.

In addition, the`agent` option accepts a function that returns`http`(s)`.Agent` instance given current[URL](https://nodejs.org/api/url.html), this is useful during a redirection chain across HTTP and HTTPS protocol.