How to add headers info using Transport in golang net/http

I am trying to control keep-alives session to reuse the tcp connection by creating a Trasport.

Here is my snippet and I am not sure how to add headers info for authentication.

url := "http://localhost:8181/api/v1/resource"
tr := &http.Transport{
    DisableKeepAlives:   false,
    MaxIdleConns:        0,
    MaxIdleConnsPerHost: 0,
    IdleConnTimeout:     time.Second * 10,
}
client := &http.Client{Transport: tr}
resp, err := client.Get(url)

This may not be what you want for your specific question - setting it in the request makes more sense in your case, but to answer your question directly, you should be able to add a default header to all the requests going through the transport by using a custom RoundTrip method for your Transport.

Check out https://golang.org/pkg/net/http/#RoundTripper

Something like :

type CustomTransport struct {
  http.RoundTripper
}

func (ct *CustomTransport) RoundTrip(req *http.Request) (*http.Response, error) {
	req.Header.Add("header-key", "header-value")
	return ct.RoundTripper.RoundTrip(req)
}

url := "http://localhost:8181/api/v1/resource"
tr := &CustomTransport{
    DisableKeepAlives:   false,
    MaxIdleConns:        0,
    MaxIdleConnsPerHost: 0,
    IdleConnTimeout:     time.Second * 10,
}
client := &http.Client{Transport: tr}
resp, err := client.Get(url)

I found this useful when I didn't have direct access to the http Client used by an API client library (or each request object directly), but it allowed me to pass in a transport.

Don't mix the Client from the Request.
The client uses a Transport and run the request: client.Do(req)

You set header on the http.Request with (h Header) Set(key, value string):

req.Header.Set("name", "value")

This is what I found:

    package main

    import (
        "fmt"
        "io/ioutil"
        "net/http"
    )

    var URL = "http://httpbin.org/ip"

    func main() {
        tr := &http.Transport{DisableKeepAlives: false}
        req, _ := http.NewRequest("GET", URL, nil)
        req.Header.Set("Authorization", fmt.Sprintf("Bearer %s", "Token"))
        req.Close = false

        res, err := tr.RoundTrip(req)
        if err != nil {
            fmt.Println(err)
        }
        body, _ := ioutil.ReadAll(res.Body)
        fmt.Println(string(body))
    }

And it works.