[http] How to set headers in http get request?

I'm doing a simple http GET in Go:

client := &http.Client{}
req, _ := http.NewRequest("GET", url, nil)
res, _ := client.Do(req)

But I can't found a way to customize the request header in the doc, thanks

Pay attention that in http.Request header "Host" can not be set via Set method

req.Header.Set("Host", "domain.tld")

but can be set directly:

req.Host = "domain.tld":

req, err := http.NewRequest("GET", "http://10.0.0.1/", nil)
if err != nil {
    ...
}

req.Host = "domain.tld"
client := &http.Client{}
resp, err := client.Do(req)

Go's net/http package has many functions that deal with headers. Among them are Add, Del, Get and Set methods. The way to use Set is:

func yourHandler(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("header_name", "header_value")
}