Most efficient way to read HTTP headers from a file? - go

Question

I'm looking for an efficient way to read HTTP headers from a textfile to be later sent with an HTTP request. Consider the following code (which currently contains basic net/http request functionality):
func MakeRequest(target string, method string) {
client := &http.Client{}
req, _ := http.NewRequest(method, target, nil)
//Headers manually..
req.Header.Add("If-None-Match", `some value`)
response, _ := client.Do(req)
body, _ := ioutil.ReadAll(response.Body)
fmt.Println(string(body))
}
I started by using ioutil.ReadFile like this:
func main() {
data, _ := ioutil.ReadFile("/opt/tests/req.txt")
fmt.Print(string(data))
}
But taking this text, splitting it by some indicator (lets say ":") and then placing the information in req.Header.Add("var1", "var2") per-header seems like an over-kill.
Question: Any better way to send HTTP requests with headers from a text file in go?

Answer 1

net/http has a method ReadRequest which can create a new Request object from a bufio.Reader. Assuming that your file contains a real HTTP request (instead of only the part of the request which consists of lines with key: value) all you need to do is create a new bufio.Reader from the file, i.e. like this (error handling omitted):
rdr,_ := os.Open("req.txt")
req,_ := http.ReadRequest(bufio.NewReader(rdr))
fmt.Printf("%+v\n", req)

Answer 2

If you only want some headers defined, another option is to define the headers in a Json file and apply the following code (file reading not included):
var jsonMap map[string]string
err = json.Unmarshal(jsonBytesFromFile, &jsonMap)
if err != nil {
log.Fatal("unable to parse json: ", err)
}
for k, v := range jsonMap {
log.Printf("setting Header : %s : %s", k, v)
responseWriter.Header().Add(k, v) // you may prefer Set()
}
The json looks like this:
{
"Content-type": "text/plain",
"Cache-Control": "only-if-cached"
}