Proxying a REST API using golang

Question

I m actually learning golang and try to implement a proxy on a an Rest API that I've made in another language

For now, I only want to query my golang API, extract they actual path parameters and query the other API based on it.

I want the result to be "exactly" the same (or at least, the body part), just like a simple JSON.

For now, I don't want to create a structure for my data, I just want to simply get and retrieve the content.

Here's what I have:

package main

import (
    "fmt"
    "net/http"

    "github.com/gorilla/mux"
)

const API_URL string = "https://my-api-path/"

func setHeaders(w http.ResponseWriter) {
    w.WriteHeader(http.StatusOK)
    w.Header().Set("Content-Type", "application/json")
}

func extractParams(r *http.Request) map[string]string {
    return mux.Vars(r)
}

func getHandler(w http.ResponseWriter, r *http.Request) {
    setHeaders(w)
    params := extractParams(r)

    url := API_URL + params["everything"]
    response, err := http.Get(url)

    if err != nil {
        fmt.Fprint(w, err)
    }

    fmt.Fprint(w, response)

}

func main() {
    router := mux.NewRouter()
    router.HandleFunc("/{everything}", getHandler)
    http.ListenAndServe(":8080", router)
}

My problem

For now, I m not able to retrieve JSON information from my other API. I only have a text/plain Content-Type which is weird since I enforce application/json and I only have some header details in the response body, something like:

&{200 OK 200 HTTP/2.0 2 0 map[Allow:[GET, HEAD, OPTIONS] Expect-Ct:[max-age=86400, report-uri="https://report-uri.cloudflare.com/cdn-cgi/beacon/expect-ct"] Server:[cloudflare] Cf-Ray:[some-ray] Date:[Tue, 12 Jun 2018 14:38:57 GMT] Content-Type:[application/json] Set-Cookie:[__cfduid=lolol; expires=Wed, 12-Jun-19 14:38:56 GMT; path=/; domain=some-domain; HttpOnly; Secure] Vary:[Accept-Encoding Cookie] X-Frame-Options:[SAMEORIGIN] X-Xss-Protection:[1; mode=block]] 0xc4201926f0 -1 [] false true map[] 0xc420150800 0xc4200e8370}

Do you have any idea on how I can proxy this request (or the JSON result) ?

Try io.Copy(w, response.Body). And please do close the response body i.e. defer response.Body.Close(). Also when Get returns an error and you write it to the reponse there is no reason to also write a nil response, so add a return statement to the end of the if err != nil ... conditional's body. — mkopriva
– mkopriva, Commented Jun 12, 2018 at 14:47

eugenioy · Accepted Answer · 2018-06-12 14:53:37Z

5

About the Content-Type header not being written to your response:

Seems to be expected due to the order in which you are performing these operations:

w.WriteHeader(http.StatusOK)
w.Header().Set("Content-Type", "application/json")

See here: https://golang.org/pkg/net/http/#ResponseWriter

Changing the header map after a call to WriteHeader (or Write) has no effect unless the modified headers are trailers.

Try inverting those to read:

w.Header().Set("Content-Type", "application/json")
w.WriteHeader(http.StatusOK)

edited Jun 12, 2018 at 14:53

answered Jun 12, 2018 at 14:52

eugenioy

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1 Comment

mfrachet Over a year ago

Thanks for this, it solved the Content-Type part of my problem :D

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