Golang: http.NewRequest POST with JSON payload returns error 500

Question

I'm working on a library for an API. There's an API endpoint (POST) which when you issue a curl command is:

curl -H "X-API-TOKEN: API-TOKEN" 'http://interest-graph.getprismatic.com/text/topic' \
  --data "title=Clojure" \
  --data "body=Clojure is a dynamic programming language that targets the Java Virtual Machine (and the CLR, and JavaScript). It is designed to be a general-purpose language, combining the approachability and interactive development of a scripting language with an efficient and robust infrastructure for multithreaded programming.Clojure is a compiled language - it compiles directly to JVM bytecode, yet remains completely dynamic. Every feature supported by Clojure is supported at runtime."

I'm trying to perform the above command using http.NewRequest:

   var jsonReq = []byte(`{"title": "Clojure", "body": "Clojure is a dynamic programming language that targets the Java Virtual Machine 
        (and the CLR, and JavaScript). It is designed to be a general-purpose language, 
        combining the approachability and interactive development of a 
        scripting language with an efficient and robust infrastructure for multithreaded programming.
        Clojure is a compiled language - it compiles directly to JVM bytecode, 
        yet remains completely dynamic. Every feature supported by Clojure is supported at runtime."}`)

    buf := new(bytes.Buffer)

    err := json.NewEncoder(buf).Encode(jsonReq)
    if err != nil {
        fmt.Println(err)
    }

    u := "http://interest-graph.getprismatic.com/text/topic"
    ApiToken := "API-TOKEN"
    req, err := http.NewRequest("POST", u, buf)
    req.Header.Set("Content-Type", "application/json")
    req.Header.Set("X-API-TOKEN", ApiToken)

    if err != nil {
        log.Fatal(err)
    }
    c := http.DefaultClient
    resp, err := c.Do(req)
    if err != nil {
        log.Fatal(err)
    }

    defer resp.Body.Close()

    r, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(string(r))

Not sure if I'm doing this right, because I keep getting an error 500. Any idea what I'm doing wrong?

I am pretty sure we need more details. What is in err? Also, what does the console say? Any errors? — Sverri M. Olsen
– Sverri M. Olsen, Commented Feb 20, 2015 at 9:08
Is it me or you're are trying to encode something that is already JSON? try with just buf := bytes.NewBuffer(jsonReq) — GreyHands
– GreyHands, Commented Feb 20, 2015 at 9:15
Sending some naked JSON in the response body is something completely different than what curl's --data does. You'll have to set the content type to application/x-www-form-urlencoded and you'll have to send your two values url-encoded. There is no magic happening here, your jason request body is not magically converted to a form post, you'll have to do that yourself. — Volker
– Volker, Commented Feb 20, 2015 at 9:22
Volker is definitely right, I didn't notice the --data flag in the curl command line. — GreyHands
– GreyHands, Commented Feb 20, 2015 at 9:29

jwesonga · Accepted Answer · 2015-02-20 11:28:43Z

The correct code:

package main

import (
    "bytes"
    "fmt"
    "io/ioutil"
    "log"
    "net/http"
    "net/url"
)

func main() {

    u := "http://interest-graph.getprismatic.com/text/topic"
    ApiToken := "API-CODE"

    data := url.Values{}
    data.Set("title", "Clojure")
    data.Set("body", `Clojure is a dynamic programming language that targets the Java Virtual Machine 
        (and the CLR, and JavaScript). It is designed to be a general-purpose language, 
        combining the approachability and interactive development of a 
        scripting language with an efficient and robust infrastructure for multithreaded programming.
        Clojure is a compiled language - it compiles directly to JVM bytecode, 
        yet remains completely dynamic. Every feature supported by Clojure is supported at runtime.`)

    b := bytes.NewBufferString(data.Encode())

    req, err := http.NewRequest("POST", u, b)
    req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
    req.Header.Set("X-API-TOKEN", ApiToken)

    if err != nil {
        log.Fatal(err)
    }
    c := http.DefaultClient
    resp, err := c.Do(req)
    if err != nil {
        log.Fatal(err)
    }

    defer resp.Body.Close()

    r, err := ioutil.ReadAll(resp.Body)
    if err != nil {
        log.Fatal(err)
    }

    fmt.Println(string(r))

}

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