Making HTTP responses with JSON [duplicate]

Question

I am new to Go, and I am trying to practice with building a simple HTTP server. However I met some problems with JSON responses. I wrote following code, then try postman to send some JSON data. However, my postman always gets an empty response and the content-type is text/plain; charset=utf-8. Then I checked a sample in http://www.alexedwards.net/blog/golang-response-snippets#json. I copied and pasted the sample, and it was working well. But I cannot see any difference between mine and the sample. Can someone give some help?

package main

import (
    "encoding/json"
    "net/http"
)

type ResponseCommands struct {
    key   string
    value bool
}

func main() {
    http.HandleFunc("/", handler)
    http.ListenAndServe(":5432", nil)
}

func handler(rw http.ResponseWriter, req *http.Request) {
    responseBody := ResponseCommands{"BackOff", false}

    data, err := json.Marshal(responseBody)
    if err != nil {
        http.Error(rw, err.Error(), http.StatusInternalServerError)
        return
    }
    rw.WriteHeader(200)
    rw.Header().Set("Content-Type", "application/json")
    rw.Write(data)
}

Answer 1

The main difference is that the variable in the struct are public (exported)

type Profile struct {
  Name    string
  Hobbies []string
}

In your case, they are not (lowercase).

type ResponseCommands struct {
    key   string
    value bool
}

See "Lowercase JSON key names with JSON Marshal in Go".