Parse a JSON http POST in GoLang

parse_json_post.go

package main

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

type test_struct struct {
	Test string
}

func parseGhPost(rw http.ResponseWriter, request *http.Request) {
	decoder := json.NewDecoder(request.Body)

	var t test_struct
	err := decoder.Decode(&t)

	if err != nil {
		panic(err)
	}

	fmt.Println(t.Test)
}

func main() {
	http.HandleFunc("/", parseGhPost)
	http.ListenAndServe(":8080", nil)
}

Test it with: curl -X POST -d "{"test": "that"}" http://localhost:8080

thank you

Don't you need to close the request.Body?

Nevermind. I read in the docs that

The Server will close the request body. The ServeHTTP Handler does not need to.

Thanks for posting the example.

https://golang.org/pkg/net/http/#Request

invalid character 't' looking for beginning of object key string

try curl -X POST -d "{\"test\": \"that\"}" http://localhost:8080

curl -X POST -d '{"test": "that"}' http://localhost:8080

I get an empty response when running this:
`$ curl -X POST -d "{"test":"something"}" http://localhost:8080

$ `

`$ ./parse_json_post

`

EDIT: Apparently the keyname does matter, but it's not intuitive (for me at least) that the struct member is capitalized and the json key name is not.

How would you tackle parsing different kinds of request. I am struggling passing in a struct to the function.

Don't forget

defer r.Body.Close()

Example

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"
        "time"

	"github.com/gorilla/mux"
)

type player struct {
	Name string
	Club string
	Age  uint8
}

func mainLogic(w http.ResponseWriter, r *http.Request) {
	if r.Method == "POST" {
		var tempPlayer player
		decoder := json.NewDecoder(r.Body)
		err := decoder.Decode(&tempPlayer)

		if err != nil {
			panic(err)
		}
		defer r.Body.Close()

		fmt.Printf("Got %s age %d club %s\n", tempPlayer.Name, tempPlayer.Age, tempPlayer.Club)
		w.WriteHeader(http.StatusOK)
		json.NewEncoder(w).Encode(tempPlayer)
	} else {
		w.WriteHeader(http.StatusMethodNotAllowed)
		w.Write([]byte("Method not allowed."))
	}
}

func main() {
	r := mux.NewRouter()

	r.HandleFunc("/", mainLogic).Methods("POST")
	srv := &http.Server{
		Handler:      r,
		Addr:         "localhost:8000",
		WriteTimeout: 15 * time.Second,
		ReadTimeout:  15 * time.Second,
	}

	log.Fatal(srv.ListenAndServe())
}

Go JSON content-type using the middleware

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"time"

	"github.com/gorilla/mux"
)

type player struct {
	Name string
	Club string
	Age  uint8
}

func middleware(handler http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		fmt.Println("Executing Content-type middleware before the request phase!")

		if r.Header.Get("Content-type") != "application/json" {
			w.WriteHeader(http.StatusUnsupportedMediaType)
			w.Write([]byte("415 - Unsupported Media Type. Only JSON files are allowed"))
			return
		}

		// Pass control back to the handler
		handler.ServeHTTP(w, r)
	})
}

func mainLogic(w http.ResponseWriter, r *http.Request) {
	// Business logic here
	if r.Method == "POST" {
		fmt.Println("INSIDE LOGIC")
		var tempPlayer player
		decoder := json.NewDecoder(r.Body)
		err := decoder.Decode(&tempPlayer)

		if err != nil {
			panic(err)
		}
		defer r.Body.Close()

		fmt.Printf("Got %s age %d club %s\n", tempPlayer.Name, tempPlayer.Age, tempPlayer.Club)
		w.WriteHeader(http.StatusOK)
		json.NewEncoder(w).Encode(tempPlayer)
	} else {
		w.WriteHeader(http.StatusMethodNotAllowed)
		w.Write([]byte("Method not allowed."))
	}
}

func main() {
	r := mux.NewRouter()

	r.HandleFunc("/", mainLogic).Methods("POST")
	r.Use(middleware)

	srv := &http.Server{
		Handler:      r,
		Addr:         "localhost:8000",
		WriteTimeout: 15 * time.Second,
		ReadTimeout:  15 * time.Second,
	}

	log.Fatal(srv.ListenAndServe())
}

A simple middleware function to check if the POST request is in JSON format.

invalid character 't' looking for beginning of object key string

I fixed it by replacing first and last double quotes to single quotes: -d "{"test": "that"}" -> -d '{"test": "that"}'

Thank you. It helped me to resolved issue.