Problem with showing JSON data of an incoming HTTP POST request

小能豆

Problem with showing JSON data of an incoming HTTP POST request

Server-Side Go Code

package main

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

    type Authentication struct {
        username string 
        password string
    }

    func main() {

        mux := http.NewServeMux()

        mux.HandleFunc("/auth", func(w http.ResponseWriter, req *http.Request) {
            decoder := json.NewDecoder(req.Body)
            var auth Authentication
            err := decoder.Decode(&auth)

            if err != nil {
                http.Error(w, "Failed to decode JSON", http.StatusBadRequest)
                return
            }

            fmt.Printf("Received authentication: %+v\n", auth)
        })

        mux.Handle("/",http.FileServer(http.Dir("./static")))

        fmt.Printf("Starting server at port 3000\n")

        http.ListenAndServe(":3000", mux)
    }

Client-Side Javascript Code:

   //--Variables--//
    let signin = document.getElementById("Signin");
    let username = document.getElementById("Username");
    let password = document.getElementById("Password");

    signin.onclick = () => {
      let data = {
        username: username.value,
        password: password.value,
      };
      sendData("/auth", data);
      console.log(data.username, "   ", data.password);
    };

    //--Functions--//
    const sendData = (url, data) => {
    fetch(url, {
        method: "POST",
        headers: {
          Accept: "application/json",
          "Content-Type": "application/json",
        },
        body: JSON.stringify(data),
      });
    };

The Problem im having is that yes, the POST Request does go trough and can be seen on the Server-Side but i cant actually see the contents of the POST Request. This is what is printed on the Server-Side when a request comes trough: Received authentication: {username: password:} Its empty. My question is: Why is it empty, im pretty new to Go and im not sure on how to encode Json Data. ChatGPT said the code should work fine.

I’ve searched for other Stackoverflow posts and tried them out, but they never seemed to work. Probably because im doing something wrong though.

阅读 71

2023-12-19

共1个答案

小能豆

The issue you’re facing is due to the fact that the fields in your Authentication struct in Go are not exported (i.e., they start with a lowercase letter). In Go, fields that start with a lowercase letter are not exported and cannot be accessed by external packages, including the json package.

To fix this issue, you should export the fields in your Authentication struct by starting their names with an uppercase letter:

package main

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

type Authentication struct {
    Username string `json:"username"`
    Password string `json:"password"`
}

func main() {
    mux := http.NewServeMux()

    mux.HandleFunc("/auth", func(w http.ResponseWriter, req *http.Request) {
        decoder := json.NewDecoder(req.Body)
        var auth Authentication
        err := decoder.Decode(&auth)

        if err != nil {
            http.Error(w, "Failed to decode JSON", http.StatusBadRequest)
            return
        }

        fmt.Printf("Received authentication: %+v\n", auth)
    })

    mux.Handle("/", http.FileServer(http.Dir("./static")))

    fmt.Printf("Starting server at port 3000\n")

    http.ListenAndServe(":3000", mux)
}

Note the changes in the Authentication struct where username and password are now Username and Password. Additionally, I added struct tags (json:"username" and json:"password") to specify the JSON field names for serialization/deserialization. This ensures that the JSON keys match the struct field names. In your JavaScript code, you are sending JSON with keys “username” and “password,” and these should match the struct field names in Go.

With these changes, your Go server should now correctly decode the JSON data received from the client.

2023-12-19