How to make an HTTP POST request with JSON body in Go?
Jul 31, 2025 am 10:28 AM
To make an HTTP POST request with a JSON body in Go, use the net/http package. 1. Prepare the JSON payload using either a struct or map. 2. Marshal the data into JSON format. 3. Use http.Post for simple cases or http.NewRequest with http.Client for more control over headers. 4. Set required headers like Content-Type to application/json and optionally Authorization. 5. Send the request and handle the response by checking errors, reading the body, and inspecting the status code. 6. Always close the response body with defer resp.Body.Close() to avoid leaks. 7. Reuse http.Client for multiple requests for better performance.
To make an HTTP POST request with a JSON body in Go, you'll typically use the net/http package, which is part of the standard library. The process involves creating the JSON payload, setting the appropriate headers, and sending the request.
Here's a quick example to set the context:
package main
import (
"bytes"
"encoding/json"
"fmt"
"net/http"
)
func main() {
// Define the request body as a map
requestBody := map[string]string{
"username": "testuser",
"password": "123456",
}
// Marshal the map into a JSON byte slice
jsonData, _ := json.Marshal(requestBody)
// Create a new POST request
resp, err := http.Post("https://example.com/api/login", "application/json", bytes.NewBuffer(jsonData))
if err != nil {
fmt.Println("Error making request:", err)
return
}
defer resp.Body.Close()
fmt.Println("Response status:", resp.Status)
}Now, let’s break down the key parts of this process in more detail.
Creating the JSON Payload
Before making the request, you need to prepare the data you want to send. In Go, it’s common to use a map[string]interface{} or a struct to represent the JSON body.
For example:
type User struct {
Username string `json:"username"`
Password string `json:"password"`
}
user := User{
Username: "testuser",
Password: "123456",
}
jsonData, err := json.Marshal(user)- Using a struct gives you more control over field names and types.
- If you're just prototyping or sending simple data, a map is often easier.
Setting Up the POST Request
Once you have the JSON data, you can create the request. The http.Post function is a convenient way if you don't need to customize the request headers beyond content type.
But if you need more control (like adding headers such as Authorization), you can use http.NewRequest and http.Client:
req, err := http.NewRequest("POST", "https://example.com/api/login", bytes.NewBuffer(jsonData))
if err != nil {
// handle error
}
req.Header.Set("Content-Type", "application/json")
req.Header.Set("Authorization", "Bearer your_token_here")
client := &http.Client{}
resp, err := client.Do(req)This gives you more flexibility:
- Add custom headers
- Set timeouts
- Handle redirects
Handling the Response
After sending the request, always check the response and handle it properly:
- Check for errors from
client.Do() - Use
defer resp.Body.Close()to avoid resource leaks - Read and inspect the response body if needed
Example:
body, err := io.ReadAll(resp.Body)
if err != nil {
fmt.Println("Error reading response body:", err)
return
}
fmt.Println("Response Body:", string(body))Also, make sure to check the status code:
if resp.StatusCode != http.StatusOK {
fmt.Println("Unexpected status code:", resp.StatusCode)
}Common Gotchas and Tips
-
Don’t forget to set
Content-Type: application/json, or the server might not interpret the body correctly. -
Always close the response body using
defer resp.Body.Close()to avoid memory leaks. - If you're making multiple requests, reuse the
http.Client— it handles connection pooling automatically. - For more complex use cases (like retries or middleware), consider using a library like
restyor building a wrapper.
That’s the core of making a POST request with a JSON body in Go. It’s straightforward once you get the structure right, but there are a few small details that can trip you up if you're not careful.
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