Go http client
last modified April 11, 2024
In this article we show how to create HTTP requests with net/http in Golang. An http client sends HTTP requests and receives HTTP responses from a resource identified by an URL.
$ go version go version go1.22.2 linux/amd64
We use Go version 1.22.2.
HTTP
The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems. HTTP protocol is the foundation of data communication for the World Wide Web.
Go net/http
The net/http package contains tool to create HTTP clients and
servers. HTTP requests can be easily created with http.Get,
http.Post, http.PostForm and http.Head
functions.
To set HTTP settings, such as headers or redirect policy, we create a client in the following way:
client := &http.Client{
CheckRedirect: redirectPolicyFunc,
}
resp, err := client.Get("http://example.com")
The response body must be closed at the end:
defer resp.Body.Close()
Go http client status code
HTTP response status codes indicate whether a specific HTTP request has been successfully completed. The responses have five groups:
- Informational responses (100–199)
- Successful responses (200–299)
- Redirects (300–399)
- Client errors (400–499)
- Server errors (500–599)
package main
import (
"fmt"
"log"
"net/http"
)
func main() {
resp, err := http.Get("http://webcode.me")
if err != nil {
log.Fatal(err)
}
fmt.Println(resp.Status)
fmt.Println(resp.StatusCode)
}
The example creates a GET request to a small website. We get the status code of the request.
fmt.Println(resp.Status) fmt.Println(resp.StatusCode)
The Status gives the status as a string and the
StatusCode as a number.
Go http client GET request
The following example creates a simple GET request in Go.
package main
import (
"fmt"
"io/ioutil"
"log"
"net/http"
)
func main() {
resp, err := http.Get("http://webcode.me")
if err != nil {
log.Fatal(err)
}
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
log.Fatal(err)
}
fmt.Println(string(body))
}
We create a GET request to the webcode.me webpage.
resp, err := http.Get("http://webcode.me")
A get request is issued with the Get function.
if err != nil {
log.Fatal(err)
}
We check for the error.
defer resp.Body.Close()
The client must close the response body when finished.
body, err := ioutil.ReadAll(resp.Body)
We read the content of the body with ReadAll.
fmt.Println(string(body))
We print the received data to the console.
$ go run get_req.go
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<link rel="stylesheet" href="format.css">
<title>My html page</title>
</head>
<body>
...
Go http client HEAD request
The HTTP HEAD method requests the headers that are returned if the specified resource would be requested with an HTTP GET method.
package main
import (
"fmt"
"log"
"net/http"
)
func main() {
resp, err := http.Head("http://webcode.me")
if err != nil {
log.Fatal(err)
}
for k, v := range resp.Header {
fmt.Printf("%s %s\n", k, v)
}
}
The example issues a HEAD request with http.Head and prints all
the data of the response header.
$ go run head_req.go Content-Length [394] Last-Modified [Sun, 23 Jan 2022 10:39:25 GMT] Connection [keep-alive] Etag ["61ed305d-18a"] Accept-Ranges [bytes] Server [nginx/1.6.2] Date [Mon, 14 Feb 2022 13:50:22 GMT] Content-Type [text/html]
User-Agent header
The User-Agent request header is a string that lets servers and
network peers identify the application, operating system, vendor, and/or version
of the requesting user agent.
package main
import (
"fmt"
"io/ioutil"
"log"
"net/http"
"time"
)
func main() {
c := http.Client{Timeout: time.Duration(3) * time.Second}
req, err := http.NewRequest("GET", "http://webcode.me/ua.php", nil)
if err != nil {
log.Fatal(err)
}
req.Header.Add("User-Agent", "Go program")
resp, err := c.Do(req)
if err != nil {
log.Fatal(err)
}
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
log.Fatal(err)
}
fmt.Println(string(body))
}
The example sets a User-Agent header for its GET request. The requested resource simply returns the client's User-Agent string.
c := http.Client{Timeout: time.Duration(3) * time.Second}
We create the http client with a 3 s timeout.
req, err := http.NewRequest("GET", "http://webcode.me/ua.php", nil)
A new request is created with http.NewRequest.
req.Header.Add("User-Agent", "Go program")
We add the User-Agent header to the request.
$ go run user_agent.go Go program
Go http.PostForm
The HTTP POST method sends data to the server.
The http.PostForm issues a POST to the specified URL, with data's
keys and values URL-encoded as the request body. The Content-Type
header is set to application/x-www-form-urlencoded.
package main
import (
"fmt"
"io/ioutil"
"log"
"net/http"
"net/url"
)
func main() {
resp, err := http.PostForm("https://httpbin.org/post",
url.Values{"name": {"John Doe"}, "message": {"Hey!"}})
if err != nil {
log.Fatal(err)
}
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
log.Fatal(err)
}
fmt.Println(string(body))
}
In the example, we send a POST request to https://httpbin.org/post website, which is an online testing service for developers.
$ go run post_form.go
{
"args": {},
"data": "",
"files": {},
"form": {
"message": "Hey!",
"name": "John Doe"
},
"headers": {
"Accept-Encoding": "gzip",
"Content-Length": "28",
"Content-Type": "application/x-www-form-urlencoded",
"Host": "httpbin.org",
"User-Agent": "Go-http-client/2.0",
"X-Amzn-Trace-Id": "Root=1-620a63eb-5b49f82c137a95e06bad94e3"
},
"json": null,
"origin": "188.167.250.179",
"url": "https://httpbin.org/post"
}
Source
Go net/http package - reference
In this article we have created GET and POST requests in Go.
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