How to Set Headers in HTTP Request in Go

In Go, you set headers on an HTTP request by using the Header.Set method on the http.Request object. First, create a request with http.NewRequest, then add headers like req.Header.Set("Key", "Value") before sending the request with an http.Client.

Syntax

To set headers in an HTTP request in Go, you first create a request object, then use the Header.Set method to add or update headers.

• http.NewRequest(method, url, body): creates a new HTTP request.
• req.Header.Set(key, value): sets a header key to a value.
• client.Do(req): sends the request.

go

req, err := http.NewRequest("GET", "https://example.com", nil)
if err != nil {
    // handle error
}
req.Header.Set("Content-Type", "application/json")
req.Header.Set("Authorization", "Bearer token")

client := &http.Client{}
resp, err := client.Do(req)
if err != nil {
    // handle error
}
defer resp.Body.Close()

Example

This example shows how to create a GET request, set two headers, send the request, and print the response status.

go

package main

import (
    "fmt"
    "net/http"
)

func main() {
    req, err := http.NewRequest("GET", "https://httpbin.org/get", nil)
    if err != nil {
        fmt.Println("Error creating request:", err)
        return
    }

    // Set headers
    req.Header.Set("User-Agent", "MyGoClient/1.0")
    req.Header.Set("Accept", "application/json")

    client := &http.Client{}
    resp, err := client.Do(req)
    if err != nil {
        fmt.Println("Error sending request:", err)
        return
    }
    defer resp.Body.Close()

    fmt.Println("Response status:", resp.Status)
}

Output

Response status: 200 OK

Common Pitfalls

Common mistakes when setting headers in Go include:

• Trying to set headers on a nil request object before creating it.
• Using req.Header.Add repeatedly for the same key when you want to replace the value (use Set instead).
• Not setting headers before sending the request.
• Confusing request headers with response headers.

go

package main

import (
    "fmt"
    "net/http"
)

func main() {
    // Wrong: setting headers before creating request
    var req *http.Request
    // This will panic because req is nil
    // req.Header.Set("Authorization", "token")

    // Correct way:
    req, err := http.NewRequest("GET", "https://example.com", nil)
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    req.Header.Set("Authorization", "token")

    // Wrong: using Add instead of Set when replacing header
    req.Header.Add("Content-Type", "application/json")
    req.Header.Add("Content-Type", "text/plain") // adds another header instead of replacing

    // Right: use Set to replace
    req.Header.Set("Content-Type", "text/plain")
}

Quick Reference

Action	Method	Description
Create request	http.NewRequest(method, url, body)	Creates a new HTTP request object
Set header	req.Header.Set(key, value)	Sets or replaces a header key with a value
Add header	req.Header.Add(key, value)	Adds a header value without replacing existing ones
Send request	client.Do(req)	Sends the HTTP request and returns a response

Key Takeaways

Always create the request with http.NewRequest before setting headers.

Use req.Header.Set to add or replace a header value.

Set all headers before sending the request with client.Do.

Avoid using Header.Add when you want to replace a header value.

Check for errors when creating requests and sending them.