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What Are HTTP Headers?

An HTTP header allows clients and servers to pass additional information with each request or response. Headers are just case-insensitive key-value pairs that pass additional metadata about the request or response.

HTTP requests from a web browser automatically carry with them many headers, including but not limited to:

The type of client (e.g. Google Chrome)
The Operating system (e.g. Windows)
The preferred language (e.g. US English)

As developers, we can also define custom headers in each request.

Headers in Go's `net/http` Package

In Go, the net/http package provides us with the necessary tools to work with HTTP headers. We can access headers through the Header type, which is essentially a map of string slices (map[string][]string). This allows us to perform various actions on our request and response headers such as retrieving, setting, and removing them.

// creating a new request
req, err := http.NewRequest("GET", "https://api.example.com/users", nil)
if err != nil {
	fmt.Println("error creating request: ", err)
	return
}

// setting a header on the new request
req.Header.Set("x-api-key", "123456789")

// making the request
client := http.Client{}
res, err := client.Do(req)
if err != nil {
	fmt.Println("error making request: ", err)
	return
}
defer res.Body.Close()

// reading a header from the response
header := res.Header.Get("last-modified")
fmt.Println("last modified: ", header)

// deleting a header from the response
res.Header.Del("last-modified")

Assignment

Complete the getContentType function. It takes a pointer to a http.Response as input and should return the Content-Type header.

Use the .Get() method on the Response struct's Header field to get what you need.

Even though we've emphasized the need to close the response body, this is a mock response without a body. Trying to .Close() it will cause a panic.

What Are HTTP Headers?

Headers in Go's net/http Package

Assignment

Headers in Go's `net/http` Package