2xx Successful
Last updated May 30, 2023

204 - No Content

Benjamin Bouchet
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The HTTP Status Code 204 means that the server successfully processed the client's request, and that the server is not returning any content.

What is HTTP Status Code 204?

HTTP status codes play a crucial role in the realm of the internet. They serve as a universal language, dictating the interactions between client and server. Among this comprehensive list of codes, one particularly unique HTTP status code is 204, better known as 'No Content'.

The Semantics of HTTP Status Code 204

According to the HTTP specification or HTTP spec, the HTTP status code 204 signifies a successful response. However, what differentiates it from other status codes in the 2xx range is its implied absence of a response body. Although the server successfully processes the request, there's no additional content or response payload body that needs to be returned to the client. In essence, a 204 status code conveys "I've done what you asked, and there's no more information to give you."

Understanding HTTP Header Fields in the 204 Response

Even though the response payload body is empty, the HTTP response may still include important HTTP header fields. For instance, the ETag header field, a response header field that assigns a version to a requested resource, can prove vital for version control systems. By including such header fields, the 204 status code allows us to manage caching and facilitate conditional requests effectively.

HTTP Status Code 204 in Different Programming Languages

Across multiple programming languages and frameworks, status code 204 is symbolized differently. For example, in Ruby on Rails, the HTTP status symbol for 204 is `:no_content`. On the other hand, the Symfony HTTP status constant is `Response::HTTP_NO_CONTENT`, and the Python2 HTTP status constant takes the form of `httplib.NO_CONTENT`.

When and How is HTTP Status Code 204 used?

The HTTP status code 204 is chiefly employed when there's no requirement for the server to return a response payload body. This situation occurs in a few particular circumstances, which we will discuss.

Use Case: DELETE Request

When a DELETE request is successfully processed by a server, the target resource is removed. Consequently, there's typically no message body to return as a response. Here, a status code 204 elegantly communicates to the user agent that the requested resource has been successfully deleted, with no new resource or additional content available to replace it.

Use Case: POST Request

Another common usage scenario for the HTTP status code 204 involves POST requests. Although a POST request usually results in creating a new resource, there can be instances where it serves a different purpose. For instance, it may be utilized for automated data transfers, where no new representation of the resource is formed. In such cases, the server can send a 204 status code as a response, asserting that the request was successfully processed, but no new resource was created.

Inclusion of HTTP Header Fields

Despite the absence of a response payload body, a 204 response can still include valuable HTTP header fields, such as 'Content-Location', 'Date', and 'ETag'. This capability is advantageous for maintaining the state of the client and server. For example, the ETag header field helps the client make conditional requests based on the version of the resource.

Status Code 204 and Caching

Lastly, status code 204 can contribute to controlling caching behavior. When a server includes the ETag field in the 204 response, the user agent can cache that ETag value. Later, if the client intends to update or delete the target resource, it can include the cached ETag in the 'If-Match' request header field. This action prevents conflicts arising from concurrent updates.

Status code 204 is indeed an invaluable tool. Although it signifies a successful response devoid of new content or response body, it carries considerable meaning and function in an HTTP response. Through effective use of HTTP header fields, it can powerfully impact web development processes. The subsequent sections of this blog post will delve deeper into more HTTP status codes, their interpretations, applications, and their integrations with different programming languages.

Example usage of HTTP Status Code 204

A Simplified Example

Imagine you're at a library then you ask the librarian to remove a book from their catalog. Of course, the librarian acknowledges your request, takes the book, and removes it from the catalog. However, she doesn't need to give you anything back, although she informs you that your request has been completed. The HTTP status code 204, or 'No Content', works similarly. When a server receives a request to delete a resource and successfully executes it, the server returns a 204 status code to signal the user agent that the task has been completed successfully, without returning any additional content.

A More Technical Example

Consider an HTTP DELETE request being made in a RESTful API context.

import requests
response = requests.delete('https://api.example.com/resources/123')

The above Python code sends a DELETE request to the server to remove a specific resource. When the server processes the request and successfully deletes the resource, it can respond with a 204 status code. The response might look like this:

HTTP/1.1 204 No Content
Date: Tue, 15 May 2023 11:45:26 GMT
Server: Apache/2.4.1 (Unix)
ETag: "123456789"
Connection: close

This server response includes the HTTP status code 204, indicating the successful deletion of the resource, but with no response body content.

What is the history of HTTP Status Code 204?

The history of HTTP status code 204 is deeply tied to the evolution of the HTTP protocol. The HTTP/1.0 specification, first documented in 1996, did not include status code 204. The advent of the HTTP/1.1 spec, as part of RFC 2616 in 1999, introduced several new status codes, among which was our subject of interest, 204 'No Content'.

The intent behind introducing HTTP status code 204 was to allow for a successful response that doesn't return a message body. This status code was seen as a valuable addition in cases where the server processes a request successfully but doesn't need to send back any entity in the response body.

How does HTTP Status Code 204 relate to other status codes?

HTTP status codes, divided into five classes, are part of the HTTP spec designed to provide standard responses to HTTP requests. The HTTP status code 204 belongs to the 2xx class, which signifies successful HTTP responses. However, the 204 status code differs from other 2xx codes such as 200 (OK) or 201 (Created) as it specifically signifies a successful request where no additional content is returned.

The 204 'No Content' is often compared to the 200 'OK', which is generally used when a GET request fetches a resource successfully, and the response payload body contains the requested resource. But with a 204 response, even though the request was successful, there's no such payload body.

In other classes, such as 3xx, 4xx, or 5xx, representing redirection, client errors, and server errors respectively, no exact equivalent to 204 exists. This status code is unique in its message: a successful request that needs no additional content in its response.

Other Interesting Things to Know About HTTP Status Code 204

Interaction with Response Header Fields

Despite not returning a response payload body, HTTP status code 204 holds a unique relationship with response header fields. A 204 status code response may incorporate various header fields such as 'Content-Location' and 'Date'.

Role of ETag Header Field

Particularly intriguing is the ETag header field. This identifier for the current state of the requested resource is vital for version control systems and conditional requests. Also, it plays a significant role in managing caching behavior.

Caching Behavior and Conflict Management

Upon receiving a 204 status along with an ETag value, a user agent can cache it. Later, when intending to update or delete the target resource, it can include the cached ETag in the 'If-Match' request header field, avoiding conflicts in concurrent updates.

Unconventional Use in POST Requests

An unexpected aspect of status code 204 relates to its use in POST requests. For automated data transfers where a POST request doesn't create a new resource, a 204 status code indicates successful execution without generating a new representation.

Usage in Different Programming Languages

Finally, the 204 status code's representation varies across Rails, Python2, and Symfony. Rails uses the HTTP status symbol `:no_content`, Python2 employs the HTTP status constant `httplib.NO_CONTENT`, and in Symfony, the HTTP status constant is `Response::HTTP_NO_CONTENT`.

These details highlight the nuanced behavior of the HTTP status code 204, underscoring its versatility in HTTP communications.

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