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3xx – HTTP Status Codes 

3xx – Redirection

This sequence of HTTP status codes indicates that the client needs to take additional action in order to finish the request. These codes are used when a resource has been relocated or when more steps are needed to complete the request. Importantly, for certain sorts of these redirections, particularly those that automatically redirect to a different location, the user agent (such as a web browser) can follow the redirection without further user input, but only if the succeeding request method is GET or HEAD. This ensures that the user agent does not modify the state of the resource without the user’s explicit consent.

300 – Multiple Choices

When a request for a resource corresponds to multiple potential representations, each with its own unique URI (Uniform Resource Identifier), this status code is used. The server responds with a 300 status code, indicating that various options for the requested resource are available and that the user must select one of these options for further action. This could occur in situations where a resource is accessible in numerous formats or languages and the server requires the user to specify their preference. The answer could offer a list of resource features and locations from which the user or user agent can choose the best one. In some circumstances, the server or user agent may be configured to choose the best alternative based on established criteria or user preferences.

Example of a 300: Multiple Choices

A user attempts to watch a video on a media website, and the server provides the movie in various formats (e.g., MP4, AVI, MKV). The server returns a 300 status code, allowing the user to select which format to view.

301 – Permanently Moved

When the requested resource has been permanently relocated to a new URL, this status code is returned. The server responds with a 301 status code, informing the client that the resource is no longer available at the previous URL and providing the new URL. This redirection does not only apply to the current request, but it also implies a permanent change, implying that all future requests should be routed to the new URL. The server’s response usually provides the new URL where the resource is currently located. To prevent infinite redirection loops, user agents such as browsers or monitoring programmes will automatically follow this redirect to the new URL, often up to a specified limit (such as 10 consecutive redirects). This status code is critical for ensuring link integrity, especially when a website or page is restructured.

Example of a 301: Moved Permanently

A user clicks on an old link to a blog article (www.exampleblog.com/old-post), but the article has been permanently relocated to a new URL (www.exampleblog.com/new-post). The server returns a 301 status code, which automatically redirects the user to the new URL.

302 – Found (Temporarily Moved)

The server has temporarily redirected the requesting resource to a different URL, as indicated by this status code. When a 302 response is issued, the server normally provides the new URL in its message. Clients should be aware that this redirection is just temporary, and they should continue to use the original request URL for subsequent tries, as the resource’s location may change again.

Originally known as “Moved Temporarily,” the usage of this code developed over time, resulting in some uncertainty. Most browsers began to view a 302 answer similarly to a “303 See Other” status, which behaves slightly differently. To explain, HTTP/1.1 included two new status codes, 303 and 307, to distinguish between the two sorts of redirection. However, some online applications and frameworks continue to utilise the 302 status code interchangeably with the 303 status code, which can lead to inconsistencies in how these replies are handled. This situation highlights the fluid nature of web standards and the significance of good communication between servers and clients.

Example of a 302: Found (Temporarily Moved)

A consumer visits a company’s website, which has temporarily moved its product page to a promotional URL in preparation for a special event. The server responds with a 302 status code, redirecting the user to the event-specific page for the time being.

303 – See Other

The server uses this status code to indicate that the requested resource is available at a different URL and should be accessed using the GET method, regardless of the original request type. When a 303 status code is returned, the server provides the updated URL in the response. This redirect instructs the user agent (such as a web browser) to use a GET request to access the resource at the specified URL. It is important to note that this redirection does not indicate that the original URL has been permanently modified; rather, it just leads the client to another address for the specific answer. The 303 status code is especially useful for form submissions (POST requests), as it can transfer clients to a new page upon successful submission, preventing multiple submissions on page refresh.

Example of a 303: See Other

When a user submits a form on a website, the server returns a 303 status code and redirects the user to a confirmation page. If the user refreshes the page, the form will not be resubmitted.

304 – Not Modified

A web server uses this status code in response to a conditional request from a user agent, which is often a web browser or a search engine. When a user agent requests a resource with particular headers (such as ‘If-Modified-Since’ or ‘If-None-Match’), the server returns 304 if the requested resource’s content has not changed since the last time the user agent visited it. This indicates that the request is valid, but there is no need to retransmit the data because the user agent already has the most recent version of the resource in its cache.

The 304 status code is critical for web performance and efficiency, particularly in eliminating unnecessary network traffic and server burden. It notifies search engines and browsers that the content of a page has not been changed, allowing them to use the cached version without having to retrieve the same data again.

This response is managed internally by the user agent and is normally not visible to web users. When a web page hasn’t changed, typical web browsers will load it from the cache instead of downloading it again, simplifying the user experience. It is vital to remember that a 304 response should not include a message body because it just confirms the resource’s unmodified state.

Example of a 304: Not Modified

A visitor returns to a news website. The browser submits a request with the ‘If-Modified-Since’ header, and because the news hasn’t been updated since the prior visit, the server returns a 304 status, allowing the browser to load the page from its cache.

305 – Use Proxy

This status code is an unusual server response that indicates the client must access the requested resource via a proxy. In its answer, the server includes the URL of the proxy, and the client is required to repeat the request through this proxy.

The 305 status code is sometimes used on websites that restrict access to specific material, allowing only users who route their requests through a specific proxy server. This method can be used as part of access control strategies to ensure that users meet specified criteria or come from specific areas before being granted access to the content.

This notification should not be displayed to users in normal online browsing scenarios. Modern web browsers are built to handle such directives automatically and redirect the request to the proxy URL provided in the server response. If a 305 status is received without a clear redirection or if the proxy URL is not appropriately provided in the response, it could indicate a server configuration issue or an incorrectly configured redirection. This status code should be used with caution, as incorrect implementation can cause user confusion or access difficulties.

Example of a 305: Use Proxy

A user tries to access a document on a corporate server, which requires all requests to be routed through a certain proxy for security reasons. The server returns a 305 status code, advising the user to access the page via the specified proxy.

306 – Switch Proxy (Unused)

In fact, the 306 status code was created in an earlier version of the HTTP protocol. It is, however, no longer in use and has been set aside for possible future use. Initially, this code indicated that future requests should use a different proxy. The 306 status code is no longer used in contemporary HTTP standards and practices, and its original function has been effectively deprecated. As a result, you won’t see this status code in modern web interactions, and it stays in the HTTP status code registry as a placeholder.

Example of a 306: Switch Proxy (Unused)

Although there is no direct example of a 306 status code in use because it is an unused and reserved code, we can concoct a situation for illustration purposes. Consider a user visiting a resource that requires initial routing through a certain proxy server. If the 306 status code was used, the server might respond with a 306 status, urging the user to use a new proxy for any future requests. However, because this code is not utilised in modern HTTP procedures and is reserved, a scenario like this does not occur in real-world web interactions.

307 – Temporary Redirect

A web server sends this status code to indicate that the resource requested by the client is temporarily located at a different URL, which the server includes in its response. Although the client is expected to comply with this redirection, future requests should still be forwarded to the original URL because the redirection is only temporary.

The 307 status code is notable for retaining the method used in the initial request. If the original request was a POST, the redirected request should be a POST as well. This is in contrast to several other redirect codes, such as 303, which often turn POST queries into GET requests during redirection.

Users should not see this message directly during normal web browsing. Web browsers are built to handle such redirection automatically, seamlessly sending users to the given temporary URL. However, if the server answer does not include an alternate URL, or if the number of redirections reaches a specific threshold (for example, 10 on your system), the 307 status may be reported. This restriction is critical to avoid monitoring agents or browsers becoming locked in an indefinite redirect loop. This status code is critical for preserving the integrity and intended behaviour of web requests during transient resource location changes.

Example of a 307: Temporary Redirect

A user opens a link to obtain a report (www.example.com/report), but the report is temporarily available at a different URL owing to ongoing maintenance. The server responds with a 307 status code, sending the user to the new URL while retaining the original HTTP method of the request.

308 – Permanent Redirect

A web server will use this status code to indicate that a resource has been permanently moved to a new URI and that all future requests for the resource should be sent to this new URI. The 308 status code is similar to the 301 status code in that it indicates a permanent redirection, but it differs in that it keeps the HTTP method used in the original request for the redirected request.

A 308 redirect, for example, ensures that the subsequent request to the new URI likewise uses the POST method if the original request to the server was performed using the POST method. This retention of the HTTP method is vital for certain types of requests, especially those involving data submission or other actions where the method is important for the semantics of the request.

The 308 status code provides a more robust mechanism for redirection, particularly for applications or services where HTTP method continuation is critical for proper request handling. This code ensures that the client’s request behaviour remains constant even if the location of the resource changes permanently.

Example of a 308: Permanent Redirect

A user submits data to an API endpoint that has been permanently relocated to a new URI using a POST request. The server returns a 308 status code, indicating that the POST request should be resubmitted at the updated URI.

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