What are HTTP errors?

Internet users who have at least a little depth in the terminology of the Network (at least a large part of them) know what the HTTP protocol is. This data transfer protocol allows users to interact with web resources through a browser. One of the functions of the protocol is the ability to return special codes that give users information about the status of the website or the status of performing a task. This includes HTTP error codes. The error codes are divided into two types: client errors and server errors. About these two categories and other useful, and most importantly - often occurring codes, let's talk about this material.

HTTP client errors

If the error was detected on the client's side, the server returns the code from the 4xx class. If there are no problems on the server, but it is still not available to the user, then the code with an explanation of the error is sent to the client.

So, client errors under the code 40x:

• 400. Invalid request - an error occurs when the server notices a syntax error in the request from the client. It will occur until the corresponding changes are made by the client. All data transfer rules for the protocol used must be observed.
• 401. No authorization - this error indicates that the HTTP server requires authentication. In this case, it is the server side that receives all the conditions for performing authentication. The cause of the error may be an invalid login name or password for authorization.
• 402. It is necessary to pay a fee - the code is not used, but is reserved in the protocol for the future. Originally conceived as an interface for making payments to gain access to a particular resource. Since nothing happened, the code 402 was adopted by Apple and Google, from time to time applying it to their web services.

• 403. Access is closed - an error occurs when the server is functioning correctly, but the user requesting access to it does not have sufficient rights to do so. Often accompanied by an authorization window.
• 404. Not Found (the resource / file is not found) is the most common error on the Internet. Typically, it occurs because of typos when typing a web address. Frequent mentioning and appearance on the Web turned this code into a popular Internet joke.
• 405. The method is forbidden - HTTP data error, which must be entered via POST or using the PUT method. In other words, the error occurs when using the GET method when it is unavailable or not supported by the server for processing certain data.
• 406. The request can not be accepted-this code is returned by the server when the requested content is not applicable to Accept headers. Most often occurs when the requested resource does not match the format that can be recognized by the client.
• 407. Requires authorization on the side of the proxy server - along with the code the server returns a special field for authorization on the proxy server.
• 408. The time for the request to quit occurs when the server stops waiting for further requests from the client. You can repeat the request at any time, even after the timeout period has elapsed.
• 409. Conflict - in what situations does this HTTP error occur? Uploading a file to a web server where an identical file or a newer version of the document is already stored. The version control system of files stored on the server does not allow you to replace the file with an earlier version, which causes a conflict under this code.

Client errors under the code 41x

• 410. Resource deleted - an error occurs if the requested resource was located at the specified address, but was deleted and is no longer available.
• 412. Prerequisites are not met - this code is displayed if the conditional header fields are not executed (at all).
• 413. The size of the request exceeds the allowable rate - an error occurs when the body of the request sent by the client is too large and the server can not process it.
• 414. Too long address - if the server returns this code, then the URL specified in the request is too long and can not be processed. Also, an error occurs when the client passes data through GET instead of POST.
• 415. Unsupported file format - an error occurs when the server refuses to work with a certain data format (the reason can be any).
• 417. A wait failed - the request header from the client side does not satisfy the requirements of the EXPECT field.
• 418 I'm a teapot - first appeared in 1998, the code that became an April Fool's joke and was never seriously involved.

Client errors under the code 42x

• 422. The element can not be processed - theoretically the server can process the request sent by the client; The file in the body of the request is also supported (it can be a table and any other media file), but for some reason a logical error has arisen that limits the activity of the server.
• 423. Access is closed - the method used is blocked on the server side. You must use a different method.
• 424. Dependency error - this code will be displayed if the operation, on the success of which the execution of the current command depends, was interrupted for one reason or another.
• 425. Wrong order of elements - the code is displayed in the event that when querying several items from the server, their order (server-side) was not met.
• 426. An update is required - a code informing you of the need to update the protocol. The fields for updating must be properly registered on the server side.
• 428. The completion of the dependent operation is necessary - with the help of this code the server notifies the client that it is necessary to include the heading-conditions in the request.
• 429. Too many requests - an error occurs if the client sends too many requests to the server, which may be a consequence of the DDoS attack, therefore it is blocked by the server.

Other client error codes

• 431. Exceeding the length of the header - if the length of the header is exceeded, the server may send this code in response, but more often it simply discards the connection.
• 434. The address is unavailable - an error signals the unavailability of the requested address.
• 449. Retry - the code is returned if the server needs additional information to process the request.
• 451. Blocked for legal reasons - the server may be blocked if the authorities have sent a request for a lock for various legal reasons.

If you are working outside the web browser, you may experience other errors, such as a critical error in updating the HTTP server, but you need to find out its causes from the owners of the application or the application in which the problem occurred.

HTTP server errors

Such codes occur when the staged operations fail through the fault of the server. Similar errors are displayed using 5xx codes and a brief explanation of the error.

Server errors under the code 50x

• 500 Internal Server Error - an HTTP server error that can not be identified. This code indicates any error for which there is no separately specified code value.
• 501. Not Implemented - this code is output by the server when the method it uses is not supported. The problem occurs when working with servers that are not configured to work correctly with standard HTTP commands.
• 502. Bad Gateway - the problem occurs when the server acting as a gateway receives an erroneous response from the "main" server.
• 503. Service Unavailable - this code often appears when the server is under maintenance or it is restarted.
• 504. Gateway Timeout - the error occurs when the server running as a gateway does not have time to receive a response from the "main" server.
• 505. HTTP Version Not Supported (the version of the protocol is not supported) - the specified server does not work with the version of the protocol specified in the request from the client.
• 507. Insufficiente Storage (a lack of space) - the problem occurs when there is not enough digital space to process the request. Most often, the problem is temporary.

Server errors under the code 51x

• 510. Not Extended - an error occurs if there is no extension on the server that the client requested.
• 511. Network Authentication Required - a similar response is sent not from the server itself, but from an intermediary in whose role the Wi-Fi paid point provider acts.

Information codes

• 100. Continue (continued) - this code notifies the client that its initial actions satisfy the server requirements, and it can continue to send commands.
• 101. Switching Protocols (interactive protocol) - an interactive code that suggests to replace the used protocol with more suitable.
• 102. Processing (in the process of processing) is a code that informs that the request was accepted, but it takes considerable time to process it.

Redirection codes

• 300. Multiple Choices (select) - occurs if the selected link can go directly to several resources located on the same server. Together with the code, a choice is given between the different options. And it can be made by both the user and the client, depending on the server settings.
• 301. Moved Permanently - the code is returned when the requested resource or file has been permanently moved and located at a different address.
• 302. Found (resource found) - the code is returned when the requested resource or file has been temporarily moved and can be found at a different address.
• 303. See Other (search by other addresses) - this code is returned by the server together with an alternative value of the Location field, so that the user from the client side can access the requested resource using the GET method.
• 304. Not Modified-an error occurs if the client requested a specific file specifying the specific modification time attributes, but the server did not detect any changes since it was downloaded.
• 305. Use Proxy (it is necessary to use a proxy server) - this code is displayed by the server when you need to use a proxy server to gain access to it. The address of the latter is indicated in the Location field. Only basic servers (not proxies) can use this code.
• 307. Temporary Redirect - a code occurs when the requested file or resource is available at a different address. Often automatic redirection occurs.