Why the 404 error ?

#webdev #beginners #productivity #codenewbie

Hello everyone, today we're going to look at HTTP errors, you know like when you get a page not found with the 404 error. In reality there are almost a hundred different error codes. Don't worry, it's difficult to know them all by heart, but there are techniques to find out roughly where the error comes from. You are ready, so let's go !

Why did you invent these numbers ?

But then why did we invent these error numbers? The answer is actually quite simple, when a user requests a web page through his browser, the browser will send a request to the server under the world famous HTTP protocol. The server will also respond in HTTP format, and if all goes well will send the requested resource (in our case the web page). But everything gets complicated when there is an error. Knowing that there is an error is good, but knowing where is even better. This is why error numbers were quickly assigned to each different type of error. This is much more practical and saves time for many developers. For example, errors starting with 5 are problems at the server level.

The five categories of error

To simplify the whole thing, and to put some order in all these errors, categories have been created. There are three different categories:
1 - Informations
2 - Success
3 - Redirects
4 - Web client errors
5 - Server errors

So if an error number starts with 4, we know directly that the problem comes from the web client.

Why 404 error ?

But why 404 errors? If you have been following this, you will notice that the first number is a 4 and that the error comes directly from the web client and not from the server. Indeed, the 404 error means that the resource is not found, the server has searched for it on its side but has not found it, so the error comes from the web client which has not provided the right url.

Going further with error 418

The HTTP error 418 has nothing to do with the other errors. Indeed its meaning is "I'm a teapot". It is actually a joke since it first appeared in the famous RFC 2324 on April 1, 1998. The explanations given by the developers are: " There is coffee all over the world. Increasingly, in a world in which computing is ubiquitous, the computists want to make coffee. Coffee brewing is an art, but the distributed intelligence of the web- connected world transcends art. Thus, there is a strong, dark, rich requirement for a protocol designed expressly for the brewing of coffee. Coffee is brewed using coffee pots. Networked coffee pots require a control protocol if they are to be controlled".
In other words, the famous Hyper Text Coffee Pot Control Protocol, or HTCPCP, is intended to send an error back to all those who would like to control a coffee pot remotely, telling them that they have mistakenly addressed themselves to ... a teapot 😂.
This April 1st "joke" had its heyday at the time and is still featured on a number of official links in which its error code has been preserved.
There are still people asking questions about this 418 error, even today!

Specific errors

For those who wish to find a specific error, you can refer to these different tables classified by categories.
Some codes are not yet in use, but are intended for future use. Other codes do not result in any specific display to the user, but are implied (e.g. codes 200 or 304, which are never seen by the client as they concern the majority of successful requests).

All major HTTP errors are represented in these different tables, of the different error types:

Codes beginning with 1 (Informations):

Code	Message	Meaning
100	Continue	Waiting for the application to be processed.
101	Switching Protocols	Acceptance of the change of protocol.
102	Processing	Processing in progress (prevents the customer from exceeding the waiting time limit).
103	Early Hints	While waiting for the final response, the server returns links that the client can start downloading.

Codes beginning with 2 (Success):

Code	Message	Meaning
200	OK	Request successfully processed. The response will depend on the query method used.
201	Created	Request successfully processed and document created.
202	Accepted	Request processed, but no guarantee of result.
203	Non-Authoritative Information	Information returned, but generated by an uncertified source.
204	No Content	Request successfully processed but no information to return.
205	Reset Content	Request successfully processed, current page can be deleted.
206	Partial Content	Only part of the resource has been transmitted.
207	Multi-Status	Multiple answers.(WebDav)
208	Already Reported	The document was previously sent in this collection.(WebDav)
210	Content Different	The copy of the resource on the client side differs from that on the server (content or properties).(WebDav)
226	IM Used	The server has completed the request for the resource, and the response is a representation of the result of one or more instance manipulations applied to the current instance.

Codes beginning with 3 (Redirects):

Code	Message	Meaning
300	Multiple Choices	The requested URI refers to several resources.
301	Moved Permanently	Permanently moved document.
302	Found	Document moved temporarily.
303	See Other	The answer to this request lies elsewhere.
304	Not Modified	Document not modified since the last request.
305	Use Proxy (since HTTP/1.1)	The request must be re-addressed to the proxy.
306	Switch Proxy	Code used by an older version of RFC 26167, now reserved. It meant "The following requests must use the specified proxy ".
307	Temporary Redirect	The request must be temporarily redirected to the specified URI.
308	Permanent Redirect	The request must be permanently redirected to the specified URI.
310	Too many Redirects	The request has to be redirected too many times, or falls victim to a redirection loop.

Codes beginning with 4 (Web client errors):

Code	Message	Meaning
400	Bad Request	The syntax of the query is wrong.
401	Unauthorized	Authentication is required to access the resource.
402	Payment Required	Payment required to access the resource.
403	Forbidden	The server has understood the request, but refuses to execute it. Unlike the 401 error, authenticating will not make any difference. On servers where authentication is required, this usually means that authentication has been accepted but the access rights do not allow the client to access the resource.
404	Not Found	Resource not found.
405	Method Not Allowed	Unauthorised query method.
406	Not Acceptable	The requested resource is not available in a format that would respect the "Accept" headers of the request.
407	Proxy Authentication Required	Access to the resource allowed by identification with the proxy.
408	Request Time-out	The amount of time a request from the client has been waiting on the server side. According to the HTTP specification: "The client did not produce a request within the time the server was willing to wait. The client MAY repeat the request without modification at any later time ".
409	Conflict	The request cannot be processed at this time.
410	Gone	The resource is no longer available and no redirection address is known.
411	Length Required	The length of the request was not specified.
412	Precondition Failed	Preconditions sent by the request not checked.
413	Request Entity Too Large	Treatment abandoned due to too high a demand.
414	Request-URI Too Long	URI too long.
415	Unsupported Media Type	Unsupported query format for a given method and resource.
416	Requested range unsatisfiable	Incorrect "range" query header fields.
417	Expectation failed	Expected and defined behaviour in the header of the unsatisfactory request.
418	I’m a teapot	"I am a teapot": This code is defined in RFC 232410 dated 1 April 1998, Hyper Text Coffee Pot Control Protocol. It is a webmaster's joke, intended to send an error back to anyone who wants to remotely control a coffee pot, telling them that they have mistakenly addressed a teapot :)
421	Bad mapping / Misdirected Request	The request has been sent to a server that is not capable of producing a response (for example, because a connection has been reused).
422	Unprocessable entity	The entity provided with the request is incomprehensible or incomplete.(WebDAV)
423	Locked	The operation cannot take place because the resource is locked.(WebDAV)
424	Method failure	A method in the transaction has failed.(WebDAV)
425	Too Early	The server cannot process the request as it may be replayed.
426	Upgrade Required	The client should change the protocol, for example to TLS/1.0.
428	Precondition Required	The request must be conditional.
429	Too Many Requests	The customer has made too many requests within a given time frame.
431	Request Header Fields Too Large	The HTTP headers sent exceed the maximum size allowed by the server.
449	Retry With	Code defined by Microsoft. The request should be returned after performing an action.
450	Blocked by Windows Parental Controls	Code set by Microsoft. This error occurs when Windows Parental Controls are enabled and block access to the page.
451	Unavailable For Legal Reasons	This error code indicates that the requested resource is inaccessible for legal reasons.
456	Unrecoverable Error	Unrecoverable error.(WebDAV)

Codes beginning with 5 (Server errors):

Code	Message	Meaning
500	Internal Server Error	Internal server error.
501	Not Implemented	Claimed functionality not supported by the server.
502	Bad Gateway ou Proxy Error	By acting as a proxy or gateway server, the server received an invalid response from the remote server.
503	Service Unavailable	Service temporarily unavailable or under maintenance.
504	Gateway Time-out	Time taken to wait for a response from a server to an intermediate server.
505	HTTP Version not supported	HTTP version not supported by the server.
506	Variant Also Negotiates	Negotiation error.
507	Insufficient storage	Insufficient space to edit properties or build the collection.(WebDAV)
508	Loop detected	Loop in a resource linkage.(WebDAV)
509	Bandwidth Limit Exceeded	Used by many servers to indicate a quota overrun.
510	Not extended	The request does not respect the extended HTTP resource access policy.
511	Network authentication required	The client must authenticate to access the network. Used by captive portals to redirect clients to the authentication page.