Question regarding HTTP error codes

[Elias Blackman]

I am studying internet protocols as a part of my academic syllabus. In this syllabus, we have a whole chapter dedicated to HTTP protocol. As a case study, we have to make it on error codes related to various internet protocols. I have done for TCP/IP and UDP protocol. Now I am proceeding towards the HTTP protocol. I have done some research but I am unable to find much data on error codes generated by HTTP protocol. Can someone share some information on the topic I need?

[Memphis M]

Consider a client-server model for working of internet, then HTTP works as request –response protocol in this situation. The request for certain data or address when requested by client side is passed on to server with help of HTTP protocol. This protocol stores all the data including the amount of data transferred from both sides, client and server as well as address of the servers it has collected data from and so on. It creates a network between various machines and server to retrieve and send data.
It has many error codes, some of them are,

• 100 Continue – This error is generate d when the client sends a request header to the server and server approves it. After the approval is done, it will prompt the users to send request body. When the request body being sent is detected as very large to be accepted, you will see this error. This error is generated when the server rejects data from client side on basis of improper header data.
• 101 Switching Protocols - This is not an error code actually but it acts as an acknowledgement notice from server to the client. This code means that request for switching the protocol from client has been accepted and server is working on it.
• 102 Processing (RFC 2518) – This error code suggests that the server already has too many requests pending from client side and cannot accept any more requests. If any new request is sent, then it might time out and will not be overlooked by server.
• 200 OK - This is not an error code but a notification of successful acceptance of client’s request by the server. There are two types of requests that can be sent to the server which will generate such notifications. One is GET request, which will contain data of the entity related to the requested resources from the server. Another is POST request; this contains entity consisting data of results of actions taken by the server.
• 201 Created – This is also a notification suggesting that server has received client’s request and appropriate resources have been allocated.
• 202 Accepted – This is a notification which says that client’s request has been accepted and is now under processing by server. The client will need to wait for some time before any result is generated or even if it is disallowed to proceed.
• 203 Non-Authoritative Information (since HTTP/1.1) - this code notifies that server has processed the client’s request and will be sending certain data that belongs to another source.
• 204 No Content- This notifies that server has been successful in processing the client’s request but is unable to send any data in return.
• 205 Reset Content - This also notifies the same thing as code 204. It means that server has processed the request sent by client but is unable to send any data to client as the data viewer used by client is not compatible with content being sent by the server.
• 206 Partial Content – This error code is generated when the server processes the data and is sending data back to the client. But due to range set by the header of client’s request, the data cannot be sent completely. Rather the data is split into parts and is being sent in interrupted parts or downloaded into multiple simultaneous streams.
• 207 Multi-Status (WebDAV) (RFC 2518) – it suggests that XML body of the data being sent can contain various response codes based on multiple responses being made to the server from client’s side.

[Arun K]

I can provide you with information of some more error codes related to HTTP protocol. Here are some of them which I know.

1. 300 Multiple Choices error means that server can provide multiple options to the client for presenting the resources for the request that is to be completed. For example, a client has requested a video and the server will notify him that this video can be viewed in different formats or in different resolution and quality.
2. 301 Moved Permanently means that all requests related to a specific search should be redirected towards the specified URL.
3. 302 Found means that original source of the content has been changed and the client needs to be redirected to new source, HTTP/1.0 specification (RFC 1945) will process this request. This error code is also displayed many times as error code 303 or error code 304.
4. 303 See other (since HTTP/1.1) means that the data at which the client has to be directed cannot be found. So the clients request has been redirected to another source using GET method. This makes server issue the redirect to the client using separate GET message.
5. 304 Not Modified means that resources that has been requested by the client has been modified many times since the request was sent by the client. In this situation the HTTP header that comes to the server from client’s side is of If-Modified-Since header type. Since the resources that are to be allocated are modified many times, it needs to save bandwidth and processing details in the header. This data will be used as comparison while processing the whole page.
6. 305 Use Proxy (since HTTP/1.1) means that HTTP client applications are unable to handle responses sent by the server using this status code, mainly due to security reasons.
7. 307 Temporary Redirect (since HTTP/1.1) means that the original data has been temporarily moved at new source. Any user requesting this data will be redirected to this new source till data is restored at original source. This is done using POST request and it is repeated until original source is restored.

[Loverface]

Some other errors that you can use to enhance the content of your case study that you are making on HTTP error codes are,

1. 500 Internal Server Error = This error is generated when some problem is affecting the working of HTTP protocol on either side, server or client. This error code is displayed when there is no suitable response to be displayed to client.
2. 501 Not Implemented = This error is displayed when the server is unable to process the clients request due to incompatible method or format. It is also displayed when server is unable to complete the client’s request due to insufficient resources or other such reason.
3. 502 Bad Gateway = This means that server has rejected gateway or proxy request coming from client. It also means invalid response from downstream server.
4. 503 Service Unavailable = This error code is displayed when server is temporarily unavailable to process client’s request. This is shown when server temporarily has stopped taking client’s request due to excessive load of existing requests from other clients. Many times server is also temporarily disabled to make certain modifications to the data, at this time, if the client sends and requests to it, this error message will be generated.
5. 504 Gateway Timeout = This error message is displayed when the server is unable to respond to client’s request in specified period of time.
6. 505 HTTP Version Not Supported = This error message is shown when client’s HTTP protocol is of version not compatible with the version that server works on.
7. 506 Variant Also Negotiates (RFC 2295) = This error message is seen when request sent by the client faces Transparent content negotiation. In other words, circular referencing is done here.
8. 509 Bandwidth Limit Exceeded (Apache bw/limited extension) = This error message is shown when too many requests from client’s side is received on the server. The conditions in which this error message appears is not mentioned in RFCs.
9. 510 Not Extended (RFC 2774) = This error is displayed when extensions of data demanded by the server from client are not provided. Thus, leading to failure of data processing from server’s side.

[Baebi]

Some other HTTP error codes that I found which you will need are,

• 400 Bad Request – This means request sent by user or application has wrong syntax or cannot be fulfilled by the server.
• 401 Unauthorized – This means that authorization of the user or process to the server is not proper and failed. This might be caused due to improper use of protocol or no requested resource is available. To study this error in detail you can refer to topics like Basic access authentication and Digest access authentication.
• 402 Payment Required- This HTTP error code mostly on websites which require having online transactions related to money.
• 403 Forbidden – The request you sent were authorized but the server failed to respond it.
• 404 Not Found - This error is shown when resources requested by user or application is not available with server. These resources may be available in future and user can try multiple times to find the resources.
• 405 Method Not Allowed - this error is shown when request made by the user for a certain resource is not proper. This can be shown due to improper use of protocol or syntax.
• 406 Not Acceptable - This means that resources requested by a user are not capable of generating resources that are not compatible with Accept headers sent in the request.
• 407 Proxy Authentication Required - This error is shown when server needs authentication of user for proceeding with any further task.
• 408 Request Timeout - The server could not process the resources requested by a user. According to W3 HTTP specifications, this error is seen when a user does not provide request to the server in specified period of time. User can repeat request for resources repeatedly.
• 409 Conflict – This error code suggests that some interference of one request is occurring with another request. It is seen when resources cannot be sent by the server.
• 410 Gone – this error is seen when the resources requested by user are not available. It is shown when resources are temporarily moved or permanently moved. User cannot repeat the request. Once this error is seen, user shouldn’t try to request these resources.
• 411 Length Required – Request failed to specify the length of resources that is to be sent by the server to user.
• 412 Precondition Failed - This error is seen when server fails to fulfill any condition set by the user on the request.
• 413 Request Entity Too Large – This error is shown when Request sent by the user or application is large than a server can process.
• 414 Request-URI Too Long - This error is shown when URL requested by an user is longer than server‘s capabilities to process.
• 415 Unsupported Media Type - This error is shown when the format in which data should be displayed is not displayed.
• 416 Requested Range Not Satisfiable – This error is shown when server can’t display part of data requested by user or application.
• 417 Expectation Failed - This error is shown when server cannot fulfill the exception set by the request sent by the user.
• 418 I'm a teapot - this is not an error actually but an April fool’s joke by RFC 2324, Hyper Text Coffee Pot Control Protocol and none of the protocols except HTTP applies this. This was defined as traditional IETF as being short and stout.
• 422 Unprocessable Entity (WebDAV) (RFC 4918) – This error is shown when semantics was wrong but request sent by user is right.
• 423 Locked (WebDAV) (RFC 4918) - This error is shown when request sent by user and application is trying to access data on server that is locked.
• 424 Failed Dependency (WebDAV) (RFC 4918) – this error is shown when a request sent by user cannot be repeated.
• 425 Unordered Collection (RFC 3648) – In drafts of ‘WebDAV Advanced Collections Protocol’ it is defined but not in ‘Web Distributed Authoring and Versioning (WebDAV) Ordered Collections Protocol’.
• 426 Upgrade Required (RFC 2817) - this error is shown when server wants user to switch to different protocol.
• 449 Retry With - This error is shown only in Microsoft’s Operating System and is shown when some inappropriate action is done.
• 450 Blocked by Windows Parental Controls – This error too is a part of Microsoft’s Operating System. It is shown when some setting of operating system is interfering with functioning of protocol.