HTTP protocol Status Code in detail (HTTP status code)

200– Server successfully returned page 404– requested page does not exist 503– service is not available
1XX (Temporary response)
A status code that represents a temporary response and requires the requestor to continue the operation.

Code description
100 (continued) The requesting person shall continue to make the request. The server returns this code to indicate that the first part of the request was received and is waiting for the remainder.
101 (switching protocol) The requestor has asked the server to switch protocols, and the server has confirmed and is ready to switch.

2XX (Success)
Represents the status code that successfully processed the request.

Code description
200 (success) The server has successfully processed the request. Typically, this indicates that the server provided the requested Web page.
201 (created) The request was successful and the server created a new resource.
202 (accepted) the server has accepted the request but has not yet processed it.
203 (non-authoritative information) the server has successfully processed the request, but the information returned may be from another source.
204 (no content) the server successfully processed the request, but did not return any content.
205 (reset content) the server successfully processed the request, but did not return any content.
206 (partial) The server successfully processed a partial GET request.

3XX (redirected)
Indicates that further action is required to complete the request. Typically, these status codes are used for redirection.

Code description
300 (multiple options) for requests, the server can perform a variety of operations. The server can select an action based on the requestor (user agent) or provide a list of actions for the requestor to select.
301 (permanently moved) The requested page has been permanently moved to a new location. When the server returns this response (a response to a GET or HEAD request), the requestor is automatically forwarded to the new location.
302 (Temporary move) The server is currently responding to requests from a Web page in a different location, but the requestor should continue to use the original location for future requests.
303 (View other locations) The server returns this code when the requestor should use a separate GET request for the different locations to retrieve the response.
304 (not modified) The requested webpage has not been modified since the last request. When the server returns this response, the Web page content is not returned.
305 (using a proxy) the requestor can only use the proxy to access the requested Web page. If the server returns this response, it also indicates that the requestor should use the proxy.
307 (Temporary redirect) The server is currently responding to requests from a Web page in a different location, but the requestor should continue to use the original location for future requests.

4xx (Request error)
These status codes indicate a possible error in the request and hinder the processing of the server.

Code    description  
400   (Error request) The server does not understand the syntax of the request.   the
401   (unauthorized) request requires authentication. The server may return this response for pages that need to log on.  
403   (Forbidden) The server rejects the request.  
404   (not found) the server could not find the requested Web page.  
405   (method Disabled) Disables the method specified in the request.  
406   (not accepted) cannot use the requested content attribute to respond to the requested Web page.  
407   (requires proxy authorization) This status code is similar to 401 (unauthorized), but specifies that the requestor should authorize the use of the proxy.  
408   (Request timed out)   timeout occurs when the server waits for a request.  
409   (conflict)   The server conflicts when the request is completed. The server must include information about the conflict in the response.  
410   (deleted)   The server returns this response if the requested resource has been permanently deleted.  
411   (requires a valid length) the server does not accept requests that do not contain a valid Content-Length header field.  
412   (precondition not met) the server does not meet one of the prerequisites set by the requestor in the request.  
413   (Request entity is too large) the server cannot process the request because the request entity is too large to exceed the processing power of the server.  
414   (The requested URI is too long) the URI of the request (usually the URL) is too long and the server cannot process it.   The format of the
415   (Unsupported media type) request is not supported by the requested page.  
416   (the request scope does not meet the requirements) if the page cannot provide the requested scope, the server returns this status code.  
417   (unmet expectations) the server does not meet the requirements of the expected Request header field.

5XX (server error)
These status codes indicate that the server has an internal error while trying to process the request. These errors may be the error of the server itself, not the request.

Code description
500 (server internal error) the server encountered an error and could not complete the request.
501 (not yet implemented) the server does not have the capability to complete the request. For example, this code may be returned when the server does not recognize the request method.
502 (Error Gateway) The server receives an invalid response from the upstream server as a gateway or proxy.
503 (Service Unavailable) the server is not currently available (due to overloading or downtime maintenance). Typically, this is only a temporary state.
504 (Gateway Timeout) The server acts as a gateway or proxy, but does not receive requests from the upstream server in a timely manner.
505 (HTTP version not supported) the HTTP protocol version used in the request is not supported by the server.

RFC 6585 has just recently been released, and the document describes 4 new HTTP status codes.

is the HTTP protocol still changing? Yes, the HTTP protocol has been evolving, and the new status code is useful for developing REST services or HTTP-based services, and we'll give you a detailed description of the four new status codes and whether you should use them.

428 Precondition Required (prerequisites required)

A prerequisite is when a client sends an HTTP request that must meet some preset criteria if it wants the request to succeed.

A good example is the If-none-match header, which is often used in GET requests, and if If-none-match is specified, then the client receives the response only after the ETAG in the response has changed.

Another example of a prerequisite is the If-match header, which is typically used on PUT requests to indicate that only resources that have not been changed are updated, which is used to prevent the same content from being overwritten by multiple clients using HTTP services.

When the server side uses the 428 precondition Required status code, it means that the client must send the above request header to execute the request, which provides an effective way for the server to prevent the ' lost update ' issue.

429 Too Many requests (too many requests)

This status code is useful when you need to limit the number of clients requesting a service, which is the request speed limit.

Prior to this, there were some similar status codes, such as ' 509 Bandwidth Limit exceeded '. Twitter uses 420 (this is not an HTTP defined status code)

If you want to limit the number of client requests to a service, you can use a 429 status code and include a retry-after response header to tell the client how long it will take to request the service again.

431 Request Header Fields Too Large (header field too large)

In some cases, the client sends the HTTP request header to become very large, then the server can send 431 request header fields Too Large to indicate the problem.

I am not quite sure why there is no 430 status code, but jump straight from 429 to 431, I try to search but no results. The only guess is 430 Forbidden and 403 Forbidden too like, in order to avoid confusion to do so, God knows!

511 Network authentication Required (authentication required)

This status code is interesting to me, and if you're developing an HTTP server, you don't have to deal with that status code, but if you're writing an HTTP client, the status code is very important.

If you use laptops and smartphones frequently, you may notice that a large number of public WIFI services require you to accept some protocols or you must log in before you can use them.

This is annoying by intercepting HTTP traffic and returning a redirect and login when a user tries to access the network, but this is the case.

With these "intercept" clients, there are some nasty side effects. Examples of these two are mentioned in the RFC:

• If you visit a website before you log in to WiFi, the network device will intercept the first request, and these devices often have their own website icon ' Favicon.ico '. After logging in, you will find that the website icon you visited for a while has been the icon of the WiFi login website.
• If a client uses an HTTP request to find a document (possibly JSON), the network responds to a login page so that your client resolves the error and causes the client to run the exception, which is a common problem in reality.

So the 511 status code is proposed to solve this problem.

If you are writing an HTTP client, you might want to check the 511 status code to verify that authentication is required before you can access it.

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HTTP 400 Error – Invalid request

Your Web server believes that the data stream sent by the client (for example, your browser or our CheckUpDown robot) is ' malformed ' and that it does not fully comply with the HTTP protocol. Therefore, your WEB server is unable to understand and process the request. "The requested URL server is not acceptable as a parameter or the request type is inconsistent"

This error almost always means that the client system and/or your Web server programming fails.

HTTP protocol Status Code in detail (HTTP status code)