Common status codes and usage scenarios in HTTP

Hello everyone, I am the front-end developer. Today we will learn about the common status codes and usage scenarios in HTTP.

As a front-end, you often need to obtain data from the back-end, so mastering HTTP is also very important.

The HTTP status code represents the status of the current request, such as client or server error, which is also a point that is tested frequently.

1xx messages

This type of status code indicates that the request has been accepted by the server, but the server still needs to continue processing.

100 Continue

continue.

The server receives the request and indicates that it can continue. When the client is ready to push a large amount of data, 100 can be used to indicate permission.

101 Switching Protocols

Switch protocols.

It is common that in response to a WebSockets connection, the browser will first send an HTTP request with the relevant information that it wishes to upgrade to the WebSockets protocol in the request header.

After receiving the message, if the server supports WebSockets, it will return the status code 101 and switch the protocol from HTTP to WebSockets.

2xx Success

This status code indicates that the service has been processed normally.

200 OK

success.

200 is the most commonly used status code. When the front-end requests the interface and the data is returned normally, this status code will be obtained. This is the status code that everyone likes to see the most.

3xx Redirect

Indicates that further action is required from the client to complete the request.

301 Moved Permanently

Permanent redirect.

The requested resource was permanently moved to another location.

If the URL of one of our blog posts has changed permanently, but the link in the user's bookmarks is still the old one, we can return a 301 status code and assign a redirect address when the user requests the old link.

 HTTP/1.1 301 Moved PermanentlyLocation: http://www.example.org/index.asp

This way the user can jump to the correct new address.

This new redirect address will be cached by the browser. The next time the user visits the old link, he will not send a request to get a 301, but will directly jump to the redirect address.

So be careful when setting the redirect address and don't make a mistake.

Another common use is to redirect HTTP links to HTTPS links.

For example, if we visit http://zhihu.com/ , we will be redirected to https://www.zhihu.com/.

302 Found

Temporary redirection.

The original descriptive phrase was Moved Temporarily.

It is suitable for some temporary redirection operations. For example, if some pages cannot be accessed correctly due to a server crash, you can temporarily redirect them to a new address through 302 during the repair period. After the repair is completed, users can continue to access the original link.

302 will not be cached permanently, but the cache time can be set to last for a period of time.

 HTTP/1.1 302 FoundLocation: https://www-temp.example.org/Cache-control: private; max-age=600

304 Not Modified

No changes.

304 means that the resource has not changed since the last time, and the client can continue to use the previously cached resources to reduce the burden on the browser.

This involves the knowledge of strong cache and negotiation cache in HTTP cache. The 304 status code is used in negotiation cache.

For details, please refer to an article I wrote before: "HTTP Cache Strategy: Strong Cache and Negotiation Cache"

4xx Client Error

Client side issue.

400 Bad Request

Bad request.

Common client errors, indicating that the problem lies with the client, such as incorrect parameters passed.

This error is often seen when the front-end and back-end interfaces are connected, because it is easy to write the wrong parameter name, or the back-end adds or modifies parameters.

404 Not Found

Does not exist.

A well-known status code indicating that the resource corresponding to the url does not exist.

For example, when some articles are deleted, they are directly and irreversibly deleted from the database. Then when the user visits this page, the server cannot find the corresponding data, and then returns a 404 and prompts "Page does not exist".

405 Method Not Allowed

Method not allowed.

The request method is not used correctly. For example, if a request should use POST but you use GET request, you will get 405.

If you get a 405 error, it usually means that your URL is correct, but the method is wrong. If the URL is also wrong, you will get a 404 error.

5xx Server Error

If there is a problem on the server, go to the backend instead of always asking questions on the frontend.

500 Internal Server Error

Internal service error.

If there is a bug in the backend server code, such as reading a null attribute, the service will not be able to run normally. The backend will then catch the error and return 500 to inform that there is a problem with the backend server.

In severe cases, the backend service crashes directly.

502 Bad Gateway

Gateway error.

For example, if the backend service crashes, some proxy web servers (such as Ngnix) in the middle can still run correctly. However, because the backend service cannot be accessed, a 502 error is returned.

504 Gateway Timeout

Gateway timeout.

The gateway is still there, but the backend service has not responded for various reasons (such as being stuck in an infinite loop). After a period of time, the gateway still fails to receive the message and returns 504 Gateway Timeout to the client.

Conclusion

These are probably the most common HTTP status codes.