Detailed analysis of error types and causes of 4xx status codes in HTTP protocol

Detailed explanation of error types and causes of 4xx status codes in HTTP protocol

HTTP (Hypertext Transfer Protocol) protocol is the most widely used protocol on the Internet. It defines A specification for communication between client and server. The status code of the HTTP protocol is used to indicate the server's processing results of the request, including success, redirection, error and other different situations. Among them, the 4xx status code indicates that there is an error in the client request. This article will introduce in detail the different error types and causes in the 4xx status code.

1. 400 Bad Request: The request sent by the client has a syntax error and the server cannot understand it. Common reasons are:
   a. The request lacks necessary parameters or header information;
   b. The request parameter format is incorrect, such as the date format is incorrect or the number format is illegal;
   c. In the request body There is a problem with the data format, such as JSON format error.

Sample code:

import requests

url = "http://api.example.com/user"
data = {
    "username": "john",  # 缺少必要的参数"password"
}
response = requests.post(url, data=data)
print(response.status_code)  # 输出400

2. 401 Unauthorized: Unauthorized error, indicating that the client tried to access a resource that requires authentication but did not provide valid authentication information. Common reasons include:
   a. Lack of Authorization header information;
   b. The authentication information provided is invalid or expired;
   c. The client does not have sufficient permissions to access the requested resource.

Sample code:

import requests

url = "http://api.example.com/admin/user"
headers = {
    "Authorization": "Bearer invalid_token"
}
response = requests.get(url, headers=headers)
print(response.status_code)  # 输出401

3. 403 Forbidden: Forbidden access error, indicating that the client does not have permission to access the requested resource. Common reasons are:
   a. The requested resource requires authentication, but the authentication information provided by the client is invalid;
   b. The server is configured with an access control list (ACL) that limits the access rights of specific clients;
   c. The client tried to access the directory list, but the directory did not have permissions.

Sample code:

import requests

url = "http://api.example.com/private/resource"
response = requests.get(url)
print(response.status_code)  # 输出403

4. 404 Not Found: Resource not found error, indicating that the resource requested by the client does not exist on the server. Common reasons are:
   a. The accessed URL is spelled incorrectly or the path is wrong;
   b. The requested resource has been deleted or moved on the server;
   c. The requested resource is temporarily unavailable or hidden .

Sample code:

import requests

url = "http://api.example.com/nonexistent/resource"
response = requests.get(url)
print(response.status_code)  # 输出404

Summary: This article explains in detail the different error types and causes in the 4xx status code in the HTTP protocol, including 400 Bad Request, 401 Unauthorized, 403 Forbidden and 404 Not Found etc. It is very important for developers to understand the types and causes of these errors. They can perform targeted processing by judging the status codes, thereby improving the user experience and system stability.

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