1、URL：Uniform Resource Locator
2、Components of URL：
<protocol>://[<user>:<password>]@<host>:<port>/<path>[:<params>]?<query>#<fragment>
protocol：The protocol used for access, such as: http, https, ftp
host：The hostname, which can be an IP address or a domain name, for example: 192.168.10.12, www.baidu.com.
port：The port of the host when accessed. The default port for HTTP protocol is 80 and can be omitted.
path：We can locate the host through host:port, but since there are many files on the host, the path can be used to locate a specific file. For example: https://baike.baidu.com/item/软件测试/327953
params：Parameters passed to the server, generally rare.
query：The query string, used to query content from the server. For example: www.baidu.com/s?ie=utf-8&f=8&rsv_bp=1&rsv_idx=1&tn=baidu&wd=%E8%BD%AF%E4%BB%B6%E6%B5%8B%E8%AF%95
fragment：A fragment, which can divide a webpage into different sections. If you want to directly reach a specific location after accessing the webpage, you can set it in this part.
Example：
（1）Sina Stars：
http://slide.ent.sina.com.cn/star/slide_4_704_336821.html#p=1
（2）Baidu Search：
https://www.baidu.com/s?rtt=1&bsst=1&cl=2&tn=news&rsv_dl=ns_pc&word=%E8%BD%AF%E4%BB%B6%E6%B5%8B%E8%AF%95
3、HTTP Protocol：
HTTP (Hyper Text Transfer Protocol)：
It is a stateless, application-layer protocol based on a request-response model that connects using TCP, with a default port of 80.
4、HTTP Workflow：
（1）The client establishes a TCP connection with the server.
（2）The client sends a request to the server.
（3）The server receives the client’s request and returns a response based on the request.
（4）The client receives the server’s response, parses the content for frontend display; then the client disconnects from the server.
5、Characteristics of HTTP：
（1）Supports client/server model.
（2）Simple and fast: When the client requests a service from the server, it only needs to send the request method and path.
（3）Flexible: HTTP allows the transmission of any type of data object.
（4）Stateless: If subsequent processing requires previous information, it must be retransmitted.
a、Disadvantage: It may lead to an increase in data volume transmitted per connection.
b、Advantage: If the server does not require prior information, responses are faster, reducing CPU and memory consumption on the server.
c、Introduction of cookie and session mechanisms: Cookies record information on the client side to determine user identity, while sessions record information on the server side to determine user identity.
（5）Connectionless: Limits each connection to handle only one request. After the server processes the request and receives the response, it disconnects.
a、Disadvantage: Each request requires establishing and disconnecting a TCP connection, increasing communication overhead.
b、Advantage: This method can save transmission time.
c、Subsequent introduction of persistent connections (HTTP keep-alive): Multiple data can be sent continuously over a single TCP connection without disconnecting, reducing the number of TCP connection establishments; generally, the server sets a keep-alive timeout (the connection will close after this time if it exceeds after transmission) and a maximum number of connections (when the maximum number is reached, new requests will initiate connections, and previous connections will close if not timed out).
6、Disadvantages of HTTP：
（1）Eavesdropping: HTTP communication uses plaintext, and there are no encryption measures during transmission, which may be eavesdropped.
（2）Impersonation: During transmission, the identity of the communication party is not verified, which may lead to impersonation.
（3）Tampering: HTTP only parses the message but does not perform complete verification, so it cannot verify the integrity of the message, which may be tampered with.
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