Steps to parse URL

URL parsing process

URL (Uniform Resource Locator) is a resource address identifier on the Internet. It consists of multiple parts, including protocol, host name, port number, path and query parameters. When we enter a URL into the browser, the browser will parse the URL in order to correctly access and obtain the corresponding web page or resource. The following will introduce the URL parsing process.

First, the browser will check whether the protocol part (such as http:// or https://) is included in the URL. If the protocol is not specified, the http protocol will be used by default. The browser then parses the hostname portion to determine the IP address of the server to be accessed. This process usually includes domain name resolution, which converts hostnames into corresponding IP addresses. The browser will first check whether there is an IP address record for the domain name in the local cache. If there is, it will be used directly. If not, it will send a domain name resolution request to the DNS server.

Once the browser obtains the server's IP address, it can establish a TCP connection with the server. If a port number is specified in the URL, the specified port number is used, otherwise the default port number of the protocol is used (for example, http uses port 80 by default, https uses port 443 by default). By establishing a TCP connection, the browser can communicate with the server, send requests and receive responses from the server.

Next, the browser will parse the path part to determine the specific resource or page to be accessed. The path part specifies the directory structure or file path on the server, and the browser locates the resource based on the path part. If the path contains a file name, the browser will request the file; if the path is just a directory, the server will usually return the default file in the directory (such as index.html).

In addition to the path, the URL can also contain query parameters. Query parameters start with a question mark (?), and multiple parameters are separated by & symbols. Query parameters are used to pass additional data to the server so that the server can handle the request based on this data. The browser parses the query parameters into key-value pairs and adds this data to the request.

After parsing each part of the URL, the browser generates an HTTP request and sends it to the server. The request contains information such as method (GET, POST, etc.), URL, protocol version, request header, and request body. After the server receives the request, it processes the request according to the URL and other information in the request, and generates a corresponding response and returns it to the browser.

After the browser receives the response from the server, it will parse the content in the response and render the page or perform other operations based on the parsing results. The response contains information such as status code, response headers, and response body. The status code is used to indicate the result of the server processing the request, such as 200 indicating that the request was successful, 404 indicating that the resource was not found, 500 indicating a server error, etc. The response header contains server-side meta-information, such as content type, character encoding, cache control, etc. The response body contains the specific data returned by the server, such as HTML, CSS, JavaScript, images, etc.

To sum up, the URL parsing process involves steps such as protocol parsing, host name parsing, port parsing, path parsing and query parameter parsing. By parsing the URL, the browser can correctly send a request to the server and obtain the required resource or page. This process happens automatically when we use a browser to access web pages every day. We don't need to pay too much attention to it, but understanding its principles and processes has certain significance for understanding the network and web development.

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