A status code, and access baidu process

Asymmetric encryption:

Generally, there will be two keys, one public key and one private key, and the public key will be disclosed to the public
Everyone can use this key to encrypt, and the private key can only be known by the decryptor.This ensures the security of information and prevents others from deciphering the information. If you want to communicate with each other and send information, you need to know the public key of the other party first.

CA: Certificate Authority

CA is an authoritative and impartial third-party trust organization that is responsible for issuing and managing digital certificates, and is an authoritative and impartial third-party trust organization that specializes in issuing certificates, etc., and provides network identity authentication services.Document companies, such as passport agencies, etc.
He can confirm the legitimacy of the identity to prevent others from counterfeiting, and has a digital signature to prevent others from changing the content. Once it is changed, it can be discovered.

Status code:

The status code starting with 2 (request successful) indicates that the request was successfully processed.
200: Success, the server has successfully processed the request, typically this means the server served the requested page

The request is redirected at the beginning of 3) to indicate that further action is required to complete the request.Typically, these status codes are used for redirection.
301: Moved Permanently, the requested web page has been permanently moved to a new location, when the server returns this response, it will automatically redirect the requester to the new location.
302: Temporarily moved, the server is currently responding to requests from a web page in a different location, but the requester should continue to use the original location for future requests
304: Not modified, the requested web page has not been modified since the last requestHowever, when the server returns a secondary response, it will not return the page content

A status code beginning with 4 (Request Error) indicates that the request may have gone wrong, preventing the server from processing it.
401: Unauthorized, the request requires authentication.For web pages that require login, the server may return a secondary response.
402: Keep a valid ChargeTo header response
403: Forbidden, the server rejected the request.
404: Not Found, the server cannot find the requested web page.

Starting with 5 (Server Error) These status codes indicate that the server encountered an internal error while trying to process the request.These errors may be errors of the server itself, not the request.
500: Internal server error, the server encountered an error and could not complete the request.
501: Not yet implemented, the server is not capable of fulfilling the request
503: The service is unavailable, the server is currently unavailable (due to overloading or downtime for maintenance)

Access to Baidu Process:

1. First check the local dns cache to see if there is parsing data
2. Check whether the local hosts file has a Baidu IP address, if not
3. Find a local fixed DNS server or router that has itFortunately, I did not continue to look for the root domain server
4. The root domain server found the com domain and the com domain and found the baidu domain name
5. Then return the result to us
6. Now you can establish a reliable tcp connection with Baidu, after the three-way handshake
access Baidu through browser parsing.
7. The last four times to let go and end the visit