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HTTP interview questions online many, but the answer is not comprehensive, also will not condensed focus, resulting in children’s shoes and small series are difficult to remember, for these questions small series in the answer at the same time, will focus on refining out convenient memory

1. The difference between HTTP and HTTPS

HTTP is a Hypertext Transfer Protocol (Hypertext Transfer Protocol). HTTP is a Protocol and specification for transmitting Hypertext data, such as text, pictures, audio and video, between two points in the computer world

The main content of HTTP is divided into three parts: Hypertext, Transfer and Protocol.

• Hypertext is more than just text, it can also transfer pictures, audio, video, and even click on a text or imagehyperlinksThe jump.
• These concepts can be collectively referred to as data, and transmission is the process in which data is transferred from one end system to another through a series of physical media. Usually we call the party that transmits the packetThe requester, the party receiving the binary packet is calledReply party.
• Protocol refers to the norms for transferring and managing information on networks (including the Internet). Just as people need to follow certain rules to communicate with each other, computers need to follow certain rules to communicate with each other. These rules are called protocols, but network protocols.

Speaking of HTTP, the TCP/IP network model has to be mentioned, which is usually a five-tier model. As shown in the figure below

However, it can also be divided into four layers, that is, the link layer and the physical layer are expressed as the network interface layer

Another is the OSI seven-layer network model, which adds a presentation layer and a session layer on top of the five-layer protocol

The full name of HTTPS is Hypertext Transfer Protocol Secure. From its name, we can see that HTTPS is more Secure than HTTPS. In fact, HTTPS is not a new application-layer Protocol. It is a combination of HTTP + TLS/SSL, and security is what TLS/SSL does.

In other words, HTTPS is HTTP with SSL on top.

So, what are the main differences between HTTP and HTTPS?

• At its simplest, HTTP’s protocol in the address bar begins with http://, while HTTPS’s protocol in the address bar begins with https://

  www.cxuanblog.com/ www.cxuanblog.com/

• HTTP is a protocol without secure encryption. Its transmission process is easy to be monitored by attackers, data is easy to be stolen, and sender and receiver are easy to be forged. HTTPS is a secure protocol, which can solve these problems through key exchange algorithm – signature algorithm – symmetric encryption algorithm – digest algorithm.

• The default port for HTTP is 80 and the default port for HTTPS is 443.

Summary of main points:

HTTP: plaintext transmission, stateless; HTTPS :SSL+HTTP, encrypted transmission, identity authentication

HTTP: efficient, fast; HTTPS: consumes resources and time

HTTP port: 80; https:443

2. Differences between HTTP Get and Post

HTTP includes many methods. Get and Post are the two most commonly used methods in HTTP. Basically, 99% of HTTP methods are used in Get and Post methods, so it is necessary for us to have a deeper understanding of these two methods.

• For example, if you type www.cxuanblog.com in the browser address bar, you will send a GET request. The main feature of the get request is to request the server to return the resource, while the post method is usually used for submitting the

  form, which is equivalent to submitting information to the server. Waiting for the server to respond, GET is equivalent to a pull operation and POST is equivalent to a push operation.
  

• The get method is not secure, because your request parameters will be spelled after the URL in the process of sending the request, making it easy for attackers to steal your information and cause damage and forgery.

  /test/demo_form.asp? name1=value1&name2=value2

The POST method puts parameters in the request body, which is not visible to the user.

Asp HTTP/1.1 Host: w3schools.com name1=value1&name2=value2Copy the code

• A GET request has a URL with a length limit, whereas a POST request places parameters and values in the message body, with no requirement for data length.

• Get requests are actively cached by browsers, whereas POST requests are not, unless set manually.

• Get requests are harmless when repeated back/forward operations are performed in the browser, while POST operations resubmit the form request.

• A GET request generates a TCP packet during transmission. Post generates two TCP packets during sending. For get requests, the browser sends both HTTP headers and data, and the server responds with 200 (return data). For POST, the browser sends a header, the server responds with 100 continue, the browser sends data, and the server responds with 200 OK (returns data).

Summary of main points:

• The get: pull; post:push
• Get request parameter concatenation is not secure after the URL; The POST request parameters are placed in the body
• Get has a length limit; Post has no length limit
• Get is actively cached by the browser. The post will not
• Get back/forward repeatedly is harmless; The post submits the form again
• Get sends a single packet. Post sends two

3. What is stateless protocol? Is HTTP a stateless protocol

The Stateless Protocol means that the browser has no memory for transaction processing. For example, a client may close the browser after requesting a web page, and then start the browser again to log in to the site, but the server does not know that the client closed the browser once.

HTTP is a stateless protocol that has no memory for user actions. Most users probably don’t believe that. They probably think that every time they enter a username and password to log in to a site, they will not re-enter the username and password the next time they log in. That’s not really what HTTP does. What does is a mechanism called cookies. It gives the browser the ability to remember.

If your browser allows cookies, viewing the chrome: / / Settings/content/cookies

Which means your memory chip is powered up… When you want the server to send a request, the server sends you an authentication message. When the server receives the request for the first time, it creates a Session space (the Session object is created), generates a sessionId, and passes the ** set-cookie in the response header: JSESSIONID=XXXXXXX ** command to send a response to the client requesting to set cookies; After receiving the response, the client sets a Cookie with **JSESSIONID=XXXXXXX ** on the local client. The Cookie expires at the end of the browser session.

Next, when the client sends a request to the same website each time, the request header will carry the Cookie information (including the sessionId). Then, the server obtains the value named JSESSIONID by reading the Cookie information in the request header and obtains the sessionId of the request. In this way, your browser has the ability to remember.

Another way is to use the JWT mechanism, which is also a mechanism to make your browser memorable. Unlike cookies, JWT is information stored on the client and is widely used in single sign-on situations. JWT has two characteristics

• JWT Cookie information is stored inThe client, instead of server memory. In other words, JWT can directly authenticate the Token locally. After the authentication, the Token will be sent to the server in the Session with the request. In this way, the server resources can be saved and the Token can be authenticated multiple times.
• JWT supports cross-domain authentication, Cookies can only be used inThe domain of a single nodeOr itssubdomainThe effective. If they try to access through a third node, they are blocked. Using JWT can solve this problem, using JWT can passMultiple nodesUser authentication, that’s what we call itCross-domain authentication.

Summary of main points:

• HTTP has no memory of user operations
• The client sends an HTTP request and the server returns an HTTP Response +set cookie. The client sends an HTTP Request +cookie, and the server returns an HTTP Response

4. Summarize the differences between HTTP1.0/1.1/2.0

The HTTP 1.0

HTTP 1.0 was introduced in 1996, and since then its popularity has been phenomenal.

• HTTP 1.0 provides only the most basic authentication, and at this point the user name and password are not encrypted, making it easy for prying eyes.
• HTTP 1.0 was designed to use short links, where each transmission of data goes through TCP’s three-way handshake and four-way wave, which is less efficient.
• HTTP 1.0 only uses if-Modified-since and Expires in headers as criteria for cache invalidation.
• HTTP 1.0 does not support breakpoint continuation, which means that all pages and data are sent each time.
• HTTP 1.0 assumes that only one IP can be bound to each computer, so the URL in the request message does not pass the hostname.

The HTTP 1.1

HTTP 1.1 came three years after HTTP 1.0 was developed, in 1999, with the following changes

• HTTP 1.1 uses the digest algorithm for authentication
• HTTP 1.1 uses long connections by default. Long connections are established once and can be transmitted multiple times. After the transmission is complete, the connection can be disconnected only once. The connection duration of a long connection can be specified in the request headerkeep-aliveTo set the
• HTTP 1.1 added e-tag, if-unmodified-since, if-match, if-none-match and other cache control headers to control cache invalidation.
• HTTP 1.1 supports breakpoint continuation by using theRangeTo implement.
• HTTP 1.1 uses virtual networks, where multiple virtual hosts (multi-homed Web Servers) can exist on a single physical server and share a single IP address.

The HTTP 2.0

HTTP 2.0 is a standard developed in 2015 with the following major changes

• The head of compressionBecause HTTP 1.1 comes up a lotUser-agent, Cookie, Accept, Server, RangeFields like “, “and”, “can take up hundreds or even thousands of bytes, whereas” Body “is often only tens of bytes, leading to a heavy header. The HTTP 2.0 usingHPACKAlgorithm for compression.
• Binary formatHTTP 2.0 uses a binary format closer to TCP/IP and ditched ASCII to improve parsing efficiency
• Strengthen the securitySince security has become a top priority, HTTP2.0 generally runs on HTTPS.
• multiplexingThat is, each request is used for connection sharing. One request corresponds to one ID, so there can be multiple requests on a connection.

5. Describe a common HTTP request header

Common request headers: Generic, Entity, request

Common response headers:

What is a Websocket? What are the advantages? Application? (1) HTTP has a defect, that is, the connection can only be initiated by the client, not the server. Websocket is a full duplex communication method to avoid such defects. (2) WebSocket is a protocol in HTML5, supporting persistent continuous, HTTP protocol does not support persistent connection. (3) WebSocket is based on Http protocol, or borrows Http protocol to complete part of the handshake, which is the same as Http in the handshake stage.

Other features include: (1) based on THE TCP protocol, the implementation of the server side is relatively easy. (2) It has good compatibility with HTTP protocol. The default ports are also 80 and 443, and the handshake phase uses HTTP protocol, so it is not easy to mask the handshake and can pass various HTTP proxy servers. (3) The data format is relatively light, the performance overhead is small, and the communication is efficient. (4) Can send text, can also send binary data. (5) There is no source restriction, and the client can communicate with any server. (6) The protocol identifier is WS (if encrypted, WSS), and the server URL is the URL.