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[Học Giao thức HTTP] Bài 33: Các khái niệm trong HTTP Cache
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Hello everyone! ! In the previous article, we saw the most commonly used terms on the internet. Therefore, it is now event that the World We Web (www) proves a standard framework for accessing documents and resources that rese on computers connected to the Internet. Now in this post, we’ll be more specific about what we mean by the term “HTTP” we use in each URL. Information proved to users (clients) is stored on a web server in the form of web pages. Additionally, these web pages are created using a language called Hypertext Markup Language (html). These websites are connected to each other by hyperlinks (or simply links). Now, any ordinary user can view these pages using a web browser (client program), such as Google Chrome, IE, Firefox, Safari, etc. Each link now proves the browser with a Uniform Resource Locator (URL) that specifies the name of the machine hosting the web page and the name of the file containing the requested document. Hypertext Transfer Protocol (http) supports communication between web browsers (clients) and web servers. The main feature of HTTP is the ability to access information on the WWW. The protocol can retrieve data in various forms, such as, for example, plain text, hypertext, audio, video, etc. The functionality of HTTP corresponds to the combination of FTP and SMTP (discussed in previous posts). It uses TCP services. It uses a TCP connection (port 80). As with FTP, there is no separate management (control) connection. There is only data transmission between the client and the server, so there is only one connection, and that is the data connection. The data transfer of HTTP is similar to that of SMTP. The layout (format) of the message is managed using MIME-like headers. The
Working of HTTP in simple terms :
HTTP protocol mainly defines the way that the client makes a service request to the Web server to obtain the service (request information/document). So let’s understand the steps involved in this communication: First, the customer (end user) clicks a link (or enters any URL). The browser program (Chrome, Firefox, Safari, etc.) proves the required URL. Then it gets the IP address of the server via DNS (Domain Name Server). HTTP establishes a TCP connection (port 80) between client and server. The document is then transferred from the server to the client. The user then starts viewing the document. The established TCP connection is closed again after a certain timeout period.
Principle of HTTP Operation
The principle of HTTP is simple. Client sends request. The server then sends a reply. Request and response messages carry data in MIME-like letters. The client initiates a transaction by sending a request message, and the server responds by sending a response. HTTP is the application layer protocol of the web. It is an integral part of the web. It is defined in [RFC 1945] and [RFC 2616]. It mainly consists of two programs, the client program. server program. An HTTP client first initiates a TCP connection to the server. After the connection is established, the browser and server processes access TCP through their socket interfaces. Unlike SMTP, HTTP messages are not meant to be read by humans. They are read and interpreted by HTTP servers and HTTP clients (browser). Store and forward SMTP messages, but deliver HTTP messages immediately. The commands from the client to the server are then embedded in the request message.
Statelessness Associated With HTTP
With HTTP, the server sends the requested file to the client without storing any state information about the client. So it can happen that the same client repeatedly asks the server for the same information and the server doesn’t even understand it. As a result, these files are resent again and again. Since the HTTP server does not store any information about the state of the client, it is called a stateless protocol. (The concept of cookies has been explained in the previous article).
Persistent and Non – Persistent connection in HTTP
HTTP can use both non-persistent and persistent connections. HTTP uses persistent connections in its default mode. However, HTTP clients and servers can also be configured to use non-persistent connections. Non-persistent connections Non-persistent connections establish a TCP connection for each request/response. Here are the steps of the strategy: The client first opens a TCP connection and sends a request. .then the server sends a response and closes the connection. .The client then reads the data until it encounters the end-of-file marker, then closes the connection. This strategy requires opening and closing the connection N times for “N” different images in different files. The non-persistent strategy also imposes high overhead on the server, as the server requires N different buffers and requires a slow startup process every time a connection is opened. So there is more latency and wasted memory in this case. Persistent connections HTTP version 1.1 basically specifies persistent connections by default. With persistent connections, the server keeps the connection open for further requests after sending a response. The server can then close the connection at the client’s request or when a timeout is reached. The sender usually sends the length of the data with each reply. However, in some cases, the sender does not know the length of the data. This is the case when documents are created dynamically or actively. In these cases, the server first tells the client that the length is unknown, and closes the connection after sending the data, so that the client knows it has reached the end of the data.
HTTP Transaction (message formats)
The first line of the request message is called the request line, and the first line of the response message is called the status line. A request message usually contains a request line, headers, and sometimes a body. Additionally, the reply message consists of a status line, a title, and sometimes a body. The request line format is specified as follows: Request type (space) URL (space) http version The status line format is specified as follows: http version (space) Status code (space) Status phrase HTTP messages are written in ASCII text format. (Only one field is the same for both) Request Type: This field is used in the request message. Several request types were defined in HTTP version 1.1. The request types are dived into the following methods: Method Actions GET Request a document from the server POST Send some information from the client to the server PUT Send a document URL from the server to the client: computer address and file version: HTTP version Status code: this field Used in reply messages. Status code fields are similar to those in FTP and SMTP logs. It consists of three numbers. (see below) Status Phrase: This field is used in response messages. It interprets status codes in text form. Status Code Statusphrase 301 Permanent Move The requested URL is no longer used by the server. 302 Temporarily Moved The requested URL has been moved temporarily 400 Bad Request The request contains a syntax error. 403 Forbden Service Denied. 404 Not found Document not found. 500 Internal server error An error occurred on the server se, such as B. crash. 501 Not Implemented The requested operation could not be performed. 503 Service Unavailable The service is temporarily unavailable, but may be requested in the future. The
HTTP Header format
header in the response message is used to exchange additional information between the client and server. The title can be single or multiple lines. Header Name : (space) Header Value Now let’s look at some header names and their descriptions. Title Description Date Displays the current date. Content Length Displays the length of the document Server Displays the server name and version number.
HTTP Proxy Server and Caching
When the volume of requests (data) from popular websites becomes large enough, it makes sense to cache web information in a server closer to the user (extra buffer). Any ISP (Internet Service Prover) can prove a web proxy server to control traffic. HTTP supports proxy servers. A proxy server is a computer that basically keeps a copy of the response to the current request. The HTTP client then sends a request to the proxy server. The proxy server checks its cache. If the response is not cached, the proxy server then sends the request to the appropriate server. Incoming responses are further sent to the proxy server and stored for future requests by other clients. Proxy servers reduce the load on the origin server by reducing traffic, while also improving latency. However, to use a proxy server, the client must be configured to access the proxy instead of the target server. A proxy server is basically a gateway that communicates with your browser’s FTP over HTTP.
HTTP Secure (https)
This includes an additional layer of security via TSL (Transport Layer Security) or Secure Sockets Layer (SSL). It uses TCP’s port 443 (instead of TCP’s HTTP port 80) and is more secure than regular HTTP. This concludes this long article (I hope you like it :-p). In the next article, we will explore more details about other important application layer features. report this ad
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