The HTTP and Web
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The document provides an overview of HTTP, its role as a protocol for accessing and transferring multimedia resources on the World Wide Web, and discusses various aspects like URLs, client-server communication, HTTP methods, and differences between HTTP and HTTPS. It explains the structure of HTTP messages, including request and response formats, and how HTTP operates in both non-persistent and persistent modes. Additionally, it touches on the architecture of web applications, including proxies, caches, and the use of HTTPS for secure communication.
![message-header = field-name ":" [ field-value ]
HTTP message headers are used to precisely describe the
resource being fetched or the behavior of the server or the
client. There are four types of HTTP message headers:
1- General headers have general applicability for both request and
response messages.
2-Request headers provide more information about the request.
3- Response headers provide more information about the request.
4-Entity headers define meta information about the entity-body or, if
no body is present, about the resource identified by the request.
Headers](https://image.slidesharecdn.com/httpandwebstudentgouasmiazakaria2018gf189-181214165938/85/The-HTTP-and-Web-44-320.jpg)
The HTTP and Web
- 1. Web and HTTP 2018/2019Gouasmia Zakaria Master Computer Science - Information Security - Gouasmia.zakaria1@gmail.com
- 2. What is HTML ? • HTML: hypertext markup language –Definitions of tags that are added to Web documents to control their appearance
- 4. What is a website ?
- 5. Website is • a group of World Wide Web pages usually containing hyperlinks to each other and made available online by an individual, company, educational institution, government, or organization
- 6. The TCP/IP protocol layers Application Transport Internet Data link Physical Get useful work done – retrieve Web pages, copy files, send and receive email, etc. Make client-server connections and optionally control transmission speed, check for errors, etc. Route packets between networks Route data packets within the local area network Specify what medium connects two nodes, how binary ones and zeros are differentiated, etc, The application program is king – it gets work done using the lower level layers for communication between the client and server.
- 7. What is URL ? Is the address of a resource (such as a document or website) on the Internet that consists of a communications protocol followed by the name or address of a computer on the network and that often includes additional locating information (such as directory and file names)
- 8. URL
- 9. URL (Uniform Resource Locator)
- 10. WHAT IS A protocol ? • In diplomatic circles, a protocol is the set of rules governing a conversation between people • We have seen that the client and server carry on a machine-to-machine conversation • A network protocol is the set of rules governing a conversation between a client and a server • There are many protocols, HTTP is just one
- 11. • I would like to open a connection • GET <file location> • Display response • Close connection • OK • Send page or error message • OK Client Server HTTP is the set of rules governing the format and content of the conversation between a Web client and server An HTTP conversation
- 12. HTTP is an application layer protocol • The Web client and the Web server are application programs • Application layer programs do useful work like retrieving Web pages, sending and receiving email or transferring files • Lower layers take care of the communication details • The client and server send messages and data without knowing anything about the communication network
- 13. The application layer is boss – the top layer • Your boss says: Send this package to Miami -- I don't care if you use Federal Express, UPS, or any other means. Also, let me know when it arrives or if it cannot be delivered for some reason. • The application program says: Send this request to the server -- I don't care how you do it or whether it goes over phone lines, radio, or anything else about the details. Just send the message, and let me know when it arrives or if it cannot be delivered for some reason. Layer Function Application Do useful work like Web browsing, email, and file transfer Lower layers Handle communication between the client and server There are five TCP/IP layers, the application layer and four lower layers.
- 14. Many application layer protocols are used on the Internet, HTTP is only one Protocol Application HTTP: Hypertext Transfer Retrieve and view Web pages FTP: File Transfer Copy files from client to server or from server to client SMTP: Simple Mail Transport Send email POP: Post Office Read email
- 15. Let’s talk more about HTTP
- 16. The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web.
- 17. COMMUNICATION
- 18. HTTP IS • is connectionless protocol • Can deliver any sort of data • Is stateless
- 19. 1. HTTP follows a classical "client-server" model 2. HTTP is a TCP/IP based communication protocol 3. The standard port for HTTP connections is port 80 4. The version of HTTP in common use is HTTP/1.1 HTTP/2 was published in May 2015
- 20. Resources
- 21. HTTP is used to transmit resources. A resource is some of information that can be identified by a URL (it's the R in URL). The most common kind of resource is a file, but a resource may also be a dynamically-generated query result, the output of a CGI script, a document that is available in several languages, or something else...
- 23. PPT OUR COURSE 2-23 HTTP connections non-persistent HTTP • at most one object sent over TCP connection – connection then closed • downloading multiple objects required multiple connections persistent HTTP • multiple objects can be sent over single TCP connection between client, server
- 24. PPT OUR COURSE 2-24 Non-persistent HTTP suppose user enters URL: 1a. HTTP client initiates TCP connection to HTTP server (process) at www.someSchool.edu on port 80 2. HTTP client sends HTTP request message (containing URL) into TCP connection socket. Message indicates that client wants object someDepartment/home.inde x 1b. HTTP server at host www.someSchool.edu waiting for TCP connection at port 80. “accepts” connection, notifying client 3. HTTP server receives request message, forms response message containing requested object, and sends message into its sockettime (contains text, references to 10 jpeg images) www.someSchool.edu/someDepartment/home.index
- 25. PPT OUR COURSE 2-25 Non-persistent HTTP (cont.) 5. HTTP client receives response message containing html file, displays html. Parsing html file, finds 10 referenced jpeg objects 6. Steps 1-5 repeated for each of 10 jpeg objects 4. HTTP server closes TCP connection. time
- 26. PPT OUR COURSE 2-26 Non-persistent HTTP: response time RTT (definition): time for a small packet to travel from client to server and back HTTP response time: • one RTT to initiate TCP connection • one RTT for HTTP request and first few bytes of HTTP response to return • file transmission time • non-persistent HTTP response time = 2RTT+ file transmission time time to transmit file initiate TCP connection RTT request file RTT file received time time
- 27. PPT OUR COURSE 2-27 Persistent HTTP non-persistent HTTP issues: • requires 2 RTTs per object • OS overhead for each TCP connection • browsers often open parallel TCP connections to fetch referenced objects persistent HTTP: server leaves connection open after sending response subsequent HTTP messages between same client/server sent over open connection client sends requests as soon as it encounters a referenced object as little as one RTT for all the referenced objects
- 28. Transaction
- 29. Transaction
- 30. HTTP session consists of three phases: 1- The client establishes a TCP connection 2- The client sends its request and then waits for the answer. 3- The server processes the request and sends back its answer, containing a status code and the appropriate data. The connection is closed.
- 31. HTTP supports several different request commands, called HTTP methods. Every HTTP request message has a method. The method tells the server what action to perform. Methods
- 32. Methods Method Description GET Retrieve information from the server. HEAD Same as GET, but transfers the status line and header section only. POST Send data to the server for processing. PUT Store the body of the request on the server. DELETE Remove a document from the server. TRACE Trace the message through proxy servers to the server. OPTION Determine what methods can operate on a server. CONNECT Converts the request connection to a transparent TCP/IP tunnel. PATCH Applies partial modifications to a resource
- 33. Messages ( request )
- 34. The message format consists of the following 3 items. Start-line Header Fields Message Body
- 36. 2-36 HTTP request message • two types of HTTP messages: request, response • HTTP request message: – ASCII (human-readable format) request line (GET, POST, HEAD commands) header lines carriage return, line feed at start of line indicates end of header lines GET /index.html HTTP/1.1rn Host: www-net.cs.umass.edurn User-Agent: Firefox/3.6.10rn Accept: text/html,application/xhtml+xmlrn Accept-Language: en-us,en;q=0.5rn Accept-Encoding: gzip,deflatern Accept-Charset: ISO-8859-1,utf-8;q=0.7rn Keep-Alive: 115rn Connection: keep-alivern rn carriage return character line-feed character * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive/
- 37. 2-37 HTTP request message: general format request line header lines body method sp sp cr lfversionURL cr lfvalueheader field name cr lfvalueheader field name ~~ ~~ cr lf entity body~~ ~~
- 38. 2-38 HTTP response message status line (protocol status code status phrase) header lines data, e.g., requested HTML file HTTP/1.1 200 OKrn Date: Sun, 26 Sep 2010 20:09:20 GMTrn Server: Apache/2.0.52 (CentOS)rn Last-Modified: Tue, 30 Oct 2007 17:00:02 GMTrn ETag: "17dc6-a5c-bf716880"rn Accept-Ranges: bytesrn Content-Length: 2652rn Keep-Alive: timeout=10, max=100rn Connection: Keep-Alivern Content-Type: text/html; charset=ISO-8859- 1rn rn data data data data data ... * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive/
- 40. Status Codes 1xx Informational 2xx Success 3xx Redirection 4xx Client Error 5xx Server Error
- 41. Response code
- 42. START LINES All HTTP messages begin with a start line. The start line for a request message says ‘what to do ’ . The start line for a response message says what happened. GET /hello.htm HTTP/1.1 (This is Request-Line sent by the client) HTTP/1.1 200 OK (This is Status-Line sent by the server)
- 44. message-header = field-name ":" [ field-value ] HTTP message headers are used to precisely describe the resource being fetched or the behavior of the server or the client. There are four types of HTTP message headers: 1- General headers have general applicability for both request and response messages. 2-Request headers provide more information about the request. 3- Response headers provide more information about the request. 4-Entity headers define meta information about the entity-body or, if no body is present, about the resource identified by the request. Headers
- 45. Header format
- 46. General headers
- 47. Request headers
- 48. Response headers
- 49. Entity headers
- 50. Body The message-body (if any) of an HTTP message is used to carry the entity-body associated with the request or response. The message-body differs from the entity-body only when a transfer-coding has been applied, as indicated by the Transfer-Encoding header field
- 51. Let’s try some commands
- 52. "Tell me and I forget. Show me and I remember. Involve me and I understand." Chinese proverb
- 53. GET Example
- 54. Post example
- 55. What is Telnet • Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers. Through Telnet, an administrator or another user can access someone else's computer remotely. On the Web, HTTP and FTP protocols allow you to request specific files from remote computers, but not to actually be logged on as a user of that computer. With Telnet, you log on as a regular user with whatever privileges you may have been granted to the specific application and data on that computer.
- 56. Let’s use Telnet
- 58. We can use the browser also
- 59. Other Example • rainmaker.wunderground.com :: weather via telnet! • nyancat.dakko.us :: art animation • telehack.com :: talk to Eliza
- 60. Latest version is http 2 The world with http 1.1 and http 2
- 62. 1- HTTPS URLs begin with "https://" and use port 443 by default, whereas HTTP URLs begin with "http://" and use port 80 by default. 2- HTTP is not encrypted and is vulnerable to man-in-the-middle and eavesdropping attacks, which can let attackers gain access to website accounts and sensitive information, and modify webpages to inject malware or advertisements. 3- HTTPS is designed to withstand such attacks and is considered secure against them (with the exception of older, deprecated versions of SSL).
- 63. - Deploying HTTPS also allows the use of HTTP/2, that are new generations of HTTP, designed to reduce page load times and latency. - Netscape Communications created HTTPS in 1994 for its Netscape Navigator web browser.Originally, HTTPS was used with the SSL protocol. As of April 5th, 2016, 41.7% of the Internet's 141,160 most popular websites have a secure implementation of HTTPS.
- 64. Working in HTTPS
- 65. • Web browsers know how to trust HTTPS websites based on certificate authorities that come pre-installed in their software. Certificate authorities (such as Symantec(verisign), Comodo, Go Daddy and Global Sign) are in this way being trusted by web browser creators to provide valid certificates.
- 66. Everything in the HTTPS message is encrypted, including the headers, and the request/response load. The attacker can only know that a connection is taking place between the two parties and their domain names and IP addresses.
- 67. For example, Google’s search engine now defaults to HTTPS connections. This means that people can’t see what you’re searching for on Google.com
- 68. Architectural Components of the Web • In this overview chapter, we've focused on how two web applications (web browsers and web servers) send messages back and forth to implement basic transactions. There are many other web applications that you interact with on the Internet. In this section, we'll outline several other important applications, including:
- 69. • Proxies : HTTP intermediaries that sit between clients and servers • Caches : HTTP storehouses that keep copies of popular web pages close to clients. • Gateways : Special web servers that connect to other applications . • Tunnels : Special proxies that blindly forward HTTP communications • Agents : Semi-intelligent web clients that make automated HTTP requests
- 70. Proxies
- 71. Caches
- 72. Gateways
- 73. Tunnels
- 74. Agents
- 75. The End of the Beginning • That's it for our quick introduction to HTTP. In this chapter, we highlighted HTTP's role as a multimedia transport protocol. We outlined how HTTP uses URIs to name multimedia resources on remote servers, we sketched how HTTP request and response messages are used to manipulate multimedia resources on remote servers, and we finished by surveying a few of the web applications that use HTTP.