Hypertext Transfer Protocol
The Hypertext Transfer Protocol is an application protocol for distributed, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, where hypertext documents include hyperlinks to other resources that the user can access, for example by a mouse click or by tapping the screen in a web browser. HTTP was developed to facilitate the World Wide Web. Development of HTTP was initiated by Tim Berners-Lee at CERN in 1989. Development of HTTP standards was coordinated by the Internet Engineering Task Force and the World Wide Web Consortium, culminating in the publication of a series of Requests for Comments; the first definition of HTTP/1.1, the version of HTTP in common use, occurred in RFC 2068 in 1997, although this was made obsolete by RFC 2616 in 1999 and again by the RFC 7230 family of RFCs in 2014. A version, the successor HTTP/2, was standardized in 2015, is now supported by major web servers and browsers over Transport Layer Security using Application-Layer Protocol Negotiation extension where TLS 1.2 or newer is required.
HTTP functions as a request–response protocol in the client–server computing model. A web browser, for example, may be the client and an application running on a computer hosting a website may be the server; the client submits an HTTP request message to the server. The server, which provides resources such as HTML files and other content, or performs other functions on behalf of the client, returns a response message to the client; the response contains completion status information about the request and may contain requested content in its message body. A web browser is an example of a user agent. Other types of user agent include the indexing software used by search providers, voice browsers, mobile apps, other software that accesses, consumes, or displays web content. HTTP is designed to permit intermediate network elements to improve or enable communications between clients and servers. High-traffic websites benefit from web cache servers that deliver content on behalf of upstream servers to improve response time.
Web browsers cache accessed web resources and reuse them, when possible, to reduce network traffic. HTTP proxy servers at private network boundaries can facilitate communication for clients without a globally routable address, by relaying messages with external servers. HTTP is an application layer protocol designed within the framework of the Internet protocol suite, its definition presumes an underlying and reliable transport layer protocol, Transmission Control Protocol is used. However, HTTP can be adapted to use unreliable protocols such as the User Datagram Protocol, for example in HTTPU and Simple Service Discovery Protocol. HTTP resources are identified and located on the network by Uniform Resource Locators, using the Uniform Resource Identifiers schemes http and https. URIs and hyperlinks in HTML documents form interlinked hypertext documents. HTTP/1.1 is a revision of the original HTTP. In HTTP/1.0 a separate connection to the same server is made for every resource request. HTTP/1.1 can reuse a connection multiple times to download images, stylesheets, etc after the page has been delivered.
HTTP/1.1 communications therefore experience less latency as the establishment of TCP connections presents considerable overhead. The term hypertext was coined by Ted Nelson in 1965 in the Xanadu Project, in turn inspired by Vannevar Bush's 1930s vision of the microfilm-based information retrieval and management "memex" system described in his 1945 essay "As We May Think". Tim Berners-Lee and his team at CERN are credited with inventing the original HTTP, along with HTML and the associated technology for a web server and a text-based web browser. Berners-Lee first proposed the "WorldWideWeb" project in 1989—now known as the World Wide Web; the first version of the protocol had only one method, namely GET, which would request a page from a server. The response from the server was always an HTML page; the first documented version of HTTP was HTTP V0.9. Dave Raggett led the HTTP Working Group in 1995 and wanted to expand the protocol with extended operations, extended negotiation, richer meta-information, tied with a security protocol which became more efficient by adding additional methods and header fields.
RFC 1945 introduced and recognized HTTP V1.0 in 1996. The HTTP WG planned to publish new standards in December 1995 and the support for pre-standard HTTP/1.1 based on the developing RFC 2068 was adopted by the major browser developers in early 1996. By March that year, pre-standard HTTP/1.1 was supported in Arena, Netscape 2.0, Netscape Navigator Gold 2.01, Mosaic 2.7, Lynx 2.5, in Internet Explorer 2.0. End-user adoption of the new browsers was rapid. In March 1996, one web hosting company reported that over 40% of browsers in use on the Internet were HTTP 1.1 compliant. That same web hosting company reported that by June 1996, 65% of all browsers accessing their servers were HTTP/1.1 compliant. The HTTP/1.1 standard as defined in RFC 2068 was released in January 1997. Improvements and updates to the HTTP/1.1 standard were released under RFC 2616 in June 1999. In 2007, the HTTPbis Working Group was formed, in part, to revise and clarify the HTTP/1.1 specification. In June 2014, the WG released an updated six-part specification obsoleting RFC 2616: RFC 7230, HTTP/1.1: Message Syntax and Routing RFC 7231, HTTP/1.1: Semantics and Content RFC 7232, HTTP/1.1: Conditional Requests RFC 7233, HTTP/1.1: Range Requests RFC 7234, HTTP/1.1: Caching RFC 7235, HTTP/1
Private browsing, privacy mode or incognito mode is a privacy feature in some web browsers to disable browsing history and the web cache. This allows a person to browse the Web without storing local data that could be retrieved at a date. Privacy mode will disable the storage of data in cookies and Flash cookies; this privacy protection is only within the browser application as it may leave traces on the hard drive and memory of the device, or via websites by associating the IP address at the web server. The earliest reference to private browsing was in May 2005, was used to discuss the privacy features in the Safari browser bundled with Mac OS X Tiger; the feature has since been adopted in other browsers, led to popularization of the term in 2008 by mainstream news outlets and computing websites when discussing beta versions of Internet Explorer 8. However, privacy modes operate as shields because browsers do not remove all data from the cache after the session. Plug-ins, like Silverlight, are able to set cookies.
The common web browser plugin Adobe Flash Player began supporting privacy mode in Chrome, Internet Explorer, Safari with the release of version 10.1 in June 2010.. Some browsers allow users to select the privacy mode for single tabs, whereas others create a more isolated environment protected by password and cryptography. Private browsing has multiple uses, including: Reducing history, including autofill and personal information. Performing "pure searches" that are not influenced by prior browsing history or networks or friends' recommendations, which may weight and more rank certain results than others. Preventing accidental saving of login credentials to accounts. Signing into multiple accounts via multiple tabs. Testing websites. Preventing other users of the computer from finding one's search history. Viewing explicit material without outside knowledge; the Mozilla Foundation performed a study about the user behavior when the feature is switched on and how long the session lasts. The results were that most sessions last only about 10 minutes, though there are periods where activation increases.
Private browsing is known by different names in different browsers. In 2012, Brazilian researchers published the results of a research project where they applied forensic techniques to extract information about the users browsing activities on Internet Explorer and Firefox browsers with their private mode enabled, they were able to collect enough data to identify pages visited and partially reconstruct them. This research was extended to include Chrome and Safari browsers; the gathered data proved that browsers' private mode implementations are not able to hide users' browsing activities and that browsers in private mode leave traces of activities in caching structures and files related to the paging process of the operating system. Another independent security analysis, performed by a group of researchers at Newcastle University in 2014, shows a range of security vulnerabilities in the implementation of the private mode across four major browsers; the results are summarized below. Browser extensions are potential threats to the user privacy.
By design, existing browsers choose to enable extensions in the private mode by default. This however allows an installed extension to secretly record the visited websites without the user's awareness. Newer versions of Chrome disable extensions in the private mode by default, but allow the private and the normal modes to run in parallel; this makes it possible for an installed extension in the normal mode to learn the user activities in the private mode by measuring the usage of shared computing resources. Data erasure by the browser alone is found to be insufficient. For example, the records of visited websites during the private session can be retained in memory for a long time after the private session is closed. In addition, the visited website records are kept by the operating system in the local DNS cache. Furthermore, the modified timestamps of certain profile files saved on the disk may reveal if the private mode was turned on and when it was turned on. Software bugs present in some browsers are found to degrade the security of the private mode.
For example, in some earlier versions of Safari, the browser retained private browsing history records if the browser program was not closed or if the user acted to add a bookmark within the private mode. Depending on whether the session is in the private or the normal mode, web browsers exhibit different user interfaces and traffic characteristics; this allows a remote website to tell if the user is in the private mode, for example, by checking the color of the hyperlinks or measuring the time of writing cookies. In 2010, professors at Stanford University found that while Firefox won't record your history during a private browsing session, it still records the sites on which you've installed SSL certificates and allows specific permissions. If you download an SSL certificate from a website or told that site to stop displaying pop-ups and downloading cookies, all of that information is still stored on Firefox. In 2015, researchers from Pennsylvania State University found that a cons
Cascading Style Sheets
This cascading priority scheme is predictable. The CSS specifications are maintained by the World Wide Web Consortium. Internet media type text/css is registered for use with CSS by RFC 2318; the W3C operates a free CSS validation service for CSS documents. In addition to HTML, other markup languages support the use of CSS including XHTML, plain XML, SVG, XUL. CSS has a simple syntax and uses a number of English keywords to specify the names of various style properties. A style sheet consists of a list of rules; each rule or rule-set consists of one or more selectors, a declaration block. In CSS, selectors declare which part of the markup a style applies to by matching tags and attributes in the markup itself. Selectors may apply to the following: all elements of a specific type, e.g. the second-level headers h2 elements specified by attribute, in particular: id: an identifier unique within the document class: an identifier that can annotate multiple elements in a document elements depending on how they are placed relative to others in the document tree.
Classes and IDs are case-sensitive, start with letters, can include alphanumeric characters and underscores. A class may apply to any number of instances of any elements. An ID may only be applied to a single element. Pseudo-classes are used in CSS selectors to permit formatting based on information, not contained in the document tree. One example of a used pseudo-class is:hover, which identifies content only when the user “points to” the visible element by holding the mouse cursor over it, it is #elementid: hover. A pseudo-class classifies document elements, such as:link or:visited, whereas a pseudo-element makes a selection that may consist of partial elements, such as::first-line or::first-letter. Selectors may be combined in many ways to achieve great flexibility. Multiple selectors may be joined in a spaced list to specify elements by location, element type, id, class, or any combination thereof; the order of the selectors is important. For example, div.myClass applies to all elements of class myClass that are inside div elements, whereas.myClass div applies to all div elements that are in elements of class myClass.
The following table provides a summary of selector syntax indicating usage and the version of CSS that introduced it. A declaration block consists of a list of declarations in braces; each declaration itself consists of a property, a colon, a value. If there are multiple declarations in a block, a semi-colon must be inserted to separate each declaration. Properties are specified in the CSS standard; each property has a set of possible values. Some properties can affect any type of element, others apply only to particular groups of elements. Values may be keywords, such as "center" or "inherit", or numerical values, such as 200px, 50vw or 80%. Color values can be specified with keywords, hexadecimal values, RGB values on a 0 to 255 scale, RGBA values that specify both color and alpha transparency, or HSL or HSLA values. Before CSS, nearly all presentational attributes of HTML documents were contained within the HTML markup. All font colors, background styles, element alignments and sizes had to be explicitly described repeatedly, within the HTML.
CSS lets authors move much of that information to another file, the style sheet, resulting in simpler HTML. For example, sub-headings, sub-sub-headings, etc. are defined structurally using HTML. In print and on the screen, choice of font, size and emphasis for these elements is presentational. Before CSS, document authors who wanted to assign such typographic characteristics to, all h2 headings had to repeat HTML presentational markup for each occurrence of that heading type; this made documents more complex and more error-prone and difficult to maintain. CSS allows the separation of presentation from structure. CSS can define color, text alignment, borders, spacing and many other typographic characteristics, can do so independently for on-screen and printed views. CSS defines non-visual styles, such as reading speed and emphasis for aural text readers; the W3C has now deprecated the use of all presentational HTML markup. For example, under pre-CSS HTML, a heading element defined with red text would be written as: Using CSS, the sam
In the context of the World Wide Web, a bookmark is a Uniform Resource Identifier, stored for retrieval in any of various storage formats. All modern web browsers include bookmark features. Bookmarks are called favorites or Internet shortcuts in Internet Explorer, by virtue of that browser's large market share, these terms have been synonymous with bookmark since the first browser war. Bookmarks are accessed through a menu in the user's web browser, folders are used for organization. In addition to bookmarking methods within most browsers, many external applications offer bookmark management. Bookmarks have been incorporated in browsers since the Mosaic browser in 1993. Bookmark lists were called Hotlists in previous versions of Opera. Other early web browsers such as ViolaWWW and Cello had bookmarking features. With the advent of social bookmarking, shared bookmarks have become a means for users sharing similar interests to pool web resources, or to store their bookmarks in such a way that they are not tied to one specific computer or browser.
Live bookmarks are updated automatically. Comparison of browser synchronizers Enterprise bookmarking Favicon Smart keyword Social bookmark link generator Social bookmarking XBEL Bookmark Managers at Curlie
Hypertext Transfer Protocol Secure is an extension of the Hypertext Transfer Protocol. It is used for secure communication over a computer network, is used on the Internet. In HTTPS, the communication protocol is encrypted using Transport Layer Security, or its predecessor, Secure Sockets Layer; the protocol is therefore often referred to as HTTP over TLS, or HTTP over SSL. The principal motivation for HTTPS is authentication of the accessed website and protection of the privacy and integrity of the exchanged data while in transit, it protects against man-in-the-middle attacks. The bidirectional encryption of communications between a client and server protects against eavesdropping and tampering of the communication. In practice, this provides a reasonable assurance that one is communicating without interference by attackers with the website that one intended to communicate with, as opposed to an impostor. HTTPS connections were used for payment transactions on the World Wide Web, e-mail and for sensitive transactions in corporate information systems.
Since 2018, HTTPS is used more by web users than the original non-secure HTTP to protect page authenticity on all types of websites. The Uniform Resource Identifier scheme HTTPS has identical usage syntax to the HTTP scheme. However, HTTPS signals the browser to use an added encryption layer of SSL/TLS to protect the traffic. SSL/TLS is suited for HTTP, since it can provide some protection if only one side of the communication is authenticated; this is the case with HTTP transactions over the Internet, where only the server is authenticated. HTTPS creates a secure channel over an insecure network; this ensures reasonable protection from eavesdroppers and man-in-the-middle attacks, provided that adequate cipher suites are used and that the server certificate is verified and trusted. Because HTTPS piggybacks HTTP on top of TLS, the entirety of the underlying HTTP protocol can be encrypted; this includes the request URL, query parameters and cookies. However, because host addresses and port numbers are part of the underlying TCP/IP protocols, HTTPS cannot protect their disclosure.
In practice this means that on a configured web server, eavesdroppers can infer the IP address and port number of the web server that one is communicating with, as well as the amount and duration of the communication, though not the content of the communication. Web browsers know how to trust HTTPS websites based on certificate authorities that come pre-installed in their software. Certificate authorities are in this way being trusted by web browser creators to provide valid certificates. Therefore, a user should trust an HTTPS connection to a website if and only if all of the following are true: The user trusts that the browser software implements HTTPS with pre-installed certificate authorities; the user trusts the certificate authority to vouch only for legitimate websites. The website provides a valid certificate; the certificate identifies the website. The user trusts. HTTPS is important over insecure networks, as anyone on the same local network can packet-sniff and discover sensitive information not protected by HTTPS.
Additionally, many free to use and paid WLAN networks engage in packet injection in order to serve their own ads on webpages. However, this can be exploited maliciously in many ways, such as injecting malware onto webpages and stealing users' private information. HTTPS is very important for connections over the Tor anonymity network, as malicious Tor nodes can damage or alter the contents passing through them in an insecure fashion and inject malware into the connection; this is one reason why the Electronic Frontier Foundation and the Tor project started the development of HTTPS Everywhere, included in the Tor Browser Bundle. As more information is revealed about global mass surveillance and criminals stealing personal information, the use of HTTPS security on all websites is becoming important regardless of the type of Internet connection being used. While metadata about individual pages that a user visits is not sensitive, when combined, they can reveal a lot about the user and compromise the user's privacy.
Deploying HTTPS allows the use of HTTP/2, that are new generations of HTTP, designed to reduce page load times and latency. It is recommended to use HTTP Strict Transport Security with HTTPS to protect users from man-in-the-middle attacks SSL stripping. HTTPS should not be confused with the little-used Secure HTTP specified in RFC 2660; as of April 2018, 33.2% of Alexa top 1,000,000 websites use HTTPS as default, 57.1% of the Internet's 137,971 most popular websites have a secure implementation of HTTPS, 70% of page loads use HTTPS. Most browsers display a warning. Older browsers, when connecting to a site wit
A web browser is a software application for accessing information on the World Wide Web. Each individual web page and video is identified by a distinct Uniform Resource Locator, enabling browsers to retrieve these resources from a web server and display them on the user's device. A web browser is not the same thing as a search engine, though the two are confused. For a user, a search engine is just a website, such as google.com, that stores searchable data about other websites. But to connect to a website's server and display its web pages, a user needs to have a web browser installed on their device; the most popular browsers are Chrome, Safari, Internet Explorer, Edge. The first web browser, called WorldWideWeb, was invented in 1990 by Sir Tim Berners-Lee, he recruited Nicola Pellow to write the Line Mode Browser, which displayed web pages on dumb terminals. 1993 was a landmark year with the release of Mosaic, credited as "the world's first popular browser". Its innovative graphical interface made the World Wide Web system easy to use and thus more accessible to the average person.
This, in turn, sparked the Internet boom of the 1990s when the Web grew at a rapid rate. Marc Andreessen, the leader of the Mosaic team, soon started his own company, which released the Mosaic-influenced Netscape Navigator in 1994. Navigator became the most popular browser. Microsoft debuted Internet Explorer in 1995. Microsoft was able to gain a dominant position for two reasons: it bundled Internet Explorer with its popular Microsoft Windows operating system and did so as freeware with no restrictions on usage; the market share of Internet Explorer peaked at over 95% in 2002. In 1998, desperate to remain competitive, Netscape launched what would become the Mozilla Foundation to create a new browser using the open source software model; this work evolved into Firefox, first released by Mozilla in 2004. Firefox reached a 28% market share in 2011. Apple released its Safari browser in 2003, it remains the dominant browser on Apple platforms. The last major entrant to the browser market was Google, its Chrome browser, which debuted in 2008, has been a huge success.
Once a web page has been retrieved, the browser's rendering engine displays it on the user's device. This includes video formats supported by the browser. Web pages contain hyperlinks to other pages and resources; each link contains a URL, when it is clicked, the browser navigates to the new resource. Thus the process of bringing content to the user begins again. To implement all of this, modern browsers are a combination of numerous software components. Web browsers can be configured with a built-in menu. Depending on the browser, the menu may be named Options, or Preferences; the menu has different types of settings. For example, users can change their home default search engine, they can change default web page colors and fonts. Various network connectivity and privacy settings are usually available. During the course of browsing, cookies received from various websites are stored by the browser; some of them contain login credentials or site preferences. However, others are used for tracking user behavior over long periods of time, so browsers provide settings for removing cookies when exiting the browser.
Finer-grained management of cookies requires a browser extension. The most popular browsers have a number of features in common, they allow users to browse in a private mode. They can be customized with extensions, some of them provide a sync service. Most browsers have these user interface features: Allow the user to open multiple pages at the same time, either in different browser windows or in different tabs of the same window. Back and forward buttons to go back to the previous page forward to the next one. A refresh or reload button to reload the current page. A stop button to cancel loading the page. A home button to return to the user's home page. An address bar to display it. A search bar to input terms into a search engine. There are niche browsers with distinct features. One example is text-only browsers that can benefit people with slow Internet connections or those with visual impairments. Mobile browser List of web browsers Comparison of web browsers Media related to Web browsers at Wikimedia Commons
Shanghai is one of the four municipalities under the direct administration of the central government of the People's Republic of China, the largest city in China by population, the second most populous city proper in the world, with a population of 24.18 million as of 2017. It is a transport hub, with the world's busiest container port. Located in the Yangtze River Delta, it sits on the south edge of the estuary of the Yangtze in the middle portion of the East China coast; the municipality borders the provinces of Jiangsu and Zhejiang to the north and west, is bounded to the east by the East China Sea. As a major administrative and trading city, Shanghai grew in importance in the 19th century due to trade and recognition of its favourable port location and economic potential; the city was one of five treaty ports forced open to foreign trade following the British victory over China in the First Opium War. The subsequent 1842 Treaty of Nanking and 1844 Treaty of Whampoa allowed the establishment of the Shanghai International Settlement and the French Concession.
The city flourished as a centre of commerce between China and other parts of the world, became the primary financial hub of the Asia-Pacific region in the 1930s. During the World War II, the city was the site of the major Battle of Shanghai. After the war, with the Communist Party takeover of the mainland in 1949, trade was limited to other socialist countries, the city's global influence declined. In the 1990s, the economic reforms introduced by Deng Xiaoping resulted in an intense re-development of the city, aiding the return of finance and foreign investment to the city, it has since re-emerged as a hub for international finance. Shanghai has been described as the "showpiece" of the booming economy of mainland China; the two Chinese characters in the city's name are 上 and 海, together meaning "Upon-the-Sea". The earliest occurrence of this name dates from the 11th-century Song dynasty, at which time there was a river confluence and a town with this name in the area. There are disputes as to how the name should be understood, but Chinese historians have concluded that during the Tang dynasty Shanghai was on the sea.
Shanghai is abbreviated 沪 in Chinese, a contraction of 沪渎, a 4th- or 5th-century Jin name for the mouth of Suzhou Creek when it was the main conduit into the ocean. This character appears on all motor vehicle license plates issued in the municipality today. Another alternative name for Shanghai is Shēn or Shēnchéng, from Lord Chunshen, a 3rd-century BC nobleman and prime minister of the state of Chu, whose fief included modern Shanghai. Sports teams and newspapers in Shanghai use Shen in their names, such as Shanghai Shenhua F. C. and Shen Bao. Huating was another early name for Shanghai. In AD 751, during the mid-Tang dynasty, Huating County was established by the Governor of Wu Commandery Zhao Juzhen at modern-day Songjiang, the first county-level administration within modern-day Shanghai. Today, Huating appears as the name of a four-star hotel in the city; the city has various nicknames in English, including "Pearl of the Orient" and "Paris of the East". During the Spring and Autumn period, the Shanghai area belonged to the Kingdom of Wu, conquered by the Kingdom of Yue, which in turn was conquered by the Kingdom of Chu.
During the Warring States period, Shanghai was part of the fief of Lord Chunshen of Chu, one of the Four Lords of the Warring States. He ordered the excavation of the Huangpu River, its former or poetic name, the Chunshen River, gave Shanghai its nickname of "Shēn". Fishermen living in the Shanghai area created a fish tool called the hù, which lent its name to the outlet of Suzhou Creek north of the Old City and became a common nickname and abbreviation for the city. During the Tang and Song dynasties, Qinglong Town in modern Qingpu District was a major trading port. Established in 746, it developed into what contemporary sources called a "giant town of the Southeast", with thirteen temples and seven pagodas; the famous Song scholar and artist Mi Fu served as its mayor. The port had a thriving trade with provinces along the Yangtze River and the Chinese coast, as well as foreign countries such as Japan and Silla. By the end of the Song dynasty, the center of trading had moved downstream of the Wusong River to Shanghai, upgraded in status from a village to a market town in 1074, in 1172 a second sea wall was built to stabilize the ocean coastline, supplementing an earlier dike.
From the Yuan dynasty in 1292 until Shanghai became a municipality in 1927, central Shanghai was administered as a county under Songjiang Prefecture, whose seat was at the present-day Songjiang District. Two important events helped promote Shanghai's development in the Ming dynasty. A city wall was built for the first time in 1554 to protect the town from raids by Japanese pirates, it measured 10 metres high and 5 kilometres in circumference. During the Wanli reign, Shanghai received an important psychological boost from the erection of a City God Temple in 1602; this honour was reserved for prefectural capitals and not given to a mere county seat such as Shang