Wikipedia

URL

For other uses, seeURL (disambiguation).

Auniform resource locator(URL), colloquially known as anaddresson theWeb,[1]is a reference to aresourcethat specifies its location on acomputer networkand a mechanism for retrieving it. A URL is a specific type ofUniform Resource Identifier(URI),[2][3]although many people use the two terms interchangeably.[4][a]URLs occur most commonly to referenceweb pages(HTTP/HTTPS) but are also used for file transfer (FTP), email (mailto), database access (JDBC), and many other applications.

URL
Uniform resource locator
AbbreviationURL
StatusPublished
First published1994;30 years ago(1994)
Latest versionLiving Standard
2023
OrganizationInternet Engineering Task Force(IETF)
CommitteeWeb Hypertext Application Technology Working Group(WHATWG)
SeriesRequest for Comments (RFC)
EditorsAnne van Kesteren
AuthorsTim Berners-Lee
Base standards
  • RFC1738.– Uniform Resource Locators (URL).
  • RFC3986.– Uniform Resource Identifier (URI): Generic Syntax.
  • RFC4248.– The telnet URI Scheme.
  • RFC4266.– The gopher URI Scheme.
  • RFC6068.– The 'mailto' URI Scheme.
  • RFC6196.– Moving mailserver: URI Scheme to Historic.
  • RFC6270.– The 'tn3270' URI Scheme.
Related standardsURI,URN
DomainWorld Wide Web
LicenseCC BY 4.0
Websiteurl.spec.whatwg.org

Mostweb browsersdisplay the URL of a web page above the page in anaddress bar.A typical URL could have the formhttp://www.example.com/index.html,which indicates a protocol (http), ahostname(www.example.com), and a file name (index.html).

History

Uniform Resource Locators were defined inRFC1738in 1994 byTim Berners-Lee,the inventor of theWorld Wide Web,and the URI working group of theInternet Engineering Task Force(IETF),[7]as an outcome of collaboration started at the IETF Living Documentsbirds of a feathersession in 1992.[7][8]

The format combines the pre-existing system ofdomain names(created in 1985) withfile pathsyntax, whereslashesare used to separatedirectoryandfilenames.Conventions already existed where server names could be prefixed to complete file paths, preceded by a double slash (//).[9]

Berners-Lee later expressed regret at the use of dots to separate the parts of thedomain namewithinURIs,wishing he had used slashes throughout,[9]and also said that, given the colon following the first component of a URI, the two slashes before the domain name were unnecessary.[10]

EarlyWorldWideWebcollaborators including Berners-Lee originally proposed the use of UDIs: Universal Document Identifiers. An early (1993) draft of the HTML Specification[11]referred to "Universal" Resource Locators. This was dropped some time between June 1994 (RFC1630) and October 1994 (draft-ietf-uri-url-08.txt).[12]In his bookWeaving the Web,Berners-Lee emphasizes his preference for the original inclusion of "universal" in the expansion rather than the word "uniform", to which it was later changed, and he gives a brief account of the contention that led to the change.

Syntax

Main article:Uniform Resource Identifier § Syntax

Every HTTP URL conforms to the syntax of a generic URI. The URI generic syntax consists of fivecomponentsorganized hierarchically in order of decreasing significance from left to right:[13]: §3  

URI = scheme ":" [ "//" authority] path [ "?" query] [ "#" fragment]

A component isundefinedif it has an associated delimiter and the delimiter does not appear in the URI; the scheme and path components are always defined.[13]: §5.2.1 A component isemptyif it has no characters; the scheme component is always non-empty.[13]: §3 

The authority component consists ofsubcomponents: 

authority = [userinfo "@" ] host [ ":" port]

This is represented in asyntax diagramas:

The URI comprises:

  • A non-emptyschemecomponent followed by a colon (:), consisting of a sequence of characters beginning with a letter and followed by any combination of letters, digits, plus (+), period (.), or hyphen (-). Although schemes are case-insensitive, the canonical form is lowercase and documents that specify schemes must do so with lowercase letters. Examples of popular schemes includehttp,https,ftp,mailto,file,dataandirc.URI schemes should be registered with theInternet Assigned Numbers Authority (IANA),although non-registered schemes are used in practice.[b]
  • An optionalauthoritycomponent preceded by two slashes (//), comprising:
    • An optionaluserinfosubcomponent followed by an at symbol (@), that may consist of auser nameand an optionalpasswordpreceded by a colon (:). Use of the formatusername:passwordin the userinfo subcomponent is deprecated for security reasons. Applications should not render as clear text any data after the first colon (:) found within a userinfo subcomponent unless the data after the colon is the empty string (indicating no password).
    • Ahostsubcomponent, consisting of either a registered name (including but not limited to ahostname) or anIP address.IPv4addresses must be indot-decimal notation,andIPv6addresses must be enclosed in brackets ([]).[13]: §3.2.2 [c]
    • An optionalportsubcomponent preceded by a colon (:), consisting of decimal digits.
  • Apathcomponent, consisting of a sequence of path segments separated by a slash (/). A path is always defined for a URI, though the defined path may be empty (zero length). A segment may also be empty, resulting in two consecutive slashes (//) in the path component. A path component may resemble or map exactly to afile system pathbut does not always imply a relation to one. If an authority component is defined, then the path component must either be empty or begin with a slash (/). If an authority component is undefined, then the path cannot begin with an empty segment—that is, with two slashes (//)—since the following characters would be interpreted as an authority component.[16]: §3.3 
By convention, inhttpandhttpsURIs, the last part of apathis namedpathinfoand it is optional. It is composed by zero or more path segments that do not refer to an existing physical resource name (e.g. a file, an internal module program or an executable program) but to a logical part (e.g. a command or a qualifier part) that has to be passed separately to the first part of the path that identifies an executable module or program managed by aweb server;this is often used to select dynamic content (a document, etc.) or to tailor it as requested (see also:CGIand PATH_INFO, etc.).
Example:
URI:"http://www.example.com/questions/3456/my-document"
where:"/questions"is the first part of thepath(an executable module or program) and"/3456/my-document"is the second part of thepathnamedpathinfo,which is passed to the executable module or program named"/questions"to select the requested document.
AnhttporhttpsURI containing apathinfopart without aquerypart may also be referred to as a 'clean URL,' whose last part may be a 'slug.'
Query delimiter Example
Ampersand (&) key1=value1&key2=value2
Semicolon (;)[d] key1=value1;key2=value2
  • An optionalquerycomponent preceded by a question mark (?), consisting of aquery stringof non-hierarchical data. Its syntax is not well defined, but by convention is most often a sequence ofattribute–value pairsseparated by adelimiter.
  • An optionalfragmentcomponent preceded by ahash(#). The fragment contains afragment identifierproviding direction to a secondary resource, such as a section heading in an article identified by the remainder of the URI. When the primary resource is anHTMLdocument, the fragment is often anidattributeof a specific element, and web browsers will scroll this element into view.

A web browser will usuallydereferencea URL by performing anHTTPrequest to the specified host, by default on port number 80. URLs using thehttpsscheme require that requests and responses be made over asecure connection to the website.

Internationalized URL

Internet users are distributed throughout the world using a wide variety of languages and alphabets, and expect to be able to create URLs in their own local alphabets. AnInternationalized Resource Identifier(IRI) is a form of URL that includesUnicodecharacters. All modern browsers support IRIs. The parts of the URL requiring special treatment for different alphabets are the domain name and path.[18][19]

The domain name in the IRI is known as anInternationalized Domain Name(IDN). Web and Internet software automatically convert the domain name intopunycodeusable by theDomain Name System;for example, the Chinese URLhttp:// lệ tử. Quyển đồng chỉbecomeshttp://xn--fsqu00a.xn--3lr804guic/.Thexn--indicates that the character was not originallyASCII.[20]

The URL path name can also be specified by the user in the local writing system. If not already encoded, it is converted toUTF-8,and any characters not part of the basic URL character set are escaped ashexadecimalusingpercent-encoding;for example, the Japanese URLhttp://example.com/ dẫn き cát り.htmlbecomeshttp://example.com/%E5%BC%95%E3%81%8D%E5%89%B2%E3%82%8A.html.The target computer decodes the address and displays the page.[18]

Protocol-relative URLs

Protocol-relative links (PRL), also known as protocol-relative URLs (PRURL), are URLs that have no protocol specified. For example,//example.comwill use the protocol of the current page, typically HTTP or HTTPS.[21][22]

See also

Notes

  1. ^A URL implies the means to access an indicated resource and is denoted by a protocol or an access mechanism, which is not true of every URI.[5][4]Thushttp://www.example.comis a URL, whilewww.example.comis not.[6]
  2. ^The procedures for registering new URI schemes were originally defined in 1999 byRFC2717,and are now defined byRFC7595,published in June 2015.[14]
  3. ^For URIs relating to resources on the World Wide Web, some web browsers allow.0portions of dot-decimal notation to be dropped or raw integer IP addresses to be used.[15]
  4. ^HistoricRFC1866(obsoleted byRFC2854) encourages CGI authors to support ';' in addition to '&'.[17]: §8.2.1 

Citations

  1. ^W3C (2009).
  2. ^"Forward and Backslashes in URLs".zzz.buzz.Archivedfrom the original on 2018-09-04.Retrieved2018-09-19.
  3. ^RFC 3986 (2005).
  4. ^abJoint W3C/IETF URI Planning Interest Group (2002).
  5. ^RFC 2396 (1998).
  6. ^Miessler, Daniel."The Difference Between URLs and URIs".Archivedfrom the original on 2017-03-17.Retrieved2017-03-16.
  7. ^abW3C (1994).
  8. ^IETF (1992).
  9. ^abBerners-Lee (2015).
  10. ^BBC News (2009).
  11. ^Berners-Lee, Tim;Connolly, Daniel "Dan"(March 1993).Hypertext Markup Language (draft RFCxxx)(Technical report). p. 28.Archivedfrom the original on 2017-10-23.Retrieved2017-10-23.
  12. ^Berners-Lee, Tim;Masinter, Larry;McCahill, Mark Perry(October 1994).Uniform Resource Locators (URL)(Technical report).(This Internet-Draft was published as a Proposed Standard RFC,RFC 1738 (1994)) Cited inAng, C. S.; Martin, D. C. (January 1995).Constituent Component Interface++(Technical report). UCSF Library and Center for Knowledge Management.Archivedfrom the original on 2017-10-23.Retrieved2017-10-23.
  13. ^abcdT. Berners-Lee;R. Fielding;L. Masinter(January 2005).Uniform Resource Identifier (URI): Generic Syntax.Network Working Group.doi:10.17487/RFC3986.STD 66.RFC3986.Internet Standard 66.ObsoletesRFC2732,2396and1808.Updated byRFC6874,7320and8820.UpdatesRFC1738.
  14. ^Hansen, Tony; Hardie, Ted (June 2015). Thaler, Dave (ed.).Guidelines and Registration Procedures for URI Schemes.Internet Engineering Task Force.doi:10.17487/RFC7595.ISSN2070-1721.BCP 35.RFC7595.Best Current Practice.Updated byRFC8615.ObsoletesRFC4395.
  15. ^Lawrence (2014).
  16. ^T. Berners-Lee;R. Fielding;L. Masinter (August 1998).Uniform Resource Identifiers (URI): Generic Syntax.Network Working Group.doi:10.17487/RFC2396.RFC2396.Obsolete.Obsoleted byRFC3986.Updated byRFC2732.UpdatesRFC1808and1738.
  17. ^Berners-Lee, Tim;Connolly, Daniel W. (November 1995).Hypertext Markup Language - 2.0.Network Working Group.doi:10.17487/RFC1866.RFC1866.Historic.Obsoleted byRFC2854.
  18. ^abW3C (2008).
  19. ^W3C (2014).
  20. ^IANA (2003).
  21. ^Glaser, J. D. (2014-03-10).Secure Development for Mobile Apps: How to Design and Code Secure Mobile Applications with PHP and JavaScript(1st ed.).CRC Press.p. 193.ISBN978-1-48220903-7.Retrieved2015-10-12.
  22. ^Schafer, Steven M. (2011).HTML, XHTML, and CSS Bible(1st ed.).John Wiley & Sons.p. 124.ISBN978-1-11808130-3.Retrieved2015-10-12.

References

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