Network Working Group T. Berners-Lee
Request for Comments: 1738 CERN
Category: Standards TRACK L. MASINTER
Xerox Corporation
M. McCahill
University of Minnesota
Editors
Decemcer 1994
UNIFORM Resource Locators (URL)
STATUS OF this Memo
This Document Specifies An Internet Standards TRACK PROTOCOL for TRACK PROTOCOL for TRACK
Internet Community, And Requests Discussion and Suggestions for
Improvements. please refer to the current edition of the "internet" INTERNet
Official Protocol Standards "(std 1) for the standardization stat
And Status of this Protocol. Distribution of this Memo is unlimited.
Abstract
THIS Document Specifies a Uniform Resource Locator (URL), The Syntax
And Semantics of Formalized Information for Location and Access of Access
Resources via the internet.
INTRODUCTION
This Document Describes The Syntax and Semantics for a Compact String
Representation for a resource available via the internet. these
Strings Are CALLED "Uniform Resource Locators" (URLs).
The specification is deived from concects introduced by the world
Wide Web Global Information Initiative, Whose is Of Such Objects
Dates from 1990 and is described in "Universal Resource Identifiers
In www ", RFC 1630. The Specification of Urls is designed to meet
Requirements Laid Out in "Functional Requirements for Internet
Resource Locators "[12].
This Document Was Written by The Uri Working Group of the Internet
Engineering Task Force. Comments May Be Addressed to the Editors, OR
To The URI-WG
At
RFC 1738 Uniform Resource Locators (URL) Decemcer 1994
2. General URL SYNTAX
Just As There, DiffERENT METHODS OF Access To Resources,
There Are Several Schemes for describing the location of so
RESOURCES.
The Generic Syntax for Urls Province A Framework for New Schemes To
Be Established Using Protocols Other Than Those Defined in this
Document.
Urls area used to `locate 'resources, by providing an abstract
Identification of the resource location. Having located a resource,
A System May Perform A Variety of Operations on the resource, AS
Might Be Characterized by Such Words As `Access ',` Update',
`Replace ',` Find Attributes'. in General, ONLY THE` ACCESS' METHOD
Needs to be specified for any url scheme.
2.1. The main parts of urls
A Full Bnf Description of the Url Syntax Is Given In Section 5.
In General, Urls Are Written As Follows:
A URL Contains The Name of the Scheme Being Used (
By a colon and then a string (the
Interpretation Depends on The Scheme.
Scheme Names Consist of A Sequence of Characters. The Lower Case
Letters "a" - "Z", DIGITS, AND THE Characters Plus (" "), PERIOD
("."), and hyphen ("-") area allowed. for resilience, programs
Interpreting Urls Should Treat Upper Case Letters As Equivalent To
Lower Case In Scheme Names (E.G., Allow "HTTP" AS Well AS "http").
2.2. URL Character Encoding Issues
Urls Are Sequences of Characters, I., Letters, Digits, And Specialcharacters. A Urls May Be Reperesented in A Variety of Ways: E.G., Ink
ON Paper, OR a sequence of osts in a coded character set. The
Interpretation of a URL Depends ONLY ON The Identity of The
CHARACTERS USED.
IN MOST URL Schemes, The Sequences of Characters in Different Parts
Of a url area used to represent sequences of octen used in internet
Protocols. For Example, In The FTP Scheme, The Host Name, DIRECTORY
Name and file names are self such sequences of octets, represented by
Parts of the url. within those parts, an oclet may be represented by
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The Chararacter Which Has That OcTet As ITS Code with the US-ASCII
[20] Coded Character Set.
In Addui, OcTets May Be Encode by a Character Triplet Consisting
Followed by The Two Hexadecimal Digits (from "Followed by the Two Hexadecimal Digits
"0123456789ABCDEF") Which Forming The Hexadecimal Value of The OcTet.
(The Characters "Abcdef" May Also BE Used in Hexadecimal EncoDings.)
OcTets Must Be Encoded If They Have No Corresponding Graphic
Character With Us Us, IF The Use of the USA
Corresponding Character is unsafe, or if the corresponding character
Is Reserved for Some Other Interpretation within the particular URL
Scheme.
NO CORRESPONDING Graphic US-ASCII:
Urls Are Written Only with The Graphic Printable Characters of The Graphic Printable Characters of Thae
US-ASCII Coded Character Set. The Octets 80-FF Hexadecimal Are Not
Used in us-ascii, and the octets 00-1f and 7f Hexadecimal Represent
Control Characters; these Must Be encoded.
Unsafe:
Characters Can Be Unsafe for a Number of Reasons. The Space
Character IS unsafe Because Significant Spaces May Disappear and
Insignificant Spaces May BE Introduces WHEN URLS Are Transcribed OR
TypeSet or Subjected to the Treatment of Word-Processing Programs.
The Characters "<" and ">" Are unsafe because the is useed as the
Delimiters Around Urls in Free Text; The Quote Mark ("") Is Used To
Delimit Urls in Some Systems. The Character "#" is unsafe and should
Always Be Encode Because It Is Used in World Wide Web and in Other
Systems to delimit a URL from a fragment / anchor identifier thing might
FOLLOW It. The Character "%" IS unsafe because it is buy for
ENCODINGS OF Other Characters. Other Characters Are Unsafe Because
Gateway and other transport agent is known in the country
Such Characters. Thase Characters Are "{", "}", "|", "/", "^", "~",
"[", "]", and "` ".
All UNSAFE Characters Must Always Be Encode Withnin A URL. FOR
Example, The Character "#" Must Be Encode Withnin Urls Even in
Systems That Do Not Normal DEAL with FRAGMENT OR ANCHOR
Identifiers, SO That if the URL IS Copied Into Another System That
Does use the the url encoding.
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Reserved:
MANY URL Schemes Reserve Certain Characters for a Special Meaning:
THEIR APPEARANCE IN THEME-Specific Part of The URL HAS A
Designated semantics. if the character corresponding to an ocTet IS
Reserved in a scheme, The @ "," ",": @ "," = "and": "@", "=" and ":" @ "," = ":" @ "," = ":" @ @ @
Reserved for Special Meaning Withnin a scheme. no Other Characters MAY
BE RESERVED WITHIN A Scheme.
USUALLY a URL HAS The Same Interpretation When An OcTet IS
REPRESENTED BY A Character and when Encoded. However, this is not
True for Reserved Characters: Encoding a Character Reserved for a
Particular Scheme May Change The Semantics of a URL.
Thus, ONLY AlphaCTERICS, The Special Characters "$ -_. ! * '(),", And And
Reserved Characters use for their reserved purposes may be available
Unencoded Withnin A URL.
On The Other Hand, Characters That Are Not Required To Be Encoded
(including alphaumerics) May Be encoded within the scheme-specific
Part of a URL, As Long As They Are Not Being Used for a Reserved
Purpose.
2.3 Hierarchical Schemes and Relative Links
In Some Cases, Urls Are Used to Locate Resources That Contain
Pointers to Other Resources. in Some Cases, Those Pointers Are
Represented As Relative Links Where The Expression of the Location of
The Second Resource is in Terms of "in The Same Place as this one
Except with the folowing relative path ". Relative Links Are Not
Described in this document. However, The Use of Relative Links
Depends on the Original Url Containing a hierarchical structure
Against Which The Relative Link is based.
Some Url Schemes (Such As The FTP, HTTP, AND File Schemes) Contain
Names That Can Be Considered Hierarchical; The Components of The
Hierarchy is Separated by "/".
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3. Specific Schemes
The mapping for some existing standard and experimental protocols IS
Outlined in the bnf syntax definition. Notes on Particular Protocols
FOLLOW. The Schemes Covered Are:
FTP File Transfer Protocol
HTTP Hypertext Transfer Protocol
Gopher the gopher protocol
Mailto Electronic Mail Address
News usenet news
NNTP Usenet News Using NNTP Access
Telnet Reference to Interactive Sessions
WAIS Wide Area Information Servers
File Host-Specific File Names
Prospero Prospero Directory Service
Other Schemes May Be Specified by Future Specifications. Section 4 of
THIS Document Describes How New Schemes May Be Registered, And Lists
Some Scheme Names That Are Under Development.
3.1. Common Internet Scheme Syntax
While the syntax for the rest of the url may value depending on the URL MAY
Particular Scheme Selected, URL Schemes That Involve The Direct USE
Of an ip-based protocol to a specified host on the internet us
Common Syntax for the Scheme-Specific Data:
//
Some or all of the parts "
":
Data Start with a double slash "//" To Indicate That IT Complies with
The Common Internet Scheme Syntax. The Different Components Obey The DiffERENT COMPONENTS OBEY
FOLLOWING RULES:
User
An Optional User Name. Some Schemes (E.G., FTP) Allow Thepecification of a User Name.
Password
An Optional Password. If present, IT FOLLOWS THE User
Name Separated from it by a colon.
The user name (and password), IF present, is FOLLOWED BY A
Commercial At-Sign "@". within the user and password field, any ":",
"@", or "/" must be encoded.
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Note That An Empty User Name or Password Is Different Than No User
Name or password; there is no way to specify a password without
Specifying a user name. E.G.,
User name and no password,
While
Empty Password.
Host
The full Qualified Domain Name of a network host, or its ip
Address as a set of four decimal digit groups sedated by
"." Fully Qualified Domain Names Take The Form As Described
In Section 3.5 of RFC 1034 [13] and Section 2.1 of RFC 1123
[5]: a sepance of domain labels Separated by ".", Each Domain
Label Starting and Ending With an alphaumeric character and
Possibly Also Containing "-" Characters. The Rightmost Domain
Label Will Never Start with a Digit, Though, Which
Syntactically Distinguishes All Domain Names from the ip
Addresses.
port
The Port Number to Connect To. Most Schemes Designate
Protocols That Have A Default Port Number. Another Port Number
May Optionally BE Supplied, in Decimal, Separated from the
Host by a colon. if the port is omitted, the colon is as well.URL-path
THE REST of the Locator Consists of data specific to the
Scheme, and is known as the "url-path". Itsupplies the
Details of how the specified resource can be accessed. Note
That the "/" Between the host (or port) and the url-path is
NOT Part of the URL-PATH.
THE URL-PATH SYNTAX Depends on The Scheme Being Used, As Does The
Manner in which it is interpreted.
3.2. Ftp
The FTP URL Scheme IS Used to Designate Files and Directories ON
Internet Hosts Accessible Using The FTP Protocol (RFC959).
A FTP URL FOLLOW THE SYNTAX DESCRIBED in Section 3.1. If:
Omitted, The Port Defaults to 21.
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3.2.1. FTP Name and Password
A user name and password may be support; they is used in the FTP
"User" and "pass" Commands After First Making The Connection To The
FTP Server. If no user name or password is support and one IS
Requested by the ftp server, The Conventions for "anonymous" ftp Are
To BE Used, As Follows:
The user name "anonymous" is support.
The Password Is Supplied as The Internet E-mail Address
Of the end user accessing the resource.
If The URL Supplies a User Name But no Password, and the remote
Server Requests a Password, The Program InterpreNG The FTP URL
SHOULD Request One from the user.
3.2.2. FTP URL-PATH
The URL-path of a ftp url has the folloading syntax:
WHERE
"; TYPE =
Empty. The whole url-path may be omitted, including the "/"
Delimiting it from the prefix containing user, password, host, and
Port.
The URL-path is Interpreted As a Series of FTP Commands as Follows:
Each of the
Argument to a CWD (Change Working Directory) Command.
IF The Typecode IS "D", Perform A NLST (Name List) Command with
Directory Listing.
OtherWise, Perform A Type Command with
And the access the file whose name is
The retrin.)
Withnin a name or cwd component, the characters "/" and ";" Are
Reserved and must be encoded. The Components Are Decoded Prior To
Their use in the ftp protocol. in particular, if the appropriate ftp
Sequence to Access A Particular File Requires Supplying A String
Containing a "/" as an argument to a cwd or retrin, IT IS
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Necessary to Encode EACH "/".
For Example, The Url
Interpreted by ftp-ing to "host.dom", logging in as "myname"
(Prompting for a password if it is asked for), and the executing
"CWD / ETC" and the "retr MOTD". This has a different meaning from
"Retr Motd"; The Initial "CWD" Might Be Executed Relative To The
Default Directory for "MyName". on The Other Hand,
Argument, Then "CWD ETC", and the "retr MOTD".
FTP Urls May Also Be Used for Other Operations; for Example, IT IS
Possible to Update a File on a Remote File Server, or Infer
Information About It from The Directory Listings. The Mechanism for
Doing so is not spelled out here.
3.2.3. Ftp Typecode is Optional
The entire; type =
Omitted, The Client Program Interpreting The Url Must Guess
ApproPriate Mode To Use. in General, The Data Content Type of A File
Can Only Be Guessed from The Name, E.G., from the suffix of the name
The appropriate Type Code to be used for Transfer of the File Can
THEN BE DEDUCED from the data content of the file.
3.2.4 Hierarchy
For Some File Systems, The "/" Used to Denote The Hierarchical
Structure of the url corresponds to the delimiter used to construct a
File Name Hierarchy, And Thus, The FileName Will Look Similar To The
URL PATH. THIS DOES Not Mean That The URL IS A UNIX FileName.
3.2.5. Optimization
Clients Accessing Resources Via FTP May Employ Additional Heuristics
To Optimize the interaction. for some ftp servers, for example, IT
May Be Reasonable To Keep The Control Connection Open While Accessing
Multiple Urls from The Same Server. However, There is no compon
Hierarchical Model To The FTP Protocol, SO if A Directory ChangeCommand Has Been Given, IT IS IMPOSSIBLE IN General To Deduce What
Sequence Should Be Given to Navigate To Another Directory for A
Second Retrieval, IF The Paths Are Different. The Only Reliable
Algorithm is to Disconnect and Reestablish The Control Connection.
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3.3. Http
The http url scheme is buy to designate Internet Resources
Accessible Using HTTP (Hypertext Transfer Protocol).
The Http Protocol is Specified Elsewhere. This Specification ONLY
Describes The Syntax of HTTP URLs.
An HTTP URL Takes The Form:
http://
WHERE
IS Omitted, The Port Defaults to 80. No User Name or Password IS
Allowed.
String. The
Preceding "?". if neither
May also be omitted.
Withnin the
RESERVED. The "/" Character May Be used within http to designate a
Hierarchical structure.
3.4. Gopher
The Gopher Url Scheme Is Used to Designate Internet Resources
Accessible Using The Gopher Protocol.
The Base Gopher Protocol Is Described in RFC 1436 and Supports Items
And Collections of items (Directories). The Gopher Protocol IS A Set
Of Upward Compatible Extensions To The Base Gopher Protocol and isdescribed in [2]. Gopher Supports Associating Arbitrary Sets of
Attributes and Alternate Data Representations with gopher items.
Gopher Urls Accommodate Both Gopher and Gopher Items and Item
Attribute.
3.4.1. Gopher Url Syntax
A gopher url takes the form:
Gopher: //
Where
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IF:
SINGLE-Character Field to Denote The Gopher Type of The Resource To
Which the url refers. The entire
Which case the delimiting "/" is also optional and the
DEFAULTS to "1".
Gopher Selector Strings Are A SEQUENCE OETETS Which May Contain
Any Octets Excepter 09 Hexadecimal (US-ASCII HT or Tab) 0A Hexadecimal
(US-ASCII Character LF), And 0D (US-ASCII Character CR).
Gopher Clients Specify Which Item to Retrieve by Sending The Gopher
Selector String to a gopher server.
WITHIN THE
Note That Some Gopher
The Gopher Selector String May Be An Empty String;
This Is How Gopher Clients Refer to The Top-Level Directory On Agopher Server.
3.4.2 Specifying Urls for Go Gopher Search Engines
IF the url refers to a search to be substed to a gopher search
ENGINE, THE SELECTOR IS FOLLOWED by an encoded tab (% 09) and the
Search string. To Submit a search to a gopher search engine, the
Gopher Client Sends the
And the search string to the gopher server.
3.4.3 URL SYNTAX for Gopher items
Urls for Gopher Items Have A Second Encoded Tab (% 09) And A Gopher
String. Note That in this case, The% 09
Supplied, Although The
The
Retrieval of The Gopher item. Gopher items May Have Alternate
Views, Arbitrary Sets of Attributes, And May Have Electronic Forms
Associated with them.
To Retrieve The Data Associated with a gopher URL, A Client Will
Connect to the Server and send the gopher selector, Followed by a Tab
And the search string (Which year be empty), FOLLOWED by a tab and the
Gopher Commands.
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3.4.4 Default Gopher Data Repesentation
WHEN a Gopher Server Returns A Directory Listing to a Client, The
Gopher Items Are Tagged with Either A " " (Denoting Gopher Items)
OR A "?" (Denoting Gopher Items Which Have A Ask Form Associated
WITH THEM. A Gopher Url with a gopher string consisting of only a a
" " refers to the default view (data representation) of the itemwhile a gopher string containing only a "?" Refer to an item with a
Gopher Electronic Form Associated with it.
3.4.5 GOPHER ITEMS with electric main
Gopher Items Which Have A Ask Associated with Them (I.E. Gopher
Items tagged with a "?") Require the client to fetch the item's ask
Attribute to get the form definition, and then ask the user to fill
Out the form and return the user's responses along with the selector
String to Retrieve The Item. Gopher Clients Know How To Do this But
Depend on the "?" Tag in the gopher item description to know when To
Handle this case. The "?" IS Used in the gopher string to be
CONSISTENT WITH Protocol's Use of this Symbol.
3.4.6 Gopher Item Attribute Collectes
To Refer to the Gopher Attributes of An Item, The Gopher Url '
Gopher String Consists of "!" Or "$". "!" Refers to the all of a
Gopher item's attributes. "$" Refers to all the item attributes for
All Items in a gopher directory.
3.4.7 Referring to Specific Gopher Attributes
To Refer to Specific Attributes, THE URL'S GOPHER _STRING IS
"!
THE Attribute Containing The Abstract of An Item, The Gopher __String
Would Be "! Abstract".
To Refer to Several Attributes, The Gopher _String Consists of the
Attribute Names Separated by Coded Spaces. for Example,
"! Abstract% 20 SMell" Refers to the Abstract and SMELL Attributes
of an item.3.4.8 URL SYNTAX for Gopher Alternate Views
Gopher Allows for Optional Alternate Data Representations (Alternate
Views of items. To Retrieve A Gopher Alternate View, A Gopher
Client sends the appropriate View and Language Identifier (Found in
The item's view attribute). TO Refer to a specific Gopher Alternate
View, The Url's Gopher String Would Be in The form:
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For Example, A Gopher String of " Application / PostScript% Tuple"
Refers to the spanish language PostScript Alternate View of a gopher
Item.
3.4.9 URL SYNTAX for GOPHER ELECTRONIC FORMS
The Gopher _String for a Url That Refers To An Item Reference By A
Gopher Electronic Form (an ask block) Filled out with specific
VALUES IS a Coded Version of What The Client Sends To The Server.
The gopher _String is of the form:
% 091% 0D% 0A -1% 0D% 0A
To Retrieve this Item, The Gopher Client Sends:
-1
To the gopher server.
3.5. Mailto
THE Mailto Url Scheme Is Used to Designate The Internet Mailing
Address of An Individual Or Service. No Additional Information Other
Than An Internet Mailing Address is present or import.
A Mailto Url Takes The Form:
Mailto:
WHERE
CHARACTERS.
Note That The Percent Sign ("%") IS Commonly Used Withnin RFC 822
Addresses and must be encoded.
Unlike Many Urls, The Mailto Scheme Does Not Repesent A Data Object
To Be Accessed Directly; There Is No Sense In Which It Designates An
Object. it has a different of it Than a message / external-body type in
MIME.
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3.6. News
The news url scheme is buy to refer to each either news groups
Individual Articles of UseNet News, AS Specified In RFC 1036.
A News Url Takes One of Two Forms:
News:
News:
A
"comp.infosystems.www.misc". A
Message-ID of Section 2.1.5 of RFC 1036, WITHOUT The Enclosing "<"
And ">"; it takes the form
Identifier May Be distinguished from a news group name by the
Presence of the Commercial AT "@" Character. No Additional Characters
Are Reserved Withnin The Components of a News URL.
If
To "all available news groups".
The news Urls Are Unusual in That by Themselves, They Do Not Contain
Sufficient Information To Locate A Single Resource, But, Rather, Are
Location-independent.
3.7. NNTP
The nntp url scheme is an alternative method of Referencing News News
Articles, USEful for Specifying News Articles from NNTP Servers.
A NNTP URL Take Take:
NNTP: //
WHERE
IS OMIMITTED, The Port Defaults to 119.
The Number> is The Numeric id of the articles. Note That While Nntp: Urls Specify a Unique Location for the Article Resource, MOST NNTP Servers Currently on the Internet Today Are Configured Only To Allow Access from Local Clients, and thus NNTP Urls Do Not Designate Global Accessible Resources. Thus, The news: Form of URL IS Preferred As a Way of Identifying News Articles. Berners-Lee, Masinter & McCahill [Page 13] RFC 1738 Uniform Resource Locators (URL) Decemcer 1994 3.8. Telnet The Telnet URL Scheme IS Used to Designate Intective Services That May Be Accessed by the telnet protocol. A Telnet Url Takes The Form: Telnet: // As specified in section 3.1. The final "/" character may be omitted. IF: Be omitted, as well as the whole This Url Does Not Designate A Data Object, But Rather An Intective Service. Remote Interactive Services Vary Widely In The Means By Which They Allow Remote logins; in Practice, The MRELY Advise The User of The SuggeSted Username and Password. 3.9. Waisthe WAIS URL Scheme IS Used to Designate Wais Databases, Searches, OR Individual Documents Available from A Wais Database. Wais IS Described in [7]. The Wais Protocol Is Described in RFC 1625 [17]; Although The Wais Protocol Is Based on Z39.50-1988, The WAIS URL Scheme is not intended for Use with Arbitrary Z39.50 Services. A WAIS URL Takes One of the Following Forms: WAIS: // WAIS: // WAIS: // WHERE Is Omitted, The Port Defaults to 210. The First Form Designates A WAIS Database That Is Available for Searching. The Second Form Designates a Particular Search. Database being queried. The Third Form Designates a Particular Document Withnin A WAIS Database to be retrieved. in this form Designation of the Type of the Object. Many Wais Implementations Require That aclient know the "type" of an object prior to Retrieval, The Type Being Returned Along with The Internal Object Identifier in the search response. The URL in Order To Allow The Client Interpreting The URL ADEQUATE Information to actually retrieve the document. Berners-Lee, Masinter & McCahill [Page 14] RFC 1738 Uniform Resource Locators (URL) Decemcer 1994 The As Necessary Using The Method Described in Section 2.2. The WAIS Document-id Should Be Treated Opaquely; It May Only Be Decomposed Bythe Server That Issued IT. 3.10 FILES The File Url Scheme Is Used to Designate Files Accessible ON A Particular Host Computer. This Scheme, Unlike Most Other Url Schemes, Does Not Designate a Resource That Iss Universally Accessible over the INTERNET. A File Url Takes The Form: File: // WHERE Which the Directory Path of The Form For Example, A VMS file Disk $ user: [my.notes] Note123456.txt Might Become AS A Special Case, String; this is interpreted as `the machine from Which the URL IS Being interpreted '. The File Url Scheme Is Unusual In That It Does Not Specify An Internet Protocol OR Access Method for Such Files; As Such, ITS UTILITY IN NETWORK PROTOCOLS BETWEEN HOSTS IS LIMITED. 3.11 Prospero The Prospero Url Scheme Is Used To Designate Resources That Are Accessed Via The Prospero Directory Service. The Prospero Protocol IS Described elsewhere [14]. A Prospero Urls Takes The Form: Prospero: // WHERE IS omitted, the port defaults to 1525. no username or password is Berners-Lee, Masinter & Mccahill [Page 15] RFC 1738 Uniform Resource Locators (URL) Decemcer 1994 ALOWED. THE The Prospero Server. THE SEMICOLON ";" IS Reserved and May Not Appear without quoting in the Prospero Urls Are Interpreted by Contacting a Prospeo Directory Server On The Specified Host and Port to Determine Appropriate Access Methods for A Resource, Which Might Themselves Be Repesented AS DiffERENT URLS. External Prospero Links Are Represented AS Urls of The Underlying Access Method and Are Not Repented AS Prospero URLS. Note That a Slash "/" May Appear in the NO Significance May Be Assumed by The Application. Though Slashes May Indicate Hierarchical Structure on The Server, Such Structure IS Not Guaranteed. Note That Many Which case the host or port will be followed by a double slash: the Slash from the url syntax, followed by the initial slash from the In Addition, After the Associated with a prospelo link may be specified as part of the url. When present, Each Field / Value Pair is Separated from Each Other and From the rest of the url by a ";" (SEMICOLON). The name of the field AND ITS Value Are Separated by a "=". IF present, THESE Fields Serve To Identify The Target of The Url. for Example, The Object-version Field Can Be Specified to Identify A Specific Version OF A Object. 4. Registration of New Schemes A New Scheme May Be Introducesd by Defining A Mapping Onto Aconforming Url Syntax, Urls for Experimental Schemes May Be Used by Mutual Agreement Between Parties. Scheme Names Starting with the characters "X" Are Reserved for Experimental Purposes. The Internet Assigned Numbers Authority (IANA) WILL Maintain A Registry of url schemes. Any Submission of A New URL Scheme MUST INCLUDE A Definition of An Algorithm for Accessing Of Resources For use scheme and the syntax for representing such a scheme. Url Schemes Must Have Demonstrable Utility and Operability. One Way To Provide Such a Demonstration Is Via a Gateway Which Province Objects in the New Scheme for Clients Using An Existing Protocol. IF Berners-Lee, Masinter & McCahill [Page 16] RFC 1738 Uniform Resource Locators (URL) Decemcer 1994 THE New Scheme Does Not Locate Resources That Are Data Objects, The Properties of names in the new space must be clearly defined. New Schemes SHOULD TRY TO FOLLOW The Same Syntactic Conventions of Existing Schemes, Where Appropriate. it is likeewise recommented That, WHERE A Protocol Allows for Retrieval By Url, That The Client Software Have Provision for Being Configured To Use Specific Gateway Locators for Indirect Access THROUGH NAMING Schemes. The Following Scheme Have Been Proposed At Various Times, But this Document Does Not De define their syntax or us at this time. it is Suggested That Iana Reserve Their Scheme Names for Future Definition: AFS Andrew File System Global File Names. Mid Message Identifiers for Electronic Mail. CID Content Identifiers for Mime Body Parts. NFS Network File System (NFS) File Names.tn3270 Interactive 3270 Emulation Sessions. MailServer Access to Data Available from mail servers. Z39.50 Access to ANSI Z39.50 SERVICES. 5. Bnf for specific url schemes This Is A Bnf-Like Description of the Uniform Resource Locator Syntax, Using The Conventions of RFC822, Except That | "IS Used To Designate Alternatives, And Brackets [] Are Used Around Optional OR REPEATED Elements. Briefly, Literals Are Quoted with "" Optional Elements Are Enclosed in [Brackets], And Elements May Be Preceded WITH ELEMENT; N Defaults TO. The Generic Form of a URL IS: GenericURL = Scheme ":" Schemepart Specific Predefined Schemes Are Defined Here; New Schemes May Be Registered with Iana URL = HTTPURL | FTPURL | NewsURL | NNTPURL | TELNETURL | GOPHERURL | Waisurl | MailTourl | fileurl | ProSperourn | OtherURL ; New Schemes Follow The General Syntax OtherURL = genericurl The Scheme IS in Lower Case; Interpreters Should Use Case-Ignore Scheme = 1 * [Lowalpha | Digit | "|" - "|". "] Berners-Lee, Masinter & McCahill [Page 17] RFC 1738 Uniform Resource Locators (URL) Decemcer 1994 Schemepart = * xChar | ip-schemepart URL Schemeparts for IP Based Protocols: IP-Schemepart = "//" Login ["/" URLPATH] Login = [user [":" Password] "@"] hostport Hostport = Host [":" Port] Host = hostname | Hostnumber Hostname = * [Domainlabel "."] TopLabeldomainLabel = alphadigit | alphadigit * [alphadigit | "-"] alphadigit Toplabel = alpha | alpha * [alphadigit | "-"] alphadigit AlphaDigit = alpha | DIGIT Hostnumber = DIGITS "." DIGITS "." DIGITS ". Port = DIGITS User = * [uchar | ";" | "|" & "|" = "] Password = * [uchar | ";" |? "|" & "|" = "] URLPATH = * xChar; Depends on protocol see section 3.1 ; The predefined schemes: ; Ftp (see also rfc959) ftpurl = "ftp: //" Login ["/" fpath ["; type =" ftptype]] fpath = fsegment * ["/" fsegment] FSEGMENT = * [Uchar | "?" | ":" @ "|" & "|" = "] FTPTYPE = "a" | "i" | "D" | "a" | "i" | "d" FILE FileURL = "file: //" [Host | "LocalHost"] "/" fpath HTTP httpurl = "http: //" Hostport ["/" HPATH ["?" Search]] Hpath = hsegment * ["/" hsegment] HSEGMENT = * [UCHAR | ";" | ":" @ "|" & "|" = "] Search = * [UCHAR | ";" | "|" @ "|" & "|" = "] Gopher (see Also RFC1436) Gopherurl = "gopher: //" Hostport [/ [gtype [selector ["% 09" Search ["% 09" Gopher _String]]]]]]]] gtype = xchar Selector = * XCHARGOPHER _STRING = * xchar Berners-Lee, Masinter & McCahill [Page 18] RFC 1738 Uniform Resource Locators (URL) Decemcer 1994 Mailto (See Also RFC822) Mailtourl = "MailTo:" Encode822Addr ENCODED822ADDR = 1 * xchar; further defined in RFC822 News (see also rfc1036) NewsURL = "News:" GroupPart Grouppart = "*" | group | article Group = alpha * [alpha | DIGIT | "-" | "|" "|" _ "] Article = 1 * [UCHAR | ";" | "/" | "|": "|" = "]" @ "Host NNTP (See Also RFC977) nntpurl = "nntp: //" Hostport "/" group ["/" digits] Telnet TelnetURL = "telnet: //" Login ["/"] WAIS (See Also RFC1625) Waisurl = Waisdatabase | WaisIndex | Waisdoc Waisdatabase = "wais: //" hostport "/" database WaisIndex = "WAIS: //" Hostport "/" Database "?" Search Waisdoc = "WAIS: //" Hostport "/" database "/" wtype "/" wpath Database = * uchar Wtype = * uchar WPATH = * uchar PROSPERO ProSperource = "Prospero: //" Hostport "/" ppath * [fieldspec] PPath = PSEGMENT * ["/" psegment] PSEGMENT = * [UCHAR | "?" | ":" @ "|" & "|" = "] FieldSpec = ";" FieldName "=" FieldValue FieldName = * [uchar | "?" | ":" "@" | "&"] fieldvalue = * [uchar | "?" | ":" | "@" | "&"] Miscellaneous Definitions Lowalpha = "a" | "B" | "C" | "D" | "e" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z" HIALPHA = "a" | "B" | "C" | "D" | "f" | "g" | "h" | "i" | "J" | "K" | "L" | "M" | "N" | "P" | "q" | "r" | "S" | "T" | "U" | "V" | "w" | "x" | "y" | "z" Berners-Lee, Masinter & McCahill [Page 19] RFC 1738 Uniform Resource Locators (URL) Decemcer 1994 Alpha = Lowalpha | HIALPHA Digit = "0" | "1" | "2" | "4" | "5" | "6" | "7" | "8" | "9" SAFE = "$" | "-" | "_" | "." " " EXTRA = "!" | "*" | "|" ("|") "|", " National = "{" | "}" | "|" | "^" | "~" | "[" | "]" | "` " Puncture = "<" | "#" | "%" | <"> reserved ="; "|" / "|" | ":" | "@" | "&" | "=" HEX = DIGIT | "A" | "B" | "C" | "D" | "e" | "f" | "a" | "b" | "c" | "d" | "e" | "f" Escape = "%" HEX HEX Unreserved = alpha | DIGIT | SAFE | EXTRA Uchar = unreserved | escape XCHAR = unreserved | reserved | escape DIGITS = 1 * DIGIT 6. Security Considances The Url Scheme Does Not in Itself Pose A Security Threat. Users SHOULD BEWARE THATE IS No General Guarance That A URL Which At One Time Points To a Given Object Continues To Do So, And Does Not Even at some Later Time Point to a Different Object Due to the THE Movement of Objects on Servers. A url-limited security threat is that it is solimes possible to Construct a URL Such That An Attempt To Perform A Harmless Idempotent Operation Such as The Retrieval of the Object Will in Fact Cause A POSSIBLY DAMAGING Remote Operation To Occur. The Unsafe URL IS Typically constructed by Specifying a port number other THAN THT NUMBER OTHER THAT Reserved for the network protocol in question. The client Unwittingly Contacts a Server Which IS in Fact Running A Different Protocol. The Content of the URL Contains Instructions Which by Interpreted According to this Other Protocol Cause An Unexpected Operation. An Example Has Been The Use of Gopher Urls To Cause A Rude Message to Be Sent Via A SMTP Server. Caution Should Be Used WHEN Using any url Which specifies a port number other than the defaultfor the protocol, especially des a number with Space. Care Should Be Taken When Urls Contain Embedded Encoded Delimiters For A Given Protocol (for EXAMPLE, CR AND LF Characters for Telnet Protocols) That Sests....... .s. THIS. THIS Would Violate The Protocol But Could Be Used To Simulate An Extra Operation or Parameter, Again Causeing An Unexpected and Possible Harmful Remote Operation to be performed. Berners-Lee, Masinter & McCahill [Page 20] RFC 1738 Uniform Resource Locators (URL) Decemcer 1994 The Use of Urls Containing Passwords That Should Be Secret IS CLEARLY Unwise. 7. ACKNOWEDGEMENTS THIS paper builds on the basic www design (RFC 1630) And Much Discussion of these Issues by Many People on The Network. THE Discussion Was Particularly Stimulated by Articles by Clifford Lynch, BY CLIFFORD LYNCH, Brewster Kahle [10] and usngyik yeong [18]. Contributions from John Curran, Clifford Neuman, ED VIELMETTI AND LATER THE IETF URL BOF AND URI Working Group WERE INCORPORATED. Most Recently, Careful Readings and Comments by Dan Connolly, NED FREED, ROY FIELDING, GUIDO VAN ROSSUM, Michael Dolan, Bert Bos, John Kunze, Olle Jarnefors, Peter Svanberg and Many Others Have Helped REFINE THIS RFC. Berners-Lee, Masinter & McCahill [Page 21] RFC 1738 Uniform Resource Locators (URL) Decemcer 1994 Appendix: Recommendations for Urls in Context Uris, incruding Urls, Are Intended to Be Transmitted THROUGH Protocols Which Provide a context for their interpretation. In Some Cases, IT Will Be Necessary To Distinguish Urls from Otherpossible Data Structures in A SyntActic Structure. In this case, IS Recommended That Urls Be Precededed With A Prefix Consisting of The Characters "URL:". for example, this prefix may be used to DISTINGUISH URLS from Other Kinds of Uris. In Addition, There Are Many Occasions WHEN URLS Are Included in Other Kinds of text; Examples include Electronic Mail, USENET NEWS Messages, or Printed on Paper. in Such Cases, IT IS Convenient To Have a Separate Syntactic Wrapper That Delimits the URL and Separates IT from the rest of the text, and in particular from puncture Marks That Might Be Mistaken for Part of The Url. For this purpose, Is Recommended That Angle Bracket ("<" and ""), Along with the Prefix "URL:", Be buy to delimit the boundaries of the url. this Wrapper Does Not Form Part of The Url and Should Not Be Used in Contexts in Which Delimiters Aready Specified. In the case where a fragment / anchor identifier is associate with a URL (Following a "#"), The Identifier Would Be Placed within THE Brackets as well. In Some Cases, Extra Whitespace (Spaces, Linebreaks, Tabs, ETC.) Need to be added to break long urls across lines. The Whitespace SHOULD BE IGNORED WHEN EXTRACTING THE URL. NO Whitespace SHOULD BE INTRODUCED AFTER A HYPHEN ("-") CHARACTER. BECAUSE SOME TYPESETS AND Printers May (Erroneously) Introduce A HYPHEN AT THE End of Line When Breaking A Line, The Interpreter of A URL Containing a Line Break Immediately After a Hyphen Should Ignore All unencoded Whitespace Around The Line Break, And Should Be Aware That the Hyphen May or May Not Actually Be Part of the Url.examples: YES, JIM, I FOUND IT Under TYPE = D> But you can probably pick it up from Ternic.net/rfc>. Note The Warning IN Net / instructions / overview.html # Warning>. Berners-Lee, Masinter & McCahill [Page 22] RFC 1738 Uniform Resource Locators (URL) Decemcer 1994 References [1] Anklesaria, F., McCahill, M., Lindner, P., Johnson, D., Torrey, D., And B. Alberti, "The Internet Gopher Protocol (a Distributed Document Search and Retrieval Protocol), RFC 1436, University of Minnesota, March 1993. [2] Anklesaria, F., Lindner, P., McCahill, M., Torrey, D., Johnson, D., And B. Alberti, "GOPHER : UPWARD COMPATIBLE Enhancements to the internet gopher protocol, University of Minnesota, July 1993. / Gopher /gopher .txt> [3] Berners-Lee, T., "Universal Resource Identifiers IN WWW: A Unifying syntax for the expression of names and addresses of name Objects on the network as buy in the world-wide web, RFC 1630, Cern, June 1994. [4] Berners-Lee, T., "Hypertext Transfer Protocol (HTTP)", Cern, November 1993. [5] BRADEN, R., Editor, "Requirements for Internet Hosts - Application and support ", STD 3, RFC 1123, IETF, OCTOBER 1989. [6] CROCKER, D. "Standard for the format of arpa internet text measureages", STD 11, RFC 822, UDel, April 1982. [7] Davis, F., Kahle, B., Morris, H., Salem, J., SHEN, T., WANG, R., Sui, J., And M. Grinbaum, "WAIS Interface Protocol Prototype Functional Specification, (v1.5), Thinking Machines Corporation, April 1990. [8] Horton, M. And R. Adams, "Standard for Interchange of UseNet Messages, RFC 1036, AT & T Bell Laboratories, Center for Seismic Studies, December 1987. [9] HuItema, C., "Naming: Strategies and Techniques", Computer NetWorks and ISDN Systems 23 (1991) 107-110. Berners-Lee, Masinter & McCahill [Page 23] RFC 1738 Uniform Resource Locators (URL) Decemcer 1994 [10] Kahle, B., "Document Identifiers, Or International Standard", OR INTERNATIONAL STANDARD Book Numbers for the Electronic Age, 1991. [11] Kantor, B. And P. Lapsley, "NetWork News Transfer Protocol: A proposed Standard for the stream-based transmission of news, RFC 977, UC San Diego & UC Berkeley, February 1986. [12] Kunze, J., "Functional Requirements for Internet Resource Locators, Work In Progress, December 1994. /DRAFT-IETF-URI-IRL-FUN-REQ-02.TXT> [13] Mockapetris, P., "Domain Names - Concepts and Facilities", STD 13, RFC 1034, USC / INFORMATION sciences institute, NOVEMBER 1987. USC / INFORMATION sciences institute, June 1993. /prospeo-protocol.ps.z> [15] Postel, J. And J. Reynolds, "File Transfer Protocol (FTP)", STD 9, RFC 959, USC / INFORMATION sciences institute, October 1985. [16] Sollins, K. And L. Masinter, "Functional Requirements for Uniform Resource Names, RFC 1737, MIT / LCS, Xerox Corporation, DECEMBER 1994. [17] St. Pierre, M, Fullton, J., Gamiel, K., Goldman, J., Kahle, B., Kunze, J., Morris, H., And F. Schiettecatte, "Wais over Z39.50-1988 ", RFC 1625, WAIS, Inc., CNIDR, Thinking Machines Corp., UC Berkeley, FS Consulting, June 1994. [18] Yeong, W. "Towards Networked Information Retrieval", Technical Report 91-06-25-01, Performance Systems INTERNATIONAL, INC. [19] Yeong, W., "Repesenting Public Archives in The Directory", Work in progravel, november 1991. Berners-Lee, Masinter & McCahill [Page 24] RFC 1738 Uniform Resource Locators (URL) Decemcer 1994 [20] "Coded Character Set - 7-Bit American Standard Code for Information interchange ", ANSI X3.4-1986. Editors' Addresses Tim Berners-Lee World-wide web project Cern, 1211 Geneva 23, Switzerland Phone: 41 (22) 767 3755 Fax: 41 (22) 767 7155 Email: Timbl@info.Cern.ch Larry Masinter Xerox Parc 3333 COYOTE HILL ROAD Palo Alto, CA 94034PHONE: (415) 812-4365 Fax: (415) 812-4333 Email: masinter@parc.xerox.com Mark McCahill Computer and Information Services, University of Minnesota Room 152 Shepherd Labs 100 Union Street SE Minneapolis, MN 55455 Phone: (612) 625 1300 Email: mpm@boombox.micro.umn.edu Berners-Lee, Masinter & McCahill [Page 25]
