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Network Working Group                                       B. Hoehrmann
Internet-Draft                                           August 24, 2009
Intended status: Informational
Expires: February 25, 2010

              The 'javascript' resource identifier scheme

Status of this Memo

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   This memo defines the 'javascript' resource identifier scheme.  Using
   this scheme, executable script code can be specified in contexts that
   support resource identifiers.

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1.  Introduction

   The 'javascript' resource identifier scheme allows to encode script
   code in a resource identifier in a way similar to the 'data' scheme,
   but with extended semantics.  This document defines the scheme and
   two operations that describe how existing implementations handle it.

   The first operation, content retrieval, defines which script code a
   given 'javascript' resource identifier represents.  This operation is
   fully defined in this document and some applications might take
   advantage of only this operation.

   The second operation, in-context evaluation, is often implemented by
   web browser applications, and provides a means to run custom script
   code when the resource identifier is dereferenced.  As an example,
   consider a HTML document containing a hyperlink like:

      <a href='javascript:doSomething()'>...</a>

   In typical implementations, when the user activates the hyperlink,
   the web browser will pass control to the doSomething() function, and
   render its result, if any, in place of the current document.

   Some semantics of this operation are out of scope of this document.
   For instance, in the example above, if the doSomething() function
   returns a string object, the implementation would lack clues, like an
   Internet media type, how to process it; it could treat it as a
   script, style sheet, HTML document, resource identifier, or other
   type of resource, as appropriate for the context.

   In order not to limit the applicability of this scheme for certain
   applications, this document just describes this operation in terms of
   an abstract model; it is expected that, where needed, other
   specifications define the semantics in more detail using this model.

2.  Terminology and Conformance

   Resource identifiers, including percent-encoding and requirements for
   IRIs, are defined in STD 66, [RFC3986] and [RFC3987].  Source text
   and the media type application/javascript are defined in [RFC4329],
   the 'data' scheme in [RFC2397], and UTF-8, including the term byte
   order mark, in STD 63, [RFC3629].

   An application that generates resource identifiers conforms to this
   specification if and only if, given a valid application/javascript
   entity, it generates only 'javascript' resource identifiers that
   conform to this specification.

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   An application that dereferences 'javascript' resource identifiers
   conforms to this specification if and only if it implements the
   content retrieval operation as defined in this specification.

   A resource identifier conforms to this specification if and only if
   it is a valid IRI and application of the content retrieval operation
   yields a valid application/javascript entity without generating any
   error.  Use of a byte order mark is discouraged; percent-encoding of
   "/" (U+002F SOLIDUS) characters is encouraged.

   A resource identifier is said to have encoding errors when applying
   the content retrieval operation results in one or more errors.
   Resource identifiers with encoding errors do not conform to this
   specification.  The considerations for handling encoding errors in
   application/javascript entities apply.

3.  Operations

   This section defines two operations that can be applied to resource
   identifiers that conform to this specification.  Other operations may
   be defined in other specifications.

3.1.  Content retrieval

   This operation retrieves the source text that is included in the
   scheme-specific part of a given 'javascript' resource identifier.

      1.  Represent the scheme-specific part as sequence of octets in
          the UTF-8 character encoding.

      2.  Replace any percent-encoded octet by its corresponding octet.

      3.  If the sequence starts with the sequence 0xEF 0xBB 0xBF (the
          UTF-8 signature, or byte order mark), discard this sequence.

      4.  Decode the octet sequence using the UTF-8 character encoding
          and transform the result into source text.

3.2.  In-context evaluation

   This operation defines a model under which applications may evaluate
   the source text included in a given 'javascript' resource identifier.

      1.  Retrieve the source text using the content retrieval

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      2.  Determine the dereference context for further processing.

      3.  Evaluate the source text in this context and memorize the
          result as dereference by-product.

      4.  Process the dereference by-product as appropriate for the
          dereference context.

4.  Interoperability Considerations

   The character "#" is used to separate a fragment identifier from the
   scheme-specific part of a resource identifier and consequently needs
   to be percent-encoded when used as data in the scheme-specific part.
   In certain protocol elements some existing implementations treat the
   character as data regardless of whether it is percent-encoded.

   Protocol element designers who wish to sanction this behavior should
   specify a pre-processing step that applies percent-encoding to this
   character for the relevant protocol elements.  Such a step precludes
   use of fragment identifiers for 'javascript' resource identifiers.

   The in-context evaluation operation is not fully defined in this memo
   and inherently context-dependant; it follows that implementations can
   differ in how they support this operation in a given context and some
   resource identifiers may only function in specific contexts.

   For instance, a 'javascript' resource identifier might be embedded in
   a HTML document and depened on properties of the document.  A typical
   consequence is that hyperlinks using this scheme can be activated in
   a specific document, but trying to open it in a new browser window or
   a different document fails.

   Specifications for protocol elements that permit resource identifiers
   usually do not include special provisions for the 'javascript' scheme
   and implementations consequently vary in where and how they support
   them.  In the interest of interoperability it is therefore advisable
   to use the scheme only where no viable alternatives exist.

   The definition of the scheme does not permit specification of out of
   band information like which particular incarnation of the underlying
   scripting language is used by a resource identifier.  In consequence
   version-specific language features may perform unreliably.

5.  Security Considerations

   A 'javascript' resource identifier contains a application/javascript

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   entity and the security considerations for such entities apply.  The
   content retrieval operation has no considerations beyond that; other
   specifications may define operations in addition to the ones defined
   in this document; security considerations for them are out of scope.

   The in-context evalutation operation necessitates extreme caution in
   deciding where resource identifiers using this scheme are recognized
   and permitted and what facilities are made available to script code,
   like access to private information and operations with side effects.

6.  Internationalization Considerations

   None beyond those inherent to resource identifiers and entities of
   type application/javascript.  Characters are encoded using UTF-8.

7.  IANA Considerations

   This document registers the 'javascript' scheme as permanent scheme
   in the IANA Uniform Resource Identifier scheme registry per BCP 115.

8.  References

8.1.  Normative References

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [RFC4329]  Hoehrmann, B., "Scripting Media Types", RFC 4329,
              April 2006.

8.2.  Informative References

   [RFC2397]  Masinter, L., "The "data" URL scheme", RFC 2397,
              August 1998.

   [RFC4395]  Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
              Registration Procedures for New URI Schemes", BCP 115,
              RFC 4395, February 2006.

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Author's Address

   Bjoern Hoehrmann
   Mittelstrasse 50
   39114 Magdeburg

   Email: mailto:bjoern@hoehrmann.de
   URI:   http://bjoern.hoehrmann.de

   Note: Please write "Bjoern Hoehrmann" with o-umlaut (U+00F6) wherever
   possible, e.g., as "Bj&#246;rn H&#246;hrmann" in HTML and XML.

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