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Internet Engineering                                        A. Brashears
Task Force                                               M. Hamrick, Ed.
Internet-Draft                                              M. Lentczner
Intended status: Informational                     Linden Research, Inc.
Expires: August 8, 2009                                 February 4, 2009


                       Linden Lab Structured Data
                         draft-hamrick-llsd-00

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   This Internet-Draft will expire on August 8, 2009.

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   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   to this document.

Abstract

   This document describes the Linden Lab Structured Data (LLSD)



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   abstract type system, interface description and serialization
   formats.  LLSD is a language-neutral facility for maintaining and
   transporting structured data.  It provides dynamic data features for
   loosely-coupled collections of software components, even in
   statically-typed languages.  LLSD includes an abstract type system,
   an interface description language (LLIDL) and three canonical
   serialization schemes (XML, JSON and Binary).


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
   2.  Abstract Type System . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Simple Types . . . . . . . . . . . . . . . . . . . . . . .  5
       2.1.1.  Undefined  . . . . . . . . . . . . . . . . . . . . . .  5
       2.1.2.  Boolean  . . . . . . . . . . . . . . . . . . . . . . .  5
       2.1.3.  Integer  . . . . . . . . . . . . . . . . . . . . . . .  6
       2.1.4.  Real . . . . . . . . . . . . . . . . . . . . . . . . .  6
       2.1.5.  String . . . . . . . . . . . . . . . . . . . . . . . .  6
       2.1.6.  UUID (Universally Unique ID) . . . . . . . . . . . . .  7
       2.1.7.  Date . . . . . . . . . . . . . . . . . . . . . . . . .  8
       2.1.8.  URI (Uniform Resource Identifier)  . . . . . . . . . .  8
       2.1.9.  Binary . . . . . . . . . . . . . . . . . . . . . . . .  8
     2.2.  Composite Types  . . . . . . . . . . . . . . . . . . . . .  8
       2.2.1.  Array  . . . . . . . . . . . . . . . . . . . . . . . .  8
       2.2.2.  Map  . . . . . . . . . . . . . . . . . . . . . . . . .  9
     2.3.  Converting Between Real and String Types . . . . . . . . .  9
     2.4.  Converting Between Date and String Types . . . . . . . . .  9
   3.  Serialization  . . . . . . . . . . . . . . . . . . . . . . . . 10
     3.1.  XML Serialization  . . . . . . . . . . . . . . . . . . . . 10
       3.1.1.  Serializing Simple Types . . . . . . . . . . . . . . . 10
       3.1.2.  Serializing Composite Types  . . . . . . . . . . . . . 11
       3.1.3.  Example of XML LLSD Serialization  . . . . . . . . . . 11
     3.2.  JSON Serialization . . . . . . . . . . . . . . . . . . . . 12
       3.2.1.  Examples of JSON LLSD Serialization  . . . . . . . . . 13
     3.3.  Binary Serialization . . . . . . . . . . . . . . . . . . . 13
       3.3.1.  Example of BINARY LLSD Serialization . . . . . . . . . 15
   4.  Interface Description Language . . . . . . . . . . . . . . . . 18
     4.1.  Abstract Data Types and Names  . . . . . . . . . . . . . . 18
     4.2.  Abstract Data Structures . . . . . . . . . . . . . . . . . 18
     4.3.  Variant Data Structures  . . . . . . . . . . . . . . . . . 19
     4.4.  Variant Discriminators . . . . . . . . . . . . . . . . . . 20
     4.5.  Resource Description . . . . . . . . . . . . . . . . . . . 20
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
   6.  MIME Type Registrations  . . . . . . . . . . . . . . . . . . . 21
     6.1.  MIME Type Registration for application/llsd+xml  . . . . . 21
     6.2.  MIME Type Registration for application/llsd+json . . . . . 22



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     6.3.  MIME Type Registration for application/llsd+binary . . . . 23
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 25
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 25
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 26
   Appendix A.  ABNF of Real Values . . . . . . . . . . . . . . . . . 27
   Appendix B.  XML Serialization DTD . . . . . . . . . . . . . . . . 28
   Appendix C.  ABNF of LLIDL . . . . . . . . . . . . . . . . . . . . 28
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 30










































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1.  Introduction

   Linden Lab Structured Data (LLSD) is an abstract type system intended
   to provide a language-neutral facility for the representation of
   structured data.  It provides a type system, a serialization system
   and an interface description language.

   The type system of LLSD defines nine simple types (Undefined,
   Boolean, Integer, Real, String, UUID, Date, URI and Binary) and two
   composite types (Array and Map.)  It is used to represent an ideal
   dynamic type system in programming languages that may not exhibit
   dynamic type behaviors.  This type system is advantageous in
   computing environments that make use of loosely-coupled components,
   each of which may be implemented in a different programming language.

   When loosely-coupled systems need to communicate structured data,
   LLSD instances are serialized into a neutral format for transmission
   across a process or system boundary.  LLSD instances may be
   serialized into one of three defined formats: XML, JSON and binary.

   When meta-information regarding LLSD instances is required, an
   interface description language (LLIDL) may be used to define the
   structure of LLSD instances.  LLIDL is especially suited to
   describing the structure of requests and responses in distributed
   systems using representational state transfer (RESTful) semantics.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].


2.  Abstract Type System

   The abstract type system describes the semantics of LLSD data passed
   between two systems.  These types characterize the data when
   serialized for transport, when stored in memory, and when accessed by
   applications.

   The types are designed to be common enough that native types in
   existing serializations and programming languages will be usable
   directly.  It is anticpiated that LLSD data may be serialized in
   systems with fewer types or stored in native programming language
   structures with less precise types, and still interoperate in a
   predictable, reliable manner.  To support this, conversions are
   defined to govern how data received or stored as one type may be read
   as another.



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   For example: If an application expects to read an LLSD value as an
   Integer, but the serialization used to transport the value only
   supported Reals, then a conversion governs how the application will
   see the transported value.  Another case would be where an
   application wants to read an LLSD value as a URL, but the programing
   language only supports String as a data type.  Again, there is a
   defined conversion for this case.

   The intention is that applications will interact with LLSD data via
   interfaces in terms of these types, even if the underlying language
   or transports do not directly support them, while retaining as much
   direct compatibility with those native types as possible.

   An LLSD value is either a simple datum or a composite structure.  A
   simple data value can have one of nine simple types: Undefined,
   Boolean, Integer, Real, String, UUID, Date, URI or Binary.  Composite
   structures can be either of the types Array or Map.

2.1.  Simple Types

   For each type, conversions are defined to that type.  That is, if a
   process is accessing a particular LLSD value, and treating it as a
   particular type, but the underlying type (as transmitted, or stored
   in memory) is different, then the indicated conversion, if defined,
   is applied.  If a conversion is not specified from a particular type,
   then if a value of that type is accessed, the result is the default
   value for the expected type.  For example: When reading a value as an
   integer, if the underlying value is binary, then the value read is
   zero.

2.1.1.  Undefined

   Data of type Undefined has only one value, called undef.  The default
   value is undef.  There are no defined conversions to Undefined.

   The Undefined type is a placeholder for a value.

2.1.2.  Boolean

   Data of type Boolean can have one of only two values: true or false.
   The default value is false.

   Conversions:

   Integer  A zero value (0) is converted to false.  All other values
       are converted to true.





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   Real  A zero value (0.0) and invalid floating point values (NaNs) are
       converted to false.  All other values are converted to true.

   String  An empty String is converted to false.  Anything else is
       converted to true.

2.1.3.  Integer

   Data of type Integer can have the values of natural numbers between
   -2147483648 and 2147483647 inclusive.  The default value for Integer
   is zero (0).

   Conversions:

   Boolean  The value true is converted to the Integer 1.  The value
       false is converted to the Integer 0.

   Real  Real are rounded to the nearest representable Integer, with
       ties being rounded to the nearest even number.  Invalid floating
       point values (NaNs) are converted to the Integer 0.

   String  The string is first converted to type Real, see Section 2.3.
       Then the resulting Real is converted to Integer as specified
       above.

2.1.4.  Real

   Data of type contain signed floating precision numeric values from
   the range available with IEEE 754-1985 64-bit double precision
   values, as well as the special non-numeric values (NaNs and Infs)
   available with that format.  The default value for Real is zero
   (0.0).

   Conversions:

   Boolean  The value true is converted to the floating point value 1.0.
       The value false is converted to the floating point value 0.0.

   Integer  Integers promoted to floating point values are converted to
       the nearest representable number.

   String  See Section 2.3.

2.1.5.  String

   Data of type String contain a sequence of zero or more Unicode code
   points.  The default value for String is a sequence of zero code
   points, the empty string ("").



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   The characters are restricted to the following code points:

      U+0009, U+000A, U+000D

      U+0020 through U+D7FF

      U+E000 through U+FFFD

      U+10000 through U+10FFFF

   Strings may be normalized during transport, storage or processing.
   When an implementation does normalize, it should use Normalization
   Form C (NFC) described in Unicode Standard Annex #15 [TR15].  Line
   endings may be normalized to U+000A.

   Conversions:

   Boolean  The value true is represented as the string "true".  The
       value false is represented as the empty string ("").

   Integer  Integers converted to Strings are represented as signed
       decimal representation.

   Real  See Section 2.3.

   UUID  UUIDs converted to Strings are represented in the 36 character,
       8-4-4-4-12 format defined in RFC 4122 [RFC4122].

   Date  See Section 2.4.

   URI URIs converted to Strings are simply Unicode representations of
       the URI.

2.1.6.  UUID (Universally Unique ID)

   UUIDs represent a universally unique identifier.  Data of type UUID
   is a 128 bit identifier with a structure defined in RFC 4122
   [RFC4122].  The default UUID value is the null UUID, (00000000-0000-
   0000-0000-000000000000).

   Conversions:

   String  A valid 8-4-4-4-12 string representation of a UUID is
       converted to the UUID it represents.  All other values are
       converted to the null UUID (00000000-0000-0000-0000-
       000000000000).





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2.1.7.  Date

   Dates represent a moment in time.  Data of type Date may have the
   value of any time in the from January 1, 1970 though at least January
   1, 2038, to at least second accuracy.  The default date is defined as
   the beginning of the Unix(tm) epoch, midnight, January 1, 1970 in the
   UTC time zone.

   Conversions:

   String  See Section 2.4.

2.1.8.  URI (Uniform Resource Identifier)

   Data of type URI has the value of a Uniform Resource Identifier as
   defined in RFC 3986 [RFC3986].  The default URI is an empty URI

   Conversions:

   String  The characters of the String data are interpreted as a URI,
       if legal.  Other Strings results in the default URI.

2.1.9.  Binary

   Data of type Binary contains a sequence of zero or more octets.  The
   default Binary is a sequence of zero octets.

   There are no defined conversions for Binary.

2.2.  Composite Types

   LLSD values can be composed of other LLSD values in two ways: Arrays
   or Maps.  In either case, the values with the composite can be any
   heterogeneous mix of other LLSD types, both simple and composite.

2.2.1.  Array

   An Array is an ordered collection of zero or more values.  The values
   are considered consecutive, with no gaps.  The value undef (of type
   Undefined) may be used to indicate, within an Array, an intentionally
   left out value.

   Arrays are considered to have a definite length, including any
   leading or trailing undef values in the sequence.  This length can be
   viewed by an application.  Accessing beyond the end of an array acts
   as if the value undef were stored at the accessed location.
   Nonetheless, systems that transmit or store Arrays SHOULD NOT add or
   remove undef values at the end of an Array value, so as to make a



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   best effort to retain the definite length as originally created.

2.2.2.  Map

   A Map is an unordered collection of associations between keys and
   values.  Within a given Map value, each key must be unique, each with
   one value.  Keys are String values.  The associated values can be of
   any LLSD type.

   Maps are considered to have a definite set of keys, including keys
   whose associated value is undef.  The number of such keys, and set of
   keys can be accessed by an application.  Accessing a value for a key
   that is not in a Map value's key set acts as if the value under were
   stored at that key.  Nontheless, systems that transmite or store Maps
   SHOULD NOT add or remove keys associated with undef to a Map value,
   so as to make a best effort to retain the key set as originally
   coreated.

   Note on key equality: Two keys are considered equal if they contain
   the same number and sequence of Unicode codepoints.  Since keys are
   String values, and String values may be normalized on transport or
   storage, it follows that only String values that are already
   normalized as allowed by the String type are reliable as Map keys.
   Since the Maps are intended to be primarily used with keys set forth
   in protocol descriptions, this not a particular problem.  However, if
   arbitray user supplied data is to be used as key values in some
   application, then the possibility of normalization and perhaps key
   collision during transport must be considered.

2.3.  Converting Between Real and String Types

   Real values are represented using the ABNF provided in Appendix A

2.4.  Converting Between Date and String Types

   The textual representation of Date values is based on ISO 8601
   [ISO8601], and further specified in RFC 3339 [RFC3339].  When Date
   values are converted to or from String values, the character sequence
   of the string must conform to the following production based on the
   ABNF in RFC 3339 [RFC3339]:
   full-date "T" partial-time "Z"
   When converting from String values, if the sequence of characters
   does not exactly match this production, then the result is the
   default Date value.







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3.  Serialization

   When used as part of a protocol, LLSD is serialized into a common
   form.  Three serialization schemes are currently defined: XML, JSON
   and Binary.

3.1.  XML Serialization

   XML serialization of LLSD data is in common use in protocols
   implementing virtual worlds.  When used to communicate protocol data
   with a transport that requires the use of a Type, the type
   'application/llsd+xml' is used.

   When serializing an instance of LLSD structured data into an XML
   document, the DTD given in Appendix B is used.  This DTD defines
   elements for each of the defined LLSD types.  Immediately subordinate
   to the root LLSD element, XML documents representing LLSD serialized
   data include either a single instance of an simple type (Undefined,
   Boolean, Integer, Real, UUID, String, Date, URI or Binary) or a
   single composite type (Array or Map).

3.1.1.  Serializing Simple Types

   Most simple types are serialized by placing the string representation
   of the data between beginning and ending tags associated with the
   value's type.  This is true for undefined, boolean, integer, real,
   UUID, string, date and URI typed values.  Values of type binary are
   serialized by placing the BASE64 encoding (defined in RFC 4648
   [RFC4648] ) of the binary data within beginning and ending 'binary'
   tags.  It is expected that future versions of this specification may
   allow encodings other than BASE64, so the mandatory attribute
   'encoding' is used to identify the method used to encode the binary
   data.

   The following example shows an XML document representing the
   serialization of the integer -559038737.

   <?xml version="1.0" encoding="UTF-8"?>
   <llsd>
     <integer>-559038737</integer>
   </llsd>










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   While this example shows the serialization of a binary array of
   octets containing the values 222, 173, 190 and 239.

   <?xml version="1.0" encoding="UTF-8"?>
   <llsd>
     <binary encoding="base64">3q2+7w==</binary>
   </llsd>

3.1.2.  Serializing Composite Types

   Composite types in the XML serialization scheme are represented with
   'array' and 'map' elements.  Both of these elements may contain
   elements enclosing simple types or other composite types.  Array
   elements, which represent a collection of values indexed by position,
   contain a simple list of typed values.  Map elements represent a
   collection of values indexed by a string identifier.  They contain a
   list of key-value pairs where the 'key' element describes the
   indexing identifier while the value (which follows the 'key' element)
   is its XML representation.

   Note that elements of an array may be of differing types.  Also note
   that composite types may contain other composite types; it is not an
   error for an array or map to contain another array, map or simple
   type.

3.1.3.  Example of XML LLSD Serialization

   This example shows the XML serialization of an array which contains
   an integer, a UUID and a map.

<?xml version="1.0" encoding="UTF-8"?>
<llsd>
 <array>
  <integer>42</integer>
  <uuid>6bad258e-06f0-4a87-a659-493117c9c162</uuid>
  <map>
   <key>hot</key>
   <string>cold</string>
   <key>higgs_boson_rest_mass</key>
   <undef/>
   <key>info_page</key>
   <uri>https://example.org/r/6bad258e-06f0-4a87-a659-493117c9c162</uri>
   <key>status_report_due_by</key>
   <date>2008-10-13T19:00.00Z</date>
  </map>
 </array>
</llsd>




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3.2.  JSON Serialization

   LLSD may also be serialized using the JSON [RFC4627] subset of the
   JavaScript programming language.  When serializing LLSD data using
   JSON, the 'application/llsd+json' media type is used.  This
   specification REQUIRES that LLSD data serialized into a JSON document
   use UTF-8 character encoding.  To allow the serialization of non-
   composite elements, this specification defines the contents of a
   JSON-serialized LLSD message in terms of the 'value' non-terminal
   from RFC 4627 instead of the commonly used 'JSON-text' non-terminal.

   The following table lists type conversions between LLSD and JSON:

   Undefined  LLSD 'Undefined' values are represented by the JSON
       terminal 'null'.

   Boolean  LLSD 'Boolean' values are represented by the JSON terminals
       'true' and 'false'.

   Integer  LLSD 'Integer' values are represented by the JSON non-
       terminal 'number'.

   Real  LLSD 'Real' values are represented by the JSON non-terminal
       'number'.

   String  LLSD 'String' values are represented by the JSON 'string'
       non-terminal.  Note that this specification inherits JSON's
       behavior of requiring control characters, reverse solidus and
       quotation mark characters to be escaped.

   UUID  LLSD 'UUID' values are represented by a JSON string, and are
       rendered in the common 8-4-4-4-12 format defined by the 'UUID'
       non-terminal in RFC 4122 [RFC4122].

   Date  LLSD 'Date' values are represented by the JSON 'string' non-
       terminal, the contents of which is a valid ISO 8601 value with
       years, months, days, hours, seconds and time zone indicator.

   URI LLSD 'URI' values are represented by the JSON 'string' non-
       terminal, the contents of which is a valid URI as defined by RFC
       3986 [RFC3986].

   Binary  LLSD 'Binary' values are represented as a JSON 'array'.  That
       is, they follow the RFC 4627 [RFC4627] 'array' non-terminal whose
       members are integer numbers representing each octet of the binary
       array.





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   Array  LLSD 'Array' values are represented by the JSON 'array' non-
       terminal.

   Map LLSD 'Map' values are represented by the JSON 'object' non-
       terminal.  Each key-value pair of the map is represented by the
       JSON 'member' non-terminal where the LLSD map key is the 'string'
       prior to the 'name-separator' terminal and the LLSD map value is
       the 'value' after the 'name-separator' terminal.

   LLSD defines additional types over those defined by JSON.  The LLSD
   types UUID, Date and URI are serialized as JSON strings whose
   contents are generated using the <Type> to String converstion defined
   in Abstract Type System section above.

3.2.1.  Examples of JSON LLSD Serialization

   Example 1.  The following example shows the JSON encoding of the
   integer 42.  Note that while this serialization does not conform to
   the 'JSON-text' non-terminal defined in RFC 4627, it does conform to
   the 'value' non-literal.

   42

   Example 2.  The following example shows the JSON encoding of the
   example given in the section above on XML serialization
   (Section 3.1.2).

   [
    42,
    "6bad258e-06f0-4a87-a659-493117c9c162",
    {
     "hot": "cold",
     "higgs_boson_rest_mass": null,
     "info_page":
       "https://example.org/r/6bad258e-06f0-4a87-a659-493117c9c162",
     "status_report_due_by": "2008-10-13T19:00.00Z"
    }
   ]

3.3.  Binary Serialization

   The LLSD Binary Serialization is an encoding syntax appropriate for
   situations where high message entropy is required or limiting
   processing power for parsing messages is available.

   Encoding LLSD structured data using the binary serialization scheme
   involves generating tag, (optional) size values, and serialization of
   simple values.  Composite types are serialized by iterating across



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   all members of the collection, serializing each simple or composite
   member in turn.  For each element in an LLSD structured data object,
   the following process is used to generate a binary output stream of
   serialized data:

   o  A one octet type tag is emitted to the output stream.  See the
      table below for tag octets.

   o  If the size of the element being serialized is variable (as it
      will be for strings, URIs, arrays and maps), the size or length of
      the element is output to the stream as a network-order 32 bit
      value.  Elements of types with fixed lengths such as undefined
      values, booleans, integers, reals, uuids and dates will not
      include size information in the output stream.

   o  Finally, the binary representation of the element is appended to
      the output stream.

   Undefined  Undefined values are serialized with a single exclamation
       point character ('!').  Undefined values append neither size
       information or data to the output stream.

   Boolean  True values are serialized with a single '1' character.
       False values are serialized with a single '0' character.
       Booleans append neither size information or data to the output
       stream.

   Integer  Integer values are serialized by emitting the 'i' character
       to the output stream followed by the four octets representing the
       integer's 32 bits in network order.

   Real  Real values are serialized by emitting the 'r' character to the
       output stream followed by the eight octets representing the real
       value's 64 bits in network order.

   String  String values are serialized by emitting the 's' character to
       the output stream followed by the string's length in octets
       represented as a network-order 32 bit integer, followed by the
       string's UTF-8 encoding.

   UUID  UUID values are serialized by emitting the 'u' character to the
       output stream followed by the sixteen octets representing the
       UUID's 128 bits, with the most significant byte coming first.

   Date  Date values are serialized by emitting the 'd' character to the
       output stream followed by the number of seconds since the start
       of the epoch, represented as a 64-bit real value.




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   URI URI values are serialized by emitting the 'l' character to the
       output stream followed by the uri's length in octets represented
       as a network-order 32 bit integer, followed by the binary
       representation of the URI.

   Binary  Binary values are serialized by emitting the 'b' character to
       the output stream followed by the binary array's length in octets
       represented as a network-order 32 bit integer, followed by the
       octets of the binary array.

   Array  Arrays are serialized by emitting the left square bracket
       ('[') character, followed by the count of objects in the array
       represented as a network-order 32 bit integer, followed by each
       array element in order.  Note that compliant implementations MUST
       preserve the order of array elements.

   Map Maps are serialized by emitting the left curly brace ('{')
       character, followed by the count of objects in the map
       represented as a network-order 32 bit integer, followed by each
       key-value element.  Map keys are represented as strings except
       that they use the character 'k' instead of the character 's' as a
       tag.  Note that preserving the order of maps is not REQUIRED.

3.3.1.  Example of BINARY LLSD Serialization



























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   The LLSD object given as an example in the section above on XML
   serialization (Section 3.1.2) would look as follows would it have
   been serialized using the binary scheme.  The following example
   encodes octets as hexadecimal values.















































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    Offset   Hex Data                  Char Data
   -------- ------------------------- -----------
   00000000  5B                       '['
   00000001  00 00 00 03              '....'
   00000005  69                       'i'
   00000006  00 00 00 2A              '...*'
   0000000A  75                       'u'
   0000000B  6B AD 25 8E 06 F0 4A 87  'k.%...J.'
   00000013  A6 59 49 31 17 C9 C1 62  '.YI1...b'
   0000001B  7B                       '{'
   0000001C  00 00 00 04              '....'
   00000020  6B                       'k'
   00000021  00 00 00 03              '....'
   00000025  68 6F 74                 'hot'
   00000028  73                       's'
   00000029  00 00 00 04              '....'
   0000002D  63 6F 6C 64              'cold'
   00000031  6B                       'k'
   00000032  00 00 00 13              '....'
   00000036  68 69 67 67 73 5F 62 6F  'higgs_bo'
   0000003E  73 6F 6E 5F 72 65 73 74  'son_rest'
   00000046  5f 6d 61 73 73           '_mass'
   0000004B  21                       '!'
   0000004C  68                       'k'
   0000004D  00 00 00 09              '....'
   00000051  69 6E 66 6F 5F 70 61 67  'info_pag'
   00000059  65                       'e'
   0000005A  6C                       'l'
   0000005B  00 00 00 3A              '...:'
   0000005F  68 74 74 70 73 3A 2f 2F  'https://'
   00000067  65 78 61 6D 70 6C 65 2E  'example.'
   0000006F  6F 72 67 2F 72 2F 36 62  'org/r/6b'
   00000077  61 64 32 35 38 65 2D 30  'ad258e-0'
   0000007F  36 66 30 2D 34 61 38 37  '6f0-4a87'
   00000087  2D 61 36 35 39 2D 34 39  '-a659-49'
   0000008F  33 31 31 37 63 39 63 31  '3117c9c1'
   00000097  36 32                    '62'
   00000099  68                       'k'
   0000009A  00 00 00 14              '....'
   0000009E  73 74 61 74 75 73 5F 72  'status_r'
   000000A7  65 70 6F 72 74 5F 64 75  'eport_du'
   000000AF  65 5F 62 79              'e_by'
   000000B3  00 00 00 08              '....'
   000000B7  64                       'd'
   000000B8  41 D2 3C E6 AC 00 00 00  'A.<.....'






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4.  Interface Description Language

   The Linden Lab Interface Description Language (LLIDL) is the used to
   describe a RESTful interface to remote resources.  LLIDL
   unambiguously defines interfaces independent of serialization
   schemes.  Rather than defining independent XML, JSON and Binary
   interfaces, resource interfaces are described in terms of in terms of
   LLIDL.  Network entities generating or parsing LLSD messages may use
   the LLIDL interface descriptions to mechanically generate
   serialization specific software to manipulate LLSD data.  Despite the
   emphasis on automated parsing, LLIDL has been designed as BOTH human
   and machine readable.

4.1.  Abstract Data Types and Names

   LLIDL describes data structures in terms of name-type pairs.  LLIDL
   data structure members are defined by providing the member name, a
   colon and an simple LLSD type:
    name : simple_type

4.2.  Abstract Data Structures

   Data structures may be composed using arrays and maps.  Arrays are
   collections of members, accessed with numeric indices.  Simple array
   descriptions are described in LLIDL using the open brace character
   ('['), one or more simple LLSD types, and a close brace character
   (']').  Maps are collections of members, accessed by string keys.
   Map descriptions begin with an open curly brace character ('{'), on
   or more name-type pairs and a close curly brace character ('}').
   Name-Type pairs in map descriptions are separated by commas (',').
   The first example below defines an array with three real values.  The
   second defines a map with two string members whose names are
   'first_name' and 'last_name'.

   [ real, real, real ]

   { first_name: string, last_name: string }

   The form above defines only fixed-length arrays.  To define an array
   of arbitrary length, the ellipsis ("...") is used.  The following
   example defines a list of one or more string values.

   [ string ... ]








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   Using an ellipsis in an array definition with more than one member
   describes an arbitrary length array whose members' types are defined
   by the listed type, each in turn.  In the first example below, the
   first element of the array is an integer while the second is a
   string.  If there are more than two elements in the array, even
   elements (assuming that array indexes begin with zero (0) ) will be
   integers while odd elements will be strings.  Also note that such an
   array will always contain an even number of members.  In the second
   example, the first element would be a string, the second would be a
   UUID and the third would be a floating point value.  If the array
   contained more than three elements, starting from the beginning,
   every third element would be a string; the next would be a UUID while
   the one following would be a real.  An array defined in the second
   example would always be an multiple of three.

   [ integer, string ... ]

   [ string, uuid, real ... ]

4.3.  Variant Data Structures

   It is often advantageous to represent several different variants of a
   message.  LLIDL defines variants with repeated assignments to the
   same variant name.  In the example below, two variants are defined,
   the first with two strings, and the second with a number and a
   string.

   &exception = {
     class       : string ,
     description : string
   }

   &exception = {
     class       : int ,
     description : string
   }















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4.4.  Variant Discriminators

   In the example above, two variants of a structure differ by the type
   defined for the "class" structure member.  Because it is possible for
   name-value pairs to be absent from the serialization of an LLIDL
   object, it is often useful to use boolean or string literals to
   distinguish variants of an object.  In the example below the success
   member is used to identify which variant is being used.  When
   serialized, if the value associated with the success member was true,
   a compliant parser would know it was not an encoding error for the
   err_num member to not be present.  In other words, it signals that
   the second variant is in use.

   &response = {
     success     : false ,
     description : string ,
     err_num     : integer
   }

   &response = {
     success     : true,
     description : string
   }

4.5.  Resource Description

   Defining interfaces is the underlying purpose of LLIDL.  Each
   interface has a name, an input definition and an output definition.
   They are specified using the following format:

   %% resource name -> request <- response


5.  IANA Considerations

   In accordance with [RFC5226], this document registers the following
   mime types:

       application/llsd+xml

       application/llsd+json

       application/llsd+binary

   See the MIME Type Registrations section (Section 6) below for
   detailed information on MIME Type registrations.





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6.  MIME Type Registrations

   This section provides media-type registration applications (as per
   RFC 4288 [RFC4288].)

6.1.  MIME Type Registration for application/llsd+xml

   To: ietf-types@iana.org

   Subject: Registration of media type application/llsd+xml

   Type name: application

   Subtype name: llsd+xml

   Required Parameters: none

   Optional Parameters: none

   Encoding Considerations:  The Extensible Markup Language (XML)
       specification allows for the use of multiple character sets.  The
       character set used to encode the body of the message is defined
       as part of the XML header.  If no character set is indicated in
       the XML header, compliant systems MUST assume UTF-8.

   Security Considerations:  LLSD XML serialized data contains "plain"
       text and generally poses no immediate risk to system security of
       either the sender or the receiver.  Still, it is possible for a
       malicious adversary to include arbitrary binary data in an
       attempt to exploit specific vulnerabilities (if they exist.)  It
       is the obligation of the receiver of LLSD XML serialized messages
       to ensure such vulnerabilities are mitigated in a timely fashion.

       If sensitive information is to be encoded into a LLSD XML
       serialized message, it is the responsibility of the transport,
       network or link layers to ensure the confidentiality, message
       integrity and origin integrity of the message.

   Interoperability Considerations:  While it is possible for compliant
       implementations to specify the use of character sets other than
       UTF-8, such systems MUST accept UTF-8 input and SHOULD generate
       UTF-8 output.

   Published specification:  Linden Lab Structured Data (LLSD) is
       defined in the internet draft draft-hamrick-llsd-01
       [I-D.hamrick-llsd].





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   Applications that use this media type:  Virtual world, tele-presence
       and content management systems related to "virtual reality"
       systems.

   Additional Information:

       Magic Number(s): none

       File Extension: lsdx

       Macintosh File Type Code(s): TEXT

   Person & email address to contact for further information:  Meadhbh
       Hamrick <infinity@lindenlab.com>

   Intended Usage: COMMON

   Author: IESG

   Change Controller: IESG

6.2.  MIME Type Registration for application/llsd+json

   To: ietf-types@iana.org

   Subject: Registration of media type application/llsd+json

   Type name: application

   Subtype name: llsd+json

   Required Parameters: none

   Optional Parameters: none

   Encoding Considerations: Use of UTF-8 is Mandatory  RFC 4627 : The
       application/json Media Type for JavaScript Object Notation (JSON)
       [RFC4627] allows the use of UTF-8, UTF-16 and UTF-32.  This
       specification REQUIRES the use of UTF-8.

   Security Considerations:  Like the application/json media type
       defined in RFC 4627 [RFC4627], the contents of messages
       identified with this media type are expected to be passed into
       ECMAScript's 'eval()' function.  RFC 4627 provides a regular
       expression to ensure that only "safe" characters (i.e. -
       characters used to describe JSON tokens) are included outside
       string literal definitions.  Users of the application/llsd+json
       media type are strongly encouraged to use this (or similar) tests



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       to ensure message safety.

       If sensitive information is to be encoded into a LLSD JSON
       serialized message, it is the responsibility of the transport,
       network or link layers to ensure the confidentiality, message
       integrity and origin integrity of the message.

   Interoperability Considerations:  Note that unlike RFC 4627, this
       specification REQUIRES the use of UTF-8.

   Published specification: This specification.

   Applications that use this media type:  Virtual world, tele-presence
       and content management systems related to "virtual reality"
       systems.

   Additional Information:

       Magic Number(s): none

       File Extension: lsdj

       Macintosh File Type Code(s): TEXT

   Person & email address to contact for further information:  Meadhbh
       Hamrick <infinity@lindenlab.com>

   Intended Usage: COMMON

   Author: IESG

   Change Controller: IESG

6.3.  MIME Type Registration for application/llsd+binary

   To: ietf-types@iana.org

   Subject: Registration of media type application/llsd+binary

   Type name: application

   Subtype name: llsd+binary

   Required Parameters: none







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   Optional Parameters: none

   Encoding Considerations: LLSD Binary Serialization REQUIRES the use
   of binary content-transfer-encoding  Section 5 of RFC 2045 [RFC2045]
       describes the binary Content-Transfer-Encoding header field.
       This specification REQUIRES the use of this header to alert
       intermediary systems that information being included in the
       message should be interpreted as binary data with no end-of-line
       semantics which could be considerably longer than allowed in an
       RFC 821 transport.

   Security Considerations:  This serialization format defines the use
       of tagged binary fields with embedded length information.  In the
       past, similar binary encoding systems have fallen prey to
       exploits when parsing implementations fail to check for non-
       sensical lengths.  Implementers are therefore strongly encouraged
       to consider all failure modes of such a system.

       If sensitive information is to be encoded into a LLSD JSON
       serialized message, it is the responsibility of the transport,
       network or link layers to ensure the confidentiality, message
       integrity and origin integrity of the message.

   Interoperability Considerations: none

   Published specification:  Linden Lab Structured Data (LLSD) is
       defined in the internet draft draft-hamrick-llsd-01
       [I-D.hamrick-llsd].

   Applications that use this media type:  Virtual world, tele-presence
       and content management systems related to "virtual reality"
       systems.

   Additional Information:

       Magic Number(s): none

       File Extension: lsdb

       Macintosh File Type Code(s): LSDB

   Person & email address to contact for further information:  Meadhbh
       Hamrick <infinity@lindenlab.com>

   Intended Usage: COMMON






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   Author: IESG

   Change Controller: IESG


7.  Security Considerations

   Security considerations for this specification are, fortunately,
   either simple or beyond the scope of this document.  RFC 3552
   [RFC3552] describes several aspects to use when evaluating the
   security of a specification or implementation.  We believe most
   common security concerns users of this specification will encounter
   are more appropriately considered as transport, network or link layer
   issues.  Or, as higher level "application security" issues.

   This document specifies the content, media type identifiers and
   content encoding requirements for LLSD.  It does not specify
   mechanisms to transmit LLSD messages between network peers.  We
   believe that many communication security considerations such as
   confidentiality, data integrity and peer entity authentication are
   more appropriately the domain of message, transport, network or link
   layer protocols.  Users of this protocol should seriously consider
   the use Secure MIME, Transport Layer Security (TLS), IPSec or related
   technologies.


8.  References

8.1.  Normative References

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3339]  Klyne, G., Ed. and C. Newman, "Date and Time on the
              Internet: Timestamps", RFC 3339, July 2002.

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

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              July 2005.




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   [RFC4288]  Freed, N. and J. Klensin, "Media Type Specifications and
              Registration Procedures", BCP 13, RFC 4288, December 2005.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [TR15]     Davis, M. and M. Durst, "Unicode Standard Annex #15 :
              UNICODE NORMALIZATION FORMS", 2008,
              <http://unicode.org/reports/tr15/>.

   [XML2006]  Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and
              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fourth
              Edition)", 2006.

8.2.  Informative References

   [I-D.hamrick-llsd]
              Brashears, A., Hamrick, M., and M. Lentczner, "Linden Lab
              Structured Data", 2008.

   [ISO8601]  "ISO 8601 - Date and Time Formats".

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              July 2003.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.
















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Appendix A.  ABNF of Real Values

   The following is the Augmented Backus-Naur Form (ABNF) of valid Real
   values for the purposes of converting strings into real values.  ABNF
   is described in RFC 5234 [RFC5234].
   real              =  zero
   real              =/ negative-infinity
   real              =/ negative-zero
   real              =/ positive-zero
   real              =/ positive-infinity
   real              =/ signaling-nan
   real              =/ quiet-nan
   real              =/ realnumber

   negative-infinity =  %x2D.49.6E.66.69,6E.69.74.79   ; "-Infinity"
   negative-zero     =  %x2D.5A.65.72.6F               ; "-Zero"
   zero              =  %x30.2E.30                     ; "0.0"
   positive-zero     =  %x2B.5A.65.72.6F               ; "+Zero"
   positive-infinity =  %x2B.49.6E.66.69,6E.69.74.79   ; "+Infinity"
   signaling-nan       =  %4E.61.4E.53                   ; "NaNS"
   quiet-nan         =  %4E.61.4E.51                   ; "NaNQ"

   realnumber        =  mantissa exponent

   mantissa          =  ( positive-number [ "." *decimal-digit ])
   mantissa          =/ ( "0." *("0") positive-number )

   exponent          =  "E" ( "0" / ( [ "-" ] positive-number ) )

   positive-number   =  non-zero-digit *decimal-digit

   decimal-digit       =  %x30-39
   non-zero-digit    =  %x31-39


















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Appendix B.  XML Serialization DTD

   The following Document Type Definition (DTD) describes the format of
   LLSD XML Serialization.  DTDs are described in the Extensible Markup
   Language (XML) 1.0 (Fourth Edition) [XML2006] specification.

   <!DOCTYPE llsd [
   <!ELEMENT llsd (DATA)>
   <!ELEMENT DATA (SIMPLE|map|array)>
   <!ELEMENT
     SIMPLE (undef|boolean|integer|real|uuid|string|date|uri|binary)>
   <!ELEMENT KEYDATA (key,DATA)>
   <!ELEMENT key (#PCDATA)>
   <!ELEMENT map (KEYDATA*)>
   <!ELEMENT array (DATA*)>
   <!ELEMENT undef (EMPTY)>
   <!ELEMENT boolean (#PCDATA)>
   <!ELEMENT integer (#PCDATA)>
   <!ELEMENT real (#PCDATA)>
   <!ELEMENT uuid (#PCDATA)>
   <!ELEMENT string (#PCDATA)>
   <!ELEMENT date (#PCDATA)>
   <!ELEMENT uri (#PCDATA)>
   <!ELEMENT binary (#PCDATA)>

   <!ATTLIST string xml:space (default|preserve) 'preserve'>
   <!ATTLIST binary encoding CDATA "base64">
   ]>


Appendix C.  ABNF of LLIDL

   The following is the Augmented Backus-Naur Form (ABNF) of the Linden
   Lab Interface Description Language (LLIDL).  ABNF is described in RFC
   5234 [RFC5234].


   value           =  type / array / map / selector / variant

   type            =  "undef"
   type            =/ "string"
   type            =/ "bool"
   type            =/ "int"
   type            =/ "real"
   type            =/ "date"
   type            =/ "uri"
   type            =/ "uuid"
   type            =/ "binary"



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   array           =  "[" s value-list s "]"
   array           =/ "[" s value-list s "..." s "]"

   map             =  "{" s member-list s "}"
   map             =/ "{" s "$" s ":" s value s "}"

   value-list      = value [ s "," [ s value-list ] ]

   member-list     = member [ s "," [ s member-list ] ]
   member          = name s ":" s value

   selector        =  quote name quote
   selector        =/ "true" / "false"
   selector        =/ 1*digit

   variant         = "&" name


   definitions     = *( s / variant-def / resource-def )

   variant-def     = "&" name s "=" s value

   resource-def    = res-name s res-request s res-response
   res-name        = "%%" s name
   res-request     = "->" s value
   res-response    = "<-" s value


   s               = *( tab / newline / sp / comment )
   comment         = ";" *char newline
   newline         = lf / cr / (cr lf)

   tab             = %x0009
   lf              = %x000A
   cr              = %x000D
   sp              = %x0020
   quote           = %x0022
   digit           = %x0030-0039
   char            = %x09 / %x20-D7FF / %xE000-FFFD / %x10000-10FFFF

   name            = name_start *name_continue
   name_start      = id_start    / "_"
   name_continue   = id_continue / "_" / "/"
   id_start        = %x0041-005A / %x0061-007A ; ALPHA
   id_continue     = id_start / %x0030-0039    ; DIGIT






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Authors' Addresses

   Aaron Brashears
   Linden Research, Inc.
   945 Battery St.
   San Francisco, CA  94111
   US

   Phone: +1 415 243 9000
   Email: aaronb@lindenlab.com


   Meadhbh Siobhan Hamrick (editor)
   Linden Research, Inc.
   945 Battery St.
   San Francisco, CA  94111
   US

   Phone: +1 650 283 0344
   Email: infinity@lindenlab.com


   Mark Lentczner
   Linden Research, Inc.
   945 Battery St.
   San Francisco, CA  94111
   US

   Phone: +1 415 243 9000
   Email: zero@lindenlab.com





















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