Virtual World Region Agent A. Brashears
Protocol M. Hamrick
Internet-Draft M. Lentczner
Intended status: Standards Track July 5, 2010
Expires: January 6, 2011
VWRAP : Abstract Type System for the Transmission of Dynamic Structured
Data
draft-ietf-vwrap-type-system-00
Abstract
This document describes the LLIDL interface description language, the
related LLSD abstract type system and three serialization formats for
LLIDL messages. LLIDL (pronounced "little") is a language-neutral
facility for describing transport independent message flows for
RESTful resource access. LLIDL itself is an abstract meta-grammar
for producing and recognizing valid request / response messages
affecting state change in application layer objects by way of RESTful
resource access. It may be used by protocol developers and system
deployers to describe the composition of application layer protocol
exchanges without adopting transport specific message semantics or
programming language specific type semantics. The type behavior of
individual message elements is described by the LLSD abstract type
system. Abstract LLIDL messages are concretized using one of three
defined LLSD serialization schemes. Serialization / deserialization
rules are provided in this document for XML, JSON and Binary schemes.
This abstract messaging and type system is intended to be used by
other specifications to describe application layer protocol
exchanges, independent of implementation language or message
transport protocol.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on January 6, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 6
2. The LLSD Abstract Type System . . . . . . . . . . . . . . . . 6
2.1. Simple Types . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.1. Undefined . . . . . . . . . . . . . . . . . . . . . . 7
2.1.2. Boolean . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.3. Integer . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.4. Real . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.5. String . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.6. UUID (Universally Unique ID) . . . . . . . . . . . . . 9
2.1.7. Date . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.8. URI (Uniform Resource Identifier) . . . . . . . . . . 9
2.1.9. Binary . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2. Composite Types . . . . . . . . . . . . . . . . . . . . . 10
2.2.1. Array . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.2. Map . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3. Converting Between Real and String Types . . . . . . . . . 11
2.4. Converting Between Date and String Types . . . . . . . . . 11
3. The LLIDL Interface Description Language . . . . . . . . . . . 11
3.1. Interfaces and Resources . . . . . . . . . . . . . . . . . 11
3.2. Simple Types . . . . . . . . . . . . . . . . . . . . . . . 12
3.3. Composite Types . . . . . . . . . . . . . . . . . . . . . 12
3.3.1. Arrays . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3.2. Maps . . . . . . . . . . . . . . . . . . . . . . . . . 13
3.4. Named Types . . . . . . . . . . . . . . . . . . . . . . . 14
3.5. Variant Type Definitions . . . . . . . . . . . . . . . . . 15
4. Serialization . . . . . . . . . . . . . . . . . . . . . . . . 16
4.1. XML Serialization . . . . . . . . . . . . . . . . . . . . 16
4.1.1. Serializing Simple Types . . . . . . . . . . . . . . . 17
4.1.2. Serializing Composite Types . . . . . . . . . . . . . 17
4.1.3. Example of XML LLSD Serialization . . . . . . . . . . 18
4.2. JSON Serialization . . . . . . . . . . . . . . . . . . . . 18
4.2.1. Examples of JSON LLSD Serialization . . . . . . . . . 20
4.3. Binary Serialization . . . . . . . . . . . . . . . . . . . 20
4.3.1. Example of BINARY LLSD Serialization . . . . . . . . . 22
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
6. MIME Type Registrations . . . . . . . . . . . . . . . . . . . 25
6.1. MIME Type Registration for application/llidl . . . . . . . 25
6.2. MIME Type Registration for application/llsd+xml . . . . . 26
6.3. MIME Type Registration for application/llsd+json . . . . . 28
6.4. MIME Type Registration for application/llsd+binary . . . . 29
7. Security Considerations . . . . . . . . . . . . . . . . . . . 30
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
8.1. Normative References . . . . . . . . . . . . . . . . . . . 31
8.2. Informative References . . . . . . . . . . . . . . . . . . 32
Appendix A. ABNF of Real Values . . . . . . . . . . . . . . . . . 33
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Appendix B. XML Serialization DTD . . . . . . . . . . . . . . . . 34
Appendix C. ABNF of LLIDL . . . . . . . . . . . . . . . . . . . . 34
Appendix D. Glossary . . . . . . . . . . . . . . . . . . . . . . 36
Appendix E. Acknowledgements . . . . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39
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1. Introduction
It is characteristic of modern network services that they are
deployed across multiple network hosts. For performance, fault
tolerance, ease of deployment or organizational reasons, software and
systems implementing network services must now work well in a
distributed environment. It is generally believed that such
distributed services may be made more robust by making their
components "loosely coupled."[Kaye2003] This document describes an
interface description language and a related abstract type system
used to define interfaces to loosely coupled network services in a
programming language, network transport and message serialization
independent manner.
The LLIDL interface description language may be used to define
protocol exchanges for accessing resources exhibiting characteristics
of the Representational State Transfer (REST) architecture style.
[Fielding2000] LLIDL describes abstract interfaces intended to be
reified over HTTP [RFC2616] or HTTPS [RFC2817]. LLIDL resource
definitions describe the structure of data provided in an access
request, the structure of the data in the access' response and the
HTTP verbs which may be used to access the resource.
The LLSD abstract type system defines nine simple types (Undefined,
Boolean, Integer, Real, String, UUID, Date, URI and Binary) and two
composite types (Array and Map.) This system provides a programming
language independent framework for describing type semantics of
elements in LLIDL messages. Three serialization schemes are defined
by this document: XML, JSON and Binary. These schemes are used to
concretize LLSD data into octet streams for transmission over a data
network. Each serialization scheme has a related MIME content type
definition, allowing compliant applications to identify the specific
serialization scheme used.
LLIDL and LLSD form an abstract system for reasoning about
application layer exchanges without having to repeatedly reference
the details of the transport used to deliver messages. Other
specifications use LLIDL and LLSD to describe the content of RESTful
resource access. This document describes how resource accesses are
reified as HTTP(S) protocol exchanges. LLIDL is intended to separate
the semantics of application messages from the details of the
protocol that carries them. It gives system deployers a tool for
succinctly defining application layer exchanges.
The LLSD serialization schemes describe how simple and composite
types are converted into an octet stream and provides guidelines for
transmission across a network. It does not describe the
concretization of abstract LLSD messages into programming language
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constructs.
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. The LLSD Abstract Type System
The LLSD abstract type system describes the semantics of data passed
between two network hosts. 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 anticipated 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.
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
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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.
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.
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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 ("").
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:
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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).
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:
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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
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. Nonetheless, systems that transmit 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
created.
Note on key equality: Two keys are considered equal if they contain
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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
arbitrary 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.
3. The LLIDL Interface Description Language
3.1. Interfaces and Resources
A LLIDL "Interface" is comprised conceptually of collection of zero
or more related resources and named type definitions. The LLIDL
grammar defines an "Interface Definition" as being zero or more
comments, named type definitions or resource definitions.
A LLIDL "Resource" represents information or state maintained by a
remote system, accessed via HTTP(S). A "Resource Definition" is the
grammatical construction used to represent a resource. Resources are
partitioned into "method access classes" based on the HTTP verbs used
to access them. Method access classes include: "GET", "GET/PUT",
"GET/PUT/DELETE" and "POST". Method access classes are notated in
the LLIDL grammar using "Method Access Delimeters": "<<" for GET,
"<>" for GET/PUT, "<x>" for GET/PUT/DELETE and POST is notated with
the pair of strings "->" and "<-".
Resource definitions also include a message body defining the
structure of requests and responses. GET, GET/PUT and GET/PUT/DELETE
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resources define a single message body following the method access
delimiter. POST resources define two message bodies. The first
follows the "->" delimiter and represents the request. The second
follows the "<-" delimiter and represents the response.
A single simple type definition or "flat" map may be defined in
conjunction with the resource that describes the contents of
arguments to be placed in the query string of the request. A flat
map is a map containing only simple types (i.e. - it does not contain
arrays or maps.)
A resource definition has the format:
'%%' <resource-name> [ '??' <query-body> ]
<resource-delimeter> <message-body> [ <- <message-body> ]
The resource-name identifies the resource (not the URL at which it is
located.) Resource-names are strings that may contain alphabetic
characters, numbers, the slash character ('/') and the underbar
character ('_').
3.2. Simple Types
LLIDL uses the nine simple types from LLSD to define the type
behavior of scalar elements in a resource. These types are
undefined, boolean, integer, real, string, UUID, URI, date and
binary. They are declared in LLIDL with different identifiers that
are (respectively): undef, bool, int, real, string, uuid, uri, date
and binary. Note that the undefined, boolean and integer types are
declared using a more compact textual description of the type.
3.3. Composite Types
Composite Types are resource elements that contain more than one
value. LLIDL uses the two composite types from LLSD: array and map.
3.3.1. Arrays
Arrays represent a sequence of simple types. Each element in an
array is accessed by an ordinal value. An array declaration begins
with the open bracket character ('[') and ends with the close bracket
character (']'). Within the definition of an array, comma delimited
type declarations describing the type of each element are given.
The format for an array declaration is:
'[' <type> [ ',' <type> ] ... ']'
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The following example declares a five element array whose elements'
types are three integers, a string and a URI:
[ int , int , int , string , uri ]
LLIDL arrays may also be of indeterminate length. The ellipsis
trigraph ("...") appended to the end of a sequence of types in an
array declaration indicates the previously defined sequence of types
is repeated indefinitely.
The following examples describe (first) an arbitrary lengthed array
comprising of strings and (second) an arbitrary lengthed array
comprising of three real values followed by a string:
[ string , ... ]
[ real , real , real , string , ... ]
Note that the ellipsis trigraph indicates that the entire sequence is
repeated, not only the last element.
It is acceptable for an array to contain composite types like arrays
or maps. The following example describes an array whose elements are
an array of three real values and a string:
[ [ real , real , real ] , string, ... ]
3.3.2. Maps
Maps are collections of simple types whose elements are accessed via
alphanumeric strings. Maps declarations begin with the open brace
character ('{') and end with the close brace character ('}'). Within
the map declaration are a sequence of comma delimited map entries.
Map entries are comprised of a map entry name and a map entry type,
separated by a colon character (':'). Map entry names are
alphanumeric strings intended to be indicative of their function in
the resource definition.
The format of a map definition is:
'{' <map-entry-name> ':' <map-entry-type>
[ ',' <map-entry-name> ':' <map-entry-type> ] ... '}'
The following example describes a map with three elements named:
name, position and current_balance. The name entry is declared as a
string, the position entry is declared as an array with a string and
three real values, and the current_balance entry is declared as an
integer.
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{
name : string,
position : [ string , real , real , real ],
current_balance : int
}
As implied by the previous example, it is perfectly acceptable for a
map to contain entries whose types are maps and arrays.
It is also possible to define a map in which map entry names that are
explicitly unknown at the time a resource is defined. For example, a
service may wish to produce or consume a map whose keys come from
user data such as stock ticker symbols, avatar names or the names of
regions in a virtual world. It is impractical to attempt to define
the complete set of possibilities in these cases, so LLIDL allows the
resource developer to specify that map names may come from data known
only at the time the resource is accessed.
The dollar character ('$') is used to specify a map whose entries'
names are determined after the resource is defined and deployed. A
map with "deferred entry names" is one in which this situation
occurs. Such maps are defined with a single entry whose name is the
dollar character and a single type.
The following example shows a map with "deferred entry names" whose
map entry types are all URIs.
{ $ : uri }
At most one deferred entry name specifier (i.e. - one dollar sign) is
allowed in a map. A map defined with a deferred entry name specifier
may contain no other defined entries.
Deferred entry names do not signify that a later specification will
complete the definition of the resource, but that the map's entries'
names cannot be determined before the resource is accessed.
3.4. Named Types
LLIDL defines a named type feature. This feature allows a resource
developer to define a single alphanumeric symbol that represents a
complete type definition. The ampersand ('&') character is used in
both the definition and reference of a named type. To define a named
type, the following format is used:
'&' <named-type-symbol> '=' <named-type-value>
The named type symbol must be a valid alphanumeric symbol consisting
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of upper and lower case letters, numbers, the slash character ('/')
or the underbar ('_'). The named type value must be a valid type
definition.
The following examples are all valid named type definitions:
&example = string
&info = { name : string, id : uuid }
&position = [ real, real, real ]
Named types are referenced using only the ampersand and a symbol.
The following example describes two resources whose response bodies
are defined using a named type:
&error = { errno : int, desc : string, more : uri }
%% session/search -> string <- &error
%% session/continue -> uuid <- &error
3.5. Variant Type Definitions
It may be advantageous for a resource to accept more than one form.
In this case, a variant type definition may be used. Variant type
definitions are defined using the named type feature to define a
named type using the same named type symbol for multiple named type
definitions.
For example, the following resource defines a response with two
forms. The first describes a success condition while the second an
error.
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&request = {
name : string,
secret : binary
}
&response = {
success : true,
session_id : uuid
}
&response = {
success : false,
error : int,
next : uri
}
%% session/establish -> &request <- &response
In this example, the first named type (whose named type symbol is
'request') is a simple named type. It is later used in a resource
definition to represent the contents of a request to the resource.
The second and third named types define a variant. That is, the
named type symbol is used more than once. The 'response' variant
defined in this example indicates that the response from the resource
access will be one of the two 'response' forms.
A "selector" may be used to help determine which variant should be
used. A selector is a literal value included in a map entry that
appears in each variant. In the example above, the map entry named
'success' has two literal values in the two variants in which it is
defined. It is possible to have multiple selectors in a map variant,
and the same literal value may be reused.
4. 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.
4.1. 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
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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).
When encoding binary data using RFC 4648 [RFC4648], characters
outside the base alphabet are explicitly allowable and should be
ignored.
4.1.1. 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>
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>
4.1.2. 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
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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.
4.1.3. 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>
4.2. JSON Serialization
LLSD may also be serialized using the JSON [ECMA262r5] subset of the
JavaScript programming language. When serializing LLSD data using
JSON, the 'application/llsd+json' media type is used. The grammar of
LLSD objects serialized using the JSON serialization MUST conform to
the JSONText production.
The following table lists type conversions between LLSD and JSON:
Undefined LLSD 'Undefined' values are represented by the JSON non-
terminal 'JSONNullLiteral'.
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Boolean LLSD 'Boolean' values are represented by the JSON non-
terminal 'JSONBooleanLiteral'.
Integer LLSD 'Integer' values are represented by the JSON non-
terminal 'JSONNumberLiteral'.
Real LLSD 'Real' values are represented by the JSON non-terminal
'JSONNumberLiteral'.
String LLSD 'String' values are represented by the JSON 'JSONString'
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 'JSONArray'.
That is, they follow the ECMA-262 [ECMA262r5] 'JSONArray' non-
terminal whose members are integer numbers representing each
octet of the binary array.
Array LLSD 'Array' values are represented by the JSON 'JSONArray'
non-terminal.
Map LLSD 'Map' values are represented by the JSON 'JSONObject' non-
terminal. Each key-value pair of the map is represented by the
JSON 'JSONMember' non-terminal where the LLSD map key is the
'JSONString' prior to the name separator terminal (':') and the
LLSD map value is the 'JSONValue' after the name separator.
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 conversion defined
in Abstract Type System section above.
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4.2.1. Examples of JSON LLSD Serialization
Example 1. The following example shows the JSON encoding of the
integer 42.
42
Example 2. The following example shows the JSON encoding of the
example given in the section above on XML serialization
(Section 4.1.2).
[
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"
}
]
4.3. 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
all members of the collection, serializing each simple or composite
member in turn, and adding a closing tag. 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.
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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.
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. Following the elements in
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the array, a single octet closing tag is appended to the
enclosing. The closing tag for arrays is a single right square
bracket (']').
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.
Following the elements in the map, a single octet closing tag is
appended to the enclosing. The closing tag for arrays is a
single right curly brace ('}').
4.3.1. Example of BINARY LLSD Serialization
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The LLSD object given as an example in the section above on XML
serialization (Section 4.1.2) 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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5. IANA Considerations
In accordance with [RFC5226], this document registers the following
mime types:
application/llidl
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.
6. MIME Type Registrations
This section provides media-type registration applications (as per
RFC 4288 [RFC4288].)
6.1. MIME Type Registration for application/llidl
To: ietf-types@iana.org
Subject: Registration of media type application/llidl
Type name: application
Subtype name: llidl
Required Parameters: none
Optional Parameters: none
Encoding Considerations: LLIDL may be used with any character set
that encodes character points identical to ASCII for the first
127 characters. Compliant systems SHOULD use UTF-8 and if no
character set is indicated, UTF-8 MUST be assumed.
Security Considerations: LLIDL interface descriptions contain
"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 to ensure such
vulnerabilities are mitigated in a timely fashion
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In the unlikely event that sensitive information is to be
expressed as an LLIDL interface, 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: The grammar of LLIDL is defined in the
internet draft draft-ietf-vwrap-type-system-00
[I-D.ietf-vwrap-type-system].
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: llidl
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+xml
To: ietf-types@iana.org
Subject: Registration of media type application/llsd+xml
Type name: application
Subtype name: llsd+xml
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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: The LLSD XML Serialization is defined in
the internet draft draft-ietf-vwrap-type-system-00
[I-D.ietf-vwrap-type-system].
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
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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+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: This specification requires that LLSD
objects encoded using the JSON serialization scheme encode their
data using Unicode. It is assumed that the transport will carry
meta-data describing the character encoding used (UTF-8, UTF-16,
UTF-32, etc.) The UTF-8 character encoding is assumed if a
character encoding is not specified.
Security Considerations: The contents of messages identified with
this media type are expected to be passed into ECMAScript's
'parse()' function. RFC 4627 [RFC4627] 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
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: none
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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
6.4. 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
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.
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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
nonsensical 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: The LLSD binary serialization is defined in
the internet draft draft-hamrick-llsd-01
[I-D.ietf-vwrap-type-system].
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
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
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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
[ECMA262r5]
ECMA International, "Standard ECMA-262, 5th Edition :
ECMAScript Language Specification", December 2009, <http:/
/www.ecma-international.org/publications/standards/
Ecma-262.htm>.
[I-D.ietf-vwrap-type-system]
Brashears, A., Hamrick, M., and M. Lentczner, "VWRAP :
Abstract Type System for the Transmission of Dynamic
Structured Data", July 2010.
[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.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2817] Khare, R. and S. Lawrence, "Upgrading to TLS Within
HTTP/1.1", RFC 2817, May 2000.
[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.
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[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
July 2005.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
Registration Procedures", BCP 13, RFC 4288, December 2005.
[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
[Fielding2000]
University of California, Irvine, "Architectural Styles
and the Design of Network-based Software Architectures",
2000.
[ISO8601] "ISO 8601 - Date and Time Formats".
[Kaye2003]
The Conversations Network, "Loosely Coupled : The Missing
Pieces of Web Services", 2003.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
July 2003.
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.
[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.
<!ELEMENT llsd
(undef|boolean|integer|real|string|uuid|date|uri|binary|array|map)*>
<!ELEMENT undef EMPTY>
<!ELEMENT boolean (#PCDATA)>
<!ELEMENT integer (#PCDATA)>
<!ELEMENT real (#PCDATA)>
<!ELEMENT string (#PCDATA)>
<!ELEMENT uuid (#PCDATA)>
<!ELEMENT date (#PCDATA)>
<!ELEMENT uri (#PCDATA)>
<!ELEMENT binary (#PCDATA)>
<!ELEMENT array
(undef|boolean|integer|real|string|uuid|date|uri|binary|array|map)*>
<!ELEMENT map
(key,(undef|boolean|integer|real|string|uuid|date|uri|binary|array
|map))*>
<!ELEMENT key (#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 LLIDL
Interface Description Language. ABNF is described in RFC 5234
[RFC5234].
llidl = *( s / resource-def / variant-def )
resource-def = res-name s res-transaction
res-name = "%%" s name
res-transaction = res-get / res-getput / res-getputdel / res-post
res-get = "<<" s value
res-getput = "<>" s value
res-getputdel = "<x>" s value
res-post = res-request s res-response
res-request = "->" s value
res-response = "<-" s value
variant-def = "&" name s "=" s value
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value = type / array / map / selector / variant
type = %x75.6E.64.65.66 ; "undef"
type =/ %x73.74.72.69.6E.67 ; "string"
type =/ %x62.6F.6F.6C ; "bool"
type =/ %x69.6E.74 ; "int"
type =/ %x72.65.61.6C ; "real"
type =/ %x64.61.74.65 ; "date"
type =/ %x75.72.69 ; "uri"
type =/ %x75.75.69.64 ; "uuid"
type =/ %x62.69.6E.61.72.79 ; "binary"
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 =/ %x74.72.75.65 ; "true"
selector =/ %x66.61.6C.73.65 ; "false"
selector =/ 1*digit
variant = "&" name
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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Appendix D. Glossary
Access See Resource Access.
Array An array is a collection in which elements are accessed by
numeric index. By default arrays are fixed length, but a
trailing ellipsis in an array definition denotes an array of
indeterminate length.
Array Definition An array definition is a feature of the LLIDL
grammar used to denote arrays of fixed or indeterminate size. An
array definition is a comma delimited sequence of type
definitions describing the type of each array element.
Composite Type A composite type in LLIDL and LLSD is an abstract
representation of an array or a map.
Deferred Entry Name A map defined with a single "Deferred Entry Name
Specifier" (i.e. - the dollar sign), signifies that the map
entry's names will be determined at the time the resource is
accessed, not when the resource is defined.
Defined Type A defined type is a feature of the LLIDL grammar used
to represent one of the eleven (11) predefined types. Defined
types are in contrast to literals and map variants. The eleven
predefined types are: undefined, boolean, integer, real, date,
uuid, uri, string, binary, array and map.
GET (Method Access) The GET method access, denoted in LLIDL with the
double less-than digraph ("<<") indicates a given resource should
be accessed via the HTTP GET verb. In LLIDL, a single message
body definition comes after the double less-than digraph and
indicates the composition of the message the client should expect
from the server.
GET/PUT (Method Access) The GET/PUT method access, denoted in LLIDL
with the less-than / greater-than digraph ("<>") indicates a
given resource should be accessed via either the HTTP GET or HTTP
PUT verbs. In LLIDL, a single message body definition comes
after the less-than / greater-than digraph and indicates the
composition of the message the client should expect from the
server (if the GET HTTP verb is used) or the composition of the
message the server should expect from the client (if the PUT HTTP
verb is used.)
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GET/PUT/DELETE (Method Access) The GET/PUT/DELETE method access,
denoted in LLIDL with the less-than / x / greater-than trigraph
("<x>") indicates a given resource should be accessed via either
the HTTP GET, HTTP PUT or HTTP DELETE verbs. In LLIDL, a single
message body definition comes after the less-than / x / greater-
than trigraph and indicates the composition of the message the
client should expect from the server (if the GET HTTP verb is
used) or the composition of the message the server should expect
from the client (if the PUT HTTP verb is used.)
Interface An LLIDL Interface is a collection of zero or more
resources and any variant record definitions they reference.
Literal Values in LLIDL resource definitions usually represent
types. A literal value may be used when an element in a message
body is to be fixed to a particular value. Literals are in
contrast to defined types or map variants.
LLIDL LLIDL is an interface description language for describing
RESTful resources accessed via HTTP or HTTPS.
LLSD LLSD is an abstract type system used to describe the structure
of data in LLIDL Resource Definitions.
Map A map is a collection in which elements are accessed by a string
key.
Map Definition A map definition is a feature of the LLIDL grammar
used to denote maps. Map definitions are comprised of zero or
more comma delimited map entries.
Map Entry A map entry is a component of a map definition and is
composed of a key name and a type definition separated by a
colon.
Map Variant See Variant Map.
Method Access A method access is a feature of the LLIDL grammar used
to describe which set HTTP verbs a client should use to access a
resource. Method access classes include 'GET', 'GET/PUT', 'GET/
PUT/DELETE' and 'POST'.
Message Body A message body is a feature of the LLIDL grammar that
describes the contents of a message flowing between a client and
a server. A message body is the type definition that describes
completely the structure of a message flowing between systems.
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Named Type A named type is a developer declared name for a type,
array or map definition.
POST (Method Access) The POST method access, denoted in LLIDL with
the hyphen / greater-than ("->") and less-than / hyphen ("<-")
digraphs, indicates a given resource should be accessed via the
HTTP POST verb. In LLIDL, a message body definition comes after
both digraphs. The message body definition following the first
digraph indicates the composition of the message the client
should POST to the resource's URL while the second message body
definition describes the response the client should expect from
the server.
Resource A Resource is an abstract representation of information or
state maintained by a remote process, potentially on a remote
host. LLIDL may be used to describe the structure of a resource
and resources may be accessed by sending and receiving messages
serialized using one of the three serialization schemes via
HTTP(S).
Resource Access The act of accessing a RESTful resource.
Resource Definition An LLIDL Resource Definition is a statement in
the LLIDL language describing a single RESTful resource exported
by a remote service. Resource definitions include a resource
class, optional query parameters, a method access indicating
which HTTP verbs are acceptable to the service, the structure of
the resource access' request and/or the structure of the resource
access' response. Resource definitions may be used along with a
serialization scheme to format or parse a resource request or
response.
Resource Class A Resource Class is the textual identifier associated
with a resource. It is used to uniquely identify a resource in
an interface.
Selector See Variant Selector.
Selector Literal A literal used to identify which variant in a map
variant should be expected is a "selector literal."
Serialization Scheme A serialization scheme defines rules used to
convert a data structure into an octet stream suitable for
transmission across a network. Three schemes are defined in this
document: XML, JSON and Binary.
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Simple Type In LLSD and LLIDL, a "simple type" is a defined type
that is not a collection. It is one of: undefined, boolean,
integer, real, date, uuid, uri, string or binary.
Type Definition A type definition is a feature of the LLIDL grammar
used to declare the type of a data element in a message body. It
may be a literal, a defined type or a variant map.
Variant Definition A map used as one of several options in a variant
map.
Variant Map A variant type definition in which a map is used for one
of the variants. Variant maps may include a selector to assist
in matching the most appropriate variant.
Variant Selector A map entry whose value is set as a literal. Used
to determine which variant definition of a variant map is to be
used.
Variant Type Definition A type definition comprised of more than one
definition. Variant type definitions are defined using the named
type feature of LLIDL.
Appendix E. Acknowledgements
The authors gratefully acknowledge the contributions of: Lora Baines,
Alan Bradley, Suzy Deffeyes, Morgaine Dinova, Kevin Flynn, Valentyn
Gatsuk, Walter Gibbs, John Hurliman, Dave Huseby, Charles Krinke,
Jennifer Leech, David Levine, Steven Lisberger, Dan Olivares,
Catherine Pfeffer, Jon Watte and Ryan Williams.
Authors' Addresses
Aaron Brashears
Meadhbh Siobhan Hamrick
P.O. Box 783
Boulder Creek, CA 95006
US
Phone: +1 650 283 0344
Email: OhMeadhbh@gmail.com
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Mark Lentczner
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