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 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 8, 2009. Copyright Notice Copyright (c) 2009 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document describes the Linden Lab Structured Data (LLSD) Brashears, et al. Expires August 8, 2009 [Page 1] Internet-Draft Linden Lab Structured Data February 2009 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 Brashears, et al. Expires August 8, 2009 [Page 2] Internet-Draft Linden Lab Structured Data February 2009 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 Brashears, et al. Expires August 8, 2009 [Page 3] Internet-Draft Linden Lab Structured Data February 2009 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. Brashears, et al. Expires August 8, 2009 [Page 4] Internet-Draft Linden Lab Structured Data February 2009 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. Brashears, et al. Expires August 8, 2009 [Page 5] Internet-Draft Linden Lab Structured Data February 2009 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 (""). Brashears, et al. Expires August 8, 2009 [Page 6] Internet-Draft Linden Lab Structured Data February 2009 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). Brashears, et al. Expires August 8, 2009 [Page 7] Internet-Draft Linden Lab Structured Data February 2009 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 Brashears, et al. Expires August 8, 2009 [Page 8] Internet-Draft Linden Lab Structured Data February 2009 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. Brashears, et al. Expires August 8, 2009 [Page 9] Internet-Draft Linden Lab Structured Data February 2009 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. -559038737 Brashears, et al. Expires August 8, 2009 [Page 10] Internet-Draft Linden Lab Structured Data February 2009 While this example shows the serialization of a binary array of octets containing the values 222, 173, 190 and 239. 3q2+7w== 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. 42 6bad258e-06f0-4a87-a659-493117c9c162 hot cold higgs_boson_rest_mass info_page https://example.org/r/6bad258e-06f0-4a87-a659-493117c9c162 status_report_due_by 2008-10-13T19:00.00Z Brashears, et al. Expires August 8, 2009 [Page 11] Internet-Draft Linden Lab Structured Data February 2009 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. Brashears, et al. Expires August 8, 2009 [Page 12] Internet-Draft Linden Lab Structured Data February 2009 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 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 Brashears, et al. Expires August 8, 2009 [Page 13] Internet-Draft Linden Lab Structured Data February 2009 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. Brashears, et al. Expires August 8, 2009 [Page 14] Internet-Draft Linden Lab Structured Data February 2009 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 Brashears, et al. Expires August 8, 2009 [Page 15] Internet-Draft Linden Lab Structured Data February 2009 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. Brashears, et al. Expires August 8, 2009 [Page 16] Internet-Draft Linden Lab Structured Data February 2009 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.<.....' Brashears, et al. Expires August 8, 2009 [Page 17] Internet-Draft Linden Lab Structured Data February 2009 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 ... ] Brashears, et al. Expires August 8, 2009 [Page 18] Internet-Draft Linden Lab Structured Data February 2009 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 } Brashears, et al. Expires August 8, 2009 [Page 19] Internet-Draft Linden Lab Structured Data February 2009 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. Brashears, et al. Expires August 8, 2009 [Page 20] Internet-Draft Linden Lab Structured Data February 2009 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]. Brashears, et al. Expires August 8, 2009 [Page 21] Internet-Draft Linden Lab Structured Data February 2009 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 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 Brashears, et al. Expires August 8, 2009 [Page 22] Internet-Draft Linden Lab Structured Data February 2009 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 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 Brashears, et al. Expires August 8, 2009 [Page 23] Internet-Draft Linden Lab Structured Data February 2009 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 Intended Usage: COMMON Brashears, et al. Expires August 8, 2009 [Page 24] Internet-Draft Linden Lab Structured Data February 2009 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. Brashears, et al. Expires August 8, 2009 [Page 25] Internet-Draft Linden Lab Structured Data February 2009 [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, . [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. Brashears, et al. Expires August 8, 2009 [Page 26] Internet-Draft Linden Lab Structured Data February 2009 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 Brashears, et al. Expires August 8, 2009 [Page 27] Internet-Draft Linden Lab Structured Data February 2009 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. ]> 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" Brashears, et al. Expires August 8, 2009 [Page 28] Internet-Draft Linden Lab Structured Data February 2009 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 Brashears, et al. Expires August 8, 2009 [Page 29] Internet-Draft Linden Lab Structured Data February 2009 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 Brashears, et al. Expires August 8, 2009 [Page 30]