--- 1/draft-ietf-netmod-yang-json-00.txt 2014-10-13 04:15:40.214591431 -0700
+++ 2/draft-ietf-netmod-yang-json-01.txt 2014-10-13 04:15:40.242592120 -0700
@@ -1,435 +1,340 @@
-NETMOD L. Lhotka
+NETMOD Working Group L. Lhotka
Internet-Draft CZ.NIC
-Intended status: Standards Track April 21, 2014
-Expires: October 23, 2014
+Intended status: Standards Track October 13, 2014
+Expires: April 16, 2015
JSON Encoding of Data Modeled with YANG
- draft-ietf-netmod-yang-json-00
+ draft-ietf-netmod-yang-json-01
Abstract
- This document defines rules for representing configuration and state
- data defined using YANG as JSON text. It does so by specifying a
- procedure for translating the subset of YANG-compatible XML documents
- to JSON text, and vice versa. A JSON encoding of XML attributes is
- also defined so as to allow for including metadata in JSON documents.
+ This document defines encoding rules for representing configuration,
+ state data, RPC input and output parameters, and notifications
+ defined using YANG as JavaScript Object Notation (JSON) text.
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."
- This Internet-Draft will expire on October 23, 2014.
+ This Internet-Draft will expire on April 16, 2015.
Copyright Notice
Copyright (c) 2014 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. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
- 2. Terminology and Notation . . . . . . . . . . . . . . . . . . 4
- 3. Specification of the Translation Procedure . . . . . . . . . 5
- 3.1. Names and Namespaces . . . . . . . . . . . . . . . . . . 6
- 3.2. Mapping XML Elements to JSON Objects . . . . . . . . . . 8
- 3.2.1. The "leaf" Data Node . . . . . . . . . . . . . . . . 8
- 3.2.2. The "container" Data Node . . . . . . . . . . . . . . 8
- 3.2.3. The "leaf-list" Data Node . . . . . . . . . . . . . . 9
- 3.2.4. The "list" Data Node . . . . . . . . . . . . . . . . 9
- 3.2.5. The "anyxml" Data Node . . . . . . . . . . . . . . . 10
- 3.3. Mapping YANG Datatypes to JSON Values . . . . . . . . . . 11
- 3.3.1. Numeric Datatypes . . . . . . . . . . . . . . . . . . 11
- 3.3.2. The "string" Type . . . . . . . . . . . . . . . . . . 11
- 3.3.3. The "boolean" Type . . . . . . . . . . . . . . . . . 11
- 3.3.4. The "enumeration" Type . . . . . . . . . . . . . . . 11
- 3.3.5. The "bits" Type . . . . . . . . . . . . . . . . . . . 12
- 3.3.6. The "binary" Type . . . . . . . . . . . . . . . . . . 12
- 3.3.7. The "leafref" Type . . . . . . . . . . . . . . . . . 12
- 3.3.8. The "identityref" Type . . . . . . . . . . . . . . . 12
- 3.3.9. The "empty" Type . . . . . . . . . . . . . . . . . . 12
- 3.3.10. The "union" Type . . . . . . . . . . . . . . . . . . 13
- 3.3.11. The "instance-identifier" Type . . . . . . . . . . . 13
- 4. Encoding Metadata in JSON . . . . . . . . . . . . . . . . . . 14
- 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
- 6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
- 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
- 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
- 8.1. Normative References . . . . . . . . . . . . . . . . . . 17
- 8.2. Informative References . . . . . . . . . . . . . . . . . 17
- Appendix A. A Complete Example . . . . . . . . . . . . . . . . . 18
- Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20
+ 2. Terminology and Notation . . . . . . . . . . . . . . . . . . 3
+ 3. Validation of JSON-encoded
+ Instance Data . . . . . . . . . . . . . . . . . . . . . . . . 3
+ 4. Names and Namespaces . . . . . . . . . . . . . . . . . . . . 4
+ 5. Encoding of YANG Data Node Instances . . . . . . . . . . . . 6
+ 5.1. The "leaf" Data Node . . . . . . . . . . . . . . . . . . 6
+ 5.2. The "container" Data Node . . . . . . . . . . . . . . . . 7
+ 5.3. The "leaf-list" Data Node . . . . . . . . . . . . . . . . 7
+ 5.4. The "list" Data Node . . . . . . . . . . . . . . . . . . 7
+ 5.5. The "anyxml" Data Node . . . . . . . . . . . . . . . . . 8
+ 6. The Mapping of YANG Datatypes to JSON Values . . . . . . . . 8
+ 6.1. Numeric Datatypes . . . . . . . . . . . . . . . . . . . . 9
+ 6.2. The "string" Type . . . . . . . . . . . . . . . . . . . . 9
+ 6.3. The "boolean" Type . . . . . . . . . . . . . . . . . . . 9
+ 6.4. The "enumeration" Type . . . . . . . . . . . . . . . . . 9
+ 6.5. The "bits" Type . . . . . . . . . . . . . . . . . . . . . 9
+ 6.6. The "binary" Type . . . . . . . . . . . . . . . . . . . . 9
+ 6.7. The "leafref" Type . . . . . . . . . . . . . . . . . . . 10
+ 6.8. The "identityref" Type . . . . . . . . . . . . . . . . . 10
+ 6.9. The "empty" Type . . . . . . . . . . . . . . . . . . . . 10
+ 6.10. The "union" Type . . . . . . . . . . . . . . . . . . . . 11
+ 6.11. The "instance-identifier" Type . . . . . . . . . . . . . 11
+ 7. I-JSON Compliance . . . . . . . . . . . . . . . . . . . . . . 12
+ 8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
+ 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
+ 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
+ 10.1. Normative References . . . . . . . . . . . . . . . . . . 13
+ 10.2. Informative References . . . . . . . . . . . . . . . . . 14
+ Appendix A. A Complete Example . . . . . . . . . . . . . . . . . 14
+ Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 16
+ B.1. Changes Between Revisions -00 and -01 . . . . . . . . . . 16
+ Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
- The aim of this document is define rules for representing
- configuration and state data defined using the YANG data modeling
- language [RFC6020] as JavaScript Object Notation (JSON)
- text [RFC7159]. The result can be potentially applied in two
- different ways:
-
- 1. JSON may be used instead of the standard XML [XML] encoding in
- the context of the NETCONF protocol [RFC6241] and/or with
- existing data models expressed in YANG. An example application
- is the RESTCONF Protocol [RESTCONF].
-
- 2. Other documents that choose JSON to represent structured data can
- use YANG for defining the data model, i.e., both syntactic and
- semantic constraints that the data have to satisfy.
-
- JSON mapping rules could be specified in a similar way as the XML
- mapping rules in [RFC6020]. This would however require solving
- several problems. To begin with, YANG uses XPath [XPath] quite
- extensively, but XPath is not defined for JSON and such a definition
- would be far from straightforward.
-
- In order to avoid these technical difficulties, this document employs
- an alternative approach: it defines a relatively simple procedure
- which allows for translating the subset of XML that can be modeled
- using YANG to JSON, and vice versa. Consequently, validation of a
- JSON text against a data model can done by translating the JSON text
- to XML, which is then validated according to the rules stated in
- [RFC6020].
-
- The translation procedure is adapted to YANG specifics and
- requirements, namely:
-
- 1. The translation is driven by a concrete YANG data model and uses
- information about data types to achieve better results than
- generic XML-JSON translation procedures.
-
- 2. Various document types are supported, namely configuration data,
- configuration + state data, RPC input and output parameters, and
- notifications.
-
- 3. XML namespaces specified in the data model are mapped to
- namespaces of JSON objects. However, explicit namespace
- identifiers are rarely needed in JSON text.
-
- 4. Section 4 defines JSON encoding of XML attributes. Although XML
- attributes cannot be modeled with YANG, they are often used for
- attaching metadata to elements, and a standard JSON encoding is
- therefore needed.
-
- 5. Translation of XML mixed content, comments and processing
- instructions is outside the scope of this document.
-
- Item 1 above also means that, depending on the data model, the same
- XML element can be translated to different JSON objects. For
- example,
-
- 123
-
- is translated to
- "foo": 123
+ The NETCONF protocol [RFC6241] uses XML [W3C.REC-xml-20081126] for
+ encoding data in its Content Layer. Other management protocols might
+ want to use other encodings while still benefiting from using YANG
+ [RFC6020] as the data modeling language.
- if the "foo" node is defined as a leaf with the "uint8" datatype, or
- to
+ For example, the RESTCONF protocol [I-D.ietf-netconf-restconf]
+ supports two encodings: XML (media type "application/yang.data+xml")
+ and JSON (media type "application/yang.data+json).
- "foo": ["123"]
+ The specification of the YANG data modelling language [RFC6020]
+ defines only XML encoding for data instances, i.e. contents of
+ configuration datastores, state data, RFC input and output
+ parameters, and event notifications. The aim of this document is to
+ define rules for encoding the same data as JavaScript Object Notation
+ (JSON) text [RFC7159].
- if the "foo" node is defined as a leaf-list with the "string"
- datatype, and the element has no siblings of the same name.
+ In order to achieve maximum interoperability while allowing
+ implementations to use a variety of available JSON parsers, the JSON
+ encoding rules follow, as much as possible, the constraints of the
+ I-JSON restricted profile [I-D.ietf-json-i-json]. Section Section 7
+ discusses I-JSON conformance in more detail.
2. Terminology and Notation
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 [RFC2119].
The following terms are defined in [RFC6020]:
o anyxml
o augment
o container
o data node
- o data tree
-
- o datatype
-
- o feature
-
o identity
o instance identifier
o leaf
o leaf-list
o list
o module
o submodule
- The following terms are defined in [XMLNS]:
-
- o local name
-
- o prefixed name
-
- o qualified name
-
-3. Specification of the Translation Procedure
-
- The translation procedure defines a 1-1 correspondence between the
- subset of YANG-compatible XML documents and JSON text. This means
- that the translation can be applied in both directions and it is
- always invertible.
-
- The translation procedure is applicable only to data hierarchies that
- are modelled by a YANG data model. An input XML document MAY contain
- enclosing elements representing NETCONF "Operations" and "Messages"
- layers. However, these enclosing elements do not appear in the
- resulting JSON document.
-
- Any YANG-compatible XML document can be translated, except documents
- with mixed content. This is only a minor limitation since mixed
- content is marginal in YANG - it is allowed only in anyxml data
- nodes.
-
- The following sections specify rules mainly for translating XML
- documents to JSON text. Rules for the inverse translation are stated
- only where necessary, otherwise they can be easily inferred.
-
- REQUIRED parameters of the translation procedure are:
-
- o YANG data model consisting of a set of YANG modules,
-
- o type of the input document,
-
- o optional features (defined via the "feature" statement) that are
- considered active.
-
- The permissible types of input documents are listed in Table 1
- together with the corresponding part of the data model that is used
- for the translation.
-
- +------------------------------+---------------------------------+
- | Document Type | Data Model Section |
- +------------------------------+---------------------------------+
- | configuration and state data | main data tree |
- | | |
- | configuration | main data tree ("config true") |
- | | |
- | RPC input parameters | "input" data nodes under "rpc" |
- | | |
- | RPC output parameters | "output" data nodes under "rpc" |
- | | |
- | notification | "notification" data nodes |
- +------------------------------+---------------------------------+
-
- Table 1: YANG Document Types
-
- When translating XML to JSON, the type of the input document can
- often be determined form the encapsulating elements belonging to the
- "Operations" or "Messages" layer as defined by the NETCONF protocol
- (see Sec. 1.2 in [RFC6241]).
+3. Validation of JSON-encoded Instance Data
- A particular application MAY decide to support only a subset of
- document types from Table 1.
+ Instance data validation as defined in [RFC6020] is only applicable
+ to XML-encoded data. For one, semantic constraints in "must"
+ statements are expressed using XPath 1.0 [W3C.REC-xpath-19991116],
+ which can be properly interpreted only in the XML context.
- XML documents can be translated to JSON text only if they are valid
- instances of the YANG data model and selected document type, also
- taking into account the active features, if there are any.
+ This document along with the corresponding "XML Mapping Rules"
+ sections from [RFC6020] also define an implicit schema-driven mapping
+ of JSON-encoded instances to XML-encoded instances (and vice versa).
+ This mapping is mostly straightforward. In cases where doubts could
+ arise, this document gives explicit instructions for mapping JSON-
+ encoded instances to XML.
- The resulting JSON document is always a single object ([RFC7159],
- Sec. 4) whose members are translated from the original XML document
- using the rules specified in the following sections.
+ In order to validate a JSON instance document, it MUST first be
+ mapped, at least conceptually, to the corresponding XML instance
+ document. By definition, the JSON document is then valid if and only
+ if the XML document is valid according to the rules stated in
+ [RFC6020].
-3.1. Names and Namespaces
+4. Names and Namespaces
- The local part of a JSON name is always identical to the local name
- of the corresponding XML element.
+ Instances of YANG data nodes (leafs, containers, leaf-lists, lists
+ and anyxml nodes) are always encoded as members of a JSON object,
+ i.e., as name/value pairs. This section defines how the name part is
+ formed, and the following sections deal with the value part.
- Each JSON name lives in a namespace which is uniquely identified by
- the name of the YANG module where the corresponding data node is
- defined. If the data node is defined in a submodule, then the
- namespace identifier is the name of the main module to which the
- submodule belongs. The translation procedure MUST correctly map YANG
- namespace URIs to YANG module names and vice versa.
+ Except in the cases specified below, the member name is identical to
+ the identifier of the corresponding YANG data node. Every such name
+ belongs to a namespace which is associated with the YANG module where
+ the corresponding data node is defined. If the data node is defined
+ in a submodule, then the namespace is determined by the main module
+ to which the submodule belongs.
- The namespace SHALL be expressed in JSON text by prefixing the local
- name in the following way:
+ If the namespace of a member name has to be explicitly specified, the
+ module name SHALL be used as a prefix to the (local) member name.
+ Both parts of the member name SHALL be separated with a colon
+ character (":"). In other words, the namespace-qualified name will
+ have the following form:
:
Figure 1: Encoding a namespace identifier with a local name.
- The namespace identifier MUST be used for local names that are
- ambiguous, i.e., whenever the data model permits a sibling data node
- with the same local name. Otherwise, the namespace identifier is
- OPTIONAL.
+ Names with namespace identifiers in the form shown in Figure 1 MUST
+ be used for all top-level YANG data nodes, and also for all nodes
+ whose parent node belongs to a different namespace. Otherwise, names
+ with namespace identifiers MUST NOT be used.
For example, consider the following YANG module:
module foomod {
+
namespace "http://example.com/foomod";
- prefix "fm";
- container foo {
- leaf bar {
- type boolean;
+
+ prefix "foo";
+
+ container top {
+ leaf foo {
+ type uint8;
}
}
}
If the data model consists only of this module, then the following is
- a valid JSON document:
+ a valid JSON-encoded configuration:
{
- "foo": {
- "bar": true
+ "foomod:top": {
+ "foo": 54
}
}
- Now, assume the container "foo" is augmented from another module:
+ Note that the top-level container instance contains the namespace
+ identifier (module name) but the "foo" leaf doesn't because it is
+ defined in the same module as its parent container.
+
+ Now, assume the container "top" is augmented from another module,
+ "barmod":
module barmod {
+
namespace "http://example.com/barmod";
- prefix "bm";
+
+ prefix "bar";
+
import foomod {
- prefix fm;
+ prefix "foo";
}
- augment "/fm:foo" {
+
+ augment "/foo:top" {
leaf bar {
- type uint8;
+ type boolean;
}
}
}
- In the data model combining "foomod" and "barmod", we have two
- sibling data nodes with the same local name, namely "bar". In this
- case, a valid JSON document has to specify an explicit namespace
- identifier (module name) for both leaves:
+ A valid JSON-encoded configuration containing both leafs may then
+ look like this:
{
- "foo": {
- "foomod:bar": true,
- "barmod:bar": 123
+ "foomod:top": {
+ "foo": 54,
+ "barmod:bar": true
}
}
-3.2. Mapping XML Elements to JSON Objects
+ The name of the "bar" leaf must be prefixed with the namespace
+ identifier because its parent is defined in a different module, hence
+ it belongs to another namespace.
- An XML element that is modelled as a YANG data node is translated to
- a name/value pair where the name is formed from the name of the XML
- element using the rules in Section 3.1. The value depends on the
- type of the data node as specified in the following sections.
+ Explicit namespace identifiers are sometimes needed when encoding
+ values of the "identityref" and "instances-identifier" types. The
+ same form as shown in Figure 1 is then used as well. See Sections
+ 6.8 and 6.11 for details.
-3.2.1. The "leaf" Data Node
+5. Encoding of YANG Data Node Instances
- An XML element that is modeled as YANG leaf is translated to a name/
- value pair and the type of the value is derived from the YANG
- datatype of the leaf (see Section 3.3 for the datatype mapping
- rules).
+ Every complete JSON instance document, such as a configuration
+ datastore content, is an object. Its members are instances of all
+ top-level data nodes defined by the YANG data model.
+
+ Character encoding MUST be UTF-8.
+
+ Any data node instance is encoded as a name/value pair where the name
+ is formed from the data node identifier using the rules of Section 4.
+ The value depends on the category of the data node as explained in
+ the following subsections.
+
+5.1. The "leaf" Data Node
+
+ A leaf instance is encoded as a name/value pair where the value can
+ be a string, number, literal 'true' or 'false' or the special array
+ '[null]', depending on the type of the leaf (see Section 6 for the
+ type encoding rules).
Example: For the leaf node definition
leaf foo {
type uint8;
}
- the XML element
-
- 123
-
- corresponds to the JSON name/value pair
+ the following is a valid JSON-encoded instance:
"foo": 123
-3.2.2. The "container" Data Node
+5.2. The "container" Data Node
- An XML element that is modeled as YANG container is translated to a
- name/object pair.
+ An container instance is encoded as a name/object pair. The
+ container's child data nodes are encoded as members of the object.
Example: For the container definition
+
container bar {
leaf foo {
type uint8;
}
}
- the XML element
-
-
- 123
-
-
- corresponds to the JSON name/value pair
+ the following is a valid instance:
"bar": {
"foo": 123
}
-3.2.3. The "leaf-list" Data Node
+5.3. The "leaf-list" Data Node
- A sequence of one or more sibling XML elements with the same
- qualified name that is modeled as YANG leaf-list is translated to a
- name/array pair, and the array elements are primitive values whose
- type depends on the datatype of the leaf-list (see Section 3.3).
+ A leaf-list is encoded as a name/array pair, and the array elements
+ are values whose type depends on the datatype of the leaf-list (see
+ Section 6).
Example: For the leaf-list definition
leaf-list foo {
type uint8;
}
- the XML elements
-
- 123
- 0
- 123
- zig
-
-
- 0
- zag
-
-
- correspond to the JSON name/value pair
+ the following is a valid instance:
"bar": [
{
"foo": 123,
"baz": "zig"
},
{
- "foo": 0,
- "baz": "zag"
+ "baz": "zag",
+ "foo": 0
}
]
-3.2.5. The "anyxml" Data Node
+5.5. The "anyxml" Data Node
- An XML element that is modeled as a YANG anyxml data node is
- translated to a name/object pair. The content of such an element is
- not modelled by YANG, and there may not be a straightforward mapping
- to JSON text (e.g., if it is a mixed XML content). Therefore,
- translation of anyxml contents is necessarily application-specific
- and outside the scope of this document.
+ An anyxml instance is translated to a name/value pair. The value can
+ be of any valid JSON type, i.e. an object, array, number, string or
+ any of the literals 'true', 'false' and 'null'.
+
+ This document defines no mapping between the contents of JSON- and
+ XML-encoded anyxml instances. It is not necessary because anyxml
+ contents are not subject to YANG-based validation (see sec. 7.10 in
+ [RFC6020]).
Example: For the anyxml definition
anyxml bar;
- the XML element
+ the following is a valid instance:
-
-
- This is very cool.
-
-
+ "bar": [true, null, true]
- may be translated to the following JSON name/value pair:
+6. The Mapping of YANG Datatypes to JSON Values
- {
- "bar": {
- "p": "This is *very* cool."
- }
- }
+ The type of the JSON value in an instance of the leaf or leaf-list
+ data node depends on the datatype of that data node as specified in
+ the following subsections.
-3.3. Mapping YANG Datatypes to JSON Values
+6.1. Numeric Datatypes
-3.3.1. Numeric Datatypes
+ A value of the "int8", "int16", "int32", "uint8", "uint16" is
+ represented as a JSON number.
- A value of one of the YANG numeric datatypes ("int8", "int16",
- "int32", "int64", "uint8", "uint16", "uint32", "uint64" and
- "decimal64") is mapped to a JSON number using the same lexical
- representation.
+ A value of the "int64", "uint64" or "decimal64" type is encoded as a
+ JSON string whose contents is the lexical representation of that
+ numeric value as specified in sections 9.2.1 and 9.3.1 of [RFC6020].
-3.3.2. The "string" Type
+ For example, if the type of the leaf "foo" in Section 5.1 was
+ "unit64" instead of "uint8", the instance would have to be encoded as
- A "string" value is mapped to an identical JSON string, subject to
- JSON encoding rules.
+ "foo": "123"
-3.3.3. The "boolean" Type
+ The special handling of 64-bit numbers follows from I-JSON
+ recommendation to encode numbers exceeding the IEEE 754-2000 double
+ precision range as strings, see sec. 2.2 in [I-D.ietf-json-i-json].
- A "boolean" value is mapped to the corresponding JSON value 'true' or
- 'false'.
+6.2. The "string" Type
-3.3.4. The "enumeration" Type
+ A "string" value encoded as a JSON string, subject to JSON encoding
+ rules.
+
+6.3. The "boolean" Type
+
+ A "boolean" value is mapped to the corresponding JSON literal name
+ 'true' or 'false'.
+
+6.4. The "enumeration" Type
An "enumeration" value is mapped in the same way as a string except
that the permitted values are defined by "enum" statements in YANG.
+ See sec. 9.6 in [RFC6020].
-3.3.5. The "bits" Type
+6.5. The "bits" Type
- A "bits" value is mapped to a string identical to the lexical
+ A "bits" value is mapped to a JSON string identical to the lexical
representation of this value in XML, i.e., space-separated names
- representing the individual bit values that are set.
+ representing the individual bit values that are set. See sec. 9.7 in
+ [RFC6020].
-3.3.6. The "binary" Type
+6.6. The "binary" Type
A "binary" value is mapped to a JSON string identical to the lexical
representation of this value in XML, i.e., base64-encoded binary
- data.
+ data. See sec. 9.8 in [RFC6020].
-3.3.7. The "leafref" Type
+6.7. The "leafref" Type
A "leafref" value is mapped according to the same rules as the type
of the leaf being referred to.
-3.3.8. The "identityref" Type
+6.8. The "identityref" Type
- An "identityref" value is mapped to a string representing the
- qualified name of the identity. Its namespace MAY be expressed as
- shown in Figure 1. If the namespace part is not present, the
- namespace of the name of the JSON object containing the value is
- assumed.
+ An "identityref" value is mapped to a string representing the name of
+ an identity. Its namespace MUST be expressed as shown in Figure 1 if
+ it is different from the namespace of the leaf node containing the
+ identityref value, and MAY be expressed otherwise.
-3.3.9. The "empty" Type
+ For example, consider the following schematic module:
+
+ module exmod {
+ ...
+ import ietf-interfaces {
+ prefix if;
+ }
+ import iana-if-type {
+ prefix ianaift;
+ }
+ ...
+ leaf type {
+ type identityref {
+ base "if:interface-type";
+ }
+ }
+ }
+
+ A valid instance of the "type" leaf is then encoded as follows:
+
+ "type": "iana-if-type:ethernetCsmacd"
+
+ The namespace identifier "iana-if-type" must be present in this case
+ because the "ethernetCsmacd" identity is not defined in the same
+ module as the "type" leaf.
+
+6.9. The "empty" Type
An "empty" value is mapped to '[null]', i.e., an array with the
- 'null' value being its only element.
+ 'null' literal being its only element.
This encoding was chosen instead of using simply 'null' in order to
facilitate the use of empty leafs in common programming languages.
When used in a boolean context, the '[null]' value, unlike 'null',
- evaluates to 'true'.
+ evaluates to true.
Example: For the leaf definition
leaf foo {
type empty;
}
- the XML element
-
-
-
- corresponds to the JSON name/value pair
+ a valid instance is
"foo": [null]
-3.3.10. The "union" Type
+6.10. The "union" Type
- YANG "union" type represents a choice among multiple alternative
- types. The actual type of the XML value MUST be determined using the
- procedure specified in Sec. 9.12 of [RFC6020] and the mapping rules
- for that type are used.
+ A value of the "union" type is encoded as the value of any of the
+ member types.
+
+ Unlike XML, JSON conveys part of the type information already in the
+ encoding. When validating a value of the "union" type, this
+ information MUST also be taken into account.
For example, consider the following YANG definition:
- leaf-list bar {
+ leaf bar {
type union {
type uint16;
type string;
}
}
- The sequence of three XML elements
+ In RESTCONF [I-D.ietf-netconf-restconf], it is fully acceptable to
+ set the value of "bar" in the following way when using the
+ "application/yang.data+xml" media type:
- 6378
- 14.5
- infinity
+ 13.5
- will then be translated to this name/array pair:
+ because the value may be interpreted as a string, i.e., the second
+ member type of the union. When using the "application/
+ yang.data+json" media type, however, this is an error:
- "bar": [6378, "14.5", "infinity"]
+ "bar": 13.5
-3.3.11. The "instance-identifier" Type
+ In this case, the JSON encoding indicates the value is supposed to be
+ a number rather than string.
- An "instance-identifier" value is a string representing a simplified
- XPath specification. It is mapped to an analogical JSON string in
- which all occurrences of XML namespace prefixes are either removed or
- replaced with the corresponding module name according to the rules of
- Section 3.1.
+6.11. The "instance-identifier" Type
- When translating such a value from JSON to XML, all components of the
- instance-identifier MUST be given appropriate XML namespace prefixes.
- It is RECOMMENDED that these prefixes be those defined via the
- "prefix" statement in the corresponding YANG modules.
+ An "instance-identifier" value is encoded as a string that is
+ analogical to the lexical representation in XML encoding, see
+ sec. 9.13.3 in [RFC6020]. The only difference is that XML namespace
+ prefixes used for qualifying node names in the instance-identifier
+ value are replaced by the corresponding module names according to the
+ rules of Section 4.
- For example, assume "ex" is the prefix defined for the "example"
- module. Then the XML-encoded instance identifier
+ Conversely, when translating such a value from JSON to XML, the
+ namespace identifier (YANG module name) in each component of the
+ instance-identifier MUST be replaced by the XML namespace prefix that
+ is associated with the namespace URI reference of the module.
+
+ For example, assume "ex" is the prefix associated with the namespace
+ URI that is defined in the "example" module. Then the XML-encoded
+ instance-identifier
/ex:system/ex:user[ex:name='fred']
- corresponds to the following JSON-encoded instance identifier:
+ corresponds to the following JSON-encoded instance-identifier:
/example:system/example:user[example:name='fred']
- or simply
-
- /system/user[name='fred']
-
- if the local names of the data nodes "system", "user" and "name" are
- unambiguous.
-
-4. Encoding Metadata in JSON
-
- By design, YANG does not allow for modeling XML attributes. However,
- attributes are often used in XML instance documents for attaching
- various types of metadata information to elements. It is therefore
- desirable to have a standard way for representing attributes in JSON
- documents as well.
-
- The metadata encoding defined in the rest of this section satisfies
- the following two important requirements:
-
- 1. There has to be a way for adding metadata to instances of all
- types of YANG data nodes, i.e., leafs, containers, list and leaf-
- list entries, and anyxml nodes.
-
- 2. The encoding of YANG data node instances as defined in the
- previous sections must not change.
-
- Existing proposals for metadata encoding in JSON, such as
- [JSON-META], are oriented on rather specific uses of metadata, and
- fall short with respect to the first requirement.
-
- All attributes assigned to an XML element are mapped in JSON to
- members (name/value pairs) of a single object, henceforth denoted as
- the metadata object. The placement of this object depends on the
- type of the element from YANG viewpoint, as specified in the
- following paragraphs.
-
- For an XML element that is translated to a JSON object (i.e., a
- container, anyxml node and list entry), the metadata object is added
- as a new member of that object with the name "@".
-
- Examples:
-
- o If "cask" is a container or anyxml node, the XML instance with
- attributes
-
-
- ...
-
-
- is mapped to the following JSON object:
-
- "cask": {
- "@": {
- "foo": "a",
- "bar": "b"
- }
- ...
- }
-
- o If "seq" is a list, then the pair of XML elements
-
-
- one
-
-
- two
-
-
- is mapped to the following JSON array:
-
- "seq": [
- {
- "@": {
- "foo": "a"
- },
- "name": "one"
- },
- {
- "@": {
- "bar": "b"
- },
- "name": "two"
- }
- ]
-
- In order to assign attributes to a leaf instance, a sibling name/
- value pair is added, where the name is the symbol "@" concatenated
- with the identifier of the leaf.
-
- For example, the element
-
- true
-
- is mapped to the following two name/value pairs:
-
- "flag": true,
- "@flag": {
- "foo": "a",
- "bar": "b"
- }
+7. I-JSON Compliance
- Finally, for a leaf-list instance, which is represented as a JSON
- array with primitive values, attributes may be assigned to one or
- more entries by adding a sibling name/value pair, where the name is
- the symbol "@" concatenated with the identifier of the leaf-list, and
- the value is a JSON array whose i-th element is the metadata object
- with attributes assigned to the i-th entry of the leaf-list, or nil
- if the i-th entry has no attributes.
+ I-JSON [I-D.ietf-json-i-json] is a restricted profile of JSON that
+ guarantees maximum interoperability for protocols that use JSON in
+ their messages, no matter what JSON encoders/decoders are used in
+ protocol implementations. The encoding defined in this document
+ therefore observes the I-JSON requirements and recommendations as
+ closely as possible.
- Trailing nil values in the array, i.e., those following the last non-
- nil metadata object, MAY be omitted.
+ In particular, the following properties are guaranteed:
- For example, a leaf-list instance with four entries
+ o Character encoding is UTF-8.
- 6
- 3
- 7
- 8
+ o Member names within the same JSON object are always unique.
- is mapped to the following two name/value pairs:
+ o The order of JSON object members is never relied upon.
- "folio": [6, 3, 7, 8],
- "@folio": [nil, {"foo": "a"}, {"bar": "b"}]
+ o Numbers of any type supported by YANG can be exchanged reliably.
+ See Section 6.1 for details.
- The encoding of attributes as specified above has the following two
- limitations:
+ The only two cases where a JSON instance document encoded according
+ to this document may deviate from I-JSON were dictated by the need to
+ be able to encode the same instance data in both JSON and XML. These
+ two exceptions are:
- o Mapping of namespaces of XML attributes is undefined.
+ o Leaf values encoded as strings may contain code points identifying
+ Noncharacters that belong to the XML character set (see sec. 2.2
+ in [W3C.REC-xml-20081126]).
- o Attribute values can only be strings, other data types are not
- supported.
+ o Values of the "binary" type are encoded with the base64 encoding
+ scheme (see sec. 9.8.2 in [RFC6020]) whereas I-JSON recommends
+ base64url instead. However, the use of base64 should not cause
+ any interoperability problems because these values never appear in
+ an URL.
-5. IANA Considerations
+8. Security Considerations
- TBD - register application/yang.data+json media type?
+ This document defines an alternative encoding for data modeled in the
+ YANG data modeling language. As such, it doesn't contribute any new
+ security issues beyond those discussed in sec. 15 of [RFC6020].
-6. Security Considerations
+ JSON is rather different from XML, and JSON parsers may thus suffer
+ from other types of vulnerabilities than their XML counterparts. To
+ minimize these security risks, it is important that client and server
+ software supporting JSON encoding behaves as required in sec. 3 of
+ [I-D.ietf-json-i-json]. That is, any received JSON data that violate
+ any of I-JSON strict constraints MUST NOT be trusted nor acted upon.
+ Violations due to the presence of Unicode Noncharacters in the data
+ exceptions (see Section 7) SHOULD be carefully examined.
- TBD.
+9. Acknowledgments
-7. Acknowledgments
+ The author wishes to thank Andy Bierman, Martin Bjorklund, Juergen
+ Schoenwaelder and Phil Shafer for their helpful comments and
+ suggestions.
- The author wishes to thank Andy Bierman, Martin Bjorklund and Phil
- Shafer for their helpful comments and suggestions.
+10. References
-8. References
+10.1. Normative References
-8.1. Normative References
+ [I-D.ietf-json-i-json]
+ Bray, T., "The I-JSON Message Format", draft-ietf-json-
+ i-json-03 (work in progress), August 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
- [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
+ [RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
Network Configuration Protocol (NETCONF)", RFC 6020,
- September 2010.
+ October 2010.
[RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
- Bierman, "NETCONF Configuration Protocol", RFC 6241, June
- 2011.
+ Bierman, "Network Configuration Protocol (NETCONF)", RFC
+ 6241, June 2011.
- [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
+ [RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, March 2014.
- [XMLNS] Bray, T., Hollander, D., Layman, A., Tobin, R., and H.
- Thompson, "Namespaces in XML 1.0 (Third Edition)", World
- Wide Web Consortium Recommendation REC-xml-names-20091208,
- December 2009,
- .
-
- [XML] Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and
+ [W3C.REC-xml-20081126]
+ Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20081126, November 2008,
- .
-
-8.2. Informative References
+ .
- [IF-CFG] Bjorklund, M., "A YANG Data Model for Interface
- Management", draft-ietf-netmod-interfaces-cfg-16 (work in
- progress), January 2014.
+10.2. Informative References
- [JSON-META]
- Sakimura, N., "JSON Metadata", draft-sakimura-json-
- metadata-01 (work in progress), November 2013.
+ [I-D.ietf-netconf-restconf]
+ Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
+ Protocol", draft-ietf-netconf-restconf-02 (work in
+ progress), October 2014.
- [RESTCONF]
- Bierman, A., Bjorklund, M., Watsen, K., and R. Fernando,
- "RESTCONF Protocol", draft-ietf-netconf-restconf-00 (work
- in progress), March 2014.
+ [RFC7223] Bjorklund, M., "A YANG Data Model for Interface
+ Management", RFC 7223, May 2014.
- [XPath] Clark, J., "XML Path Language (XPath) Version 1.0", World
- Wide Web Consortium Recommendation REC-xpath-19991116,
- November 1999,
+ [W3C.REC-xpath-19991116]
+ Clark, J. and S. DeRose, "XML Path Language (XPath)
+ Version 1.0", World Wide Web Consortium Recommendation
+ REC-xpath-19991116, November 1999,
.
Appendix A. A Complete Example
- The JSON document shown below was translated from a reply to the
- NETCONF request that can be found in Appendix D of [IF-CFG].
+ The JSON document shown below represents the same data as the reply
+ to the NETCONF request appearing in Appendix D of [RFC7223].
The data model is a combination of two YANG modules: "ietf-
interfaces" and "ex-vlan" (the latter is an example module from
- Appendix C of [IF-CFG]). The "if-mib" feature defined in the "ietf-
+ Appendix C of [RFC7223]). The "if-mib" feature defined in the "ietf-
interfaces" module is considered to be active.
{
- "interfaces": {
+ "ietf-interfaces:interfaces": {
"interface": [
{
"name": "eth0",
"type": "iana-if-type:ethernetCsmacd",
"enabled": false
},
{
"name": "eth1",
"type": "iana-if-type:ethernetCsmacd",
"enabled": true,
- "vlan-tagging": true
+ "ex-vlan:vlan-tagging": true
},
{
"name": "eth1.10",
"type": "iana-if-type:l2vlan",
"enabled": true,
- "base-interface": "eth1",
- "vlan-id": 10
+ "ex-vlan:base-interface": "eth1",
+ "ex-vlan:vlan-id": 10
},
{
"name": "lo1",
"type": "iana-if-type:softwareLoopback",
"enabled": true
}
]
},
- "interfaces-state": {
+ "ietf-interfaces:interfaces-state": {
"interface": [
{
"name": "eth0",
"type": "iana-if-type:ethernetCsmacd",
"admin-status": "down",
"oper-status": "down",
"if-index": 2,
"phys-address": "00:01:02:03:04:05",
"statistics": {
"discontinuity-time": "2013-04-01T03:00:00+00:00"
@@ -897,16 +734,45 @@
"oper-status": "up",
"if-index": 1,
"statistics": {
"discontinuity-time": "2013-04-01T03:00:00+00:00"
}
}
]
}
}
+Appendix B. Change Log
+
+ RFC Editor: Remove this section upon publication as an RFC.
+
+B.1. Changes Between Revisions -00 and -01
+
+ o Metadata encoding was moved to a separate I-D, draft-lhotka-
+ netmod-yang-metadata.
+
+ o JSON encoding is now defined directly rather than via XML-JSON
+ mapping.
+
+ o The rules for namespace encoding has changed. This affect both
+ node instance names and instance-identifiers.
+
+ o I-JSON-related changes. The most significant is the string
+ encoding of 64-bit numbers.
+
+ o When validating union type, the partial type info present in JSON
+ encoding is taken into account.
+
+ o Added section about I-JSON compliance.
+
+ o Updated the example in appendix.
+
+ o Wrote Security Considerations.
+
+ o Removed IANA Considerations as there are none.
+
Author's Address
Ladislav Lhotka
CZ.NIC
Email: lhotka@nic.cz