3.3. Metadata Inheritance and Override

In the metadata object model, a HostMetadata object can contain multiple PathMetadata objects (via PathMatch objects). Each PathMetadata object can in turn contain other PathMetadata objects. HostMetadata and PathMetadata objects form an inheritance tree where each node in the tree inherits or overrides the property values set by its parent.

GenericMetadata objects of a given type override all GenericMetadata objects of the same type previously defined by any parent object in the tree. GenericMetadata objects of a given type previously defined by a parent object in the tree are inherited when no object of the same type is defined by the child object. For example, if HostMetadata for the host "example.com" contains GenericMetadata objects of type LocationACL and TimeWindowACL, while a PathMetadata object which applies to "example.com/movies/*" defines an alternate GenericMetadata object of type TimeWindowACL, then:

• the TimeWindowACL defined in the PathMetadata would override the TimeWindowACL defined in the HostMetadata for all User Agent requests for content under "example.com/movies/", and
• the LocationACL defined in the HostMetadata would be inherited for all User Agent requests for content under "example.com/movies/".

A single HostMetadata or PathMetadata object MUST NOT contain multiple GenericMetadata objects of the same type. If a list of GenericMetadata contains objects of duplicate types, the receiver MUST ignore all but the first object of each type.

4. CDNI Metadata objects

Section 4.1 provides the definitions of each metadata object type introduced in Section 3. These metadata objects are described as structural metadata objects as they provide the structure for host and URI path-based inheritance and identify which GenericMetadata objects apply to a given User Agent content request.

Section 4.2 provides the definitions for a base set of core metadata objects which can be contained within a GenericMetadata object. These metadata objects govern how User Agent requests for content are handled. GenericMetadata objects can contain other GenericMetadata as properties; these can be referred to as sub-objects). As with all CDNI metadata objects, the value of the GenericMetadata sub-objects can be either a complete serialized representation of the sub-object, or a Link object that contains a URI that can be dereferenced to retrieve the complete serialized representation of the property sub-object.

Section 6.5 discusses the ability to extend the base set of GenericMetadata objects specified in this document with additional standards-based or vendor specific GenericMetadata objects that might be defined in the future in separate documents.

dCDNs and tCDNs MUST support parsing of all CDNI metadata objects specified in this document. A dCDN does not have to implement the underlying functionality represented by non-structural GenericMetadata objects (though that might restrict the content that a given dCDN will be able to serve). uCDNs as generators of CDNI metadata only need to support generating the CDNI metadata that they need in order to express the policies required by the content they are describing.

CDNI metadata objects MUST be encoded as I-JSON objects [RFC7493] containing a dictionary of (key,value) pairs where the keys are the property names and the values are the associated property values. See Section 6.4 for more details of the specific encoding rules for CDNI metadata objects.

Note: In the following sections, the term "mandatory-to-specify" is used to convey which properties MUST be included for a given structural or GenericMetadata object. When mandatory-to-specify is specified as "Yes" for an individual property, it means that if the object containing that property is included in a metadata response, then the mandatory-to-specify property MUST also be included (directly or by reference) in the response, e.g., a HostMatch property object without a host to match against does not make sense, therefore, the host property is mandatory-to-specify inside a HostMatch object.

4.1. Definitions of the CDNI structural metadata objects

Each of the sub-sections below describe the structural objects introduced in Section 3.1.

4.1.1. HostIndex

The HostIndex object is the entry point into the CDNI metadata hierarchy. It contains a list of HostMatch objects. An incoming content request is checked against the Hostname (or IP address) specified by each of the listed HostMatch objects to find the HostMatch object which applies to the request.

• Property: hosts
  • Description: List of HostMatch objects. Hosts (HostMatch objects) MUST be evaluated in the order they appear and the first HostMatch object that matches the content request being processed MUST be used.
  • Type: List of HostMatch objects
  • Mandatory-to-Specify: Yes.

Example HostIndex object containing two HostMatch objects, where the first HostMatch object is embedded and the second HostMatch object is referenced:

{
  "hosts": [
    {
      <Properties of embedded HostMatch object>
    },
    {
      "type": "MI.HostMatch",
      "href": "http://metadata.ucdn.example/hostmatch1234"
    }
  ]
}

4.1.2. HostMatch

The HostMatch object contains a Hostname or IP address to match against content requests. The HostMatch object also contains a HostMetadata object to apply if a match is found.

• Property: host
  • Description: Hostname or IP address to match against the requested host. In order for a Hostname or IP address in a content request to match the Hostname or IP address in the host property the value from the content request when converted to lowercase MUST be identical to the value of the host property when converted to lowercase.
  • Type: Endpoint
  • Mandatory-to-Specify: Yes.

• Property: host-metadata
  • Description: CDNI metadata to apply when delivering content that matches this host.
  • Type: HostMetadata
  • Mandatory-to-Specify: Yes.

Example HostMatch object with an embedded HostMetadata object:

{
  "host": "video.example.com",
  "host-metadata" : {
    <Properties of embedded HostMetadata object>
  }
}

Example HostMatch object referencing (via a Link object, see Section 4.3.1) a HostMetadata object:

{
  "host": "video.example.com",
  "host-metadata" : {
    "type": "MI.HostMetadata",
    "href": "http://metadata.ucdn.example/host1234"
  }
}

4.1.3. HostMetadata

A HostMetadata object contains the CDNI metadata properties for content served for a particular host (defined in the HostMatch object) and possibly child PathMatch objects.

• Property: metadata
  • Description: List of host related metadata.
  • Type: List of GenericMetadata objects
  • Mandatory-to-Specify: Yes.

• Property: paths
  • Description: Path specific rules. Path patterns (PathMatch objects) MUST be evaluated in the order they appear and the first PathMatch object that matches the content request being processed MUST be used.
  • Type: List of PathMatch objects
  • Mandatory-to-Specify: No.

Example HostMetadata object containing a number of embedded GenericMetadata objects that will describe the default metadata for the host and an embedded PathMatch object that contains a path for which metadata exists that overrides the default metadata for the host:

{
  "metadata": [
    {
      <Properties of 1st embedded GenericMetadata object>
    },
    {
      <Properties of 2nd embedded GenericMetadata object>
    },

 ... 

    {
      <Properties of Nth embedded GenericMetadata object>
    }
  ],
  "paths": [
    {
      <Properties of embedded PathMatch object>
    }
  ]
}

4.1.4. PathMatch

A PathMatch object contains PatternMatch object with a path to match against a resource's URI path, as well as a PathMetadata object with GenericMetadata to apply if the resource's URI path matches the pattern within the PatternMatch object.

• Property: path-pattern
  • Description: Pattern to match against the requested resource's URI path, i.e., against the [RFC3986] path-absolute.
  • Type: PatternMatch
  • Mandatory-to-Specify: Yes.

• Property: path-metadata
  • Description: CDNI metadata to apply when delivering content that matches the associated PatternMatch.
  • Type: PathMetadata
  • Mandatory-to-Specify: Yes.

Example PathMatch object referencing the PathMetadata object to use for URIs that match the case-sensitive URI path pattern "/movies/*" (contained within an embedded PatternMatch object):

{
  "path-pattern": {
    "pattern": "/movies/*",
    "case-sensitive": true
  },
  "path-metadata": {
      "type": "MI.PathMetadata",
      "href": "http://metadata.ucdn.example/host1234/pathDCE"
  }
}

4.1.5. PatternMatch

A PatternMatch object contains the pattern string and flags that describe the pattern expression.

• Property: pattern
  • Description: A pattern for string matching. The pattern can contain the wildcards * and ?, where * matches any sequence of characters (including the empty string) and ? matches exactly one character. The three literals $, * and ? should be escaped as $$, $* and $?. All other characters are treated as literals.
  • Type: String
  • Mandatory-to-Specify: Yes.

• Property: case-sensitive
  • Description: Flag indicating whether or not case-sensitive matching should be used.
  • Type: Boolean
  • Mandatory-to-Specify: No. Default is case-insensitive match.

• Property: ignore-query-string
  • Description: List of query parameters which should be ignored when searching for a pattern match. Matching against query parameters to ignore MUST be case-insensitive. If all query parameters should be ignored then the list MUST be empty.
  • Type: List of String
  • Mandatory-to-Specify: No. Default is to include query strings when matching.

Example PatternMatch object that matches the case-sensitive URI path pattern "/movies/*". All query parameters will be ignored when matching URIs requested from surrogates by content clients against this path pattern:

{
  "pattern": "/movies/*",
  "case-sensitive": true,
  "ignore-query-string": []
}

Example PatternMatch object that matches the case-sensitive URI path pattern "/movies/*". The query parameter "sessionid" will be ignored when matching URIs requested from surrogates by content clients against this path pattern:

{
  "pattern": "/movies/*",
  "case-sensitive": true,
  "ignore-query-string": ["sessionid"]
}

4.1.6. PathMetadata

A PathMetadata object contains the CDNI metadata properties for content requests that match against the associated URI path (defined in a PathMatch object).

Note that if DNS-based redirection is employed, then a dCDN will be unable to evaulate any metadata at the PathMetadata level or below because only the hostname of the content request is available at request routing time. dCDNs SHOULD still process all PathMetadata for the host before responding to the redirection request to detect if any unsupported metadata is specifed. If any metadata not supported by the dCDN is marked as "mandatory-to-enforce", the dCDN SHOULD NOT accept the content redirection request, in order to avoid receiving content requests that it will not be able to satisfy/serve.

• Property: metadata
  • Description: List of path related metadata.
  • Type: List of GenericMetadata objects
  • Mandatory-to-Specify: Yes.

• Property: paths
  • Description: Path specific rules. First match applies.
  • Type: List of PathMatch objects
  • Mandatory-to-Specify: No.

Example PathMetadata object containing a number of embedded GenericMetadata objects that describe the metadata to apply for the URI path defined in the parent PathMatch object, as well as a more specific PathMatch object.

{
  "metadata": [
    {
      <Properties of 1st embedded GenericMetadata object>
    },
    {
      <Properties of 2nd embedded GenericMetadata object>
    },

 ... 

    {
      <Properties of Nth embedded GenericMetadata object>
    }
  ],
  "paths": [
    {
      <Properties of embedded PathMatch object>
    }
  ]
}

4.1.7. GenericMetadata

A GenericMetadata object is a wrapper for managing individual CDNI metadata properties in an opaque manner.

• Property: generic-metadata-type
  • Description: Case-insensitive CDNI metadata object type.
  • Type: String containing the CDNI Payload Type [RFC7736] of the object contained in the generic-metadata-value property (see Table 4).
  • Mandatory-to-Specify: Yes.

• Property: generic-metadata-value
  • Description: CDNI metadata object.
  • Type: Format/Type is defined by the value of generic-metadata-type property above. Note: generic-metadata-values MUST NOT name any properties "href" (see Section 4.3.1).
  • Mandatory-to-Specify: Yes.

• Property: mandatory-to-enforce
  • Description: Flag identifying whether or not the enforcement of the property metadata is required.
  • Type: Boolean
  • Mandatory-to-Specify: No. Default is to treat metadata as mandatory to enforce (i.e., a value of True).

• Property: safe-to-redistribute
  • Description: Flag identifying whether or not the property metadata can be safely redistributed without modification.
  • Type: Boolean
  • Mandatory-to-Specify: No. Default is allow transparent redistribution (i.e., a value of True).

• Property: incomprehensible
  • Description: Flag identifying whether or not any CDN in the chain of delegation has failed to understand and/or failed to properly transform this metadata object. Note: This flag only applies to metadata objects whose safe-to-redistribute property has a value of False.
  • Type: Boolean
  • Mandatory-to-Specify: No. Default is comprehensible (i.e., a value of False).

Example GenericMetadata object containing a metadata object that applies to the applicable URI path and/or host (within a parent PathMetadata and/or HostMetadata object, respectively):

{
  "mandatory-to-enforce": true,
  "safe-to-redistribute": true,
  "incomprehensible": false,
  "generic-metadata-type": <CDNI Payload Type of this metadata object>,
  "generic-metadata-value":
    {
      <Properties of this metadata object>
    }
}

4.2. Definitions of the initial set of CDNI Generic Metadata objects

The objects defined below are intended to be used in the GenericMetadata object generic-metadata-value field as defined in Section 4.1.7 and their generic-metadata-type property MUST be set to the appropriate CDNI Payload Type as defined in Table 4.

4.2.1. SourceMetadata

Source metadata provides the dCDN with information about content acquisition, i.e., how to contact an uCDN Surrogate or an Origin Server to obtain the content to be served. The sources are not necessarily the actual Origin Servers operated by the CSP but might be a set of Surrogates in the uCDN.

• Property: sources
  • Description: Sources from which the dCDN can acquire content, listed in order of preference.
  • Type: List of Source objects (see Section 4.2.1.1)
  • Mandatory-to-Specify: No. Default is to use static configuration, out-of-band from the metadata interface.

Example SourceMetadata object (which contains two Source objects) that describes which servers the dCDN should use for acquiring content for the applicable URI path and/or host:

{
  "generic-metadata-type": "MI.SourceMetadata",
  "generic-metadata-value":
    {
      "sources": [
        {
          "endpoints": [
            "a.service123.ucdn.example",
            "b.service123.ucdn.example"
            ],
          "protocol": "http1.1"
        },
        {
          "endpoints": ["origin.service123.example"],
          "protocol": "http1.1"
        }
      ]
    }
}

4.2.1.1. Source

A Source object describes the source to be used by the dCDN for content acquisition (e.g., a Surrogate within the uCDN or an alternate Origin Server), the protocol to be used, and any authentication method to be used when contacting that source.

Endpoints within a Source object MUST be treated as equivalent/equal. A uCDN can specify a list of sources in preference order within a SourceMetadata objecct, and then for each preference ranked Source object, a uCDN can specify a list of endpoints that are equivalent (e.g., a pool of servers that are not behind a load balancer).

• Property: acquisition-auth
  • Description: Authentication method to use when requesting content from this source.
  • Type: Auth (see Section 4.2.7)
  • Mandatory-to-Specify: No. Default is no authentication required.

• Property: endpoints
  • Description: Origins from which the dCDN can acquire content. If multiple endpoints are specified they are all equal, i.e., the list is not in preference order (e.g., a pool of servers behind a load balancer).
  • Type: List of Endpoint objects (See Section 4.3.3)
  • Mandatory-to-Specify: Yes.

• Property: protocol
  • Description: Network retrieval protocol to use when requesting content from this source.
  • Type: Protocol (see Section 4.3.2)
  • Mandatory-to-Specify: Yes.

Example Source object that describes a pair of endpoints (servers) the dCDN can use for acquiring content for the applicable host and/or URI path:

{
  "endpoints": [
    "a.service123.ucdn.example",
    "b.service123.ucdn.example"
  ],
  "protocol": "http1.1"
}

4.2.2. LocationACL Metadata

LocationACL metadata defines which locations a User Agent needs to be in, in order to be able to receive the associated content.

A LocationACL which does not include a locations property results in an action of allow all, meaning that delivery can be performed regardless of the User Agent's location, otherwise a CDN MUST take the action from the first footprint to match against the User Agent's location. If two or more footprints overlap, the first footprint that matches against the User Agent's location determines the action a CDN MUST take. If the locations property is included but is empty, or if none of the listed footprints matches the User Agent's location, then the result is an action of deny.

Although the LocationACL, TimeWindowACL (see Section 4.2.3), and ProtocolACL (see Section 4.2.4) are independent GenericMetadata objects, they can provide conflicting information to a dCDN, e.g., a content request which is simultaneously allowed based on the LocationACL and denied based on the TimeWindowACL. The dCDN MUST use the logical AND of all ACLs (where 'allow' is true and 'deny' is false) to determine whether or not a request should be allowed.

• Property: locations
  • Description: Access control list which allows or denies (blocks) delivery based on the User Agent's location.
  • Type: List of LocationRule objects (see Section 4.2.2.1)
  • Mandatory-to-Specify: No. Default is allow all locations.

Example LocationACL object that allows the dCDN to deliver content to any location/IP address:

{
  "generic-metadata-type": "MI.LocationACL",
  "generic-metadata-value":
    {
    }
}

Example LocationACL object (which contains a LocationRule object which itself contains a Footprint object) that only allows the dCDN to deliver content to User Agents in the USA:

{
  "generic-metadata-type": "MI.LocationACL",
  "generic-metadata-value":
    {
      "locations": [
        {
          "action": "allow",
          "footprints": [
            {
              "footprint-type": "countrycode",
              "footprint-value": ["us"]
            }
          ]
        }
      ]
    }
}

4.2.2.1. LocationRule

A LocationRule contains or references a list of Footprint objects and the corresponding action.

• Property: footprints
  • Description: List of footprints to which the rule applies.
  • Type: List of Footprint objects (see Section 4.2.2.2)
  • Mandatory-to-Specify: Yes.

• Property: action
  • Description: Defines whether the rule specifies locations to allow or deny.
  • Type: Enumeration [allow|deny] encoded as a lowercase string
  • Mandatory-to-Specify: No. Default is deny.

Example LocationRule object (which contains a Footprint object) that allows the dCDN to deliver content to clients in the USA:

{
  "action": "allow",
  "footprints": [
    {
      "footprint-type": "countrycode",
      "footprint-value": ["us"]
    }
  ]
}
}

4.2.2.2. Footprint

A Footprint object describes the footprint to which a LocationRule can be applied to, e.g., an IPv4 address range or a geographic location.

• Property: footprint-type
  • Description: Registered footprint type (see Section 7.2). The footprint types specified by this document are: "ipv4cidr" (IPv4CIDR, see Section 4.3.5), "ipv6cidr" (IPv6CIDR, see Section 4.3.6), "asn" (Autonomous System Number, see Section 4.3.7) and "countrycode" (Country Code, see Section 4.3.8).
  • Type: Lowercase String
  • Mandatory-to-Specify: Yes.

• Property: footprint-value
  • Description: List of footprint values conforming to the specification associated with the registered footprint type. Footprint values can be simple strings (e.g., IPv4CIDR, IPv6CIDR, ASN, and CountryCode), however, other Footprint objects can be defined in the future, along with a more complex encoding (e.g., GPS coordinate tuples).
  • Type: List of footprints
  • Mandatory-to-Specify: Yes.

Example Footprint object describing a footprint covering the USA:

{
  "footprint-type": "countrycode",
  "footprint-value": ["us"]
}

Example Footprint object describing a footprint covering the IP address ranges 192.0.2.0/24 and 198.51.100.0/24:

{
  "footprint-type": "ipv4cidr",
  "footprint-value": ["192.0.2.0/24", "198.51.100.0/24"]
}

4.2.3. TimeWindowACL

TimeWindowACL metadata defines time-based restrictions.

A TimeWindowACL which does not include a times property results in an action of allow all, meaning that delivery can be performed regardless of the time of the User Agent's request, otherwise a CDN MUST take the action from the first window to match against the current time. If two or more windows overlap, the first window that matches against the current time determines the action a CDN MUST take. If the times property is included but is empty, or if none of the listed windows matches the current time, then the result is an action of deny.

Although the LocationACL (see Section 4.2.2), TimeWindowACL, and ProtocolACL (see Section 4.2.4) are independent GenericMetadata objects, they can provide conflicting information to a dCDN, e.g., a content request which is simultaneously allowed based on the LocationACL and denied based on the TimeWindowACL. The dCDN MUST use the logical AND of all ACLs (where 'allow' is true and 'deny' is false) to determine whether or not a request should be allowed.

• Property: times
  • Description: Access control list which allows or denies (blocks) delivery based on the time of a User Agent's request.
  • Type: List of TimeWindowRule objects (see Section 4.2.3.1)
  • Mandatory-to-Specify: No. Default is allow all time windows.

Example TimeWIndowACL object (which contains a TimeWindowRule object which itself contains a TimeWIndow object) that only allows the dCDN to deliver content to clients between 09:00 01/01/2000 UTC and 17:00 01/01/2000 UTC:

{
  "generic-metadata-type": "MI.TimeWindowACL",
  "generic-metadata-value":
    {
      "times": [
        {
          "action": "allow",
          "windows": [
            {
              "start": 946717200,
              "end": 946746000
            }
          ]
        }
      ]
    }
}

4.2.3.1. TimeWindowRule

A TimeWindowRule contains or references a list of TimeWindow objects and the corresponding action.

• Property: windows
  • Description: List of time windows to which the rule applies.
  • Type: List of TimeWindow objects (see Section 4.2.3.2)
  • Mandatory-to-Specify: Yes.

• Property: action
  • Description: Defines whether the rule specifies time windows to allow or deny.
  • Type: Enumeration [allow|deny] encoded as a lowercase string
  • Mandatory-to-Specify: No. Default is deny.

Example TimeWIndowRule object (which contains a TimeWIndow object) that only allows the dCDN to deliver content to clients between 09:00 01/01/2000 UTC and 17:00 01/01/2000 UTC:

{
  "action": "allow",
  "windows": [
    {
      "start": 946717200,
      "end": 946746000
    }
  ]
}

4.2.3.2. TimeWindow

A TimeWindow object describes a time range which can be applied by an TimeWindowACL, e.g., start 946717200 (i.e., 09:00 01/01/2000 UTC), end: 946746000 (i.e., 17:00 01/01/2000 UTC).

• Property: start
  • Description: The start time of the window.
  • Type: Time (see Section 4.3.4)
  • Mandatory-to-Specify: Yes.

• Property: end
  • Description: The end time of the window.
  • Type: Time (see Section 4.3.4)
  • Mandatory-to-Specify: Yes.

Example TimeWIndow object that describes a time window from 09:00 01/01/2000 UTC to 17:00 01/01/2000 UTC:

{
  "start": 946717200,
  "end": 946746000
}

4.2.4. ProtocolACL Metadata

ProtocolACL metadata defines delivery protocol restrictions.

A ProtocolACL which does not include a protocol-acl property results in an action of allow all, meaning that delivery can be performed regardless of the protocol in the User Agent's request, otherwise a CDN MUST take the action from the first protocol to match against the request protocol. If two or more request protocols overlap, the first protocol that matches the request protocol determines the action a CDN MUST take. If the protocol-acl property is included but is empty, or if none of the listed protocol matches the request protocol, then the result is an action of deny.

Although the LocationACL, TimeWindowACL, and ProtocolACL are independent GenericMetadata objects, they can provide conflicting information to a dCDN, e.g., a content request which is simultaneously allowed based on the ProtocolACL and denied based on the TimeWindowACL. The dCDN MUST use the logical AND of all ACLs (where 'allow' is true and 'deny' is false) to determine whether or not a request should be allowed.

• Property: protocol-acl
  • Description: Description: Access control list which allows or denies (blocks) delivery based on delivery protocol.
  • Type: List of ProtocolRule objects (see Section 4.2.4.1)
  • Mandatory-to-Specify: No. Default is allow all protocols.

Example ProtocolACL object (which contains a ProtocolRule object) that only allows the dCDN to deliver content using HTTP/1.1:

{
  "generic-metadata-type": "MI.ProtocolACL",
  "generic-metadata-value":
    {
      "protocol-acl": [
        {
          "action": "allow",
          "protocols": ["http1.1"]
        }
      ]
    }
}

4.2.4.1. ProtocolRule

A ProtocolRule contains or references a list of Protocol objects and the corresponding action.

• Property: protocols
  • Description: List of protocols to which the rule applies.
  • Type: List of Protocols (see Section 4.3.2)
  • Mandatory-to-Specify: Yes.

• Property: action
  • Description: Defines whether the rule specifies protocols to allow or deny.
  • Type: Enumeration [allow|deny] encoded as a lowercase string
  • Mandatory-to-Specify: No. Default is deny.

Example ProtocolRule object (which contains a ProtocolRule object) that allows the dCDN to deliver content using HTTP/1.1:

{
  "action": "allow",
  "protocols": ["http1.1"]
}

4.2.5. DeliveryAuthorization Metadata

Delivery Authorization defines authorization methods for the delivery of content to User Agents.

• Property: delivery-auth-methods
  • Description: Options for authorizing content requests. Delivery for a content request is authorized if any of the authorization methods in the list is satisfied for that request.
  • Type: List of Auth objects (see Section 4.2.7)
  • Mandatory-to-Specify: No. Default is no authorization required.

Example DeliveryAuthorization object (which contains an Auth object):

{
  "generic-metadata-type": "MI.DeliveryAuthorization",
  "generic-metadata-value":
    {
      "delivery-auth-methods": [
        {
          "auth-type": <CDNI Payload Type of this Auth object>,
          "auth-value":
          {
            <Properties of this Auth object>
          }
        }
      ]
    }
}

4.2.6. Cache

A Cache object describes the cache control parameters to be applied to the content by intermediate caches.

• Property: ignore-query-string
  • Description: Allows a Surrogate to ignore URI query string parameters when comparing the requested URI against the URIs in its cache for equivalence. Matching query parameters to ignore MUST be case-insensitive. Each query parameter to ignore is specified in the list. If all query parameters should be ignored, then the list MUST be specified and MUST be empty.
  • Type: List of String
  • Mandatory-to-Specify: No. Default is to consider query string parameters when comparing URIs.

Example Cache object that instructs the dCDN to ignore all query parameters:

{
  "generic-metadata-type": "MI.Cache",
  "generic-metadata-value":
  {
    "ignore-query-string": []
  }
}

Example Cache object that instructs the dCDN to ignore the (case-insensitive) query parameters named "sessionid" and "random":

{
  "generic-metadata-type": "MI.Cache",
  "generic-metadata-value":
  {
    "ignore-query-string": ["sessionid", "random"]
  }
}

4.2.7. Auth

An Auth object defines authentication and authorization methods to be used during content acquisition and content delivery, respectively.

• Property: auth-type
  • Description: Registered Auth type (Section 7.4).
  • Type: String
  • Mandatory-to-Specify: Yes.

• Property: auth-value
  • Description: An object conforming to the specification associated with the Registered Auth type.
  • Type: GenericMetadata Object
  • Mandatory-to-Specify: Yes.

Example Auth object:

{
  "generic-metadata-type": "MI.Auth",
  "generic-metadata-value":
  {
    "auth-type": <CDNI Payload Type of this Auth object>,
    "auth-value":
      {
        <Properties of this Auth object>
      }
  }
}

4.2.8. Grouping

A Grouping object identifies a group of content to which a given asset belongs.

• Property: ccid
  • Description: Content Collection identifier for an application-specific purpose such as logging aggregation.
  • Type: String
  • Mandatory-to-Specify: No. Default is an empty string.

Example Grouping object that specifies a Content Collection Identifier for the content associated with the Grouping object's parent HostMetdata and PathMetadata:

{
  "generic-metadata-type": "MI.Grouping",
  "generic-metadata-value":
  {
    "ccid": "ABCD"
  }
}

4.3. CDNI Metadata Simple Data Type Descriptions

This section describes the simple data types that are used for properties of CDNI metadata objects.

4.3.1. Link

A Link object can be used in place of any of the objects or properties described above. Link objects can be used to avoid duplication if the same metadata information is repeated within the metadata tree. When a Link object replaces another object, its href property is set to the URI of the resource and its type property is set to the CDNI Payload Type of the object it is replacing.

dCDNs can detect the presence of a Link object by detecting the presence of a property named "href" within the object. This means that GenericMetadata types MUST NOT contain a property named "href" because doing so would conflict with the ability for dCDNs to detect Link objects being used to reference a GenericMetadata object.

• Property: href
  • Description: The URI of the addressable object being referenced.
  • Type: String
  • Mandatory-to-Specify: Yes.

• Property: type
  • Description: The type of the object being referenced.
  • Type: String
  • Mandatory-to-Specify: No. If the container specifies the type (e.g., the HostIndex object contains a list of HostMatch objects, so a Link object in the list of HostMatch objects must reference a HostMatch), then it is not necessary to explicitly specify a type.

Example Link object referencing a HostMatch object:

{
  "type": "MI.HostMatch",
  "href": "http://metadata.ucdn.example/hostmatch1234"
}

Example Link object referencing a HostMatch object, without an explicit type, inside a HostIndex object:

{
  "hosts": [
    {
      <Properties of embedded HostMatch object>
    },
    {
      "href": "http://metadata.ucdn.example/hostmatch1234"
    }
  ]
}

4.3.2. Protocol

Protocol objects are used to specify registered protocols for content acquisition or delivery (see Section 7.3).

Type: String

Example:

"http1.1"

4.3.3. Endpoint

A Hostname (with optional port) or an IP address (with optional port).

Note: All implementations MUST support IPv4 addresses encoded as specified by the 'IPv4address' rule in Section 3.2.2 of [RFC3986]. IPv6 addresses MUST be encoded in one of the IPv6 address formats specified in [RFC5952] although receivers MUST support all IPv6 address formats specified in [RFC4291].

Type: String

Example Hostname:

"metadata.ucdn.example"

Example IPv4 address:

"192.0.2.1"

Example IPv6 address (with port number):

"[2001:db8::1]:81"

4.3.4. Time

A time value expressed in seconds since the Unix epoch in the UTC timezone.

Type: Integer

Example Time representing 09:00 01/01/2000 UTC:

946717200

4.3.5. IPv4CIDR

An IPv4address CIDR block encoded as specified by the 'IPv4address' rule in Section 3.2.2 of [RFC3986] followed by a / followed by an unsigned integer representing the leading bits of the routing prefix (i.e., IPv4 CIDR notation). Single IP addresses can be expressed as /32.

Type: String

Example IPv4 CIDR:

"192.0.2.0/24"

4.3.6. IPv6CIDR

An IPv6address CIDR block encoded in one of the IPv6 address formats specified in [RFC5952] followed by a / followed by an unsigned integer representing the leading bits of the routing prefix (i.e., IPv6 CIDR notation). Single IP addresses can be expressed as /128.

Type: String

Example IPv6 CIDR:

"2001:db8::/32"

4.3.7. ASN

An Autonomous System Number encoded as a string consisting of the characters "as" (in lowercase) followed by the Autonomous System number.

Type: String

Example ASN:

"as64496"

4.3.8. CountryCode

An ISO 3166-1 alpha-2 code [ISO3166-1] in lowercase.

Type: String

Example Country Code representing the USA:

"us"

5. CDNI Metadata Capabilities

CDNI metadata is used to convey information pertaining to content delivery from uCDN to dCDN. For optional metadata, it can be useful for the uCDN to know if the dCDN supports the underlying functionality described by the metadata, prior to delegating any content requests to the dCDN. If some metadata is "mandatory-to-enforce", and the dCDN does not support it, any delegated requests for content that requires that metadata will fail. The uCDN will likely want to avoid delegating those requests to that dCDN. Likewise, for any metadata which might be assigned optional values, it could be useful for the uCDN to know which values a dCDN supports, prior to delegating any content requests to that dCDN. If the optional value assigned to a given piece of content's metadata is not supported by the dCDN, any delegated requests for that content can fail, so again the uCDN is likely to want to avoid delegating those requests to that dCDN.

The CDNI Footprint and Capabilities Interface (FCI) provides a means of advertising capabilities from dCDN to uCDN [RFC7336]. Support for optional metadata types and values can be advertised using the FCI.

6. CDNI Metadata interface

This section specifies an interface to enable a dCDN to retrieve CDNI metadata objects from a uCDN.

The interface can be used by a dCDN to retrieve CDNI metadata objects either:

• Dynamically as required by the dCDN to process received requests. For example in response to a query from an uCDN over the CDNI Request Routing Redirection interface (RI) [I-D.ietf-cdni-redirection] or in response to receiving a request for content from a User Agent. Or;
• In advance of being required. For example in the case of pre-positioned CDNI metadata acquisition, initiated through the "CDNI Control interface / Triggers" (CI/T) interface [I-D.ietf-cdni-control-triggers].

The CDNI metadata interface is built on the principles of HTTP web services. In particular, this means that requests and responses over the interface are built around the transfer of representations of hyperlinked resources. A resource in the context of the CDNI metadata interface is any object in the object model (as described in Section 3 and Section 4).

To retrieve CDNI metadata, a CDNI metadata client (i.e., a client in the dCDN) first makes a HTTP GET request for the URI of the HostIndex which provides the CDNI metadata client with a list of Hostnames for which the uCDN can delegate content delivery to the dCDN. The CDNI metadata client can then obtain any other CDNI metadata objects by making a HTTP GET requests for any linked metadata objects it requires.

CDNI metadata servers (i.e., servers in the uCDN) are free to assign whatever structure they desire to the URIs for CDNI metadata objects and CDNI metadata clients MUST NOT make any assumptions regarding the structure of CDNI metadata URIs or the mapping between CDNI metadata objects and their associated URIs. Therefore any URIs present in the examples in this document are purely illustrative and are not intended to impose a definitive structure on CDNI metadata interface implementations.

6.1. Transport

The CDNI metadata interface uses HTTP as the underlying protocol transport.

The HTTP Method in the request defines the operation the request would like to perform. A server implementation of the CDNI metadata interface MUST support the HTTP GET and HEAD methods.

The corresponding HTTP Response returns the status of the operation in the HTTP Status Code and returns the current representation of the resource (if appropriate) in the Response Body. HTTP Responses that contain a response body SHOULD include an ETag to enable validation of cached versions of returned resources.

The CDNI metadata interface specified in this document is a read-only interface. Therefore support for other HTTP methods such as PUT, POST, DELETE, etc. is not specified. A server implementation of the CDNI metadata interface SHOULD reject all methods other than GET and HEAD.

As the CDNI metadata interface builds on top of HTTP, CDNI metadata server implementations MAY make use of any HTTP feature when implementing the CDNI metadata interface, for example, a CDNI metadata server MAY make use of HTTP's caching mechanisms to indicate that the returned response/representation can be reused without re-contacting the CDNI metadata server.

6.2. Retrieval of CDNI Metadata resources

In the general case, a CDNI metadata server makes CDNI metadata objects available via a unique URIs and thus, in order to retrieve CDNI metadata, a CDNI metadata client first makes a HTTP GET request for the URI of the HostIndex which provides a list of Hostnames for which the uCDN can delegate content delivery to the dCDN.

In order to retrieve the CDNI metadata for a particular request the CDNI metadata client processes the received HostIndex object and finds the corresponding HostMetadata entry (by matching the hostname in the request against the hostnames listed in the HostMatch objects). If the HostMetadata is linked (rather than embedded), the CDNI metadata client then makes a GET request for the URI specified in the href property of the Link object which points to the HostMetadata object itself.

In order to retrieve the most specific metadata for a particular request, the CDNI metadata client inspects the HostMetadata for references to more specific PathMetadata objects (by matching the URI path in the request against the path-patterns in any PathMatch objects listed in the HostMetadata object). If any PathMetadata are found to match (and are linked rather than embedded), the CDNI metadata client makes another GET request for the PathMetadata. Each PathMetadata object can also include references to yet more specific metadata. If this is the case, the CDNI metadata client continues requesting PathMatch and PathMetadata objects recursively. The CDNI metadata client repeats this approach of processing metadata objects and retrieving (via HTTP GETs) any linked objects until it has all the metadata objects it requires in order to process the redirection request from an uCDN or the content request from a User Agent.

In cases where a dCDN is not able to retrieve the entire set of CDNI metadata associated with a User Agent request, for example because the uCDN is unreachable or returns a HTTP 4xx or 5xx status in response to some or all of the dCDN's CDNI metadata requests, the dCDN MUST NOT serve the requested content unless the dCDN has stale versions of all the required metadata and the stale-if-error Cache-Control extension [RFC5861] was included in all previous responses that are required but cannot currently be retrieved. The dCDN can continue to serve other content for which it can retrieve (or for which it has fresh responses cached) all the required metadata even if some non-applicable part of the metadata tree is missing.

Where a dCDN is interconnected with multiple uCDNs, the dCDN needs to determine which uCDN's CDNI metadata should be used to handle a particular User Agent request.

When application level redirection (e.g., HTTP 302 redirects) is being used between CDNs, it is expected that the dCDN will be able to determine the uCDN that redirected a particular request from information contained in the received request (e.g., via the URI). With knowledge of which uCDN routed the request, the dCDN can choose the correct uCDN from which to obtain the HostIndex. Note that the HostIndexes served by each uCDN can be unique.

In the case of DNS redirection there is not always sufficient information carried in the DNS request from User Agents to determine the uCDN that redirected a particular request (e.g., when content from a given host is redirected to a given dCDN by more than one uCDN) and therefore dCDNs will have to apply local policy when deciding which uCDN's metadata to apply.

6.3. Bootstrapping

The URI for the HostIndex object of a given uCDN needs to be either configured in, or discovered by, the dCDN. All other objects/resources are then discoverable from the HostIndex object by following any links in the HostIndex object and through the referenced HostMetadata and PathMetadata objects and their GenericMetadata sub-objects.

If the URI for the HostIndex object is not manually configured in the dCDN then the HostIndex URI could be discovered. A mechanism allowing the dCDN to discover the URI of the HostIndex is outside the scope of this document.

6.4. Encoding

CDNI metadata objects MUST be encoded as I-JSON objects [RFC7493] containing a dictionary of (key,value) pairs where the keys are the property names and the values are the associated property values.

The keys of the dictionary are the names of the properties associated with the object and are therefore dependent on the specific object being encoded (i.e., dependent on the CDNI Payload Type of the returned resource). Likewise, the values associated with each property (dictionary key) are dependent on the specific object being encoded (i.e., dependent on the CDNI Payload Type of the returned resource).

Dictionary keys (properties) in I-JSON are case sensitive. By convention any dictionary key (property) defined by this document (for example the names of CDNI metadata object properties) MUST be lowercase.

6.5. Extensibility

The set of GenericMetadata objects can be extended with additional (standards based or vendor specific) metadata objects through the specification of new GenericMetadata objects. The GenericMetadata object defined in Section 4.1.7 specifies a type field and a type-specific value field that allows any metadata to be included in either the HostMetadata or PathMetadata lists.

As with the initial GenericMetadata types defined in Section 4.2, future GenericMetadata types MUST specify the information necessary for constructing and decoding the GenericMetadata object.

Any document which defines a new GenericMetadata type MUST:

1. Specify and register the CDNI Payload Type [RFC7736] used to identify the new GenericMetadata type being specified.
2. Define the set of properties associated with the new GenericMetadata object. GenericMetadata MUST NOT contain a property named "href" because doing so would conflict with the ability to detect Link objects (see Section 4.3.1).
3. Define a name, description, type, and whether or not the property is mandatory-to-specify.
4. Describe the semantics of the new type including its purpose and example of a use case to which it applies including an example encoded in I-JSON.

Note: In the case of vendor specific extensions, vendor-identifying CDNI Payload Type names will decrease the possibility of GenericMetadata type collisions.

6.6. Metadata Enforcement

At any given time, the set of GenericMetadata types supported by the uCDN might not match the set of GenericMetadata types supported by the dCDN.

In cases where a uCDN sends metadata containing a GenericMetadata type that a dCDN does not support, the dCDN MUST enforce the semantics of the "mandatory-to-enforce" property. If a dCDN does not understand or is unable to perform the functions associated with any "mandatory-to-enforce" metadata, the dCDN MUST NOT service any requests for the corresponding content.

Note: Ideally, uCDNs would not delegate content requests to a dCDN that does not support the "mandatory-to-enforce" metadata associated with the content being requested. However, even if the uCDN has a priori knowledge of the metadata supported by the dCDN (e.g., via the FCI or through out-of-band negotiation between CDN operators), metadata support can fluctuate or be inconsistent (e.g., due to mis-communication, mis-configuration, or temporary outage). Thus, the dCDN MUST always evaluate all metadata associated with redirection and content requests and reject any requests where "mandatory-to-enforce" metadata associated with the content cannot be enforced.

6.7. Metadata Conflicts

It is possible that new metadata definitions will obsolete or conflict with existing GenericMetadata (e.g., a future revision of the CDNI metadata interface could redefine the Auth GenericMetadata object or a custom vendor extension could implement an alternate Auth metadata option). If multiple metadata (e.g., MI.Auth.v2, vendor1.Auth, and vendor2.Auth) all conflict with an existing GenericMetadata object (i.e., MI.Auth) and all are marked as "mandatory-to-enforce", it could be ambiguous which metadata should be applied, especially if the functionality of the metadata overlap.

As described in Section 3.3, metadata override only applies to metadata objects of the same exact type found in HostMetadata and nested PathMetadata structures. The CDNI metadata interface does not support enforcement of dependencies between different metadata types. It is the responsibility of the CSP and the CDN operators to ensure that metadata assigned to a given piece of content do not conflict.

Note: Because metadata is inherently ordered in HostMetadata and PathMetadata lists, as well as in the PathMatch hierarchy, multiple conflicting metadata types MAY be used, however, metadata hierarchies SHOULD ensure that independent PathMatch root objects are used to prevent ambiguous or conflicting metadata definitions.

6.8. Versioning

The version of CDNI metadata objects is conveyed inside the CDNI Payload Type that is included in the HTTP Content-Type header, for example: "Content-Type: application/cdni; ptype=MI.HostIndex". We intentionally omit the ".v1" on the initial versions of metadata, for simplicity. Subsequent versions of those metadata MUST postpend a version string (e.g., ".v2"). Upon responding to a request for an object, a CDNI metadata server MUST include a Content-Type header with the CDNI Payload Type containing the version number (or implicitly, version 1) of the object. HTTP requests sent to a metadata server SHOULD include an Accept header with the CDNI Payload Type (which includes the version) of the expected object. Metadata clients can specify multiple CDNI Payload Types in the Accept header, for example if a metadata client is capable of processing two different versions of the same type of object (defined by different CDNI Payload Types) it might decide to include both in the Accept header.

6.9. Media Types

All CDNI metadata objects use the Media Type "application/cdni". The CDNI Payload Type for each object then contains the object name of that object as defined by this document, prefixed with "MI.". Table 4 lists the CDNI Paylod Type for the metadata objects (resources) specified in this document.

{
  "hosts": [
    {
      "host": "video.example.com",
      "host-metadata" : {
        "type": "MI.HostMetadata",
        "href": "http://metadata.ucdn.example/host1234"
      }
    },
    {
      "host": "images.example.com",
      "host-metadata" : {
        "type": "MI.HostMetadata",
        "href": "http://metadata.ucdn.example/host5678"
      }
    }
  ]
}

{
  "metadata": [
    {
      "generic-metadata-type": "MI.SourceMetadata",
      "generic-metadata-value": {
        "sources": [
          {
            "endpoint": "acq1.ucdn.example",
            "protocol": "http1.1"
          },
          {
            "endpoint": "acq2.ucdn.example",
            "protocol": "http1.1"
          }
        ]
      }
    },
    {
      "generic-metadata-type": "MI.LocationACL",
      "generic-metadata-value": {
        "locations": [
          {
            "footprints": [
              {
                "footprint-type": "IPv4CIDR",
                "footprint-value": "192.0.2.0/24"
              }
            ],
            "action": "deny"
          }
        ]
      }
    },
    {
      "generic-metadata-type": "MI.ProtocolACL",
      "generic-metadata-value": {
        "protocol-acl": [
          {
            "protocols": [
              "http1.1"
            ],
            "action": "allow"
          }
        ]
      }
    }
  ],
  "paths": [
    {
      "path-pattern": {
        "pattern": "/video/trailers/*"
      },
      "path-metadata": {
        "type": "MI.PathMetadata",
        "href": "http://metadata.ucdn.example/host1234/pathABC"
      }
    },
    {
      "path-pattern": {
        "pattern": "/video/movies/*"
      },
      "path-metadata": {
        "type": "MI.PathMetadata",
        "href": "http://metadata.ucdn.example/host1234/pathDEF"
      }
    }
  ]
}

{
  "metadata": [],
  "paths": [
    {
      "path-pattern": {
        "pattern": "/videos/movies/hd/*"
      },
      "path-metadata": {
        "type": "MI.PathMetadata",
        "href": 
          "http://metadata.ucdn.example/host1234/pathDEF/path123"
      }
    }
  ]
}

{
  "metadata": [
    {
      "generic-metadata-type": "MI.TimeWindowACL",
      "generic-metadata-value": {
        "times": [
          "windows": [
            {
              "start": "1213948800",
              "end": "1327393200"
            }
          ],
          "action": "allow"
        ]
      }
    }
  ]
}

Grant Watson
Velocix (Alcatel-Lucent)
3 Ely Road
Milton, Cambridge  CB24 6AA
UK

Email: gwatson@velocix.com

Kent Leung
Cisco Systems
3625 Cisco Way
San Jose, 95134
USA

Email: kleung@cisco.com