ICNRG M. Mosko
Internet-Draft C. Wood
Intended status: Experimental PARC, Inc.
Expires: October 8, 2016 April 6, 2016
The CCNx URI Scheme
draft-mosko-icnrg-ccnxurischeme-01
Abstract
This document defines an RFC3986 URI compliant identifier called a
Labeled Segment URI in which name segments carry a label. This
allows differentiation between unrelated resources with similar
identifiers. This document also specifies the CCNx URI scheme,
called "ccnx:," which conforms to the labeled segment encoding rules
presented here. The CCNx URI scheme applies specific labels to each
name segment of a URI to disambiguate between resources with similar
names. This document defines a specific set of segment labels with
label semantics.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on October 8, 2016.
Copyright Notice
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document authors. All rights reserved.
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. URI path segment grammar for label=value pairs . . . . . . . . 5
2.1. Labeled Segments . . . . . . . . . . . . . . . . . . . . . 5
2.2. URI comparison . . . . . . . . . . . . . . . . . . . . . . 7
3. Application to CCNx Names . . . . . . . . . . . . . . . . . . 9
3.1. The ccnx Scheme . . . . . . . . . . . . . . . . . . . . . 9
3.2. URI Representation . . . . . . . . . . . . . . . . . . . . 9
3.2.1. Examples . . . . . . . . . . . . . . . . . . . . . . . 11
3.3. ccnx: URI comparison . . . . . . . . . . . . . . . . . . . 11
4. IRI Considerations . . . . . . . . . . . . . . . . . . . . . . 13
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.1. Normative References . . . . . . . . . . . . . . . . . . . 17
8.2. Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
A Labeled Segment is an URI [RFC3986] compliant convention that
allows an application or protocol to embed labels in name segments,
thus disambiguating the resource identified by the path. Labeled
Segment URIs also allow for query and fragment components to follow
the Labeled Segment form.
Some protocols may wish to disambiguate name segments between
different identifier spaces, such as "version" and "page". Other
protocols may wish to use a type system such as "/str=parc/int=7" and
"/str=parc/str=7". Labeled Segment URIs provide an unambiguous and
flexible representation in systems that allow resources with
otherwise similar names.
It is not sufficient to leave the determination of type to
application-specific conventions. In a networked system with
multiple applications accessing resources generated by other
applications, there needs to be a set of common conventions. For
example, if one application uses a base 64 encoding of a frame
number, e.g. base64(0xbdea), and another uses "ver=" to represent a
document version, there is an ambiguity because base64(0xbdea) is the
string "ver=".
Labeled Segments defines "ls-segment" as "label[:param]=value", where
the value only contains unreserved, percent-encoded, or certain sub-
delim characters. In the previous example, one application would say
"/frame=%BD%EA" and the other would say "/ver=".
In this document, we use URI [RFC3986] terminology, therefore a URI
and CCNx Name are both composed of a URI path, which is a collection
of name segments. We do not use the term "name component" as was
common in old CCNx. In this document, the word "segment" alone means
"name segment."
URIs conforming to the CCNx URI scheme carry a label for each name
segment. The contents of each name segment must conform to the label
semantics. Example segment types are "Binary Segment", "Name", and
"KeyId".
We use Labeled Segment URIs as the canonical, human-readable
representation. There is an unambiguous, one-to-one correspondence
between an absolute LS-URI path and a Labeled Name. Relative URI
representations are removed during encoding, so no relative name ends
up in wire format. Some labels are URIs that are IRI [RFC3987]
compatible.
Labeled Names shall be used everywhere a Name is used in CCNx, such
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as in the Name of an Interest or Content Object. They are also used
in Links, KeyLocators, or any other place requiring a name. When
encoded for the wire, a binary representation is used, depending on
the specific wire format codec, which is outside the scope of this
document.
This document specifies:
o the ccnx scheme.
o a canonical URI representation.
Formal grammars use the ABNF [RFC5234] notation.
TODO: We have not adopted Requirements Language yet.
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].
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2. URI path segment grammar for label=value pairs
2.1. Labeled Segments
This section describes the formal grammar for Labeled Segments using
ABNF [RFC5234] notation. We do not impose restrictions on the length
of labels or values. The semantics of values are URI scheme
specific, here we only describe the meta-structure of Labeled
Segments. We begin by reviewing some definitions from [RFC3986] that
define an absolute path URI.
URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
hier-part = "//" authority path-abempty
/ path-absolute
/ <other path types>
path-absolute = "/" [ segment-nz *( "/" segment ) ]
segment = *pchar
segment-nz = 1*pchar
pchar = unreserved / pct-encoded / sub-delims / ":" / "@"
query = *( pchar / "/" / "?" )
fragment = *( pchar / "/" / "?" )
pct-encoded = "%" HEXDIG HEXDIG
unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
reserved = gen-delims / sub-delims
gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "@"
sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
/ "*" / "+" / "," / ";" / "="
Labeled Segments defines a new segment type that provides unambiguous
representation of a segment's label and its value. We define the
top-level LS-URI as the same form as a URI, wherein each part
conforms to the Label Segment grammar, which is a subset of the URI
grammar.
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LS-URI = scheme ":" ls-hier-part ["?" ls-query]
["#" fragment]
ls-hier-part = ["//" authority] ls-path-absolute
ls-path-absolute = "/" [ first-segment *( "/" ls-segment ) ]
first-segment = ls-segment-nz
ls-segment = lpv-segment / v-segment
lpv-segment = label [":" param] "=" *s-value-nz
v-segment = *s-value-nz
ls-segment-nz = lpv-segment-nz / v-segment-nz
lpv-segment-nz = label [":" param] "=" s-value-nz
v-segment-nz = s-value-nz
label = alpha-t / num-t
param = alpha-t / num-t
s-value-nz = 1*(s-pchar)
ls-query = *1 ( lpv-component / v-component
*( "&" (lpv-component / v-component) ) )
lpv-component = label [":" param] "=" q-value
v-component = q-value
q-value = *(q-pchar)
alpha-t = ALPHA *(ALPHA / DIGIT)
num-t = dec-t / hex-t
dec-t = 1*(DIGIT)
hex-t = "0x" 1*(HEXDIG)
ls-pchar = unreserved / pct-encoded / ls-sub-delims
s-pchar = ls-pchar / ":" / "@" / "&"
q-pchar = ls-pchar / ":" / "@" / "/"
ls-sub-delims = "!" / "$" / "'" / "(" / ")"
/ "*" / "+" / "," / ";"
A Labeled Segment URI (LS-URI) contains a scheme that uses Labeled
Segments, an optional authority, a labeled segment absolute path (ls-
path-aboslute), an optional labeled segment query (ls-query), and a
fragment. The authority is URI scheme specific and the fragment is
independent of the URI scheme.
the ls-path-aboslute is a first-segment followed by zero or more "/"
ls-segment. The first-segment may be empty or a non-zero ls-segment
(ls-segment-nz). If it is empty, it corresponds to a 0-lenght name
which typically is a default route. It is distinct from a 1-segment
name with no value (which is not allowed). The first-segment MUST
either be empty (the 0-lenght name) or MUST have a value. If the
first-segment is an ls-segment-nz, then it will have a value.
An ls-segment may (lpv-segment) or may not (v-segment) have a label.
A particular LS-URI scheme MUST define how unlabeled segments are
processed, and MAY disallow them. A v-segment is an implied type.
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Once the implied type is resolved, it functions like an lpv-segment.
An lpv-segment has a label, optional parameter, and optional value
(s-value-nz). An empty value is a 0-length name segment with a
defined type. This is distinct from a 0-length first-segment, which
has neither type nor value.
lpv-segment values come from the s-pchar set, which excludes the "="
equal sign. This means that the only equal sign in a name segment
must be the delimiter between the label:param and the value. Within
the value, an equal sign must be percent encoded.
lpv-segment labels and values may be alpha-numeric identifiers or
numbers (decimal or hexadecimal). For example, one scheme may define
the labels "name", "version", and "frame". A version may be of types
"date" or "serial", meaning that the version is either a date or a
monotonic serial number. Some examples of resulting LS-URIs are:
"/name=parc/name=csl/version:date=20130930" or "/name=alice_smith/
version:serial=299". The parameters may also indicate an instance of
a label, such as "/name=books/year:1=1920/year:3=1940", where there
are scheme or application semantics associated with "year:1" and
"year:3".
lpv-segment labels and parameters may also be numbers. For example,
a protocol with a binary and URI representation may not have pre-
defined all possible labels. In such cases, it could render unknown
labels as their binary value, such as "/name=marc/x2003=green".
The ls-query component is a non-hierarchical set of components
separated by "&". Each ls-query component is either a lpv-component
or a v-component, similar to segments. They are based on q-value,
which uses q-pchar that excludes "&", but includes "/". This allows
an LS-URI scheme to use type query parameters.
Labeled Segments allow for dot-segments "." and ".." in a v-segment.
They operate as normal. A single dot "." refers to the current
hierarchy level and may be elided when the URI is resolved. Double
dot ".." segments pop off the previous non-dot segment. An lpv-
segment with a value of "." or ".." is not a dot-segment. It means
that the value of the given label is "." or "..". For example
/a=parc/b=csl/.. is equivalent to "/a=parc/b=csl", but the LS-URI
"/a=parc/b=csl/c=.." does not contain a dot-segment.
2.2. URI comparison
An LS-URI scheme MUST specify the normalization rules to be used,
following the methods of Section 6 [RFC3986]. At minimum, an LS-URI
scheme SHOULD do the following:
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o Normalize unrestricted percent-encodings to the unrestricted form.
o Normalize num-t to either dec-t or hex-t.
o If the scheme allows for value-only segments or query components
and interprets them as a default type, they should be normalized
to having the type specified.
o If the scheme allows for undefined labels and represents them, for
example, as num-t, then it should normalize all labels to their
corresponding num-t. If "name", for example, is known to be %x50
in a binary encoding of the URI, then all labels should be
compared using their numeric value.
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3. Application to CCNx Names
3.1. The ccnx Scheme
This section describes the CCNx URI scheme "ccnx:" for Labeled Names.
A Labeled Name assigns a semantic type or label to each segment of
the hierarchical content Name.
Unless otherwise specified, a name segment is an arbitrary sequence
of octets.
Several name segment labels are binary unsigned integers. These are
always encoded as variable length sequences of 1 or more octets in
network byte order using the shortest representation (i.e. no leading
%x00). The value of "0" is encoded as the single byte of "%x00". A
zero-length sequence must be interpreted as "not present."
The CCNx Name segment types are:
o Name Segment: A generic name segment that includes arbitrary
octets.
o Application Type N: An application may use application-specific
parameters, numbered as integers, where N is from 0 to a system-
specific maximum, not less than 255. These are represented as
"App:1=value", for example.
It is common for an information centric networking protocol, such as
CCNx or NDN, to use a binary on-the-wire representation for messages.
Such protocols, if they use the ccnx: scheme, must have an
appropriate codec that unambiguously represents Labeled Content
Information in the chosen wire format. Relative dot-segments should
not occur in the wire format, they should be resolved before
encoding.
3.2. URI Representation
Typed Names use a standard RFC 3986 representation following the LS-
URI convention. A name segment consists of any "unreserved"
characters plus percent-encoded characters. Reserved characters must
be percent encoded.
Within an absolute path, each segment consists of an "ls-segment"
(c.f. LS-URI). A labeled segment is a type and a name component
value, with a URI representation of "type=value". The "type="
portion may be omitted if it is type Name.
Some name types take a parameter, such as the Application types.
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They are represented as "A:nnn=value", where the "nnn" is the
application type number and value is the name component.
A CCNx URI MUST NOT include an Authority, Query, or Fragment. It is
an error to include them.
Dot-segments (relative name components) are resolved when the URI is
converted to a Typed Name. The "." dot-segment is removed. The ".."
dot-segment is removed along with the previous non-dot-segment.
+-------------------+-------------+---------------------------------+
| Type | Display | Name |
+-------------------+-------------+---------------------------------+
| 'Name' | Hexadecimal | Name Segment |
| | | |
| 'IPID' | Hexadecimal | Interest Payload Identifier |
| | | segment |
| | | |
| 'App:0' - | Hexadecimal | Application Component |
| 'App:255' | | |
+-------------------+-------------+---------------------------------+
Table 1: The CCNx URI Scheme Types
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3.2.1. Examples
A name / is
ccnx:/ and is a 0-length name.
A name /Name= is
ccnx:/Name= and is a 1-segment name of 0-length.
A name /foo/bar.
ccnx:/Name=foo/Name=bar
ccnx:/foo/Name=bar
ccnx:/foo/bar
A name /foo/bar with key %xA0.
ccnx:/Name=foo/Name=bar/App:1=0xA0
A name /foo/bar with version %xA0 and App:2 value 0x09.
ccnx:/foo/bar/Version=0xA0/App:2=0x09
A name /foo/.., where the ".." is a literal name component,
not a relative dot-segment.
ccnx:/foo/Name=..
A name /foo/bar with application type 0 "hello"
and application type 1 "world".
ccnx:/Name=foo/Name=bar/App:0=hello/App:1=world
3.3. ccnx: URI comparison
While most comparisons are done using a wire format representation of
a ccnx: URI, some applications may compare the CCNx URI using their
URI representation. This section defines the rules for comparing
ccnx: URIs using the methods of Section 6 [RFC3986]
Comparing typed name URIs must be done with:
o Syntax-based normalization
o Case normalization: normalize the representation of percent
encodings. ccnx: does not use the host portion of the URI, and
should be ignored if present.
o Percent encoding normalization: Percent encodings of unreserved
characters must be converted to the unreserved character.
o Path segment normalization: dot-segments must be resolved first.
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o Scheme-based normalization: The authority should be removed and
the path represented as an absolute path.
o Protocol-based normalization: Should not be done. A trailing
slash indicates a zero-length terminal name component and
signifies a different name.
o typed-name-segment normalization: All segments should be presented
with their type, do not elide the "N=" for Name components.
o Binary unsigned integer normalization: remove any leading %x00
from numbers, leaving only the terminal %x00 for "0".
o type parameters: they must have their percent encodings
normalized. If they are integers, such as for the 'A' type, they
must not have leading zeros.
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4. IRI Considerations
International Resource Identifiers extend the unreserved character
set to include characters above U+07F and encode them using percent
encoding. This extension is compatible with the ccnx: schema. It
applies only to the "value" portion of an ls-segment.
The canonical name is determined by the URI representation of the
IRI, after applying the rules of Section 3.1 of [RFC3987] and
resolving dot-segments. The canonical name thus includes the URI
representation of language markers, including the bidirectional
components.
The value of a UTF-8 Name segment should be interpreted using IRI
rules, including bidirectional markers. They may be displayed using
localized formats.
Binary unsigned integer types are not interpreted under IRI rules,
they are specifically percent encoded numbers. They may be displayed
using a localized format.
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5. Acknowledgements
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6. IANA Considerations
This memo includes no request to IANA.
All drafts are required to have an IANA considerations section (see
Guidelines for Writing an IANA Considerations Section in RFCs
[RFC5226] for a guide). If the draft does not require IANA to do
anything, the section contains an explicit statement that this is the
case (as above). If there are no requirements for IANA, the section
will be removed during conversion into an RFC by the RFC Editor.
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7. Security Considerations
All drafts are required to have a security considerations section.
See RFC 3552 [RFC3552] for a guide.
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8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
8.2. Informative References
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003,
<http://www.rfc-editor.org/info/rfc3552>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987,
January 2005, <http://www.rfc-editor.org/info/rfc3987>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/
RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
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Authors' Addresses
Marc Mosko
PARC, Inc.
Palo Alto, California 94304
USA
Phone: +01 650-812-4405
Email: marc.mosko@parc.com
Christopher A. Wood
PARC, Inc.
Palo Alto, California 94304
USA
Phone: +01 650-812-4421
Email: christopher.wood@parc.com
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