INTERNET-DRAFT D. Eastlake
Intended status: Proposed Standard Futurewei Technologies
Expires: 25 June 2022 26 December 2021
Mapping Between MIME Types, Content-Types, and URIs
<draft-eastlake-cturi-06.txt>
Abstract
Multipurpose Internet Mail Extension (MIME) Content-Type headers, the
MIME types used therein, and Uniform Resource Identifiers (URIs) are
being used, in different contexts, to label entities. A mapping is
specified from each kind of label into the other. This makes it
possible to express the meaning of almost any URI or Content-Type in
the syntax of the other.
Status of This Document
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Distribution of this document is unlimited. Comments should be sent
to the author.
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https://www.ietf.org/1id-abstracts.html. The list of Internet-Draft
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Table of Contents
1. Introduction............................................3
1.1 Introduction to URIs and MIME Type/Content-Type........3
1.2 Definitions and Conventions............................4
1.3 Additional Features....................................4
1.4 Overview of Remaining Sections.........................5
2. Mapping of Content-Type to URI..........................6
2.1 Simple Mapping of MIME Type to URI.....................6
2.2 Mapping of Content-Type to URI.........................7
2.3 Content-Type Mapping Special Case for Closure..........7
2.4 Controlled Mapping of a Content-Type to a URI..........8
3. Mapping of URI to Content-Type..........................9
3.1 Simple Mapping of URI to Content-Type..................9
3.2 URI Mapping Special Case for Basic Closure............10
3.3 Controlled Mapping of a URI to a Content-Type.........10
4. Troublesome Characters.................................12
5. IANA Considerations and Potential Conflicts............13
6. Security Considerations................................13
Appendix..................................................15
Normative References......................................19
Informative References....................................19
Author's Address..........................................20
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1. Introduction
Both MIME types and URIs have come to be used for type labeling and
similar information. Both new MIME types and XML applications using
new URIs for type labeling are continuing to be created and there
does not appear to be any prospect that either syntax will become so
dominant that the other will wither.
In most protocols where there are provisions for a general "type
label", that label is restricted to the syntax of a URI or the syntax
of a Content-Type. In some cases, it will be useful to be able to
express labels which already exist in the "other" syntax. That is, it
may be useful in a URI syntax slot to be able to express a MIME type
or Content-Type and, conversely, it may be useful in a Content-Type
syntax slot to be able to express a URI.
Ability to express Content-Types as URIs makes is easy to talk about
them in [RDF] or other languages which refer to things with URIs. If
one is sending, via SMTP, HTTP, or any other protocol using Content-
Types, keying material or other things typed by the URI format type
labels specified in [RFC3275] or [XMLENC] it is convenient to be able
to express such URI type labels as a Content-Type header. In the
SMIL 2.0 case of the systemComponent attribute, there is a specific
URI format attribute intended to contain Content-Type information
[SMIL]. These are just a few specific examples that need a way to
convert between URI and Content-Type syntaxes.
This document specifies how to map any Content-Type into a URI and
vice versa.
1.1 Introduction to URIs and MIME Type/Content-Type
The IETF Multipurpose Internet Mail Extensions (MIME) message body
standards developed into a general tagging and bagging mechanism.
This mechanism spread from SMTP mail to HTTP, USENET, and other
protocols. In MIME, the type of an object is given in a "Content-
Type" header line. [RFC2045] [RFC2046] [RFC6838] Such a line consists
of a MIME type and, optionally, additional parameters. A MIME type
consists of a MIME top level type, a slash, and a MIME subtype.
The original Uniform Resource Locator (URL [RFC1738]), used to point
to World Wide Web (WWW) resources, grew into the more general Uniform
Resource Identifier (URI [RFC3986]). Increasingly URIs are used as
general labels for algorithms [RFC3275], XML namespaces [XML NAME],
web based protocol data types, etc. (In some of these label uses,
URIs are considered opaque while in other cases they are assumed to
be de-referencable into something which explicates their meaning.)
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1.2 Definitions and Conventions
Concerning URIs, please note the following:
(1) In this document, the term URI is used to include URI
Reference. That is, it includes the case where an octothorp
("#") followed by a fragment identifier is suffixed to a pure
URI.
(2) Only absolute URIs are mappable. Relative URIs, with just a
hierarchical part, are not included in URI as used in this
document. They must first be converted to absolute URIs as
described in [RFC3986].
(3) For presentation purposes, URIs are shown inside angle
brackets ("<...>") but these angle brackets are not actually a
part of the URI.
Concerning Content-Types, please note the following:
Content-Type values are shown preceded by "Content-Type: " and,
when long, they are line folded as per [RFC5322]. This prefix
and line folding are for presentation purposes and are not
actually a part of the Content-Type.
Concerning "URL encoding/decoding", please note the following:
These are operations on character strings represented by octet
sequences. "URL encoding" is the process of replacing certain
octets with the three octets for the character percent sign ("%")
followed by two hex digits for the value of the octet replaced.
"URL decoding" is the inverse process, i.e. replacing all three
octet sequences that start with the octet for percent sign and
the remainder of which consist of two hex digits (0-9, A-F, or a-
f) with a single octet whose value is represented by the two hex
digit sequence. The characters that are replaced by URL encoding
for the purposes of this draft are listed in Section 4.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.3 Additional Features
Note that a URI or Content-Type could get converted back and forth
multiple times between these two syntaxes. To stop such multiple
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conversions from resulting in ever longer and more complex tags, a
check is mandated so that if a conversion is of a previously
converted syntax, the previous conversion is reversed, in so far as
practical.
To improve the repeatability of the results from single or multiple
steps of syntax conversion, capitalization and punctuation
recommendations are made where tokens are case insensitive or
variable punctuation is allowed.
Finally, in cases where the default conversion does not provide for
sufficient control, optional elements are defined for inclusion in
URIs and Content-Types that provide substantial control over the
mapping output.
1.4 Overview of Remaining Sections
Sections 2 and 3 below give an explanation of the mapping specified,
more or less in English. The material is organized to start with the
simplest and most common rules and then add exceptions for special
cases and additional user control.
Section 4 lists characters that must be URI ("%") encoded when
mapping from a URI to a Content-Type.
Section 5 covers IANA Considerations and potential conflicts.
Section 6 give Security Considerations.
The Appendix presents some sample code in Perl.
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2. Mapping of Content-Type to URI
This section starts with how to map a simple MIME type to a URI, in
Section 2.1. In 2.2, this is expanded to mapping a full Content-Type
with parameters. Section 2.3 adds the special check for the mapping
of a Content-Type which appears to have originally come from a URI.
And Section 2.4 describes how to control the mapping to a URI by
means of a special Content-Type parameter.
2.1 Simple Mapping of MIME Type to URI
For the simplest case of a Content-Type consisting of just a MIME
type, create a URI with scheme "ContentType" and a scheme dependent
part consisting of the MIME type. For example
Content-Type: image/JPEG
simply converts to
<ContentType:image/jpeg>
White space is not allowed in URIs so it must be removed. Scheme
names (the part before the first ":" in a URI) are case insensitive
but for readability and repeatability, the capitalization
"ContentType" SHOULD be used. Similarly, MIME top level types and
subtypes (the fields before and after the "/" in a MIME type field,
respectively) are case insensitive but SHOULD be all lower cased when
mapped to the URI form. For example
Content-type: x-FOO?bar/biZZare#sUb#tYpe
converts to
<ContentType:x-foo%3Fbar/bizzare%23sub%23type>
Note: There is no "//" after the "ContentType:" scheme as used
herein. Such a "//" would imply a specific structuring of the
scheme dependent part appearing in the URI after the
"ContentType:" as defined in [RFC3986]. Since that full
structuring is not used, "//" is not used. The meaning of URIs
starting with "ContentType://" is reserved for future definition.
Note: "Content-Type", with hyphen, is syntactically allowed as a
scheme name. However, [RFC7595] reserves embedded hyphens in
scheme names to indicate the prefix of an alternate tree of
scheme names. Therefore, the un-hyphenated ContentType is used.
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2.2 Mapping of Content-Type to URI
A Content-Type header frequently includes more than just the
mandatory MIME type. It can also have type dependent parameters,
including private parameters, such as
Content-Type: text/plain; charset="us-ascii";
x-mac-type="54455854"; x-mac-creator="4D4F5353"
Content-Type: image/tiff; application=faxbw
Content-Type parameters are mapped into a "query portion" suffix of
the URI in much the same way that HTML form fields [HTML] are. That
is, they are concatenated to the MIME type after a "?" and, if there
is more than one parameter, separated by "&". Thus the above Content-
Types would be mapped into the following URIs:
<ContentType:text/plain?charset="us-ascii"&x-mac-type="54455854"&
x-mac-creator="4D4F5353">
<ContentType:image/tiff?application="faxbw">
Parameter values in the mapped URI MUST always be enclosed in double
quotes ('"'). If the Content-Type has a trailing ";" but no
parameters, then "?" SHOULD NOT be added to the URI.
Note: Any occurrences of the "&" separator will have to be encoded as
"&" or other appropriate character reference if the URI is
used in XML outside a CDATA construct, or most other SGML derived
languages. However, "&" is the standard separator used in CGI
(Common Gateway Interface) parsing of query section parameters
for "mailto:" [RFC6068], "http:", etc., schemes. On balance, the
continued use of "&" has been chosen.
2.3 Content-Type Mapping Special Case for Closure
A URI may have been converted to a Content-Type and get converted
back. To stop this from resulting in an ever more complex syntax, a
check MUST be made to see if the MIME subtype of a Content-Type being
converted is in the "uri." subtype tree (see section 3.2 below). If
so, the URI is computed from the subtype by stripping the "uri."
prefix and undoing one level of URI encoding. The top level MIME
type is ignored in this case. In addition, Content-Type parameters,
if any, are added as a "query portion" and any "URI-fragment"
parameter is added as a fragment.
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For example:
Content-Type: application/uri.mailto%3Auser%40host.example
Content-Type: application/uri.http%3A%2F%2Fx.test; foo="123";
bar="abcd"
Content-Type:
application/uri.http%3A%2F%2Fa%3Ab%40c.text%2Fx%2Fy;
URI-fragment="z%25z"
are mapped to
<mailto:user@host.example>
<http://x.test?foo="123"&bar="abcd">
<http://a:b@c.text/x/y#z%z>
Note: If a Content-Type or MIME Type is being written by a user and
they know that there is a URI which is a more natural expression
of the labeling desired, they can simply use an ".../uri." MIME
Type to start with.
2.4 Controlled Mapping of a Content-Type to a URI
There will be cases where greater control over the mapping is
desired. These are cases where a more natural URI exists rather than
the automatic "ContentType" URI scheme.
To accomplish this controlled mapping starting with a Content-Type, a
special Content-Type parameter "URI-body" is defined. If a Content-
Type does not have a MIME subtype in the "uri." tree and this
parameter is present, it is URL decoded to produce the non-query
portion of the URI mapped to and the original MIME top level and sub
types is preserved in a URI query parameter called "MIME-type".
For example
Content-Type: application/xml; URI-body="http://xml.example/foo"
would map to
<http://xml.example/foo?MIME-type="application/xml">
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3. Mapping of URI to Content-Type
Section 3.1 below describes the basic mapping of a URI into a
Content-Type. Section 3.2 specifies the exceptional processing when a
URI being converted to a Content-Type appears to have previously been
converted from a Content-Type. And Section 3.3 provides for greater
control over the mapping when needed.
3.1 Simple Mapping of URI to Content-Type
In the basic case, a URI maps to a Content-Type with a top level MIME
type of "application" and a MIME sub-type in the "uri." tree. The
"uri." is followed by the URL encoding of the URI excluding the query
and fragment parts. Any "query" parameters in the URI are mapped to
Content-Type parameters and, if the URI ends with a fragment
identifier, it is mapped to the special Content-Type parameter "URI-
fragment".
Note: Current URI syntax permits scheme dependent parts in which "?"
does not indicate a query section; however, no such syntaxes have
been publicly defined.
Some examples of the basic case follow:
<http://example.com/tag42>
<mailto:U@example.net?subject="misc"&body="line1%0D%0Aline2">
<xyz://abc.test/def?h=ijk#lmn>
convert to
Content-Type: application/uri.http%3A%2F%2Fexample.com%2Ftag42
Content-Type: application/uri.mailto%3AU%40example.net;
subject="misc"; body="line1%250D%250Aline2"
Content-Type: application/uri.xyz%3A%2F%2Fabc.test%2Fdef;
h="ijk"; URI-fragment="lmn"
Content-Type parameters values extracted from the query portion of a
URI MUST be surrounded with double quotes ('"'). When URI encoding,
if the hex value contains any letters (a-f), they SHOULD be upper
cased.
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3.2 URI Mapping Special Case for Basic Closure
It is desirable that an arbitrary Content-Type be recovered
semantically intact when mapped to a URI and then that URI is mapped
back to a Content-Type. To approximate this as closely as practical,
the following special case is added to the simple case described in
section 3.1 above.
If the URI scheme is "ContentType:", then the Content-Type is
computed from the remaining part of the URI (the scheme specific
part), by replacing the first question mark ("?") and all subsequent
ampersands ("&") with the two character sequence semi-colon space (";
"), and then undoing one level of URI encoding, i.e., replacing
percent sign ("%") followed by two hex digits with the octet having
that hex value.
For example
<ContentType:model/vnd.example.longish.sub%23type.name>
<ContentType:text/plain?charset="US-ASCII"&x-obscure="value">
are mapped to
Content-Type: model/vnd.example.longish.sub#type.name
Content-Type: text/plain; charset="US-ASCII"; x-obscure="value"
Note: A URI produced by simple mapping from a normal Content-Type
will never have a fragment suffix. If one appears, it should be
mapped into a URI-fragment parameter, as specified in Section 3.1
above.
Note: If a type label URI is being written by a user and they know
that there is a Content-Type which is a more natural expression
of the labeling desired, they can simply use a "ContentType:"
scheme to start with.
3.3 Controlled Mapping of a URI to a Content-Type
There will be cases where greater control over the mapping is
desired. These are cases where a more natural Content-Type exists
than the "uri." subtree MIME subtype under the "application" type.
To accomplish this controlled mapping starting with a URI, a special
query part parameter "MIME-type" is defined. If a URI is not of
scheme ContentType and this special parameter is found, then the MIME
type is set to the parameter value after URL decoding and the URI
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body (all of the URI except "query" parameters and any fragment
identifier) is preserved in a URL encoded "URI-body" Content-Type
parameter.
For example
<mailto:joe@blow.test?MIME-type="message%2Frfc822"#123>
would map to
Content-Type: message/rfc822;
URI-body="mailto:joe@blow.text"; URI-fragment="123"
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4. Troublesome Characters
Troublesome characters are defined as those not permitted in a token
in [RFC2045] with the addition of percent sign and octothorp. That
is, any character code from 0 through 32 inclusive and character code
127 and any of "(", ")", "<", ">", "@", ",", ";", ":", "\", "/", "[",
"]", "?", "%", "#", and "=" are troublesome characters.
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5. IANA Considerations and Potential Conflicts
IANA is requested to assign the following:
(1) The "ContentType" URI scheme.
(2) The "uri." MIME subtype tree. Since this subtree is totally
delegated to the URI specification, there are no independent
publication or review requirements for it. Any valid URI can be
used after the "uri." in any MIME top level type, after
troublesome characters (see section 4) in the URI are URL
encoded.
(3) In the context of URI to Content-Type mapping, a meaning is
specified for the "MIME-type" URI query section parameter.
(4) In the context of Content-Type to URI mapping, a meaning is
specified for the "URI-body" and "URI-fragment" Content-Type
parameters.
Because this document specifies the "ContentType" URI scheme and the
"uri." MIME subtype tree, no conflict can arise due to other uses of
them.
This is the first specification of a Content-Type parameters valid
across all MIME types, namely URI-body and URI-fragment. This is the
first specification of a universal URI query parameter, namely MIME-
type. The probability that any different use is currently being
made, or will in the foreseeable future have to be made, of these
names is low enough that it can be ignored.
It is possible that some processing systems are sensitive to the
presence of parameters they do not understand and will indicate
errors when presented with controlled mapping URIs or Content-Types.
However, Content-Type parameters and URI query parameters are usually
handled on receipt by such mechanisms as storing the name-value pair
in an associative array or as "environment variables" and ignoring
extra parameters. In fact, Content-Type processors are required by
[RFC2046] to ignore any parameters they do not understand and to
ignore parameter order.
6. Security Considerations
In some sense, the security considerations for MIME and content types
[RFC2046], URIs [RFC3986], and for every individual MIME type and URI
scheme can apply.
In addition, the deployment of mapping aware software may enable the
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introduction into or transmission through MIME or Content-Type
contexts of URI semantics, including possibly dangerous action
schemes such as "mailto", and the introduction into or transmission
through URI contexts of MIME and content type semantics, including
possibly dangerous executable data types or the like.
Finally, implementation of controlled mapping may enable a malicious
user, by adding one of the special parameters specified herein, to
cause a surprising change in the semantics of a URI or Content-Type
produced by the mapping from an apparently innocuous Content-Type or
URI. Particular care should be given to screening the characters
resulting from URL decoding into character code sensitive fields.
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Appendix
The following Perl code implements much of the mapping given in
Sections 2 and 3 above:
<CODE BEGINS>
# Content-Type and URI intermapping example code
# Donald E. Eastlake 3rd, November 2001
# -----------
# test driver
# -----------
use strict;
print "Type a Content-Type, a URI, or 'Quit'. Do NOT include\n";
print
"angle brackets around the URI or a 'Content-Type:' prefix.\n\n";
while ( <STDIN> ) # get test input
{
my $test;
chomp ( $_ );
if ( /^\s*([-\w\.+]+:[^\s]*)/ ) #test for URI
{
print "<$1>\n"; # echo
$test = uri2ct ( $1 );
print " Content-Type: ", $test, "\n";
$test = ct2uri ( $test );
print "<$test>\n"; # converted back
}
elsif #test for Content-Type
( m=^\s*([-_\w\.+#\$%!\?]+/[-_\w\.+#\$%!\?]+.*)= )
# (note: RFC 2405 allows other characters in type and subtype)
{
print "Content-Type: $1\n"; # echo
$test = ct2uri ( $1 );
print " <", $test, ">\n";
$test = uri2ct ( $test );
print "Content-Type: $test\n"; # converted back
}
elsif ( /^\s*$/ )
elsif ( /exit|quit|halt|stop|end/i )
{ last; }
else { print "BAD INPUT: $_\n"; }
print "\n";
}
print "EXIT\n";
sleep 1;
exit;
# ---------------------------
# convert URI to Content-Type
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# ---------------------------
sub uri2ct ($) {
my $result; my $item;
my %paramh; my @paraml;
@_[0] =~ m=\s*([^:/?#]+)?:([^?#]*)(\?([^#]*))?(#([^\s]*))?=;
# 1 2 3 4 5 6
my $scheme = lc ( $1 );
my $main = $2;
@paraml = split ( /&/, $4 );
foreach $item (@paraml)
{
$item =~ /([^=]+)=(.*)/;
$paramh{ lc ( $1 ) } = $2;
}
if ( $scheme eq "contenttype" )
{ $result = yestrouble ( $main ); }
elsif ( $result = $paramh{"mime-type"} )
{
delete ( $paramh{"mime-type"} );
$result =~ s/^"(.*)"$/$1/;
$result = yestrouble ( $result ) . '; URI-body="' .
notrouble ( $scheme . ":" . $main ) . '"';
}
else
{
$result = "application/uri." .
notrouble ( $scheme . ":" . $main );
}
if ( %paramh )
{
my $key; my $value;
while (( $key, $value ) = each ( %paramh ))
{ $result .= "; $key=" . dquote ( $value ); }
}
if ( $5 )
{ $result .= '; URI-fragment="' . notrouble ( $6 ) . '"'; }
return $result;
} # end uri2ct
# ---------------------------
# convert Content-Type to URI
# ---------------------------
sub ct2uri ($) {
my %paramh; my @paraml;
my $result; my $item; my $fragment;
@_[0] =~
m&^\s*([-_\w\.+#\$%!\?]+)/([-_\w\.+#\$%!\?]+)\s*(;\s*(.*))?&;
# 1 2 3 4
my $type = lc ( notrouble ( $1 ) . "/" . notrouble ( $2 ) );
my $minor = lc ( $2 );
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@paraml = split ( /\s*;\s*/, $4 );
foreach $item ( @paraml )
{
$item =~ /([^=\s]+)\s*=\s*(.*)/;
$paramh{ lc ( $1 ) } = $2;
}
if ( $minor =~ /^uri\.(.*)/i )
{ $result = yestrouble ( $1 ); }
elsif ( $result = $paramh{"uri-body"} )
{
delete ( $paramh{"uri-body"} );
$result = yestrouble ( $result );
$result =~ s/^"(.*)"$/$1/ ;
$paramh{"MIME-type"} = $type;
}
else
{
$result = "ContentType:" . $type;
}
if ( $fragment = $paramh{"uri-fragment"} )
{
delete ( $paramh{"uri-fragment"} );
$fragment =~ s/^"(.*)"$/$1/;
}
if ( %paramh )
{
my $key; my $value;
$result .= "?";
while (( $key, $value ) = each ( %paramh ))
{
$result .= $key . '=' . dquote ( $value ) . "&";
}
chop ( $result ); # get rid of trailing &
}
if ( $fragment )
{ $result .= '#' . yestrouble ( $fragment ) }
return $result;
} # end ct2uri
# -------------------
# support subroutines
# -------------------
# double quote string if not already double quoted
# ------------------------------------------------
sub dquote ($) {
my $string = @_[0];
if ( $string =~ /^".*"$/ )
{ return $string; }
return '"' . $string . '"';
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}
# URL encode troublesome characters
# ---------------------------------
sub notrouble ($) {
my $string = @_[0];
my $result;
while ( $string =~
m{([^%\?\(\)<>@,;:\\/\[\]="#]*)([%\?\(\)<>@,;:\\/\[\]="#])(.*)}
# 1 2 3
)
{
$result .= "$1%" . sprintf ( "%02X", ord ( $2 ) );
$string = $3;
}
return $result . $string;
} # end no trouble
# decode URL encoded string
# -------------------------
sub yestrouble ($) {
my $string = @_[0];
my $result;
while ( $string =~ /([^%]*)%([0-9a-fA-F]{2})(.*)/ )
{
$result .= $1 .
chr ( unhexify ( substr ( $2, 0, 1 ) ) * 16
+ unhexify ( substr ( $2, 1, 1 ) ) );
$string = $3;
}
return $result . $string;
} # end yestrouble
# convert hex digit to corresponding integer
# ------------------------------------------
sub unhexify ($) {
my $num = ord (@_[0]);
if ( $num >= ord ("0") && $num <= ord ("9") )
{ return ( $num - ord ("0" ) ); }
if ( $num >= ord ("A") && $num <= ord ("F") )
{ return ( $num - ord ("A" ) + 10 ); }
return ( $num - ord ("a" ) + 10 );
}
<CODE ENDS>
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Normative References
[RFC2046] - NFreed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, DOI
10.17487/RFC2046, November 1996, <https://www.rfc-
editor.org/info/rfc2046>.
[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>.
[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, <https://www.rfc-
editor.org/info/rfc3986>.
[RFC8174] - Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May
2017, <http://www.rfc-editor.org/info/rfc8174>
Informative References
[HTML] - Dave Raggett, Arnaud Le Hors, Ian Jacobs, "HTML 4.01
Specification", <http://www.w3.org/TR/html4>, December 1999.
[RDF] - O. Lassila, R. Swick, "Resource Description Framework (RDF)
Model and Syntax Specification", <http://www.w3.org/TR/REC-rdf-
syntax>, 22 February 1999.
[RFC1738] - Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
Resource Locators (URL)", RFC 1738, DOI 10.17487/RFC1738,
December 1994, <https://www.rfc-editor.org/info/rfc1738>.
[RFC2045] - Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, DOI 10.17487/RFC2045, November 1996,
<https://www.rfc-editor.org/info/rfc2045>.
[RFC3275] - Eastlake 3rd, D., Reagle, J., and D. Solo, "(Extensible
Markup Language) XML-Signature Syntax and Processing", RFC
3275, DOI 10.17487/RFC3275, March 2002, <https://www.rfc-
editor.org/info/rfc3275>.
[RFC5322] - Resnick, P., Ed., "Internet Message Format", RFC 5322,
DOI 10.17487/RFC5322, October 2008, <https://www.rfc-
editor.org/info/rfc5322>.
[RFC6068] - Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto'
D. Eastlake 3rd Expires 25 June 2022 [Page 19]
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URI Scheme", RFC 6068, DOI 10.17487/RFC6068, October 2010,
<https://www.rfc-editor.org/info/rfc6068>.
[RFC6838] - Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, RFC 6838,
DOI 10.17487/RFC6838, January 2013, <https://www.rfc-
editor.org/info/rfc6838>.
[RFC7595] - Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines
and Registration Procedures for URI Schemes", BCP 35, RFC 7595,
DOI 10.17487/RFC7595, June 2015, <https://www.rfc-
editor.org/info/rfc7595>.
[SMIL] - "Synchronized Multimedia Integration Language (SMIL 2.0)",
<http://www.w3.org/TR/2001/REC-smil20-20010807/>, 7 August
2001.
[XML NAME] - Tim Bray, Dave Hollander, Andrew Layman, "Namespaces in
XML", <http://www.w3.org/TR/REC-xml-names>, 14 January 1999.
[XMLENC] - D. Eastlake, J. Reagle, "XML Encryption Syntax and
Processing", <http://www.w3.org/TR/2001/WD-xmlenc-
core-20011018/>, 18 October 2001.
Author's Address
Donald E. Eastlake 3rd
Futurewei Technologies
2386 Panoramic Circle
Apopka, FL 32703 USA
Telephone: +1 508-333-2270
EMail: d3e3e3@gmail.com
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Copyright and IPR Provisions
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This document is subject to BCP 78 and the IETF Trust's Legal
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