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Merged
pombredanne merged 6 commits into from
Jun 4, 2025
Merged

Update "Character encoding" and related provisions #438 #461

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0beba16
Update "Character encoding" and related provisions #438
johnmhoran Apr 22, 2025
91f07a0
Clarify percent-encoding references #438
johnmhoran Apr 27, 2025
e391329
Merge branch 'main' into 438-update-character-encoding
johnmhoran Apr 27, 2025
e7119e8
Restructure and clarify character-encoding section #438
johnmhoran May 9, 2025
90b017d
Merge branch 'main' into 438-update-character-encoding
johnmhoran May 9, 2025
bc98ead
Merge branch 'main' into 438-update-character-encoding
pombredanne Jun 4, 2025
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46 changes: 28 additions & 18 deletions PURL-SPECIFICATION.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -114,9 +114,11 @@ Rules for each ``purl`` component

A ``purl`` string is an ASCII URL string composed of seven components.

Some components are allowed to use other characters beyond ASCII: these
components must then be UTF-8-encoded strings and percent-encoded as defined in
the "Character encoding" section.
Except as expressly stated otherwise in this section, each component:

- MAY be composed of any of the characters defined as "Permitted Characters" in
the "Character encoding" section
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- MUST be encoded as defined in the "Character encoding" section

The rules for each component are:

Expand Down Expand Up @@ -225,17 +227,13 @@ Character encoding
Permitted characters
--------------------

A canonical ``purl`` is an ASCII string composed of these characters:
A canonical ``purl`` is composed of these Permitted Characters:

- alphanumeric characters ``A to Z``, ``a to z``, ``0 to 9``,
- the ``purl`` separators ``:/@?=&#`` (colon ':', slash '/', at sign '@',
question mark '?', equal sign '=', ampersand '&' and pound sign '#'), and
- these punctuation marks ``%.-_~`` (percent sign '%', period '.', dash '-',
underscore '_' and tilde '~').

All other characters MUST be encoded as UTF-8 and then percent-encoded.
In addition, each component specifies its permitted characters and
its percent-encoding rules.
- the ASCII characters ``+%.-_~`` (plus '+', percent sign '%', period '.',
dash '-', underscore '_' and tilde '~').


``purl`` separators
Expand All @@ -259,14 +257,26 @@ These ``purl`` separator characters MUST NOT be percent-encoded when used as
Percent-encoding rules
----------------------

When applying percent-encoding or decoding to a string, use the rules of RFC
3986 section 2 (https://datatracker.ietf.org/doc/html/rfc3986#section-2).

Each component defines when and how to apply percent-encoding and decoding to
its content.

When percent-encoding is required, all characters MUST be encoded except for
the colon ':'.
- In the "Rules for each ``purl`` component" section above, each component
defines when and how to apply percent-encoding and decoding to its content,
including which characters to percent-encode and when percent-encoding is
required.
- When percent-encoding is required by a component definition, each
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codepoint MUST be replaced by the percent-encoded bytes of the codepoint's
UTF-8 encoding using the percent-encoding mechanism defined in RFC 3986
section 2.1 (https://datatracker.ietf.org/doc/html/rfc3986#section-2.1).
- With the exception of the percent-encoding mechanism, the rules regarding
percent-encoding are defined by this specification alone.
- Where the space ' ' is permitted, it MUST be percent-encoded as
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'%20'.
- The following characters do not need to be percent-encoded:
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- the alphanumeric characters ``A to Z``, ``a to z``, ``0 to 9``,
- the ASCII characters ``.-_~`` (period '.', dash '-', underscore
'_' and tilde '~'),
- the percent sign '%' when used to represent a percent-encoded character,
- a ``purl`` separator when being used as a ``purl`` separator, and
- the colon ':', whether used as a ``purl`` separator or otherwise.

@ppkarwasz ppkarwasz Apr 28, 2025

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Since each component specifies the arguments of the percent-encode method, I think this is not necessary.
The argument of percent-encode will never contain "characters used as purl separators"; those characters will be added afterwards.

For example:

  • percent-encode each segment of the namespace.
  • join the encoded segments with the / character.

@johnmhoran johnmhoran Apr 28, 2025

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Thanks for this comment @ppkarwasz . Not sure if you're addressing all 3 lines you excerpt or just line 278, so just in case:

  • line 277: that is definitely more than needed -- was just trying to be thorough ;-) no objections at all to deleting if others agree
  • line 278: believe it or not, there have been issues that this point addresses, e.g., does the colon between scheme and type need to be percent-encoded? See, e.g., Percent encoding spec and : and /; imho this is needed to avoid such issues in the future and make the use of a PURL as clear as possible.
  • line 279: perhaps I am misunderstanding your point here -- without line 279, how will users know that colons do not need to be percent-encoded?

@ppkarwasz ppkarwasz Apr 29, 2025 •
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  • line 278: believe it or not, there have been issues that this point addresses, e.g., does the colon between scheme and type need to be percent-encoded?

Lines 242-243 say:

purl-spec/PURL-SPECIFICATION.rst

Lines 242 to 243 in e391329

These ``purl`` separator characters MUST NOT be percent-encoded when used as
``purl`` separators:

Do we need to repeat it here too?

  • line 279: perhaps I am misunderstanding your point here -- without line 279, how will users know that colons do not need to be percent-encoded?

Sure we need to say that colon : does not need to be percent-encoded, but I think we don't need to repeat that it also does not need to be encoded when used as a separator.

Maybe we could make this paragraph less descriptive and more imperative like:

To percent-encode a string of characters:

1. encode it using UTF-8,
2. for each byte of the encoded string:
    - if the byte corresponds to:
       - an alphanumeric ASCII character (``A to Z``, ``a to z``, ``0 to 9``)
       - or one of the ASCII characters `.`, `-`, `_`, `~` and `:`.
       
      copy the byte to the output.
    - otherwise, append the percent-encoding of the byte to the output, as defined in RFC 3986
      section 2.1 (https://datatracker.ietf.org/doc/html/rfc3986#section-2.1).



How to build ``purl`` string from its components
Expand Down