Re: Other formats in pset like markdown, rst, mediawiki

From: Fabien COELHO <fabien(dot)coelho(at)mines-paristech(dot)fr>
To: Jan Michálek <godzilalalala(at)gmail(dot)com>
Cc: PostgreSQL mailing lists <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Other formats in pset like markdown, rst, mediawiki
Date: 2017-05-08 10:02:28
Message-ID: alpine.DEB.2.20.1705080822560.3983@lancre
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Hello Jan,

Please give a number to submitted patches. I think that this was v3.

The patch does NOT fix various issues I pointed out in my previous review:

- tabs introduced in "doc/src/sgml/ref/psql-ref.sgml"
- too long help line in "src/bin/psql/help.c"
- spurious space after a comma in "src/fe_utils/print.c"
and possibly elsewhere.

On Sun, 23 Apr 2017, Jan Michálek wrote:

>>> Markdown include characters/sequences which are interpreted as markers:
>>> _Italic_, **Bold**, *** => horizontal rules, > block quote... `inline
>>> code`... If they are interpreted within a table cell then probably they
>>> should be escaped somehow.
>
> I have treated "_*|<>"

Probably not enough, see below. Note the escaping chars should also be
escaped.

>> I`m able to sanitize characters, but complex sequences will be problem. I
>> will look on this, but I don`t know, if I`m able to do this.

I do not know whether only those are necessary. Have you checked? Guessing
is probably not the right approach.

Concerning MARKDOWN, and according to the following source about github
markdown implementation:

https://enterprise.github.com/downloads/en/markdown-cheatsheet.pdf

The following characters may need to be backslash escaped, although it
does not cover HTML stuff.

\ backslash
` backtick
* asterisk
_ underscore
{} curly braces
[] square brackets
() parentheses
# hash mark
+ plus sign
- minus sign (hyphen)
. dot
! exclamation

Another source https://genius.com/3057216 suggests (* # / ( ) [ ] < >),
which should protect HTML.

However, the escaping seems to be the backslash character, NOT using html
encoding &lt; as done in your version.

Where did you find the precise escaping rules for markdown? I do not think
that it should be invented...

I have looked at RST, according to this reference:

http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html#grid-tables

The good news is that you do not need to handle a special | case because
you would only produce clean tables.

I've tested UTF-8 with plane 1 (你好!) and plane 2 (𠀡) and the alignment
seems to worked well, incredible!

>> My main interest on this was in rst. I`m using markdown only in github
>> issues and my knowldge about md is poor.

Then maybe only do RST?!

It looks much simpler anyway, and if you do MARKDOWN the support needs to
be clean.

About the code:

I'm still at odds with the code which needs to test for markdown to call
for different functions in multiple places. If you keep md and in order to
avoid that, I would suggest to extend the pg_wcs* functions with a list of
caracters which may have different sizes with additionnal args, say:

pg_wcssize(// same args, plus:
char * escaped_chars, // will require escaping
int escape_len, // how many chars added when escaping
int nllen // len of newline if substituted
);

So that pg_wcssize(..., "\r", 1, 1) would behave as before (\n and \t are
rather special cases), and the various constants could be held in the
format description so the whole thing would be parametric.

Same approach with format.

That would allow to simplify the code significantly and to share it
between MARKDOWN and others. Also, the multiple "else if" list would be
simplified by using strchr or the escaped_chars string.

--
Fabien.

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