jcs.org
mutt stable branch with some hacks
1#!/usr/bin/python3
2#
3# markdown2html.py — simple Markdown-to-HTML converter for use with Mutt
4#
5# Mutt recently learnt [how to compose `multipart/alternative`
6# emails][1]. This script assumes a message has been composed using Markdown
7# (with a lot of pandoc extensions enabled), and translates it to `text/html`
8# for Mutt to tie into such a `multipart/alternative` message.
9#
10# [1]: https://gitlab.com/muttmua/mutt/commit/0e566a03725b4ad789aa6ac1d17cdf7bf4e7e354)
11#
12# Configuration:
13# muttrc:
14# set send_multipart_alternative=yes
15# set send_multipart_alternative_filter=/path/to/markdown2html.py
16#
17# Optionally, Custom CSS styles will be read from `~/.mutt/markdown2html.css`,
18# if present.
19#
20# Requirements:
21# - python3
22# - PyPandoc (and pandoc installed, or downloaded)
23# - Pynliner
24#
25# Optional:
26# - Pygments, if installed, then syntax highlighting is enabled
27#
28# Latest version:
29# https://git.madduck.net/etc/mutt.git/blob_plain/HEAD:/.mutt/markdown2html
30#
31# Copyright © 2019 martin f. krafft <madduck@madduck.net>
32# Released under the GPL-2+ licence, just like Mutt itself.
33#
34
35import pypandoc
36import pynliner
37import re
38import os
39import sys
40
41try:
42 from pygments.formatters import get_formatter_by_name
43 formatter = get_formatter_by_name('html', style='default')
44 DEFAULT_CSS = formatter.get_style_defs('.sourceCode')
45
46except ImportError:
47 DEFAULT_CSS = ""
48
49
50DEFAULT_CSS += '''
51.quote {
52 padding: 0 0.5em;
53 margin: 0;
54 font-style: italic;
55 border-left: 2px solid #ccc;
56 color: #999;
57 font-size: 80%;
58}
59.quotelead {
60 font-style: italic;
61 margin-bottom: -1em;
62 color: #999;
63 font-size: 80%;
64}
65.quotechar { display: none; }
66.footnote-ref, .footnote-back { text-decoration: none;}
67.signature {
68 color: #999;
69 font-family: monospace;
70 white-space: pre;
71 margin: 1em 0 0 0;
72 font-size: 80%;
73}
74table, th, td {
75 border-collapse: collapse;
76 border: 1px solid #999;
77}
78th, td { padding: 0.5em; }
79.header {
80 background: #eee;
81}
82.even { background: #eee; }
83'''
84
85STYLESHEET = os.path.join(os.path.expanduser('~/.mutt'),
86 'markdown2html.css')
87if os.path.exists(STYLESHEET):
88 DEFAULT_CSS += open(STYLESHEET).read()
89
90HTML_DOCUMENT = '''<!DOCTYPE html>
91<html><head>
92<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
93<meta charset="utf-8"/>
94<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes"/>
95<title>HTML E-Mail</title>
96</head><body class="email">
97{htmlbody}
98</body></html>'''
99
100
101SIGNATURE_HTML = \
102 '<div class="signature"><span class="leader">-- </span>{sig}</div>'
103
104
105def _preprocess_markdown(mdwn):
106 '''
107 Preprocess Markdown for handling by the converter.
108 '''
109 # convert hard line breaks within paragraphs to 2 trailing spaces, which
110 # is the markdown way of representing hard line breaks. Note how the
111 # regexp will not match between paragraphs.
112 ret = re.sub(r'(\S)\n(\s*\S)', r'\g<1> \n\g<2>', mdwn, flags=re.MULTILINE)
113
114 # Clients like Thunderbird need the leading '>' to be able to properly
115 # create nested quotes, so we duplicate the symbol, the first instance
116 # will tell pandoc to create a blockquote, while the second instance will
117 # be a <span> containing the character, along with a class that causes CSS
118 # to actually hide it from display. However, this does not work with the
119 # text-mode HTML2text converters, and so it's left commented for now.
120 #ret = re.sub(r'\n>', r' \n>[>]{.quotechar}', ret, flags=re.MULTILINE)
121
122 return ret
123
124
125def _identify_quotes_for_later(mdwn):
126 '''
127 Email quoting such as:
128
129 ```
130 On 1970-01-01, you said:
131 > The Flat Earth Society has members all around the globe.
132 ```
133
134 isn't really properly handled by Markdown, so let's do our best to
135 identify the individual elements, and mark them, using a syntax similar to
136 what pandoc uses already in some cases. As pandoc won't actually use these
137 data (yet?), we call `self._reformat_quotes` later to use these markers
138 to slap the appropriate classes on the HTML tags.
139 '''
140
141 def generate_lines_with_context(mdwn):
142 '''
143 Iterates the input string line-wise, returning a triplet of
144 previous, current, and next line, the first and last of which
145 will be None on the first and last line of the input data
146 respectively.
147 '''
148 prev = cur = nxt = None
149 lines = iter(mdwn.splitlines())
150 cur = next(lines)
151 for nxt in lines:
152 yield prev, cur, nxt
153 prev = cur
154 cur = nxt
155 yield prev, cur, None
156
157 ret = []
158 for prev, cur, nxt in generate_lines_with_context(mdwn):
159
160 # The lead-in to a quote is a single line immediately preceding the
161 # quote, and ending with ':'. Note that there could be multiple of
162 # these:
163 if re.match(r'^.+:\s*$', cur) and nxt.startswith('>'):
164 ret.append(f'{{.quotelead}}{cur.strip()}')
165 # pandoc needs an empty line before the blockquote, so
166 # we enter one for the purpose of HTML rendition:
167 ret.append('')
168 continue
169
170 # The first blockquote after such a lead-in gets marked as the
171 # "initial" quote:
172 elif prev and re.match(r'^.+:\s*$', prev) and cur.startswith('>'):
173 ret.append(re.sub(r'^(\s*>\s*)+(.+)',
174 r'\g<1>{.quoteinitial}\g<2>',
175 cur, flags=re.MULTILINE))
176
177 # All other occurrences of blockquotes get the "subsequent" marker:
178 elif cur.startswith('>') and prev and not prev.startswith('>'):
179 ret.append(re.sub(r'^((?:\s*>\s*)+)(.+)',
180 r'\g<1>{.quotesubsequent}\g<2>',
181 cur, flags=re.MULTILINE))
182
183 else: # pass through everything else.
184 ret.append(cur)
185
186 return '\n'.join(ret)
187
188
189def _reformat_quotes(html):
190 '''
191 Earlier in the pipeline, we marked email quoting, using markers, which we
192 now need to turn into HTML classes, so that we can use CSS to style them.
193 '''
194 ret = html.replace('<p>{.quotelead}', '<p class="quotelead">')
195 ret = re.sub(r'<blockquote>\n((?:<blockquote>\n)*)<p>(?:\{\.quote(\w+)\})',
196 r'<blockquote class="quote \g<2>">\n\g<1><p>', ret, flags=re.MULTILINE)
197 return ret
198
199
200
201def _convert_with_pandoc(mdwn, inputfmt='markdown', outputfmt='html5',
202 ext_enabled=None, ext_disabled=None,
203 standalone=True, title="HTML E-Mail"):
204 '''
205 Invoke pandoc to do the actual conversion of Markdown to HTML5.
206 '''
207 if not ext_enabled:
208 ext_enabled = [ 'backtick_code_blocks',
209 'line_blocks',
210 'fancy_lists',
211 'startnum',
212 'definition_lists',
213 'example_lists',
214 'table_captions',
215 'simple_tables',
216 'multiline_tables',
217 'grid_tables',
218 'pipe_tables',
219 'all_symbols_escapable',
220 'intraword_underscores',
221 'strikeout',
222 'superscript',
223 'subscript',
224 'fenced_divs',
225 'bracketed_spans',
226 'footnotes',
227 'inline_notes',
228 'emoji',
229 'tex_math_double_backslash',
230 'autolink_bare_uris'
231 ]
232 if not ext_disabled:
233 ext_disabled = [ 'tex_math_single_backslash',
234 'tex_math_dollars',
235 'smart',
236 'raw_html'
237 ]
238
239 enabled = '+'.join(ext_enabled)
240 disabled = '-'.join(ext_disabled)
241 inputfmt = f'{inputfmt}+{enabled}-{disabled}'
242
243 args = []
244 if standalone:
245 args.append('--standalone')
246 if title:
247 args.append(f'--metadata=pagetitle:"{title}"')
248
249 return pypandoc.convert_text(mdwn, format=inputfmt, to=outputfmt,
250 extra_args=args)
251
252
253def _apply_styling(html):
254 '''
255 Inline all styles defined and used into the individual HTML tags.
256 '''
257 return pynliner.Pynliner().from_string(html).with_cssString(DEFAULT_CSS).run()
258
259
260def _postprocess_html(html):
261 '''
262 Postprocess the generated and styled HTML.
263 '''
264 return html
265
266
267def convert_markdown_to_html(mdwn):
268 '''
269 Converts the input Markdown to HTML, handling separately the body, as well
270 as an optional signature.
271 '''
272 parts = re.split(r'^-- $', mdwn, 1, flags=re.MULTILINE)
273 body = parts[0]
274 if len(parts) == 2:
275 sig = parts[1]
276 else:
277 sig = None
278
279 html=''
280 if body:
281 body = _preprocess_markdown(body)
282 body = _identify_quotes_for_later(body)
283 html = _convert_with_pandoc(body, standalone=False)
284 html = _reformat_quotes(html)
285
286 if sig:
287 sig = _preprocess_markdown(sig)
288 html += SIGNATURE_HTML.format(sig='<br/>'.join(sig.splitlines()))
289
290 html = HTML_DOCUMENT.format(htmlbody=html)
291 html = _apply_styling(html)
292 html = _postprocess_html(html)
293
294 return html
295
296
297def main():
298 '''
299 Convert text on stdin to HTML, and print it to stdout, like mutt would
300 expect.
301 '''
302 html = convert_markdown_to_html(sys.stdin.read())
303 if html:
304 # mutt expects the content type in the first line, so:
305 print(f'text/html\n\n{html}')
306
307
308if __name__ == '__main__':
309 main()