plantuml in markdown filter for pandoc

plantuml-filter.py

#!/usr/bin/env python

"""
Pandoc filter to process code blocks with class "dot" into
plantuml-generated images.
"""

import subprocess
import hashlib
import os
import sys
from pandocfilters import toJSONFilter, Str, Para, Image, attributes

def sha1(x):
  return hashlib.sha1(x.encode('utf-8')).hexdigest()

def out(s):
    sys.stderr.write('\t[PLTUML] ' + s + '\n');

image_dir = "tmp"

def pipe(cmd, data):
    p = subprocess.Popen(cmd, shell=False, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, close_fds=True)
    p.stdin.write(data.encode('utf-8'))
    p.stdin.close()
    data = p.stdout.read()
    p.stdout.close()
    err = p.stderr.read()
    p.stderr.close()
    return data, err

def graphviz(key, value, fmt, meta):
  if key == 'CodeBlock':
    [[ident,classes,keyvals], code] = value

    caption = ""
    if "plantuml" in classes or "uml" in classes:
      path = os.path.dirname(os.path.abspath(__file__))

      filename = sha1(code)
      alt = Str(caption)
      tit = ""

      image_filename = image_dir + '/' + filename + '.png'
      src = image_filename
      if not os.path.isfile(src):
        try:
            os.mkdir(os.path.dirname(image_filename))
        except OSError:
            pass
        data, err = pipe(["plantuml", "-pipe", "-Tpng"], code)
        if (len(err) > 0):
          return Para([Str(err)])
        with open(src, 'wb') as f:
          f.write(data)
      try:
        image = Image(attributes({}), [alt], [src, tit])
        return Para([image])
      except:
        try:
          image = Image([alt], [src,tit])
          return Para([image])
        except:
          pass

if __name__ == "__main__":
  toJSONFilter(graphviz)