Simple plantUML call

main.py

import shutil
import requests

# some pieces from: https://github.com/SamuelMarks/python-plantuml

from zlib import compress

def deflate_and_encode(plantuml_text):
    """zlib compress the plantuml text and encode it for the plantuml server.
    """
    zlibbed_str = compress(plantuml_text)
    compressed_string = zlibbed_str[2:-4]
    return encode(compressed_string)


def encode(data):
    """encode the plantuml data which may be compresses in the proper
    encoding for the plantuml server
    """
    res = ""
    for i in xrange(0, len(data), 3):
        if i + 2 == len(data):
            res += _encode3bytes(ord(data[i]), ord(data[i + 1]), 0)
        elif i + 1 == len(data):
            res += _encode3bytes(ord(data[i]), 0, 0)
        else:
            res += _encode3bytes(ord(data[i]), ord(data[i + 1]), ord(data[i + 2]))
    return res


def _encode3bytes(b1, b2, b3):
    c1 = b1 >> 2
    c2 = ((b1 & 0x3) << 4) | (b2 >> 4)
    c3 = ((b2 & 0xF) << 2) | (b3 >> 6)
    c4 = b3 & 0x3F
    res = ""
    res += _encode6bit(c1 & 0x3F)
    res += _encode6bit(c2 & 0x3F)
    res += _encode6bit(c3 & 0x3F)
    res += _encode6bit(c4 & 0x3F)
    return res


def _encode6bit(b):
    if b < 10:
        return chr(48 + b)
    b -= 10
    if b < 26:
        return chr(65 + b)
    b -= 26
    if b < 26:
        return chr(97 + b)
    b -= 26
    if b == 0:
        return '-'
    if b == 1:
        return '_'
    return '?'

def get_url(plantuml_url, plantuml_text):
    """Return the server URL for the image.
    You can use this URL in an IMG HTML tag.

    :param str plantuml_text: The plantuml markup to render
    :returns: the plantuml server image URL
    """
    return plantuml_url + deflate_and_encode(plantuml_text)

umlText = """
@startuml

title "Messages - Sequence Diagram"

actor User
boundary "Web GUI" as GUI
control "Shopping Cart" as SC
entity Widget
database Widgets

User -> GUI : To boundary
GUI -> SC : To control
SC -> Widget : To entity
Widget -> Widgets : To database

@enduml
"""

url = get_url('http://www.plantuml.com/plantuml/img/', str.encode(umlText))
print(url)
response = requests.get(url, stream=True, params=umlText)
with open('img.png', 'wb') as out_file:
    shutil.copyfileobj(response.raw, out_file)