Created
April 6, 2013 14:59
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Simple Python module for baking of badges, and retrieval of assertion URLs from baked badges.
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""" | |
This small module makes it easy to bake PNG images with links to | |
Open Badge assertions. It also allows for easy retrieval of the link | |
from baked PNGs. | |
For more information on badge baking, see: | |
https://github.com/mozilla/openbadges/wiki/Badge-Baking | |
Note that this module requires the PyPNG module: | |
http://pythonhosted.org/pypng/ | |
The module can be installed via 'pip install pypng'. | |
""" | |
import os | |
import png | |
def get_baked_url(src): | |
""" | |
Return the assertion URL contained in the given baked PNG. If | |
the image isn't baked, return None. | |
Example: | |
>>> get_baked_url('baked.png') | |
'http://f.org/assertion.json' | |
""" | |
if isinstance(src, basestring): src = open(src, 'rb') | |
reader = png.Reader(file=src) | |
for chunktype, content in reader.chunks(): | |
if chunktype == 'tEXt' and content.startswith('openbadges\x00'): | |
return content.split('\x00')[1] | |
def bake_badge(src, dest, url): | |
""" | |
Bake the given PNG file with the given assertion URL. The source and | |
destination can be filenames or file objects. | |
Example: | |
>>> bake_badge('unbaked.png', 'baked.png', 'http://f.org/a.json') | |
""" | |
if isinstance(src, basestring): src = open(src, 'rb') | |
if isinstance(dest, basestring): dest = open(dest, 'wb') | |
reader = png.Reader(file=src) | |
chunks = [ | |
(chunktype, content) | |
for chunktype, content in reader.chunks() | |
if not (chunktype == 'tEXt' and content.startswith('openbadges\x00')) | |
] | |
chunks.insert(1, ('tEXt', '\x00'.join(('openbadges', url)))) | |
png.write_chunks(dest, chunks) | |
def test(show_output=False): | |
""" | |
Test suite for this module. | |
""" | |
from StringIO import StringIO | |
def eq(a, b, msg): | |
if show_output: print "%-60s" % msg, | |
if a != b: | |
raise AssertionError('%s (%s != %s)' % (msg, repr(a), repr(b))) | |
if show_output: print "OK" | |
PNG = '\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR\x00\x00\x00\x10\x00\x00\x00' \ | |
'\x10\x08\x02\x00\x00\x00\x90\x91h6\x00\x00\x00\x19IDAT(\x91c' \ | |
'\xfc\xff\xff?\x03)\x80\x89$\xd5\xa3\x1aF5\x0c)\r\x00Um\x03' \ | |
'\x1d\xe4FZ\x12\x00\x00\x00\x00IEND\xaeB`\x82' | |
unbaked = StringIO(PNG) | |
eq(get_baked_url(unbaked), None, | |
'get_baked_url() on unbaked badge returns None') | |
unbaked = StringIO(PNG) | |
baked = StringIO() | |
bake_badge(unbaked, baked, 'http://foo.org/assertion.json') | |
baked = StringIO(baked.getvalue()) | |
eq(get_baked_url(baked), 'http://foo.org/assertion.json', | |
'baking an unbaked badge works') | |
baked = StringIO(baked.getvalue()) | |
rebaked = StringIO() | |
bake_badge(baked, rebaked, 'http://another/assertion') | |
rebaked = StringIO(rebaked.getvalue()) | |
eq(get_baked_url(rebaked), 'http://another/assertion', | |
'baking an already-baked badge re-bakes it') | |
if __name__ == '__main__': | |
test(show_output=True) |
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