siriusfox/pnger
Archived
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity

Added support for a PNG file with trailing data assuming IEND is the final chunk.

Browse source
This commit is contained in:
Luke 2016-03-29 18:24:26 -07:00
parent 6bc805af89
commit 715cbc0a75
1 changed files with 40 additions and 10 deletions
Download patch file Download diff file Expand all files Collapse all files

50
pnger.py
View file

@ -7,30 +7,60 @@
'''
import sys
import argparse
import struct
# Magic number and line ending bits in the PNG header
pngFixedHeader = "\x89\x50\x4e\x47\x0d\x0a" + "\x1a\x0a"
# A colorful reference image (3 chunks)
imageData = "\x00\x00\x00\x0d\x49\x48\x44\x52\x00\x00\x00\x80\x00\x00\x00\x44\x08\x02\x00\x00\x00\xc6\x25\xaa\x3e"+\
"\x00\x00\x00\xc2\x49\x44\x41\x54\x78\x5e\xed\xd4\x81\x06\xc3\x30\x14\x40\xd1\xb7\x34\xdd\xff\xff\x6f\xb3\x74\x56\xea\x89\x12\x6c\x28\x73\xe2\xaa\x34\x49\x03\x87\xd6\xfe\xd8\x7b\x89\xbb\x52\x8d\x3b\x87\xfe\x01\x00\x80\x00\x00\x10\x00\x00\x02\x00\x40\x00\x00\x08\x00\x00\x01\x00\x20\x00\x00\x04\x00\x80\x00\x00\x10\x00\x00\x02\x00\x40\x00\x00\x08\x00\x00\x01\x00\x20\x00\x00\x00\xd4\x5e\x6a\x64\x4b\x94\xf5\x98\x7c\xd1\xf4\x92\x5c\x5c\x3e\xcf\x9c\x3f\x73\x71\x58\x5f\xaf\x8b\x79\x5b\xee\x96\xb6\x47\xeb\xf1\xea\xd1\xce\xb6\xe3\x75\x3b\xe6\xb9\x95\x8d\xc7\xce\x03\x39\xc9\xaf\xc6\x33\x93\x7b\x66\x37\xcf\xab\xbf\xf9\xc9\x2f\x08\x80\x00\x00\x10\x00\x00\x02\x00\x40\x00\x00\x08\x00\x00\x01\x00\x20\x00\x00\x04\x00\x80\x00\x00\x10\x00\x00\x02\x00\x40\x00\x00\x08\x00\x00\x01\x00\x20\x00\x00\x8c\x37\xdb\x68\x03\x20\xfb\xed\x96\x65\x00\x00\x00\x00\x49\x45\x4e\x44\xae\x42\x60\x82"
fakeimage = "\x89\x50\x4e\x47\x0d\x0a\x1a\x0a\x00\x00\x00\x0d\x49\x48\x44\x52\x00\x00\x00\x80\x00\x00\x00\x44\x08\x02\x00\x00\x00\xc6\x25\xaa\x3e\x00\x00\x00\xc2\x49\x44\x41\x54\x78\x5e\xed\xd4\x81\x06\xc3\x30\x14\x40\xd1\xb7\x34\xdd\xff\xff\x6f\xb3\x74\x56\xea\x89\x12\x6c\x28\x73\xe2\xaa\x34\x49\x03\x87\xd6\xfe\xd8\x7b\x89\xbb\x52\x8d\x3b\x87\xfe\x01\x00\x80\x00\x00\x10\x00\x00\x02\x00\x40\x00\x00\x08\x00\x00\x01\x00\x20\x00\x00\x04\x00\x80\x00\x00\x10\x00\x00\x02\x00\x40\x00\x00\x08\x00\x00\x01\x00\x20\x00\x00\x00\xd4\x5e\x6a\x64\x4b\x94\xf5\x98\x7c\xd1\xf4\x92\x5c\x5c\x3e\xcf\x9c\x3f\x73\x71\x58\x5f\xaf\x8b\x79\x5b\xee\x96\xb6\x47\xeb\xf1\xea\xd1\xce\xb6\xe3\x75\x3b\xe6\xb9\x95\x8d\xc7\xce\x03\x39\xc9\xaf\xc6\x33\x93\x7b\x66\x37\xcf\xab\xbf\xf9\xc9\x2f\x08\x80\x00\x00\x10\x00\x00\x02\x00\x40\x00\x00\x08\x00\x00\x01\x00\x20\x00\x00\x04\x00\x80\x00\x00\x10\x00\x00\x02\x00\x40\x00\x00\x08\x00\x00\x01\x00\x20\x00\x00\x8c\x37\xdb\x68\x03\x20\xfb\xed\x96\x65\x00\x00\x00\x00\x49\x45\x4e\x44\xae\x42\x60\x82"
# Reference image if we want to write data
fakeimage = pngFixedHeader+imageData
# A simple routine to search from the start of an assumed valid PNG file, and find the IEND block
# indicating the end of a file.
def findLastChunk(infile):
# Assume inital offset of PNG fixed header
with open(infile, "rb") as f:
ckStart=len(pngFixedHeader);
while f.read(1) != "":
f.seek(ckStart)
# Find the length of the current chunk
ckSize = struct.unpack(">i", f.read(4))[0]
# Get the type of the cunk
ckType = f.read(4)
# From the size compute the start of the next chunk
ckStart=(ckStart+8+ckSize+4);
# Uncomment to retreve chunk data and CRC
#ckDat = f.read(ckSize)
#ckCrc = f.read(4)
# If we're at the end of a chunk, return the end of the chunk
if ckType == "IEND":
break;
# Return the index to the trailing data.
return ckStart
def pngit(infile, outfile, nowrite=0):
outcounter = 0
with open(outfile, "wb") as theoutf:
if nowrite == 0:
theoutf.write(fakeimage)
with open(infile, "rb") as f:
if nowrite == 0:
theoutf.write(fakeimage)
else:
f.seek(nowrite)
byte = f.read(1)
while byte != "":
if outcounter >= nowrite:
theoutf.write(byte)
else:
outcounter+=1
theoutf.write(byte)
byte = f.read(1)
def unpngit(infile, outfile):
pngit(infile, outfile, 251)
dataStart = findLastChunk(infile)
pngit(infile, outfile, dataStart)
if __name__ == '__main__':
parser = argparse.ArgumentParser(description='Process some integers.')