import sys
import os
import zlib
try:
import pylzma as lzma
except ImportError:
import lzma
from io import StringIO
import struct
#-----------------------------------------------------------------------------------------------------------------------
def read_ui8(c):
return struct.unpack('<B', c)[0]
def read_ui16(c):
return struct.unpack('<H', c)[0]
def read_ui32(c):
return struct.unpack('<I', c)[0]
def parse(input):
"""Parses the header information from an SWF file."""
if hasattr(input, 'read'):
input.seek(0)
else:
input = open(input, 'rb')
header = { }
# Read the 3-byte signature field
header['signature'] = signature = b''.join(struct.unpack('<3c', input.read(3))).decode()
# Version
header['version'] = read_ui8(input.read(1))
# File size (stored as a 32-bit integer)
header['size'] = read_ui32(input.read(4))
# Payload
if header['signature'] == 'FWS':
print("The opened file doesn't appear to be compressed")
buffer = input.read(header['size'])
elif header['signature'] == 'CWS':
print("The opened file appears to be compressed with Zlib")
buffer = zlib.decompress(input.read(header['size']))
elif header['signature'] == 'ZWS':
print("The opened file appears to be compressed with Lzma")
# ZWS(LZMA)
# | 4 bytes | 4 bytes | 4 bytes | 5 bytes | n bytes | 6 bytes |
# | 'ZWS'+version | scriptLen | compressedLen | LZMA props | LZMA data | LZMA end marker |
size = read_ui32(input.read(4))
buffer = lzma.decompress(input.read())
# Containing rectangle (struct RECT)
# The number of bits used to store the each of the RECT values are
# stored in first five bits of the first byte.
nbits = read_ui8(buffer[0]) >> 3
current_byte, buffer = read_ui8(buffer[0]), buffer[1:]
bit_cursor = 5
for item in 'xmin', 'xmax', 'ymin', 'ymax':
value = 0
for value_bit in range(nbits-1, -1, -1): # == reversed(range(nbits))
if (current_byte << bit_cursor) & 0x80:
value |= 1 << value_bit
# Advance the bit cursor to the next bit
bit_cursor += 1
if bit_cursor > 7:
# We've exhausted the current byte, consume the next one
# from the buffer.
current_byte, buffer = read_ui8(buffer[0]), buffer[1:]
bit_cursor = 0
# Convert value from TWIPS to a pixel value
header[item] = value / 20
header['width'] = header['xmax'] - header['xmin']
header['height'] = header['ymax'] - header['ymin']
header['frames'] = read_ui16(buffer[0:2])
header['fps'] = read_ui16(buffer[2:4])
input.close()
return header
header = parse(sys.argv[1]);
print('SWF header')
print('----------')
print('Version: %s' % header['version'])
print('Signature: %s' % header['signature'])
print('Dimensions: %s x %s' % (header['width'], header['height']))
print('Bounding box: (%s, %s, %s, %s)' % (header['xmin'], header['xmax'], header['ymin'], header['ymax']))
print('Frames: %s' % header['frames'])
print('FPS: %s' % header['fps'])
我的印象是内置的 python 3.4 LZMA 模块与 Python 2.7 pyLZMA 模块的工作原理相同。
我提供的代码在 2.7 和 3.4 上都可以运行，但是当它在 3.4 上运行时(它没有 pylzma，所以它求助于内置的 lzma)我收到以下错误:
_lzma.LZMAError: Input format not supported by decoder
为什么 pylzma 有效而 Python 3.4 的 lzma 无效？
最佳答案
虽然我不知道为什么这两个模块的工作方式不同，但我确实有一个解决方案。
我无法让非流 LZMA lzma.decompress 工作，因为我对 LZMA/XZ/SWF 规范没有足够的了解，但是我让 lzma.LZMADecompressor 工作。为了完整起见，我相信 SWF LZMA 使用这种 header 格式(不是 100% 确认):
Bytes Length Type Endianness Description
0- 2 3 UI8 - SWF Signature: ZWS
3 1 UI8 - SWF Version
4- 7 4 UI32 LE SWF FileLength aka File Size
8-11 4 UI32 LE SWF? Compressed Size (File Size - 17)
12 1 - - LZMA Decoder Properties
13-16 4 UI32 LE LZMA Dictionary Size
17- - - - LZMA Compressed Data (including rest of SWF header)
但是 LZMA 文件格式规范说它应该是:
Bytes Length Type Endianness Description
0 1 - - LZMA Decoder Properties
1- 4 4 UI32 LE LZMA Dictionary Size
5-12 8 UI64 LE LZMA Uncompressed Size
13- - - - LZMA Compressed Data
我一直无法真正理解
Uncompressed Size 应该是什么(如果甚至可以为这种格式定义)。 pylzma 似乎并不关心这一点，而 Python 3.3 lzma 则关心。但是，似乎明确的未知大小有效，并且可以指定为 UI64 值 2^64 ，例如8*b'\xff' 或 8*'\xff' ，因此通过稍微调整标题而不是使用:buffer = lzma.decompress(input.read())
尝试:
d = lzma.LZMADecompressor(format=lzma.FORMAT_ALONE)
buffer = d.decompress(input.read(5) + 8*b'\xff' + input.read())
注意:我没有可用的本地 python3 解释器，所以只用稍微修改过的读取程序在线测试它，所以它可能无法开箱即用。
编辑:确认可以在 python3 中工作，但是有些事情需要改变，比如 Marcus 提到的解包(通过使用
buffer[0:1] 而不是 buffer[0] 很容易解决)。也没有必要读取整个文件，一小块，比如说 256 字节应该可以读取整个 SWF 头文件。 frames 字段也有点古怪，但我相信您所要做的就是进行一些位移，即:header['frames'] = read_ui16(buffer[0:2]) >> 8
SWF file format spec
LZMA file format spec