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1 #!/usr/bin/env python | |
2 # Copyright 2011 Google Inc. All Rights Reserved. | |
3 # | |
4 # Licensed under the Apache License, Version 2.0 (the "License"); | |
5 # you may not use this file except in compliance with the License. | |
6 # You may obtain a copy of the License at | |
7 # | |
8 # http://www.apache.org/licenses/LICENSE-2.0 | |
9 # | |
10 # Unless required by applicable law or agreed to in writing, software | |
11 # distributed under the License is distributed on an "AS IS" BASIS, | |
12 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
13 # See the License for the specific language governing permissions and | |
14 # limitations under the License. | |
15 | |
16 """Apply gzip/deflate to separate chunks of data.""" | |
17 | |
18 import struct | |
19 import zlib | |
20 | |
21 GZIP_HEADER = ( | |
22 '\037\213' # magic header | |
23 '\010' # compression method | |
24 '\000' # flags (none) | |
25 '\000\000\000\000' # packed time (use zero) | |
26 '\002' | |
27 '\377') | |
28 | |
29 | |
30 def compress_chunks(uncompressed_chunks, use_gzip): | |
31 """Compress a list of data with gzip or deflate. | |
32 | |
33 The returned chunks may be used with HTTP chunked encoding. | |
34 | |
35 Args: | |
36 uncompressed_chunks: a list of strings | |
37 (e.g. ["this is the first chunk", "and the second"]) | |
38 use_gzip: if True, compress with gzip. Otherwise, use deflate. | |
39 | |
40 Returns: | |
41 [compressed_chunk_1, compressed_chunk_2, ...] | |
42 """ | |
43 if use_gzip: | |
44 size = 0 | |
45 crc = zlib.crc32("") & 0xffffffffL | |
46 compressor = zlib.compressobj( | |
47 6, zlib.DEFLATED, -zlib.MAX_WBITS, zlib.DEF_MEM_LEVEL, 0) | |
48 else: | |
49 compressor = zlib.compressobj() | |
50 compressed_chunks = [] | |
51 last_index = len(uncompressed_chunks) - 1 | |
52 for index, data in enumerate(uncompressed_chunks): | |
53 chunk = '' | |
54 if use_gzip: | |
55 size += len(data) | |
56 crc = zlib.crc32(data, crc) & 0xffffffffL | |
57 if index == 0: | |
58 chunk += GZIP_HEADER | |
59 chunk += compressor.compress(data) | |
60 if index < last_index: | |
61 chunk += compressor.flush(zlib.Z_SYNC_FLUSH) | |
62 else: | |
63 chunk += (compressor.flush(zlib.Z_FULL_FLUSH) + | |
64 compressor.flush()) | |
65 if use_gzip: | |
66 chunk += (struct.pack("<L", long(crc)) + | |
67 struct.pack("<L", long(size))) | |
68 compressed_chunks.append(chunk) | |
69 return compressed_chunks | |
70 | |
71 | |
72 def uncompress_chunks(compressed_chunks, use_gzip): | |
73 """Uncompress a list of data compressed with gzip or deflate. | |
74 | |
75 Args: | |
76 compressed_chunks: a list of compressed data | |
77 use_gzip: if True, uncompress with gzip. Otherwise, use deflate. | |
78 | |
79 Returns: | |
80 [uncompressed_chunk_1, uncompressed_chunk_2, ...] | |
81 """ | |
82 if use_gzip: | |
83 decompress = zlib.decompressobj(16 + zlib.MAX_WBITS).decompress | |
84 else: | |
85 decompress = zlib.decompressobj(-zlib.MAX_WBITS).decompress | |
86 return [decompress(c) for c in compressed_chunks] | |
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