读BitTorrent码日记2

# Written by Bram Cohen
# see LICENSE.txt for license information
# filename:btfield.py btformats.py

# btfield.py
#读码日记：2004-9-1 笔者：
#笔 者：zfive5(醉马不肖 之 [孤舟蓑笠翁， 独钓寒江雪])
#注 释：这个文件主要是进行字节到比特位之间的转化的

#功能:主要是实现的列表bits位到byte的转化
#参数:1个逻辑列表 例如:[1,1,0,1,1,1,0,1]
#返回:byte流, 例如:'a/x00'
#效果:
#>>> booleans_to_bitfield([0,1,1,0,0,0,0,1])
#'a'
#>>> booleans_to_bitfield([0,1,1,0,0,0,0,1,0])
#'a/x00'
#
def booleans_to_bitfield(booleans):
r = []
for i in xrange(0, len(booleans), 8):
v = 0
p = 0x80
for j in booleans[i:i+8]:
if j:
v |= p
p >>= 1
r.append(chr(v))
return ''.join(r)

#功能:主要完成位到byte流到bits列表之间的转化
#参数:byte流,byte个数 例如:'a/x00'
#返回:逻辑bits列表,例如:[False, True, True, False, False, False, False, True]
#效果:
#>>> bitfield_to_booleans('a',8)
#[False, True, True, False, False, False, False, True]
#
def bitfield_to_booleans(bitfield, l):
extra = len(bitfield) * 8 - l
if extra < 0 or extra >= 8:
return None
r = []
for c in bitfield:
v = ord(c)
for i in xrange(8):
if v & 0x80 != 0:
r.append(True)
else:
r.append(False)
v <<= 1
if extra > 0:
if r[-extra:] != [0] * extra:
return None
del r[-extra:]
return r

#功能:测试1
def test_basic():
x = [1, 1, 1, 0, 0, 0, 1, 1, 1]
y = [1, 1, 1, 0, 0, 0, 1, 1]
for a in [x, y, []]:
assert bitfield_to_booleans(booleans_to_bitfield(a), len(a)) == a

#功能:测试2
def test_too_long():
assert bitfield_to_booleans('ab', 8) == None

#功能:测试3
def test_too_short():
assert bitfield_to_booleans('a', 9) == None

#功能:测试4
def test_nonzero_in_excess():
assert bitfield_to_booleans(chr(0xFF), 7) == None

# Written by Bram Cohen
# see LICENSE.txt for license information

# btformats.py

from types import StringType, LongType, IntType, ListType, DictType
from re import compile

reg = compile(r'^[^///.~][^///]*$')

ints = [LongType, IntType]

#功能:这里主要是检查种子文件info信息是否合法,其中包括它的子信息,
#如过不合法抛异常,从这个文件里我们可以看出种子文件的info的结构
# info(DictType){
# 'piecelength':ints(大于零),
# 'pieces':StringType(长度为20个字节的整数倍),
# 'name':StringType(不能是/ *之类的非文件名称字符),
# 'length':ints(大于零,对单个文件)
# }
#
# info(DictType){
# 'piecelength':ints(大于零),
# 'pieces':StringType(长度为20个字节的整数倍),
# 'name':StringType(不能是/ *之类的非文件名称字符),
# 'files'(ListType):[
# (DictType)
# {
# 'length':ints(大于零)
# 'path'(ListType):[ (例如: "1","2","4.txt" 代表 :"/1/2/4.txt"
# StringType,
# StringType,
# StringType,
# ....
# ]
# },
#
# (DictType)
{
# 'length':ints(大于零)
# 'path'(ListType):[
# StringType,
# StringType,
# StringType,
# ....
# ]
# }
# ....
# ]
# }
#
#这里顺序可能是种子文件有出入
def check_info(info):
if type(info) != DictType:
raise ValueError, 'bad metainfo - not a dictionary'
pieces = info.get('pieces')
if type(pieces) != StringType or len(pieces) % 20 != 0:
raise ValueError, 'bad metainfo - bad pieces key'
piecelength = info.get('piece length')
if type(piecelength) not in ints or piecelength <= 0:
raise ValueError, 'bad metainfo - illegal piece length'
name = info.get('name')
if type(name) != StringType:
raise ValueError, 'bad metainfo - bad name'
if not reg.match(name):
raise ValueError, 'name %s disallowed for security reasons' % name
if info.has_key('files') == info.has_key('length'):
raise ValueError, 'single/multiple file mix'
if info.has_key('length'):
length = info.get('length')
if type(length) not in ints or length < 0:
raise ValueError, 'bad metainfo - bad length'
else:
files = info.get('files')
if type(files) != ListType:
raise ValueError
for f in files:
if type(f) != DictType:
raise ValueError, 'bad metainfo - bad file value'
length = f.get('length')
if type(length) not in ints or length < 0:
raise ValueError, 'bad metainfo - bad length'
path = f.get('path')
if type(path) != ListType or path == []:
raise ValueError, 'bad metainfo - bad path'
for p in path:
if type(p) != StringType:
raise ValueError, 'bad metainfo - bad path dir'
if not reg.match(p):
raise ValueError, 'path %s disallowed for security reasons' % p
for i in xrange(len(files)):
for j in xrange(i):
if files[i]['path'] == files[j]['path']:
raise ValueError, 'bad metainfo - duplicate path'

#功能:这里主要是检查种子文件message信息是否合法,其中包括它的子信息,
#如过不合法抛异常,从这个文件里我们可以看出种子文件的message的结构
#这也是种子的起始地方
# message(DictType){
# 'info'(DictType):{ check_info(message.get('info'))同上}
# 'announce':StringType
# }
#这里顺序可能是种子文件有出入
def check_message(message):
if type(message) != DictType:
raise ValueError
check_info(message.get('info'))
if type(message.get('announce')) != StringType:
raise ValueError

#功能:这里主要是message信息是否合法,其中包括它的子信息,关于这个结构体，我
#还没有读到能理解的地步，先在这里打一个问号？？？？？
# message(DictType){
# 'failure reason':{ check_info(message.get('info'))同上}
# 'peers'(ListType):
# [
# (DictType)
# {
# 'ip':StringType,
# 'port':ints(大于零),
# 'peer id':StringType(len（id）==20这里我猜也是sha）
# }，
#
# (DictType)
# {
# 'ip':StringType,
# 'port':ints(大于零),
# 'peer id':StringType(len（id）==20这里我猜也是sha）
# }
# ...
#
# ]
# ‘interval’:ints(大于零),
# 'min interval':ints(大于零),
# 'tracker id':StringType,
# 'num peers':ints(大于零),
# 'done peers':ints(大于零),
# 'last':ints(大于零)
# }
#这里顺序可能是实际顺序不出入
def check_peers(message):
if type(message) != DictType:
raise ValueError
if message.has_key('failure reason'):
if type(message['failure reason']) != StringType:
raise ValueError
return
peers = message.get('peers')
if type(peers) != ListType:
raise ValueError
for p in peers:
if type(p) != DictType:
raise ValueError
if type(p.get('ip')) != StringType:
raise ValueError
port = p.get('port')
if type(port) not in ints or p <= 0:
raise ValueError
id = p.get('peer id')
if type(id) != StringType or len(id) != 20:
raise ValueError
interval = message.get('interval', 1)
if type(interval) not in ints or interval <= 0:
raise ValueError
minint = message.get('min interval', 1)
if type(minint) not in ints or minint <= 0:
raise ValueError
if type(message.get('tracker id', '')) != StringType:
raise ValueError
npeers = message.get('num peers', 0)
if type(npeers) not in ints or npeers < 0:
raise ValueError
dpeers = message.get('done peers', 0)
if type(dpeers) not in ints or dpeers < 0:
raise ValueError
last = message.get('last', 0)
if type(last) not in ints or last < 0:
raise ValueError

#写到这里大家明白bt种子文件的结构了吧!!
#(待续)