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1 # mpatch.py - Python implementation of mpatch.c
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2 #
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3 # Copyright 2009 Matt Mackall <mpm@selenic.com> and others
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4 #
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5 # This software may be used and distributed according to the terms of the
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6 # GNU General Public License version 2, incorporated herein by reference.
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7
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8 import struct
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9 try:
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10 from cStringIO import StringIO
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11 except ImportError:
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12 from StringIO import StringIO
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13
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14 # This attempts to apply a series of patches in time proportional to
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15 # the total size of the patches, rather than patches * len(text). This
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16 # means rather than shuffling strings around, we shuffle around
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17 # pointers to fragments with fragment lists.
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18 #
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19 # When the fragment lists get too long, we collapse them. To do this
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20 # efficiently, we do all our operations inside a buffer created by
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21 # mmap and simply use memmove. This avoids creating a bunch of large
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22 # temporary string buffers.
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23
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24 def patches(a, bins):
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25 if not bins: return a
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26
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27 plens = [len(x) for x in bins]
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28 pl = sum(plens)
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29 bl = len(a) + pl
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30 tl = bl + bl + pl # enough for the patches and two working texts
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31 b1, b2 = 0, bl
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32
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33 if not tl: return a
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34
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35 m = StringIO()
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36 def move(dest, src, count):
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37 """move count bytes from src to dest
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38
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39 The file pointer is left at the end of dest.
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40 """
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41 m.seek(src)
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42 buf = m.read(count)
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43 m.seek(dest)
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44 m.write(buf)
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45
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46 # load our original text
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47 m.write(a)
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48 frags = [(len(a), b1)]
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49
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50 # copy all the patches into our segment so we can memmove from them
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51 pos = b2 + bl
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52 m.seek(pos)
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53 for p in bins: m.write(p)
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54
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55 def pull(dst, src, l): # pull l bytes from src
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56 while l:
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57 f = src.pop(0)
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58 if f[0] > l: # do we need to split?
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59 src.insert(0, (f[0] - l, f[1] + l))
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60 dst.append((l, f[1]))
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61 return
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62 dst.append(f)
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63 l -= f[0]
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64
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65 def collect(buf, list):
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66 start = buf
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67 for l, p in list:
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68 move(buf, p, l)
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69 buf += l
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70 return (buf - start, start)
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71
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72 for plen in plens:
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73 # if our list gets too long, execute it
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74 if len(frags) > 128:
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75 b2, b1 = b1, b2
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76 frags = [collect(b1, frags)]
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77
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78 new = []
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79 end = pos + plen
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80 last = 0
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81 while pos < end:
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82 m.seek(pos)
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83 p1, p2, l = struct.unpack(">lll", m.read(12))
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84 pull(new, frags, p1 - last) # what didn't change
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85 pull([], frags, p2 - p1) # what got deleted
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86 new.append((l, pos + 12)) # what got added
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87 pos += l + 12
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88 last = p2
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89 frags = new + frags # what was left at the end
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90
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91 t = collect(b2, frags)
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92
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93 m.seek(t[1])
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94 return m.read(t[0])
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95
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96 def patchedsize(orig, delta):
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97 outlen, last, bin = 0, 0, 0
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98 binend = len(delta)
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99 data = 12
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100
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101 while data <= binend:
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102 decode = delta[bin:bin + 12]
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103 start, end, length = struct.unpack(">lll", decode)
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104 if start > end:
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105 break
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106 bin = data + length
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107 data = bin + 12
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108 outlen += start - last
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109 last = end
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110 outlen += length
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111
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112 if bin != binend:
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113 raise Exception("patch cannot be decoded")
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114
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115 outlen += orig - last
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116 return outlen
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