| 1 | |
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| 2 | |
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| 3 | class Spans: |
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| 4 | """I represent a compressed list of booleans, one per index (an integer). |
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| 5 | Typically, each index represents an offset into a large string, pointing |
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| 6 | to a specific byte of a share. In this context, True means that byte has |
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| 7 | been received, or has been requested. |
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| 8 | |
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| 9 | Another way to look at this is maintaining a set of integers, optimized |
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| 10 | for operations on spans like 'add range to set' and 'is range in set?'. |
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| 11 | |
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| 12 | This is a python equivalent of perl's Set::IntSpan module, frequently |
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| 13 | used to represent .newsrc contents. |
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| 14 | |
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| 15 | Rather than storing an actual (large) list or dictionary, I represent my |
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| 16 | internal state as a sorted list of spans, each with a start and a length. |
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| 17 | My API is presented in terms of start+length pairs. I provide set |
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| 18 | arithmetic operators, to efficiently answer questions like 'I want bytes |
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| 19 | XYZ, I already requested bytes ABC, and I've already received bytes DEF: |
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| 20 | what bytes should I request now?'. |
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| 21 | |
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| 22 | The new downloader will use it to keep track of which bytes we've requested |
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| 23 | or received already. |
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| 24 | """ |
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| 25 | |
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| 26 | def __init__(self, _span_or_start=None, length=None): |
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| 27 | self._spans = list() |
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| 28 | if length is not None: |
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| 29 | self._spans.append( (_span_or_start, length) ) |
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| 30 | elif _span_or_start: |
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| 31 | for (start,length) in _span_or_start: |
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| 32 | self.add(start, length) |
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| 33 | self._check() |
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| 34 | |
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| 35 | def _check(self): |
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| 36 | assert sorted(self._spans) == self._spans |
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| 37 | prev_end = None |
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| 38 | try: |
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| 39 | for (start,length) in self._spans: |
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| 40 | if prev_end is not None: |
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| 41 | assert start > prev_end |
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| 42 | prev_end = start+length |
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| 43 | except AssertionError: |
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| 44 | print("BAD:", self.dump()) |
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| 45 | raise |
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| 46 | |
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| 47 | def add(self, start, length): |
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| 48 | assert start >= 0 |
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| 49 | assert length > 0 |
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| 50 | #print(" ADD [%d+%d -%d) to %s" % (start, length, start+length, self.dump())) |
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| 51 | first_overlap = last_overlap = None |
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| 52 | for i,(s_start,s_length) in enumerate(self._spans): |
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| 53 | #print(" (%d+%d)-> overlap=%s adjacent=%s" % (s_start,s_length, overlap(s_start, s_length, start, length), adjacent(s_start, s_length, start, length))) |
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| 54 | if (overlap(s_start, s_length, start, length) |
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| 55 | or adjacent(s_start, s_length, start, length)): |
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| 56 | last_overlap = i |
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| 57 | if first_overlap is None: |
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| 58 | first_overlap = i |
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| 59 | continue |
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| 60 | # no overlap |
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| 61 | if first_overlap is not None: |
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| 62 | break |
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| 63 | #print(" first_overlap", first_overlap, last_overlap) |
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| 64 | if first_overlap is None: |
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| 65 | # no overlap, so just insert the span and sort by starting |
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| 66 | # position. |
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| 67 | self._spans.insert(0, (start,length)) |
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| 68 | self._spans.sort() |
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| 69 | else: |
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| 70 | # everything from [first_overlap] to [last_overlap] overlapped |
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| 71 | first_start,first_length = self._spans[first_overlap] |
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| 72 | last_start,last_length = self._spans[last_overlap] |
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| 73 | newspan_start = min(start, first_start) |
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| 74 | newspan_end = max(start+length, last_start+last_length) |
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| 75 | newspan_length = newspan_end - newspan_start |
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| 76 | newspan = (newspan_start, newspan_length) |
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| 77 | self._spans[first_overlap:last_overlap+1] = [newspan] |
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| 78 | #print(" ADD done: %s" % self.dump()) |
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| 79 | self._check() |
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| 80 | |
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| 81 | return self |
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| 82 | |
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| 83 | def remove(self, start, length): |
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| 84 | assert start >= 0 |
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| 85 | assert length > 0 |
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| 86 | #print(" REMOVE [%d+%d -%d) from %s" % (start, length, start+length, self.dump())) |
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| 87 | first_complete_overlap = last_complete_overlap = None |
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| 88 | for i,(s_start,s_length) in enumerate(self._spans): |
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| 89 | s_end = s_start + s_length |
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| 90 | o = overlap(s_start, s_length, start, length) |
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| 91 | if o: |
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| 92 | o_start, o_length = o |
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| 93 | o_end = o_start+o_length |
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| 94 | if o_start == s_start and o_end == s_end: |
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| 95 | # delete this span altogether |
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| 96 | if first_complete_overlap is None: |
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| 97 | first_complete_overlap = i |
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| 98 | last_complete_overlap = i |
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| 99 | elif o_start == s_start: |
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| 100 | # we only overlap the left side, so trim the start |
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| 101 | # 1111 |
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| 102 | # rrrr |
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| 103 | # oo |
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| 104 | # -> 11 |
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| 105 | new_start = o_end |
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| 106 | new_end = s_end |
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| 107 | assert new_start > s_start |
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| 108 | new_length = new_end - new_start |
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| 109 | self._spans[i] = (new_start, new_length) |
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| 110 | elif o_end == s_end: |
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| 111 | # we only overlap the right side |
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| 112 | # 1111 |
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| 113 | # rrrr |
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| 114 | # oo |
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| 115 | # -> 11 |
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| 116 | new_start = s_start |
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| 117 | new_end = o_start |
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| 118 | assert new_end < s_end |
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| 119 | new_length = new_end - new_start |
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| 120 | self._spans[i] = (new_start, new_length) |
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| 121 | else: |
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| 122 | # we overlap the middle, so create a new span. No need to |
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| 123 | # examine any other spans. |
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| 124 | # 111111 |
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| 125 | # rr |
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| 126 | # LL RR |
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| 127 | left_start = s_start |
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| 128 | left_end = o_start |
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| 129 | left_length = left_end - left_start |
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| 130 | right_start = o_end |
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| 131 | right_end = s_end |
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| 132 | right_length = right_end - right_start |
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| 133 | self._spans[i] = (left_start, left_length) |
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| 134 | self._spans.append( (right_start, right_length) ) |
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| 135 | self._spans.sort() |
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| 136 | break |
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| 137 | if first_complete_overlap is not None: |
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| 138 | del self._spans[first_complete_overlap:last_complete_overlap+1] |
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| 139 | #print(" REMOVE done: %s" % self.dump()) |
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| 140 | self._check() |
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| 141 | return self |
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| 142 | |
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| 143 | def dump(self): |
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| 144 | return "len=%d: %s" % (self.len(), |
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| 145 | ",".join(["[%d-%d]" % (start,start+l-1) |
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| 146 | for (start,l) in self._spans]) ) |
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| 147 | |
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| 148 | def each(self): |
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| 149 | for start, length in self._spans: |
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| 150 | for i in range(start, start+length): |
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| 151 | yield i |
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| 152 | |
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| 153 | def __iter__(self): |
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| 154 | for s in self._spans: |
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| 155 | yield s |
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| 156 | |
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| 157 | def __bool__(self): # this gets us bool() |
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| 158 | return bool(self.len()) |
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| 159 | |
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| 160 | #__nonzero__ = __bool__ # Python 2 backwards compatibility |
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| 161 | |
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| 162 | def len(self): |
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| 163 | # guess what! python doesn't allow __len__ to return a long, only an |
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| 164 | # int. So we stop using len(spans), use spans.len() instead. |
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| 165 | return sum([length for start,length in self._spans]) |
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| 166 | |
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| 167 | def __add__(self, other): |
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| 168 | s = self.__class__(self) |
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| 169 | for (start, length) in other: |
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| 170 | s.add(start, length) |
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| 171 | return s |
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| 172 | |
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| 173 | def __sub__(self, other): |
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| 174 | s = self.__class__(self) |
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| 175 | for (start, length) in other: |
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| 176 | s.remove(start, length) |
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| 177 | return s |
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| 178 | |
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| 179 | def __iadd__(self, other): |
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| 180 | for (start, length) in other: |
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| 181 | self.add(start, length) |
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| 182 | return self |
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| 183 | |
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| 184 | def __isub__(self, other): |
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| 185 | for (start, length) in other: |
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| 186 | self.remove(start, length) |
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| 187 | return self |
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| 188 | |
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| 189 | def __and__(self, other): |
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| 190 | if not self._spans: |
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| 191 | return self.__class__() |
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| 192 | bounds = self.__class__(self._spans[0][0], |
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| 193 | self._spans[-1][0]+self._spans[-1][1]) |
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| 194 | not_other = bounds - other |
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| 195 | return self - not_other |
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| 196 | |
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| 197 | def __contains__(self, start_and_length): |
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| 198 | (start, length) = start_and_length |
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| 199 | for span_start,span_length in self._spans: |
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| 200 | o = overlap(start, length, span_start, span_length) |
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| 201 | if o: |
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| 202 | o_start,o_length = o |
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| 203 | if o_start == start and o_length == length: |
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| 204 | return True |
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| 205 | return False |
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| 206 | |
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| 207 | def overlap(start0, length0, start1, length1): |
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| 208 | # return start2,length2 of the overlapping region, or None |
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| 209 | # 00 00 000 0000 00 00 000 00 00 00 00 |
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| 210 | # 11 11 11 11 111 11 11 1111 111 11 11 |
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| 211 | left = max(start0, start1) |
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| 212 | right = min(start0+length0, start1+length1) |
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| 213 | # if there is overlap, 'left' will be its start, and right-1 will |
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| 214 | # be the end' |
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| 215 | if left < right: |
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| 216 | return (left, right-left) |
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| 217 | return None |
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| 218 | |
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| 219 | def adjacent(start0, length0, start1, length1): |
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| 220 | if (start0 < start1) and start0+length0 == start1: |
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| 221 | return True |
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| 222 | elif (start1 < start0) and start1+length1 == start0: |
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| 223 | return True |
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| 224 | return False |
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| 225 | |
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| 226 | class DataSpans: |
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| 227 | """I represent portions of a large string. Equivalently, I can be said to |
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| 228 | maintain a large array of characters (with gaps of empty elements). I can |
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| 229 | be used to manage access to a remote share, where some pieces have been |
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| 230 | retrieved, some have been requested, and others have not been read. |
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| 231 | """ |
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| 232 | |
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| 233 | def __init__(self, other=None): |
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| 234 | self.spans = [] # (start, data) tuples, non-overlapping, merged |
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| 235 | if other: |
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| 236 | for (start, data) in other.get_chunks(): |
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| 237 | self.add(start, data) |
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| 238 | |
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| 239 | def __bool__(self): # this gets us bool() |
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| 240 | return bool(self.len()) |
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| 241 | |
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| 242 | def len(self): |
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| 243 | # return number of bytes we're holding |
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| 244 | return sum([len(data) for (start,data) in self.spans]) |
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| 245 | |
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| 246 | def _dump(self): |
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| 247 | # return iterator of sorted list of offsets, one per byte |
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| 248 | for (start,data) in self.spans: |
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| 249 | for i in range(start, start+len(data)): |
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| 250 | yield i |
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| 251 | |
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| 252 | def dump(self): |
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| 253 | return "len=%d: %s" % (self.len(), |
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| 254 | ",".join(["[%d-%d]" % (start,start+len(data)-1) |
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| 255 | for (start,data) in self.spans]) ) |
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| 256 | |
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| 257 | def get_chunks(self): |
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| 258 | return list(self.spans) |
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| 259 | |
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| 260 | def get_spans(self): |
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| 261 | """Return a Spans object with a bit set for each byte I hold""" |
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| 262 | return Spans([(start, len(data)) for (start,data) in self.spans]) |
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| 263 | |
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| 264 | def assert_invariants(self): |
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| 265 | if not self.spans: |
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| 266 | return |
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| 267 | prev_start = self.spans[0][0] |
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| 268 | prev_end = prev_start + len(self.spans[0][1]) |
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| 269 | for start, data in self.spans[1:]: |
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| 270 | if not start > prev_end: |
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| 271 | # adjacent or overlapping: bad |
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| 272 | print("ASSERTION FAILED", self.spans) |
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| 273 | raise AssertionError |
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| 274 | |
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| 275 | def get(self, start, length): |
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| 276 | # returns a string of LENGTH, or None |
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| 277 | #print("get", start, length, self.spans) |
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| 278 | end = start+length |
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| 279 | for (s_start,s_data) in self.spans: |
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| 280 | s_end = s_start+len(s_data) |
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| 281 | #print(" ",s_start,s_end) |
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| 282 | if s_start <= start < s_end: |
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| 283 | # we want some data from this span. Because we maintain |
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| 284 | # strictly merged and non-overlapping spans, everything we |
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| 285 | # want must be in this span. |
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| 286 | offset = start - s_start |
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| 287 | if offset + length > len(s_data): |
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| 288 | #print(" None, span falls short") |
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| 289 | return None # span falls short |
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| 290 | #print(" some", s_data[offset:offset+length]) |
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| 291 | return s_data[offset:offset+length] |
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| 292 | if s_start >= end: |
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| 293 | # we've gone too far: no further spans will overlap |
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| 294 | #print(" None, gone too far") |
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| 295 | return None |
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| 296 | #print(" None, ran out of spans") |
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| 297 | return None |
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| 298 | |
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| 299 | def add(self, start, data): |
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| 300 | # first: walk through existing spans, find overlap, modify-in-place |
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| 301 | # create list of new spans |
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| 302 | # add new spans |
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| 303 | # sort |
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| 304 | # merge adjacent spans |
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| 305 | #print("add", start, data, self.spans) |
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| 306 | end = start + len(data) |
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| 307 | i = 0 |
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| 308 | while len(data): |
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| 309 | #print(" loop", start, data, i, len(self.spans), self.spans) |
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| 310 | if i >= len(self.spans): |
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| 311 | #print(" append and done") |
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| 312 | # append a last span |
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| 313 | self.spans.append( (start, data) ) |
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| 314 | break |
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| 315 | (s_start,s_data) = self.spans[i] |
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| 316 | # five basic cases: |
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| 317 | # a: OLD b:OLDD c1:OLD c2:OLD d1:OLDD d2:OLD e: OLLDD |
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| 318 | # NEW NEW NEW NEWW NEW NEW NEW |
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| 319 | # |
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| 320 | # we handle A by inserting a new segment (with "N") and looping, |
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| 321 | # turning it into B or C. We handle B by replacing a prefix and |
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| 322 | # terminating. We handle C (both c1 and c2) by replacing the |
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| 323 | # segment (and, for c2, looping, turning it into A). We handle D |
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| 324 | # by replacing a suffix (and, for d2, looping, turning it into |
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| 325 | # A). We handle E by replacing the middle and terminating. |
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| 326 | if start < s_start: |
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| 327 | # case A: insert a new span, then loop with the remainder |
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| 328 | #print(" insert new span") |
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| 329 | s_len = s_start-start |
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| 330 | self.spans.insert(i, (start, data[:s_len])) |
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| 331 | i += 1 |
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| 332 | start = s_start |
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| 333 | data = data[s_len:] |
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| 334 | continue |
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| 335 | s_len = len(s_data) |
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| 336 | s_end = s_start+s_len |
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| 337 | if s_start <= start < s_end: |
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| 338 | #print(" modify this span", s_start, start, s_end) |
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| 339 | # we want to modify some data in this span: a prefix, a |
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| 340 | # suffix, or the whole thing |
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| 341 | if s_start == start: |
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| 342 | if s_end <= end: |
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| 343 | #print(" replace whole segment") |
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| 344 | # case C: replace this segment |
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| 345 | self.spans[i] = (s_start, data[:s_len]) |
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| 346 | i += 1 |
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| 347 | start += s_len |
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| 348 | data = data[s_len:] |
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| 349 | # C2 is where len(data)>0 |
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| 350 | continue |
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| 351 | # case B: modify the prefix, retain the suffix |
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| 352 | #print(" modify prefix") |
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| 353 | self.spans[i] = (s_start, data + s_data[len(data):]) |
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| 354 | break |
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| 355 | if start > s_start and end < s_end: |
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| 356 | # case E: modify the middle |
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| 357 | #print(" modify middle") |
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| 358 | prefix_len = start - s_start # we retain this much |
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| 359 | suffix_len = s_end - end # and retain this much |
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| 360 | newdata = s_data[:prefix_len] + data + s_data[-suffix_len:] |
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| 361 | self.spans[i] = (s_start, newdata) |
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| 362 | break |
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| 363 | # case D: retain the prefix, modify the suffix |
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| 364 | #print(" modify suffix") |
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| 365 | prefix_len = start - s_start # we retain this much |
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| 366 | suffix_len = s_len - prefix_len # we replace this much |
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| 367 | #print(" ", s_data, prefix_len, suffix_len, s_len, data) |
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| 368 | self.spans[i] = (s_start, |
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| 369 | s_data[:prefix_len] + data[:suffix_len]) |
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| 370 | i += 1 |
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| 371 | start += suffix_len |
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| 372 | data = data[suffix_len:] |
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| 373 | #print(" now", start, data) |
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| 374 | # D2 is where len(data)>0 |
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| 375 | continue |
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| 376 | # else we're not there yet |
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| 377 | #print(" still looking") |
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| 378 | i += 1 |
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| 379 | continue |
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| 380 | # now merge adjacent spans |
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| 381 | #print(" merging", self.spans) |
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| 382 | newspans = [] |
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| 383 | for (s_start,s_data) in self.spans: |
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| 384 | if newspans and adjacent(newspans[-1][0], len(newspans[-1][1]), |
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| 385 | s_start, len(s_data)): |
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| 386 | newspans[-1] = (newspans[-1][0], newspans[-1][1] + s_data) |
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| 387 | else: |
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| 388 | newspans.append( (s_start, s_data) ) |
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| 389 | self.spans = newspans |
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| 390 | self.assert_invariants() |
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| 391 | #print(" done", self.spans) |
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| 392 | |
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| 393 | def remove(self, start, length): |
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| 394 | i = 0 |
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| 395 | end = start + length |
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| 396 | #print("remove", start, length, self.spans) |
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| 397 | while i < len(self.spans): |
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| 398 | (s_start,s_data) = self.spans[i] |
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| 399 | if s_start >= end: |
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| 400 | # this segment is entirely right of the removed region, and |
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| 401 | # all further segments are even further right. We're done. |
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| 402 | break |
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| 403 | s_len = len(s_data) |
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| 404 | s_end = s_start + s_len |
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| 405 | o = overlap(start, length, s_start, s_len) |
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| 406 | if not o: |
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| 407 | i += 1 |
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| 408 | continue |
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| 409 | o_start, o_len = o |
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| 410 | o_end = o_start + o_len |
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| 411 | if o_len == s_len: |
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| 412 | # remove the whole segment |
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| 413 | del self.spans[i] |
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| 414 | continue |
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| 415 | if o_start == s_start: |
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| 416 | # remove a prefix, leaving the suffix from o_end to s_end |
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| 417 | prefix_len = o_end - o_start |
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| 418 | self.spans[i] = (o_end, s_data[prefix_len:]) |
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| 419 | i += 1 |
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| 420 | continue |
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| 421 | elif o_end == s_end: |
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| 422 | # remove a suffix, leaving the prefix from s_start to o_start |
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| 423 | prefix_len = o_start - s_start |
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| 424 | self.spans[i] = (s_start, s_data[:prefix_len]) |
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| 425 | i += 1 |
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| 426 | continue |
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| 427 | # remove the middle, creating a new segment |
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| 428 | # left is s_start:o_start, right is o_end:s_end |
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| 429 | left_len = o_start - s_start |
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| 430 | left = s_data[:left_len] |
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| 431 | right_len = s_end - o_end |
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| 432 | right = s_data[-right_len:] |
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| 433 | self.spans[i] = (s_start, left) |
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| 434 | self.spans.insert(i+1, (o_end, right)) |
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| 435 | break |
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| 436 | #print(" done", self.spans) |
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| 437 | |
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| 438 | def pop(self, start, length): |
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| 439 | data = self.get(start, length) |
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| 440 | if data: |
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| 441 | self.remove(start, length) |
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| 442 | return data |
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