Coverage for /pythoncovmergedfiles/medio/medio/usr/local/lib/python3.8/site-packages/pip/_vendor/cachecontrol/filewrapper.py: 20%

1# SPDX-FileCopyrightText: 2015 Eric Larson 

2# 

3# SPDX-License-Identifier: Apache-2.0 

4 

5from tempfile import NamedTemporaryFile 

6import mmap 

7 

8 

9class CallbackFileWrapper(object): 

10 """ 

11 Small wrapper around a fp object which will tee everything read into a 

12 buffer, and when that file is closed it will execute a callback with the 

13 contents of that buffer. 

14 

15 All attributes are proxied to the underlying file object. 

16 

17 This class uses members with a double underscore (__) leading prefix so as 

18 not to accidentally shadow an attribute. 

19 

20 The data is stored in a temporary file until it is all available. As long 

21 as the temporary files directory is disk-based (sometimes it's a 

22 memory-backed-``tmpfs`` on Linux), data will be unloaded to disk if memory 

23 pressure is high. For small files the disk usually won't be used at all, 

24 it'll all be in the filesystem memory cache, so there should be no 

25 performance impact. 

26 """ 

27 

28 def __init__(self, fp, callback): 

29 self.__buf = NamedTemporaryFile("rb+", delete=True) 

30 self.__fp = fp 

31 self.__callback = callback 

32 

33 def __getattr__(self, name): 

34 # The vaguaries of garbage collection means that self.__fp is 

35 # not always set. By using __getattribute__ and the private 

36 # name[0] allows looking up the attribute value and raising an 

37 # AttributeError when it doesn't exist. This stop thigns from 

38 # infinitely recursing calls to getattr in the case where 

39 # self.__fp hasn't been set. 

40 # 

41 # [0] https://docs.python.org/2/reference/expressions.html#atom-identifiers 

42 fp = self.__getattribute__("_CallbackFileWrapper__fp") 

43 return getattr(fp, name) 

44 

45 def __is_fp_closed(self): 

46 try: 

47 return self.__fp.fp is None 

48 

49 except AttributeError: 

50 pass 

51 

52 try: 

53 return self.__fp.closed 

54 

55 except AttributeError: 

56 pass 

57 

58 # We just don't cache it then. 

59 # TODO: Add some logging here... 

60 return False 

61 

62 def _close(self): 

63 if self.__callback: 

64 if self.__buf.tell() == 0: 

65 # Empty file: 

66 result = b"" 

67 else: 

68 # Return the data without actually loading it into memory, 

69 # relying on Python's buffer API and mmap(). mmap() just gives 

70 # a view directly into the filesystem's memory cache, so it 

71 # doesn't result in duplicate memory use. 

72 self.__buf.seek(0, 0) 

73 result = memoryview( 

74 mmap.mmap(self.__buf.fileno(), 0, access=mmap.ACCESS_READ) 

75 ) 

76 self.__callback(result) 

77 

78 # We assign this to None here, because otherwise we can get into 

79 # really tricky problems where the CPython interpreter dead locks 

80 # because the callback is holding a reference to something which 

81 # has a __del__ method. Setting this to None breaks the cycle 

82 # and allows the garbage collector to do it's thing normally. 

83 self.__callback = None 

84 

85 # Closing the temporary file releases memory and frees disk space. 

86 # Important when caching big files. 

87 self.__buf.close() 

88 

89 def read(self, amt=None): 

90 data = self.__fp.read(amt) 

91 if data: 

92 # We may be dealing with b'', a sign that things are over: 

93 # it's passed e.g. after we've already closed self.__buf. 

94 self.__buf.write(data) 

95 if self.__is_fp_closed(): 

96 self._close() 

97 

98 return data 

99 

100 def _safe_read(self, amt): 

101 data = self.__fp._safe_read(amt) 

102 if amt == 2 and data == b"\r\n": 

103 # urllib executes this read to toss the CRLF at the end 

104 # of the chunk. 

105 return data 

106 

107 self.__buf.write(data) 

108 if self.__is_fp_closed(): 

109 self._close() 

110 

111 return data