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zero-cost-nas/.eggs/smmap-5.0.0-py3.8.egg/smmap/buf.py

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+"""Module with a simple buffer implementation using the memory manager"""
+import sys
+
+__all__ = ["SlidingWindowMapBuffer"]
+
+
+class SlidingWindowMapBuffer:
+
+    """A buffer like object which allows direct byte-wise object and slicing into
+    memory of a mapped file. The mapping is controlled by the provided cursor.
+
+    The buffer is relative, that is if you map an offset, index 0 will map to the
+    first byte at the offset you used during initialization or begin_access
+
+    **Note:** Although this type effectively hides the fact that there are mapped windows
+    underneath, it can unfortunately not be used in any non-pure python method which
+    needs a buffer or string"""
+    __slots__ = (
+        '_c',           # our cursor
+        '_size',        # our supposed size
+    )
+
+    def __init__(self, cursor=None, offset=0, size=sys.maxsize, flags=0):
+        """Initalize the instance to operate on the given cursor.
+        :param cursor: if not None, the associated cursor to the file you want to access
+            If None, you have call begin_access before using the buffer and provide a cursor
+        :param offset: absolute offset in bytes
+        :param size: the total size of the mapping. Defaults to the maximum possible size
+            From that point on, the __len__ of the buffer will be the given size or the file size.
+            If the size is larger than the mappable area, you can only access the actually available
+            area, although the length of the buffer is reported to be your given size.
+            Hence it is in your own interest to provide a proper size !
+        :param flags: Additional flags to be passed to os.open
+        :raise ValueError: if the buffer could not achieve a valid state"""
+        self._c = cursor
+        if cursor and not self.begin_access(cursor, offset, size, flags):
+            raise ValueError("Failed to allocate the buffer - probably the given offset is out of bounds")
+        # END handle offset
+
+    def __del__(self):
+        self.end_access()
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        self.end_access()
+
+    def __len__(self):
+        return self._size
+
+    def __getitem__(self, i):
+        if isinstance(i, slice):
+            return self.__getslice__(i.start or 0, i.stop or self._size)
+        c = self._c
+        assert c.is_valid()
+        if i < 0:
+            i = self._size + i
+        if not c.includes_ofs(i):
+            c.use_region(i, 1)
+        # END handle region usage
+        return c.buffer()[i - c.ofs_begin()]
+
+    def __getslice__(self, i, j):
+        c = self._c
+        # fast path, slice fully included - safes a concatenate operation and
+        # should be the default
+        assert c.is_valid()
+        if i < 0:
+            i = self._size + i
+        if j == sys.maxsize:
+            j = self._size
+        if j < 0:
+            j = self._size + j
+        if (c.ofs_begin() <= i) and (j < c.ofs_end()):
+            b = c.ofs_begin()
+            return c.buffer()[i - b:j - b]
+        else:
+            l = j - i                 # total length
+            ofs = i
+            # It's fastest to keep tokens and join later, especially in py3, which was 7 times slower
+            # in the previous iteration of this code
+            md = list()
+            while l:
+                c.use_region(ofs, l)
+                assert c.is_valid()
+                d = c.buffer()[:l]
+                ofs += len(d)
+                l -= len(d)
+                # Make sure we don't keep references, as c.use_region() might attempt to free resources, but
+                # can't unless we use pure bytes
+                if hasattr(d, 'tobytes'):
+                    d = d.tobytes()
+                md.append(d)
+            # END while there are bytes to read
+            return bytes().join(md)
+        # END fast or slow path
+    #{ Interface
+
+    def begin_access(self, cursor=None, offset=0, size=sys.maxsize, flags=0):
+        """Call this before the first use of this instance. The method was already
+        called by the constructor in case sufficient information was provided.
+
+        For more information no the parameters, see the __init__ method
+        :param path: if cursor is None the existing one will be used.
+        :return: True if the buffer can be used"""
+        if cursor:
+            self._c = cursor
+        # END update our cursor
+
+        # reuse existing cursors if possible
+        if self._c is not None and self._c.is_associated():
+            res = self._c.use_region(offset, size, flags).is_valid()
+            if res:
+                # if given size is too large or default, we computer a proper size
+                # If its smaller, we assume the combination between offset and size
+                # as chosen by the user is correct and use it !
+                # If not, the user is in trouble.
+                if size > self._c.file_size():
+                    size = self._c.file_size() - offset
+                # END handle size
+                self._size = size
+            # END set size
+            return res
+        # END use our cursor
+        return False
+
+    def end_access(self):
+        """Call this method once you are done using the instance. It is automatically
+        called on destruction, and should be called just in time to allow system
+        resources to be freed.
+
+        Once you called end_access, you must call begin access before reusing this instance!"""
+        self._size = 0
+        if self._c is not None:
+            self._c.unuse_region()
+        # END unuse region
+
+    def cursor(self):
+        """:return: the currently set cursor which provides access to the data"""
+        return self._c
+
+    #}END interface