Add LogDog Python client library.

client/libs/logdog/varint.py

+# Copyright 2016 The LUCI Authors. All rights reserved.
+# Use of this source code is governed by the Apache v2.0 license that can be
+# found in the LICENSE file.
+
+import os
+import sys
+
+
+def write_uvarint(w, val):
+  """Writes a varint value to the supplied file-like object.
+
+  Args:
+    w (object): A file-like object to write to. Must implement write.
+    val (number): The value to write. Must be >= 0.
+
+  Returns (int): The number of bytes that were written.
+
+  Raises:
+    ValueError if 'val' is < 0.
+  """
+  if val < 0:
+    raise ValueError('Cannot encode negative value, %d' % (val,))
+
+  count = 0
+  while val > 0 or count == 0:
+    byte = (val & 0b01111111)
+    val >>= 7
+    if val > 0:
+      byte |= 0b10000000
+
+    w.write(chr(byte))
+    count += 1
+  return count
+
+
+def read_uvarint(r):
+  """Reads a uvarint from a stream.
+
+  This is targeted towards testing, and will not be used in production code.
+
+  Args:
+    r (object): A file-like object to read from. Must implement read.
+
+  Returns: (value, count)
+    value (int): The decoded varint number.
+    count (int): The number of bytes that were read from 'r'.
+
+  Raises:
+    ValueError if the encoded varint is not terminated.
+  """
+  count = 0
+  result = 0
+  while True:
+    byte = r.read(1)
+    if len(byte) == 0:
+      raise ValueError('UVarint was not terminated')
+
+    byte = ord(byte)
+    result |= ((byte & 0b01111111) << (7 * count))
+    count += 1
+    if byte & 0b10000000 == 0:
+      break
+  return result, count