Add LogDog Python client library.

client/libs/logdog/streamname.py

Index: client/libs/logdog/streamname.py
diff --git a/client/libs/logdog/streamname.py b/client/libs/logdog/streamname.py
new file mode 100644
index 0000000000000000000000000000000000000000..516226b93bf735eacfd324a756e517eee031e483
--- /dev/null
+++ b/client/libs/logdog/streamname.py
@@ -0,0 +1,44 @@
+# 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 re
+import types
+
+_SEGMENT_RE_BASE = r'[a-zA-Z0-9][a-zA-Z0-9:_\-.]*'
+_STREAM_NAME_RE = re.compile('^(' + _SEGMENT_RE_BASE + ')(/' +
+                             _SEGMENT_RE_BASE + ')*$')
+_MAX_STREAM_NAME_LENGTH = 4096
+
+_MAX_TAG_KEY_LENGTH = 64
+_MAX_TAG_VALUE_LENGTH = 4096
+
+def validate_stream_name(v, maxlen=None):
+  """Verifies that a given stream name is valid.
+
+  Args:
+    v (str): The stream name string.
+
+
+  Raises:
+    ValueError if the stream name is invalid.
+  """
+  maxlen = maxlen or _MAX_STREAM_NAME_LENGTH
+  if len(v) > maxlen:
+    raise ValueError('Maximum length exceeded (%d > %d)' % (len(v), maxlen))
+  if _STREAM_NAME_RE.match(v) is None:
+    raise ValueError('Invalid stream name')
+
+
+def validate_tag(key, value):
+  """Verifies that a given tag key/value is valid.
+
+  Args:
+    k (str): The tag key.
+    v (str): The tag value.
+
+  Raises:
+    ValueError if the tag is not valid.
+  """
+  validate_stream_name(key, maxlen=_MAX_TAG_KEY_LENGTH)
+  validate_stream_name(value, maxlen=_MAX_TAG_VALUE_LENGTH)