Merge pull request #445 from palazzem/environment-getter

[core] provide an environment getter utility to ensure consistency between env vars

Author: Emanuele Palazzetti

ddtrace/util.py

@@ -1,12 +1,10 @@
-"""
-Generic utilities for tracers
-"""
-
-from functools import wraps
+import os
 import inspect
 import logging
 import wrapt
 
+from functools import wraps
+
 
 def deprecated(message='', version=None):
     """Function decorator to report a deprecated function"""
@@ -22,6 +20,7 @@ def wrapper(*args, **kwargs):
         return wrapper
     return decorator
 
+
 def deep_getattr(obj, attr_string, default=None):
     """
     Returns the attribute of `obj` at the dotted path given by `attr_string`
@@ -66,7 +65,6 @@ def safe_patch(patchable, key, patch_func, service, meta, tracer):
       the original unpatched method we wish to trace.
 
     """
-
     def _get_original_method(thing, key):
         orig = None
         if hasattr(thing, '_dogtraced'):
@@ -112,6 +110,27 @@ def asbool(value):
     return value.lower() in ("true", "1")
 
 
+def get_env(integration, variable, default=None):
+    """Retrieves environment variables value for the given integration. It must be used
+    for consistency between integrations. The implementation is backward compatible
+    with legacy nomenclature:
+        * `DATADOG_` is a legacy prefix with lower priority
+        * `DD_` environment variables have the highest priority
+        * the environment variable is built concatenating `integration` and `variable`
+          arguments
+        * return `default` otherwise
+    """
+    key = '{}_{}'.format(integration, variable).upper()
+    legacy_env = 'DATADOG_{}'.format(key)
+    env = 'DD_{}'.format(key)
+
+    # [Backward compatibility]: `DATADOG_` variables should be supported;
+    # add a deprecation warning later if it's used, so that we can drop the key
+    # in newer releases.
+    value = os.getenv(env) or os.getenv(legacy_env)
+    return value if value else default
+
+
 def unwrap(obj, attr):
     f = getattr(obj, attr, None)
     if f and isinstance(f, wrapt.ObjectProxy) and hasattr(f, '__wrapped__'):

tests/test_utils.py

@@ -1,8 +1,9 @@
+import os
 import unittest
 
-from nose.tools import eq_
+from nose.tools import eq_, ok_
 
-from ddtrace.util import asbool
+from ddtrace.util import asbool, get_env
 
 
 class TestUtilities(unittest.TestCase):
@@ -17,3 +18,31 @@ def test_asbool(self):
         eq_(asbool(""), False)
         eq_(asbool(True), True)
         eq_(asbool(False), False)
+
+    def test_get_env(self):
+        # ensure `get_env` returns a default value if environment variables
+        # are not set
+        value = get_env('django', 'distributed_tracing')
+        ok_(value is None)
+        value = get_env('django', 'distributed_tracing', False)
+        ok_(value is False)
+
+    def test_get_env_found(self):
+        # ensure `get_env` returns a value if the environment variable is set
+        os.environ['DD_REQUESTS_DISTRIBUTED_TRACING'] = '1'
+        value = get_env('requests', 'distributed_tracing')
+        eq_(value, '1')
+
+    def test_get_env_found_legacy(self):
+        # ensure `get_env` returns a value if legacy environment variables
+        # are used
+        os.environ['DATADOG_REQUESTS_DISTRIBUTED_TRACING'] = '1'
+        value = get_env('requests', 'distributed_tracing')
+        eq_(value, '1')
+
+    def test_get_env_key_priority(self):
+        # ensure `get_env` use `DD_` with highest priority
+        os.environ['DD_REQUESTS_DISTRIBUTED_TRACING'] = 'highest'
+        os.environ['DATADOG_REQUESTS_DISTRIBUTED_TRACING'] = 'lowest'
+        value = get_env('requests', 'distributed_tracing')
+        eq_(value, 'highest')