test and document whitelist behavior (#31)

Signed-off-by: Daniel Hochman <[email protected]>

Author: danielhochman

README.md

@@ -97,10 +97,9 @@ descriptors:
 ```
 
 Each descriptor in a descriptor list must have a key. It can also optionally have a value to enable a more specific
-match. The "rate_limit" block is optional and if present sets up an actual rate limit rule. See below for how the rule
-is defined. The reason a rule might not be present is typically if a descriptor is a container for a 2nd level
-descriptor list. Each descriptor can optionally contain a nested descriptor list that allows for more complex matches
-and rate limit scenarios.
+match. The "rate_limit" block is optional and if present sets up an actual rate limit rule. See below for how the
+rule is defined. If the rate limit is not present and there are no nested descriptors, then the descriptor is
+effectively whitelisted. Otherwise, nested descriptors allow more complex matching and rate limiting scenarios.
 
 ### Rate limit definition
 

test/config/basic_config.yaml

@@ -31,6 +31,10 @@ descriptors:
       unit: minute
       requests_per_unit: 30
 
+  # First level override with no limit. This effectively whitelists the value.
+  - key: key2
+    value: value3
+
   - key: key3
     rate_limit:
       unit: hour

test/config/config_test.go

@@ -100,6 +100,11 @@ func TestBasicConfig(t *testing.T) {
 	assert.EqualValues(1, stats.NewCounter("test-domain.key2_value2.over_limit").Value())
 	assert.EqualValues(1, stats.NewCounter("test-domain.key2_value2.near_limit").Value())
 
+	rl = rlConfig.GetLimit(
+		nil, "test-domain",
+		&pb.RateLimitDescriptor{[]*pb.RateLimitDescriptor_Entry{{"key2", "value3"}}})
+	assert.Nil(rl)
+
 	rl = rlConfig.GetLimit(
 		nil, "test-domain",
 		&pb.RateLimitDescriptor{[]*pb.RateLimitDescriptor_Entry{{"key3", "foo"}}})