Add extensibility point to request_tracker to skip IP addresses

This is useful if you want to run a per IP rate limiter but want to be
able to skip some IPs with custom logic.

lib/middleware/request_tracker.rb

@@ -6,6 +6,7 @@ require_dependency 'method_profiler'
 class Middleware::RequestTracker
 
   @@detailed_request_loggers = nil
+  @@ip_skipper = nil
 
   # register callbacks for detailed request loggers called on every request
   # example:
@@ -35,7 +36,20 @@ class Middleware::RequestTracker
     if @@detailed_request_loggers.length == 0
       @detailed_request_loggers = nil
     end
+  end
 
+  # Register a custom `ip_skipper`, a function that will skip rate limiting
+  # for any IP that returns true.
+  #
+  # For example, if you never wanted to rate limit 1.2.3.4
+  #
+  # ```
+  # Middleware::RequestTracker.register_ip_skipper do |ip|
+  #  ip == "1.2.3.4"
+  # end
+  # ```
+  def self.register_ip_skipper(&blk)
+    @@ip_skipper = blk
   end
 
   def initialize(app, settings = {})
@@ -167,6 +181,8 @@ class Middleware::RequestTracker
         return false if is_private_ip?(ip)
       end
 
+      return false if @@ip_skipper.try(:call, ip)
+
       limiter10 = RateLimiter.new(
         nil,
         "global_ip_limit_10_#{ip}",

spec/components/middleware/request_tracker_spec.rb

@@ -127,6 +127,30 @@ describe Middleware::RequestTracker do
       expect(status).to eq(429)
     end
 
+    describe "register_ip_skipper" do
+      before do
+        Middleware::RequestTracker.register_ip_skipper do |ip|
+          ip == "1.1.1.2"
+        end
+        global_setting :max_reqs_per_ip_per_10_seconds, 1
+        global_setting :max_reqs_per_ip_mode, 'block'
+      end
+
+      it "won't block if the ip is skipped" do
+        env1 = env("REMOTE_ADDR" => "1.1.1.2")
+        status, _ = middleware.call(env1)
+        status, _ = middleware.call(env1)
+        expect(status).to eq(200)
+      end
+
+      it "blocks if the ip isn't skipped" do
+        env1 = env("REMOTE_ADDR" => "1.1.1.1")
+        status, _ = middleware.call(env1)
+        status, _ = middleware.call(env1)
+        expect(status).to eq(429)
+      end
+    end
+
     it "does nothing for private IPs if skipped" do
       global_setting :max_reqs_per_ip_per_10_seconds, 1
       global_setting :max_reqs_per_ip_mode, 'warn+block'
@@ -206,7 +230,7 @@ describe Middleware::RequestTracker do
     end
 
     after do
-      Middleware::RequestTracker.register_detailed_request_logger(logger)
+      Middleware::RequestTracker.unregister_detailed_request_logger(logger)
     end
 
     it "can correctly log detailed data" do