This commit is intended to fix an issue, when concurrent requests sent to an endpoint won't be protected by idempotency until the 1st request is finished.

This works adding a "lock" key in redis and returning 429 http error when concurrent requests are sent.

lib/idempotent-request/middleware.rb

@@ -14,12 +14,30 @@ module IdempotentRequest
     def process(env)
       set_request(env)
       return app.call(request.env) unless process?
-      storage = RequestManager.new(request, config)
-      storage.read || storage.write(*app.call(request.env))
+      read_idempotent_request ||
+        write_idempotent_request ||
+        concurrent_request_response
     end
 
     private
 
+    def storage
+      @storage ||= RequestManager.new(request, config)
+    end
+
+    def read_idempotent_request
+      storage.read
+    end
+
+    def write_idempotent_request
+      return unless storage.lock
+      storage.write(*app.call(request.env))
+    end
+
+    def concurrent_request_response
+      [429, {}, []]
+    end
+
     attr_reader :app, :env, :config, :request, :policy
 
     def process?

lib/idempotent-request/redis_storage.rb

@@ -8,14 +8,24 @@ module IdempotentRequest
       @expire_time = config[:expire_time]
     end
 
+    def lock(key)
+      setnx_with_expiration(lock_key(key), true)
+    end
+
     def read(key)
       redis.get(namespaced_key(key))
     end
 
     def write(key, payload)
+      setnx_with_expiration(namespaced_key(key), payload)
+    end
+
+    private
+
+    def setnx_with_expiration(key, data)
       redis.set(
-        namespaced_key(key),
-        payload,
+        key,
+        data,
         {}.tap do |options|
           options[:nx] = true
           options[:ex] = expire_time.to_i if expire_time.to_i > 0
@@ -23,10 +33,12 @@ module IdempotentRequest
       )
     end
 
-    private
+    def lock_key(key)
+      namespaced_key("lock:#{key}")
+    end
 
-    def namespaced_key(idempotency_key)
-      [namespace, idempotency_key.strip]
+    def namespaced_key(key)
+      [namespace, key.strip]
         .compact
         .join(':')
         .downcase

lib/idempotent-request/request_manager.rb

@@ -8,6 +8,10 @@ module IdempotentRequest
       @callback = config[:callback]
     end
 
+    def lock
+      storage.lock(key)
+    end
+
     def read
       status, headers, response = parse_data(storage.read(key)).values
 

spec/idempotent-request/middleware_spec.rb

@@ -42,6 +42,30 @@ RSpec.describe IdempotentRequest::Middleware do
         middleware.call(env)
       end
     end
+
+    context 'when concurrent requests' do
+      before do
+        allow_any_instance_of(IdempotentRequest::RequestManager).to receive(:lock).and_return(false)
+      end
+
+      it 'should not return data from storage' do
+        expect_any_instance_of(IdempotentRequest::RequestManager).to receive(:read).and_return(nil)
+
+        middleware.call(env)
+      end
+
+      it 'should not obtain lock' do
+        expect_any_instance_of(IdempotentRequest::RequestManager).not_to receive(:write)
+
+        middleware.call(env)
+      end
+
+      it 'returns 429' do
+        expect_any_instance_of(described_class).to receive(:concurrent_request_response)
+
+        middleware.call(env)
+      end
+    end
   end
 
   context 'when should not be idempotent' do

spec/idempotent-request/redis_storage_spec.rb

@@ -13,6 +13,16 @@ RSpec.describe IdempotentRequest::RedisStorage do
     end
   end
 
+  describe '#lock' do
+    let(:key) { 'key' }
+    let(:lock_key) { "#{namespace}:lock:#{key}" }
+
+    it 'should add lock' do
+      expect(redis).to receive(:set).with(lock_key, true, nx: true, ex: expire_time)
+      redis_storage.lock(key)
+    end
+  end
+
   describe '#write' do
     let(:key) { 'key' }
     let(:payload) { {} }

spec/idempotent-request/request_manager_spec.rb

@@ -13,6 +13,29 @@ RSpec.describe IdempotentRequest::RequestManager do
     memory_storage.clear
   end
 
+  describe '#lock' do
+    it 'delegates to storage service' do
+      expect(memory_storage).to receive(:lock).with(request.key)
+      request_storage.lock
+    end
+
+    context 'for the first lock' do
+      it 'returns true' do
+        expect(request_storage.lock).to be_truthy
+      end
+    end
+
+    context 'for the second lock' do
+      before do
+        request_storage.lock
+      end
+
+      it 'returns false' do
+        expect(request_storage.lock).to be_falsey
+      end
+    end
+  end
+
   describe '#read' do
     context 'when there is no data' do
       it 'should return nil' do

spec/support/memory_storage.rb

@@ -4,6 +4,12 @@ module IdempotentRequest
       @memory = {}
     end
 
+    def lock(key)
+      namespaced_key = lock_key(key)
+      return false if @memory.key?(namespaced_key)
+      @memory[namespaced_key] = true
+    end
+
     def read(key)
       @memory[key]
     end
@@ -15,5 +21,11 @@ module IdempotentRequest
     def clear
       @memory = {}
     end
+
+    private
+
+    def lock_key(key)
+      "lock:#{key}"
+    end
   end
 end