Add check_only feature to Rate Limit

api/envoy/service/ratelimit/v3/rls.proto

@@ -50,6 +50,12 @@ message RateLimitRequest {
   // Rate limit requests can optionally specify the number of hits a request adds to the matched
   // limit. If the value is not set in the message, a request increases the matched limit by 1.
   uint32 hits_addend = 3;
+
+  // Rate limit requests can optionally specify if they want to check the limit without actually
+  // consuming a hit. This is useful for clients that want to check if a request is over limit
+  // without consuming a hit. This is also useful for clients that want to "peek" at the headers
+  // that would be returned in a response for a given request.
+  bool check_only = 4;
 }
 
 // A response from a ShouldRateLimit call.

source/extensions/filters/common/ratelimit/ratelimit.h

@@ -86,12 +86,14 @@ class Client {
    * @param parent_span source for generating an egress child span as part of the trace.
    * @param stream_info supplies the stream info for the request.
    * @param hits_addend supplies the number of hits to add to the rate limit counter.
+   * @param check_only supplies whether to check the limit only without incrementing the counter.
    *
    */
   virtual void limit(RequestCallbacks& callbacks, const std::string& domain,
                      const std::vector<Envoy::RateLimit::Descriptor>& descriptors,
                      Tracing::Span& parent_span, const StreamInfo::StreamInfo& stream_info,
-                     uint32_t hits_addend) PURE;
+                     uint32_t hits_addend,
+                     bool check_only) PURE;
 };
 
 using ClientPtr = std::unique_ptr<Client>;

source/extensions/filters/common/ratelimit/ratelimit_impl.cc

@@ -36,9 +36,11 @@ void GrpcClientImpl::cancel() {
 void GrpcClientImpl::createRequest(envoy::service::ratelimit::v3::RateLimitRequest& request,
                                    const std::string& domain,
                                    const std::vector<Envoy::RateLimit::Descriptor>& descriptors,
-                                   uint32_t hits_addend) {
+                                   uint32_t hits_addend,
+                                   bool check_only) {
   request.set_domain(domain);
   request.set_hits_addend(hits_addend);
+  request.set_check_only(check_only);
   for (const Envoy::RateLimit::Descriptor& descriptor : descriptors) {
     envoy::extensions::common::ratelimit::v3::RateLimitDescriptor* new_descriptor =
         request.add_descriptors();
@@ -60,12 +62,13 @@ void GrpcClientImpl::createRequest(envoy::service::ratelimit::v3::RateLimitReque
 void GrpcClientImpl::limit(RequestCallbacks& callbacks, const std::string& domain,
                            const std::vector<Envoy::RateLimit::Descriptor>& descriptors,
                            Tracing::Span& parent_span, const StreamInfo::StreamInfo& stream_info,
-                           uint32_t hits_addend) {
+                           uint32_t hits_addend,
+                           bool check_only) {
   ASSERT(callbacks_ == nullptr);
   callbacks_ = &callbacks;
 
   envoy::service::ratelimit::v3::RateLimitRequest request;
-  createRequest(request, domain, descriptors, hits_addend);
+  createRequest(request, domain, descriptors, hits_addend, check_only);
 
   request_ =
       async_client_->send(service_method_, request, *this, parent_span,

source/extensions/filters/common/ratelimit/ratelimit_impl.h

@@ -51,14 +51,16 @@ class GrpcClientImpl : public Client,
   static void createRequest(envoy::service::ratelimit::v3::RateLimitRequest& request,
                             const std::string& domain,
                             const std::vector<Envoy::RateLimit::Descriptor>& descriptors,
-                            uint32_t hits_addend);
+                            uint32_t hits_addend,
+                            bool check_only);
 
   // Filters::Common::RateLimit::Client
   void cancel() override;
   void limit(RequestCallbacks& callbacks, const std::string& domain,
              const std::vector<Envoy::RateLimit::Descriptor>& descriptors,
              Tracing::Span& parent_span, const StreamInfo::StreamInfo& stream_info,
-             uint32_t hits_addend = 0) override;
+             uint32_t hits_addend = 0,
+             bool check_only = false) override;
 
   // Grpc::AsyncRequestCallbacks
   void onCreateInitialMetadata(Http::RequestHeaderMap&) override {}