feat: Handle prometheus requests in WorkQueue (#2790)

src/app/ClioApplication.cpp

@@ -182,7 +182,7 @@ ClioApplication::run(bool const useNgWebServer)
             return EXIT_FAILURE;
         }
 
-        httpServer->onGet("/metrics", MetricsHandler{adminVerifier});
+        httpServer->onGet("/metrics", MetricsHandler{adminVerifier, workQueue});
         httpServer->onGet("/health", HealthCheckHandler{});
         httpServer->onGet("/cache_state", CacheStateHandler{cache});
         auto requestHandler = RequestHandler{adminVerifier, handler};

src/app/WebHandlers.cpp

@@ -19,7 +19,10 @@
 
 #include "app/WebHandlers.hpp"
 
+#include "rpc/Errors.hpp"
+#include "rpc/WorkQueue.hpp"
 #include "util/Assert.hpp"
+#include "util/CoroutineGroup.hpp"
 #include "util/prometheus/Http.hpp"
 #include "web/AdminVerificationStrategy.hpp"
 #include "web/SubscriptionContextInterface.hpp"
@@ -31,6 +34,7 @@
 #include <boost/asio/spawn.hpp>
 #include <boost/beast/http/status.hpp>
 
+#include <functional>
 #include <memory>
 #include <optional>
 #include <string>
@@ -76,8 +80,8 @@ DisconnectHook::operator()(web::ng::Connection const& connection)
     dosguard_.get().decrement(connection.ip());
 }
 
-MetricsHandler::MetricsHandler(std::shared_ptr<web::AdminVerificationStrategy> adminVerifier)
+MetricsHandler::MetricsHandler(std::shared_ptr<web::AdminVerificationStrategy> adminVerifier, rpc::WorkQueue& workQueue)
-    : adminVerifier_{std::move(adminVerifier)}
+    : adminVerifier_{std::move(adminVerifier)}, workQueue_{std::ref(workQueue)}
 {
 }
 
@@ -86,19 +90,45 @@ MetricsHandler::operator()(
     web::ng::Request const& request,
     web::ng::ConnectionMetadata& connectionMetadata,
     web::SubscriptionContextPtr,
-    boost::asio::yield_context
+    boost::asio::yield_context yield
 )
 {
-    auto const maybeHttpRequest = request.asHttpRequest();
+    std::optional<web::ng::Response> response;
-    ASSERT(maybeHttpRequest.has_value(), "Got not a http request in Get");
+    util::CoroutineGroup coroutineGroup{yield, 1};
-    auto const& httpRequest = maybeHttpRequest->get();
+    auto const onTaskComplete = coroutineGroup.registerForeign(yield);
+    ASSERT(onTaskComplete.has_value(), "Coroutine group can't be full");
 
-    // FIXME(#1702): Using veb server thread to handle prometheus request. Better to post on work queue.
+    bool const postSuccessful = workQueue_.get().postCoro(
-    auto maybeResponse = util::prometheus::handlePrometheusRequest(
+        [this, &request, &response, &onTaskComplete = onTaskComplete.value(), &connectionMetadata](
-        httpRequest, adminVerifier_->isAdmin(httpRequest, connectionMetadata.ip())
+            boost::asio::yield_context
+        ) mutable {
+            auto const maybeHttpRequest = request.asHttpRequest();
+            ASSERT(maybeHttpRequest.has_value(), "Got not a http request in Get");
+            auto const& httpRequest = maybeHttpRequest->get();
+
+            auto maybeResponse = util::prometheus::handlePrometheusRequest(
+                httpRequest, adminVerifier_->isAdmin(httpRequest, connectionMetadata.ip())
+            );
+            ASSERT(maybeResponse.has_value(), "Got unexpected request for Prometheus");
+            response = web::ng::Response{std::move(maybeResponse).value(), request};
+            // notify the coroutine group that the foreign task is done
+            onTaskComplete();
+        },
+        /* isWhiteListed= */ true,
+        rpc::WorkQueue::Priority::High
     );
-    ASSERT(maybeResponse.has_value(), "Got unexpected request for Prometheus");
+
-    return web::ng::Response{std::move(maybeResponse).value(), request};
+    if (!postSuccessful) {
+        return web::ng::Response{
+            boost::beast::http::status::too_many_requests, rpc::makeError(rpc::RippledError::rpcTOO_BUSY), request
+        };
+    }
+
+    // Put the coroutine to sleep until the foreign task is done
+    coroutineGroup.asyncWait(yield);
+    ASSERT(response.has_value(), "Woke up coroutine without setting response");
+
+    return std::move(response).value();
 }
 
 web::ng::Response

src/app/WebHandlers.hpp

@@ -21,6 +21,7 @@
 
 #include "data/LedgerCacheInterface.hpp"
 #include "rpc/Errors.hpp"
+#include "rpc/WorkQueue.hpp"
 #include "util/log/Logger.hpp"
 #include "web/AdminVerificationStrategy.hpp"
 #include "web/SubscriptionContextInterface.hpp"
@@ -119,20 +120,23 @@ public:
  */
 class MetricsHandler {
     std::shared_ptr<web::AdminVerificationStrategy> adminVerifier_;
+    std::reference_wrapper<rpc::WorkQueue> workQueue_;
 
 public:
     /**
      * @brief Construct a new MetricsHandler object
      *
      * @param adminVerifier The AdminVerificationStrategy to use for verifying the connection for admin access.
+     * @param workQueue The WorkQueue to use for handling the request.
      */
-    MetricsHandler(std::shared_ptr<web::AdminVerificationStrategy> adminVerifier);
+    MetricsHandler(std::shared_ptr<web::AdminVerificationStrategy> adminVerifier, rpc::WorkQueue& workQueue);
 
     /**
      * @brief The call of the function object.
      *
      * @param request The request to handle.
      * @param connectionMetadata The connection metadata.
+     * @param yield The yield context.
      * @return The response to the request.
      */
     web::ng::Response
@@ -140,7 +144,7 @@ public:
         web::ng::Request const& request,
         web::ng::ConnectionMetadata& connectionMetadata,
         web::SubscriptionContextPtr,
-        boost::asio::yield_context
+        boost::asio::yield_context yield
     );
 };
 

tests/unit/app/WebHandlersTests.cpp

@@ -19,6 +19,7 @@
 
 #include "app/WebHandlers.hpp"
 #include "rpc/Errors.hpp"
+#include "rpc/WorkQueue.hpp"
 #include "util/AsioContextTestFixture.hpp"
 #include "util/MockLedgerCache.hpp"
 #include "util/MockPrometheus.hpp"
@@ -122,7 +123,9 @@ struct MetricsHandlerTests : util::prometheus::WithPrometheus, SyncAsioContextTe
         std::make_shared<testing::StrictMock<AdminVerificationStrategyMock>>()
     };
 
-    MetricsHandler metricsHandler{adminVerifier};
+    rpc::WorkQueue workQueue{1};
+
+    MetricsHandler metricsHandler{adminVerifier, workQueue};
     web::ng::Request request{http::request<http::string_body>{http::verb::get, "/metrics", 11}};
 };