infra: improve gRPC server error if a port is already in use (#1398) (#…

…2500)

Implement gRPC server "global callbacks" to check port conflicts.

silkworm/infra/grpc/server/server.hpp

@@ -31,6 +31,8 @@
 #include <silkworm/infra/grpc/server/server_context_pool.hpp>
 #include <silkworm/infra/grpc/server/server_settings.hpp>
 
+#include "silkworm/infra/grpc/server/server_callbacks.hpp"
+
 namespace silkworm::rpc {
 
 //! Base RPC server able to serve incoming requests for gRPC \ref AsyncService instances.
@@ -78,10 +80,16 @@ class Server {
         register_async_services(builder);
 
         server_ = builder.BuildAndStart();
-        SILK_TRACE << "Server " << this << " bound at selected port: " << selected_port;
+
         if (server_ == nullptr) {
+            std::string error_msg = "cannot start gRPC server at " + settings_.address_uri;
+
+            if (ServerGlobalCallbacks::check_and_clear_bad_port_error()) {
+                error_msg += " (port already in use)";
+            }
+
             SILK_ERROR << "Server " << this << " BuildAndStart failed [" << settings_.address_uri << "]";
-            throw std::runtime_error("cannot start gRPC server at " + settings_.address_uri);
+            throw std::runtime_error(error_msg);
         }
 
         // gRPC async model requires the server to register one request call for each RPC in advance.
@@ -174,6 +182,9 @@ class Server {
     //! The gRPC server instance tied to this Server lifetime.
     std::unique_ptr<grpc::Server> server_;
 
+    //! The global callbacks are shared between all instances of Servers
+    static inline const ServerGlobalCallbacks kGlobalCallbacks;
+
     //! Pool of server schedulers used to run the execution loops.
     std::unique_ptr<ServerContextPool> context_pool_;
 

silkworm/infra/grpc/server/server_callbacks.hpp

@@ -0,0 +1,62 @@
+/*
+   Copyright 2024 The Silkworm Authors
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+#pragma once
+
+#include <atomic>
+#include <mutex>
+
+#include <grpcpp/grpcpp.h>
+
+#include <silkworm/infra/common/log.hpp>
+
+namespace silkworm::rpc {
+
+class ServerGlobalCallbacks {
+  public:
+    ServerGlobalCallbacks() {
+        // NOTE: Despite its documentation, SetGlobalCallbacks() does take the ownership
+        // of the object pointer. So we just "new" and let underlying GRPC manage its lifetime.
+        static std::once_flag callback_init_flag;
+        std::call_once(callback_init_flag, []() {
+            grpc::Server::SetGlobalCallbacks(new Callbacks());
+        });
+    }
+
+    static bool check_and_clear_bad_port_error() {
+        return bad_port_error.exchange(false);
+    }
+
+  private:
+    static inline std::atomic<bool> bad_port_error{false};
+    class Callbacks final : public grpc::Server::GlobalCallbacks {
+      public:
+        Callbacks() = default;
+        ~Callbacks() override = default;
+
+        void PreSynchronousRequest(grpc::ServerContext*) override{};
+        void PostSynchronousRequest(grpc::ServerContext*) override{};
+
+        void AddPort(grpc::Server*, const std::string&,
+                     grpc::ServerCredentials*, int port) override {
+            if (port == 0) {
+                ServerGlobalCallbacks::bad_port_error.store(true, std::memory_order_release);
+            }
+        }
+    };
+};
+
+}  // namespace silkworm::rpc