// Copyright (C) 2018-2023 Internet Systems Consortium, Inc. ("ISC") // // This Source Code Form is subject to the terms of the Mozilla Public // License, v. 2.0. If a copy of the MPL was not distributed with this // file, You can obtain one at http://mozilla.org/MPL/2.0/. #ifndef HTTP_CLIENT_H #define HTTP_CLIENT_H #include #include #include #include #include #include #include #include #include #include #include namespace isc { namespace http { /// @brief A generic error raised by the @ref HttpClient class. class HttpClientError : public Exception { public: HttpClientError(const char* file, size_t line, const char* what) : isc::Exception(file, line, what) { }; }; class HttpClientImpl; /// @brief HTTP client class. /// /// This class implements an asynchronous HTTP client. The caller can schedule /// transmission of the HTTP request using @ref HttpClient::asyncSendRequest /// method. The caller specifies target URL for each request. The caller also /// specifies a pointer to the @ref HttpRequest or derived class, holding a /// request that should be transmitted to the destination. Such request must /// be finalized, i.e. @ref HttpRequest::finalize method must be called prior /// to sending it. The caller must also provide a pointer to the /// @ref HttpResponse object or an object derived from it. The type of the /// response object must match the expected content type to be returned in the /// server's response. The last argument specified in this call is the pointer /// to the callback function, which should be launched when the response is /// received, an error occurs or when a timeout in the transmission is /// signaled. /// /// The HTTP client supports multiple simultaneous and persistent connections /// with different destinations. The client determines if the connection is /// persistent by looking into the Connection header and HTTP version of the /// request. If the connection should be persistent the client doesn't /// close the connection after sending a request and receiving a response from /// the server. If the client is provided with the request to be sent to the /// particular destination, but there is an ongoing communication with this /// destination, e.g. as a result of sending previous request, the new /// request is queued in the FIFO queue. When the previous request completes, /// the next request in the queue for the particular URL will be initiated. /// /// Furthermore, the class supports two modes of operation: single-threaded /// and multi-threaded mode. In single-threaded mode, all IO is driven by /// an external IOService passed into the class constructor, and ultimately /// only a single connection per URL can be open at any given time. /// /// In multi-threaded mode an internal thread pool driven by a private /// IOService instance is used to support multiple concurrent connections /// per URL. Currently, the number of connections per URL is set to the /// number of threads in the thread pool. /// /// The client tests the persistent connection for usability before sending /// a request by trying to read from the socket (with message peeking). If /// the socket is usable the client uses it to transmit the request. /// /// This classes exposes the underlying transport socket's descriptor for /// each connection via connect, handshake and close callbacks. /// This is done to permit the sockets to be monitored for IO readiness /// by external code that's something other than boost::asio /// (e.g.select() or epoll()), and would thus otherwise starve the /// client's IOService and cause a backlog of ready event handlers. /// /// All errors are reported to the caller via the callback function supplied /// to the @ref HttpClient::asyncSendRequest. The IO errors are communicated /// via the @c boost::system::error code value. The response parsing errors /// are returned via the 3rd parameter of the callback. class HttpClient { public: /// @brief HTTP request/response timeout value. struct RequestTimeout { /// @brief Constructor. /// /// @param value Request/response timeout value in milliseconds. explicit RequestTimeout(long value) : value_(value) { } long value_; ///< Timeout value specified. }; /// @brief Callback type used in call to @ref HttpClient::asyncSendRequest. typedef std::function RequestHandler; /// @brief Optional handler invoked when client connects to the server. /// /// Returned boolean value indicates whether the client should continue /// connecting to the server (if true) or not (false). /// It is passed the IO error code along with the native socket handle of /// the connection's TCP socket. The passed socket descriptor may be used /// to monitor the readiness of the events via select() or epoll(). /// /// @note Beware that the IO error code can be set to "in progress" /// so a not null error code does not always mean the connect failed. typedef std::function ConnectHandler; /// @brief Optional handler invoked when client performs the TLS handshake /// with the server. /// /// It is called when the TLS handshake completes: /// - if the handshake succeeds it is called with error code 0 /// - if the handshake fails it is called with error code != 0 /// - if TLS is not enabled, it is not called at all /// /// Returned boolean value indicates whether the client should continue /// connecting to the server (if true) or not (false). /// @note The second argument is not used. typedef std::function HandshakeHandler; /// @brief Optional handler invoked when client closes the connection to the server. /// /// It is passed the native socket handler of the connection's TCP socket. typedef std::function CloseHandler; /// @brief Constructor. /// /// @param io_service IO service to be used by the HTTP client. /// @param multi_threading_enabled The flag which indicates if MT is enabled. /// @param thread_pool_size maximum number of threads in the thread pool. /// A value greater than zero enables multi-threaded mode and sets the /// maximum number of concurrent connections per URL. A value of zero /// (default) enables single-threaded mode with one connection per URL. /// @param defer_thread_start When true, starting of the pool threads is /// deferred until a subsequent call to @ref start(). In this case the /// pool's operational state after construction is STOPPED. Otherwise, /// the thread pool threads will be created and started, with the /// operational state being RUNNING. Applicable only when thread-pool size /// is greater than zero. explicit HttpClient(asiolink::IOService& io_service, bool multi_threading_enabled, size_t thread_pool_size = 0, bool defer_thread_start = false); /// @brief Destructor. ~HttpClient(); /// @brief Queues new asynchronous HTTP request for a given URL. /// /// The client maintains an internal connection pool which manages lists /// of connections per URL. In single-threaded mode, each URL is limited /// to a single connection. In multi-threaded mode, each URL may have /// more than one open connection per URL, enabling the client to carry /// on multiple concurrent requests per URL. /// /// The client will search the pool for an open, idle connection for the /// given URL. If there are no idle connections, the client will open /// a new connection up to the maximum number of connections allowed by the /// thread mode. If all possible connections are busy, the request is /// pushed on to back of a URL-specific FIFO queue of pending requests. /// /// If however, there is an idle connection available than a new transaction /// for the request will be initiated immediately upon that connection. /// /// Note that when a connection completes a transaction, and its URL /// queue is not empty, it will pop a pending request from the front of /// the queue and begin a new transaction for that request. The net effect /// is that requests are always pulled from the front of the queue unless /// the queue is empty. /// /// The existing connection is tested before it is used for the new /// transaction by attempting to read (with message peeking) from /// the open transport socket. If the read attempt is successful, /// the client will transmit the HTTP request to the server using /// this connection. It is possible that the server closes the /// connection between the connection test and sending the request. /// In such case, an error will be returned and the caller will /// need to try re-sending the request. /// /// If the connection test fails, the client will close the socket and /// reconnect to the server prior to sending the request. /// /// Pointers to the request and response objects are provided as arguments /// of this method. These pointers should have appropriate types derived /// from the @ref HttpRequest and @ref HttpResponse classes. For example, /// if the request has content type "application/json", a pointer to the /// @ref HttpResponseJson should be passed. In this case, the response type /// should be @ref HttpResponseJson. These types are used to validate both /// the request provided by the caller and the response received from the /// server. /// /// The callback function provided by the caller is invoked when the /// transaction terminates, i.e. when the server has responded or when an /// error occurred. The callback is expected to be exception safe, but the /// client internally guards against exceptions thrown by the callback. /// /// The first argument of the callback indicates an IO error during /// communication with the server. If the communication is successful the /// error code of 0 is returned. However, in this case it is still possible /// that the transaction is unsuccessful due to HTTP response parsing error, /// e.g. invalid content type, malformed response etc. Such errors are /// indicated via third argument. /// /// If message parsing was successful the second argument of the callback /// contains a pointer to the parsed response (the same pointer as provided /// by the caller as the argument). If parsing was unsuccessful, the null /// pointer is returned. /// /// The default timeout for the transaction is set to 10 seconds /// (10 000 ms). If the timeout occurs, the callback is invoked with the /// error code of @c boost::asio::error::timed_out. /// The timeout covers both the connect and the transaction phases /// so when connecting to the server takes too long (e.g. with a /// misconfigured firewall) the timeout is triggered. The connect /// callback can be used to recognize this condition. /// /// @param url URL where the request should be send. /// @param tls_context TLS context. /// @param request Pointer to the object holding a request. /// @param response Pointer to the object where response should be stored. /// @param request_callback Pointer to the user callback function invoked /// when transaction ends. /// @param request_timeout Timeout for the transaction in milliseconds. /// @param connect_callback Optional callback invoked when the client /// connects to the server. /// @param handshake_callback Optional callback invoked when the client /// performs the TLS handshake with the server. /// @param close_callback Optional callback invoked when the client /// closes the connection to the server. /// /// @throw HttpClientError If invalid arguments were provided. void asyncSendRequest(const Url& url, const asiolink::TlsContextPtr& tls_context, const HttpRequestPtr& request, const HttpResponsePtr& response, const RequestHandler& request_callback, const RequestTimeout& request_timeout = RequestTimeout(10000), const ConnectHandler& connect_callback = ConnectHandler(), const HandshakeHandler& handshake_callback = HandshakeHandler(), const CloseHandler& close_callback = CloseHandler()); /// @brief Check if the current thread can perform thread pool state /// transition. /// /// @throw MultiThreadingInvalidOperation if the state transition is done on /// any of the worker threads. void checkPermissions(); /// @brief Starts running the client's thread pool, if multi-threaded. void start(); /// @brief Pauses the client's thread pool. /// /// Suspends thread pool event processing. /// @throw InvalidOperation if the thread pool does not exist. void pause(); /// @brief Resumes running the client's thread pool. /// /// Resumes thread pool event processing. /// @throw InvalidOperation if the thread pool does not exist. void resume(); /// @brief Halts client-side IO activity. /// /// Closes all connections, discards any queued requests, and in /// multi-threaded mode discards the thread-pool and the internal /// IOService. void stop(); /// @brief Closes a connection if it has an out-of-band socket event /// /// If the client owns a connection using the given socket and that /// connection is currently in a transaction the method returns as this /// indicates a normal ready event. If the connection is not in an /// ongoing transaction, then the connection is closed. /// /// This is method is intended to be used to detect and clean up then /// sockets that are marked ready outside of transactions. The most common /// case is the other end of the socket being closed. /// /// @param socket_fd socket descriptor to check void closeIfOutOfBand(int socket_fd); /// @brief Fetches a pointer to the internal IOService used to /// drive the thread-pool in multi-threaded mode. /// /// @return pointer to the IOService instance, or an empty pointer /// in single-threaded mode. const asiolink::IOServicePtr getThreadIOService() const; /// @brief Fetches the maximum size of the thread pool. /// /// @return the maximum size of the thread pool. uint16_t getThreadPoolSize() const; /// @brief Fetches the number of threads in the pool. /// /// @return the number of running threads. uint16_t getThreadCount() const; /// @brief Indicates if the thread pool is running. /// /// @return True if the thread pool exists and it is in the RUNNING state, /// false otherwise. bool isRunning(); /// @brief Indicates if the thread pool is stopped. /// /// @return True if the thread pool exists and it is in the STOPPED state, /// false otherwise. bool isStopped(); /// @brief Indicates if the thread pool is paused. /// /// @return True if the thread pool exists and it is in the PAUSED state, /// false otherwise. bool isPaused(); private: /// @brief Pointer to the HTTP client implementation. boost::shared_ptr impl_; }; /// @brief Defines a pointer to an HttpClient instance. typedef boost::shared_ptr HttpClientPtr; } // end of namespace isc::http } // end of namespace isc #endif