Interview Questions.

Question 1. Can A Handler Be Changed After A Connection Is Established? Can One Be Removed?

Answer :

Yes, but now not globally.

Handlers assigned to endpoints will be robotically copied to the connections created by means of that endpoint. Changing a handler on an endpoint will most effective have an effect on destiny connections.

Once a selected connection is created, it's handlers may be modified personally through calling the set_*_handler methods. Once modified, all future occasions of that type for that connection will use the new handler.

To get rid of a handler that changed into previously set, name the set method with nullptr or NULL.

Question 2. Can I Reject Or Conditionally Accept A Connection?

Answer :

Yes. The validate handler is called after the preliminary handshake has been recieved however earlier than WebSocket++ has replied. This gives you the possibility to look into the incoming connection request, its headers, beginning, subprotocols, and the remote endpoint IP. Return proper from the validate handler to accept the relationship and false to reject it.

To set a custom HTTP error message to your rejection, use websocketpp::connection::set_status and (optionally) websocketpp::connection::set_body() to set the HTTP repute code and mistakes message body textual content. If you do no longer set frame textual content a message could be generated automatically based totally at the fame code.

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Question 3. How Do I Negotiate Subprotocols?

Answer :

The Asio transport based clients and servers use the Asio library's underlying io_service to handle asyncronous networking operations. The fashionable conduct of the io_service is to run until there are no async operations left after which return. WebSocket++, while using the Asio shipping, behaves like a trendy Asio application. If you want your WebSocket++/Asio based software to forestall network operations and cleanly close all sockets you'll need to do the subsequent:

For servers, name websocketpp::shipping::asio::endpoint::stop_listening to provoke the last of the server listening socket.
For clients, if you have engaged perpetual mode with websocketpp::delivery::asio::endpoint::start_perpetual, disable it with websocketpp::transport::asio::endpoint::stop_perpetual.
For both, run websocketpp::endpoint::near or websocketpp::connection::near on all presently high-quality connections. This will provoke the WebSocket final handshake for these connections
Wait. Asio is asyncronous. When the calls to the above methods (stop_listening, near, and so on) entire the server will nonetheless be listening, the connections will nevertheless be lively till the io_service receives round to asyncronously processing the socket and WebSocket protocol ultimate handshakes. The io_service::run approach will go out cleanly and mechanically when all operations are whole.
WARNING: Asio's io_service has a way referred to as prevent. WebSocket++ wraps this technique as websocketpp::delivery::asio::endpoint::stop. While this operation has a benign sounding name, it is a powerful and detrimental operation that should simplest be utilized in special instances. If you're the use of io_service::forestall or endpoint::prevent without a excellent motive your application is probable broken and can showcase erratic behavior. Specifically, io_service::stop stops the processing of events totally. This does not deliver modern-day operations (together with socket final handshakes) the opportunity to complete. It will depart your sockets in a hanging kingdom that may invoke operating gadget degree timeouts or other errors.

Question 4. Is There A Way To Check The Validity Of A Connection_hdl?

Answer :

Sometimes, now not normally although, because there isn’t a manner to check if a TCP connection is legitimate.

You can try upgrading your hdl to a complete connection_ptr using websocketpp::endpoint::get_con_from_hdl. If this fails, the hdl is really invalid. If it succeeds it may or might not be. The simplest way to tell definitively is to try to send something (both a message or a ping).

If you manage mistakes from strategies like ship, ping, close, and many others efficiently then you definately shouldn’t must fear about accidentally sending to dead connections. The ship/ping/pong/near methods will set or throw a selected error in the case that you attempted to send some thing but the connection become closed/gone/and so on.

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Question five. How Do I Fix The "cope with Is In Use" Error When Trying To Restart My Server?

Answer :

Normally, for protection functions, operating systems prevent applications from listening on sockets created by using different packages. When your program crashes and restarts, the new example is a distinct software from the angle of the running machine. As such it may’t pay attention on the socket address/port that the previous program was the usage of until after a timeout takes place to ensure the vintage application changed into done with it.

The the first step for coping with that is to make certain that you provide a technique (sign handler, admin websocket message, and many others) to perform a easy server shutdown.

The easy near approach may not assist in the case of crashes or different odd closures. An choice to recollect for these cases is using the SO_REUSEADDR socket alternative. That instructs the OS to not request an special lock on the socket. This way that once your application crashes the substitute you begin can immediately listen on that cope with/port blend once more.

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Question 6. How Do You Send And Recieve Binary Messages?

Answer :

When supported by using the faraway endpoint, WebSocket++ allows reading and sending messages within the two codecs laid out in RFC6455, UTF8 textual content and binary. WebSocket++ performs UTF8 validation on all outgoing textual content messages to ensure that they meet the specification. Binary messages do no longer have any additional processing and their interpretation is left entirely to the library user.

To decide the form of an incoming message, use websocketpp::message_buffer::message::get_opcode. The applicable go back values are websocketpp::body::opcode::textual content and websocketpp::frame::opcode::binary. There isn't any distinction in how payloads are retrieved between these modes, simplest in how WebSocket++ proven the contents and the way the library person is to interpret the records.

To specify the type of an outgoing message, use the frame opcode values listed above as the second one op parameter for websocketpp::connection::ship. There are  relevant overloads of send. One that takes a std::string and defaults to op=textual content. The other that takes a void const * and a size_t duration and defaults to op=binary. Note: You can send binary messages thru the string overload and text messages thru the void * overload. In the case which you are manually building a message buffer in place of the usage of the automatic ship member functions, you may bypass the opcode in as a parameter to the message buffer constructor or user the websocketpp::message_buffer::message::set_opcode member characteristic to set or re-set it later.

Question 7. Can Websocket++ Be Used Without Boost?

Answer :

Yes. WebSocket++ best uses Boost capabilities as polyfills for C++11 language features and libraries. If you've got a C++eleven compiler and wellknown library you could use WebSocket++ with out Boost. In most instances placing your construct surroundings to use the C++11 (or later) language dialect is enough to permit this mode of use.

With less commonplace compilers (and every so often very these days launch compilers) there can be specific issues with certain libraries that aren't routinely detected by the library. For these conditions there are extra defines available to satisfactory tune which C++11 libraries and functions are used. TODO: more information about them.

For the iostream/raw delivery the C++eleven trendy library is sufficient. For the Asio based transports, there's no C++11 library that gives the networking competencies that Asio does. As such inspite of a C++eleven build machine, you'll need a standalone copy of Asio to apply if Boost Asio isn't to be had.

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Question eight. Can Websocket++ Be Used With Standalone Asio?

Answer :

Yes. The system is similar to used with standalone Asio itself. Defined ASIO STANDALONE earlier than such as Asio or WebSocket++ headers. You will need to download a copy of the Asio headers one by one and make sure they're in your build gadget's consist of route.

Question 9. Can Websocket Be Used Without Tls Or Openssl?

Answer :

Yes. When the use of the iostream/raw shipping, there aren't any TLS functions and OpenSSL isn't always required. When the use of the Asio shipping TLS features are non-compulsory. You best need OpenSSL in case you want to apply TLS. You can simplest make or recieve encrypted connections (https/wss) if you have enabled TLS functions.

Whether an Asio endpoint makes use of TLS or not is determined with the aid of its config template parameter. The default bundled websocketpp::config::asio and websocketpp::config::asio_client configs do no longer support TLS, the websocketpp::config::asio_tls and websocketpp::config::asio_tls_client do.

The <websocketpp/config/asio.Hpp> and <websocketpp/config/asio_client.Hpp> headers will include both the TLS and non-TLS varients in their respective configs and require the presence of OpenSSL. The <websocketpp/config/asio_no_tls.Hpp> and <websocketpp/config/asio_no_tls_client.Hpp> headers will consist of simplest the non-TLS configs and do now not require OpenSSL.

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Question 10. Build Issues With Tls On Recent Versions Of Os X?

Answer :

Mac OS X ships a significantly old Yes. The technique is similar to used with standalone Asio itself. Defined ASIO STANDALONE earlier than which include Asio or WebSocket++ headers. You will need to download a replica of the Asio headers one by one and make certain they are to your build gadget's encompass course.

Version of the OpenSSL library. To securely use TLS with WebSocket++ on OS X you'll need to install a cutting-edge model of OpenSSL via homebrew or compiling from supply.

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Question eleven. How Do I Use Permessage-deflate In Version 0.6.0-permessage Deflate And 0.7.Zero?

Answer :

These variations of the library require a custom config to apply the permessage-deflate extension. Here is a minimal instance of the sort of custom config. You can also integrate those traces into an existing custom config.

Note that in these variations there is no great grained manipulate over which connections are compressed or not. Clients will request compression with the default settings and use it if the server helps it. Servers will accept anything parameters clients request.

Outgoing messages via default could be compressed if compression turned into automobile-negotiated throughout the handshake. There is an option to force a selected message to be sent uncompressed despite the fact that compression was negotiated. This may be beneficial for sending records which you understand to be compressed already (photos, zip files, and so on).

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Question 12. What Is Websockets?

Answer :

WebSocket is a pc communications protocol, supplying full-duplex conversation channels over a unmarried TCP connection.

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Question thirteen. How To Create A Websocket Connection?

Answer :

ws = new WebSocket('ws://localhost:8080/person');

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Question 14. Have You Implemented Websockets? What Was The Use Case?

Answer :

Have implemented WebSockets for a talk software the use of Spring Boot.