IXWebSocket/docs/usage.md

# Examples

The [*ws*](https://github.com/machinezone/IXWebSocket/tree/master/ws) folder countains many interactive programs for chat, [file transfers](https://github.com/machinezone/IXWebSocket/blob/master/ws/ws_send.cpp), [curl like](https://github.com/machinezone/IXWebSocket/blob/master/ws/ws_http_client.cpp) http clients, demonstrating client and server usage.

## Windows note

To use the network system on Windows, you need to initialize it once with *WSAStartup()* and clean it up with *WSACleanup()*. We have helpers for that which you can use, see below. This init would typically take place in your main function.

```cpp
#include <ixwebsocket/IXNetSystem.h>

int main()
{
    ix::initNetSystem();

    ...

    ix::uninitNetSystem();
    return 0;
}
```

## WebSocket client API

```cpp
#include <ixwebsocket/IXWebSocket.h>

...

// Our websocket object
ix::WebSocket webSocket;

std::string url("ws://localhost:8080/");
webSocket.setUrl(url);

// Optional heart beat, sent every 45 seconds when there is not any traffic
// to make sure that load balancers do not kill an idle connection.
webSocket.setPingInterval(45);

// Per message deflate connection is enabled by default. You can tweak its parameters or disable it
webSocket.disablePerMessageDeflate();

// Setup a callback to be fired when a message or an event (open, close, error) is received
webSocket.setOnMessageCallback([](const ix::WebSocketMessagePtr& msg)
    {
        if (msg->type == ix::WebSocketMessageType::Message)
        {
            std::cout << msg->str << std::endl;
        }
    }
);

// Now that our callback is setup, we can start our background thread and receive messages
webSocket.start();

// Send a message to the server (default to TEXT mode)
webSocket.send("hello world");

// The message can be sent in BINARY mode (useful if you send MsgPack data for example)
webSocket.sendBinary("some serialized binary data");

// ... finally ...

// Stop the connection
webSocket.stop()
```

### Sending messages

`websocket.send("foo")` will send a message.

If the connection was closed and sending failed, the return value will be set to false.

### ReadyState

`getReadyState()` returns the state of the connection. There are 4 possible states.

1. ReadyState::Connecting - The connection is not yet open.
2. ReadyState::Open       - The connection is open and ready to communicate.
3. ReadyState::Closing    - The connection is in the process of closing.
4. ReadyState::Closed     - The connection is closed or could not be opened.

### Open and Close notifications

The onMessage event will be fired when the connection is opened or closed. This is similar to the [JavaScript browser API](https://developer.mozilla.org/en-US/docs/Web/API/WebSocket), which has `open` and `close` events notification that can be registered with the browser `addEventListener`.

```cpp
webSocket.setOnMessageCallback([](const ix::WebSocketMessagePtr& msg)
    {
        if (msg->type == ix::WebSocketMessageType::Open)
        {
            std::cout << "send greetings" << std::endl;

            // Headers can be inspected (pairs of string/string)
            std::cout << "Handshake Headers:" << std::endl;
            for (auto it : msg->headers)
            {
                std::cout << it.first << ": " << it.second << std::endl;
            }
        }
        else if (msg->type == ix::WebSocketMessageType::Close)
        {
            std::cout << "disconnected" << std::endl;

            // The server can send an explicit code and reason for closing.
            // This data can be accessed through the closeInfo object.
            std::cout << msg->closeInfo.code << std::endl;
            std::cout << msg->closeInfo.reason << std::endl;
        }
    }
);
```

### Error notification

A message will be fired when there is an error with the connection. The message type will be `ix::WebSocketMessageType::Error`. Multiple fields will be available on the event to describe the error.

```cpp
webSocket.setOnMessageCallback([](const ix::WebSocketMessagePtr& msg)
    {
        if (msg->type == ix::WebSocketMessageType::Error)
        {
            std::stringstream ss;
            ss << "Error: "         << msg->errorInfo.reason      << std::endl;
            ss << "#retries: "      << msg->eventInfo.retries     << std::endl;
            ss << "Wait time(ms): " << msg->eventInfo.wait_time   << std::endl;
            ss << "HTTP Status: "   << msg->eventInfo.http_status << std::endl;
            std::cout << ss.str() << std::endl;
        }
    }
);
```

### start, stop

1. `websocket.start()` connect to the remote server and starts the message receiving background thread.
2. `websocket.stop()` disconnect from the remote server and closes the background thread.

### Configuring the remote url

The url can be set and queried after a websocket object has been created. You will have to call `stop` and `start` if you want to disconnect and connect to that new url.

```cpp
std::string url("wss://example.com");
websocket.configure(url);
```

### Ping/Pong support

Ping/pong messages are used to implement keep-alive. 2 message types exists to identify ping and pong messages. Note that when a ping message is received, a pong is instantly send back as requested by the WebSocket spec.

```cpp
webSocket.setOnMessageCallback([](const ix::WebSocketMessagePtr& msg)
    {
        if (msg->type == ix::WebSocketMessageType::Ping ||
            msg->type == ix::WebSocketMessageType::Pong)
        {
            std::cout << "pong data: " << msg->str << std::endl;
        }
    }
);
```

A ping message can be sent to the server, with an optional data string.

```cpp
websocket.ping("ping data, optional (empty string is ok): limited to 125 bytes long");
```

### Heartbeat.

You can configure an optional heart beat / keep-alive, sent every 45 seconds
when there is no any traffic to make sure that load balancers do not kill an
idle connection.

```cpp
webSocket.setPingInterval(45);
```

### Supply extra HTTP headers.

You can set extra HTTP headers to be sent during the WebSocket handshake.

```cpp
WebSocketHttpHeaders headers;
headers["foo"] = "bar";
webSocket.setExtraHeaders(headers);
```

### Subprotocols

You can specify subprotocols to be set during the WebSocket handshake. For more info you can refer to [this doc](https://hpbn.co/websocket/#subprotocol-negotiation).

```cpp
webSocket.addSubprotocol("appProtocol-v1");
webSocket.addSubprotocol("appProtocol-v2");
```

The protocol that the server did accept is available in the open info `protocol` field.

```cpp
std::cout << "protocol: " << msg->openInfo.protocol << std::endl;
```

### Automatic reconnection

Automatic reconnection kicks in when the connection is disconnected without the user consent. This feature is on by default and can be turned off.

```cpp
webSocket.enableAutomaticReconnection();  // turn on
webSocket.disableAutomaticReconnection(); // turn off
bool enabled = webSocket.isAutomaticReconnectionEnabled(); // query state
```

The technique to calculate wait time is called [exponential
backoff](https://docs.aws.amazon.com/general/latest/gr/api-retries.html). Here
are the default waiting times between attempts (from connecting with `ws connect ws://foo.com`)

```
> Connection error: Got bad status connecting to foo.com, status: 301, HTTP Status line: HTTP/1.1 301 Moved Permanently

#retries: 1
Wait time(ms): 100
#retries: 2
Wait time(ms): 200
#retries: 3
Wait time(ms): 400
#retries: 4
Wait time(ms): 800
#retries: 5
Wait time(ms): 1600
#retries: 6
Wait time(ms): 3200
#retries: 7
Wait time(ms): 6400
#retries: 8
Wait time(ms): 10000
```

The waiting time is capped by default at 10s between 2 attempts, but that value can be changed and queried.

```cpp
webSocket.setMaxWaitBetweenReconnectionRetries(5 * 1000); // 5000ms = 5s
uint32_t m = webSocket.getMaxWaitBetweenReconnectionRetries();
```

## WebSocket server API

```cpp
#include <ixwebsocket/IXWebSocketServer.h>

...

// Run a server on localhost at a given port.
// Bound host name, max connections and listen backlog can also be passed in as parameters.
ix::WebSocketServer server(port);

server.setOnConnectionCallback(
    [&server](std::shared_ptr<WebSocket> webSocket,
              std::shared_ptr<ConnectionState> connectionState)
    {
        webSocket->setOnMessageCallback(
            [webSocket, connectionState, &server](const ix::WebSocketMessagePtr msg)
            {
                if (msg->type == ix::WebSocketMessageType::Open)
                {
                    std::cerr << "New connection" << std::endl;

                    // A connection state object is available, and has a default id
                    // You can subclass ConnectionState and pass an alternate factory
                    // to override it. It is useful if you want to store custom
                    // attributes per connection (authenticated bool flag, attributes, etc...)
                    std::cerr << "id: " << connectionState->getId() << std::endl;

                    // The uri the client did connect to.
                    std::cerr << "Uri: " << msg->openInfo.uri << std::endl;

                    std::cerr << "Headers:" << std::endl;
                    for (auto it : msg->openInfo.headers)
                    {
                        std::cerr << it.first << ": " << it.second << std::endl;
                    }
                }
                else if (msg->type == ix::WebSocketMessageType::Message)
                {
                    // For an echo server, we just send back to the client whatever was received by the server
                    // All connected clients are available in an std::set. See the broadcast cpp example.
                    // Second parameter tells whether we are sending the message in binary or text mode.
                    // Here we send it in the same mode as it was received.
                    webSocket->send(msg->str, msg->binary);
                }
            }
        );
    }
);

auto res = server.listen();
if (!res.first)
{
    // Error handling
    return 1;
}

// Run the server in the background. Server can be stoped by calling server.stop()
server.start();

// Block until server.stop() is called.
server.wait();

```

## HTTP client API

```cpp
#include <ixwebsocket/IXHttpClient.h>

...

//
// Preparation
//
HttpClient httpClient;
HttpRequestArgsPtr args = httpClient.createRequest();

// Custom headers can be set
WebSocketHttpHeaders headers;
headers["Foo"] = "bar";
args->extraHeaders = headers;

// Timeout options
args->connectTimeout = connectTimeout;
args->transferTimeout = transferTimeout;

// Redirect options
args->followRedirects = followRedirects;
args->maxRedirects = maxRedirects;

// Misc
args->compress = compress; // Enable gzip compression
args->verbose = verbose;
args->logger = [](const std::string& msg)
{
    std::cout << msg;
};

//
// Synchronous Request
//
HttpResponsePtr out;
std::string url = "https://www.google.com";

// HEAD request
out = httpClient.head(url, args);

// GET request
out = httpClient.get(url, args);

// POST request with parameters
HttpParameters httpParameters;
httpParameters["foo"] = "bar";
out = httpClient.post(url, httpParameters, args);

// POST request with a body
out = httpClient.post(url, std::string("foo=bar"), args);

//
// Result
//
auto statusCode = response->statusCode; // Can be HttpErrorCode::Ok, HttpErrorCode::UrlMalformed, etc...
auto errorCode = response->errorCode; // 200, 404, etc...
auto responseHeaders = response->headers; // All the headers in a special case-insensitive unordered_map of (string, string)
auto payload = response->payload; // All the bytes from the response as an std::string
auto errorMsg = response->errorMsg; // Descriptive error message in case of failure
auto uploadSize = response->uploadSize; // Byte count of uploaded data
auto downloadSize = response->downloadSize; // Byte count of downloaded data

//
// Asynchronous Request
//
bool async = true;
HttpClient httpClient(async);
auto args = httpClient.createRequest(url, HttpClient::kGet);

// Push the request to a queue,
bool ok = httpClient.performRequest(args, [](const HttpResponsePtr& response)
    {
        // This callback execute in a background thread. Make sure you uses appropriate protection such as mutex
        auto statusCode = response->statusCode; // acess results
    }
);

// ok will be false if your httpClient is not async
```

## HTTP server API

```cpp
#include <ixwebsocket/IXHttpServer.h>

ix::HttpServer server(port, hostname);

auto res = server.listen();
if (!res.first)
{
    std::cerr << res.second << std::endl;
    return 1;
}

server.start();
server.wait();
```

If you want to handle how requests are processed, implement the setOnConnectionCallback callback, which takes an HttpRequestPtr as input, and returns an HttpResponsePtr. You can look at HttpServer::setDefaultConnectionCallback for a slightly more advanced callback example.

```cpp
setOnConnectionCallback(
    [this](HttpRequestPtr request,
           std::shared_ptr<ConnectionState> /*connectionState*/) -> HttpResponsePtr
    {
        // Build a string for the response
        std::stringstream ss;
        ss << request->method
           << " "
           << request->uri;

        std::string content = ss.str();

        return std::make_shared<HttpResponse>(200, "OK",
                                              HttpErrorCode::Ok,
                                              WebSocketHttpHeaders(),
                                              content);
}
```

## TLS support and configuration

To leverage TLS features, the library must be compiled with the option `USE_TLS=1`.

If you are using OpenSSL, try to be on a version higher than 1.1.x as there there are thread safety problems with 1.0.x.

Then, secure sockets are automatically used when connecting to a `wss://*` url.

Additional TLS options can be configured by passing a `ix::SocketTLSOptions` instance to the
`setTLSOptions` on `ix::WebSocket` (or `ix::WebSocketServer` or `ix::HttpServer`)

```cpp
webSocket.setTLSOptions({
    .certFile = "path/to/cert/file.pem",
    .keyFile = "path/to/key/file.pem",
    .caFile = "path/to/trust/bundle/file.pem", // as a file, or in memory buffer in PEM format
    .tls = true // required in server mode
});
```

Specifying `certFile` and `keyFile` configures the certificate that will be used to communicate with TLS peers.

On a client, this is only necessary for connecting to servers that require a client certificate.

On a server, this is necessary for TLS support.

Specifying `caFile` configures the trusted roots bundle file (in PEM format) that will be used to verify peer certificates.
 - The special value of `SYSTEM` (the default) indicates that the system-configured trust bundle should be used; this is generally what you want when connecting to any publicly exposed API/server.
 - The special value of `NONE` can be used to disable peer verification; this is only recommended to rule out certificate verification when testing connectivity.
 - If the value contain the special value `-----BEGIN CERTIFICATE-----`, the value will be read from memory, and not from a file. This is convenient on platforms like Android where reading / writing to the file system can be challenging without proper permissions, or without knowing the location of a temp directory.

For a client, specifying `caFile` can be used if connecting to a server that uses a self-signed cert, or when using a custom CA in an internal environment.

For a server, specifying `caFile` implies that:
1. You require clients to present a certificate
1. It must be signed by one of the trusted roots in the file