CWebSockets

A simple implementation of web socket client in c using libcurl. Note: requires libcurl version >= 7.86.0 with wss enabled

This library contains the implementation of WebSocket client operations, including connecting to a WebSocket server, sending and receiving data, managing client connections, and handling callbacks for open, close, and message events.

Installation

Make sure libcurl version >= 7.86.0 is installed. with wss enabled

To enable wss with libcurl you have to build it yourself from source. Or just execute source install_curl.sh on linux (tested with debian), which will take a while and install libcurl with WebSocket enabled.

To install this library execute the following commands:

git clone https://github.com/LakshAgg/CWebSockets.git
cd CWebSockets

make
sudo make install
make clean

To uninstall execute make uninstall.

Compile with -lcwebsockets -lcurl.

Example

Check out the example program which uses the Binance market stream and prints the latest trades for 10 seconds.

WSS_Client

struct WSS_Client
{
    /// @brief Called on successfully connecting to the socket (optional)
    void (*on_open)(struct WSS_Client *client);

    /// @brief Called after socket gets closed (optional)
    void (*on_close)(struct WSS_Client *client);

    /// @brief Called on recieving a message
    void (*on_message)(struct WSS_Client *client, void *data, unsigned long len);

    /// @brief The web socket stream url: begins with ws or wss
    char *url;
}

url

The URL to connect to. eg: wss://fstream.binance.com/ws/.

on_open(WSS_Client *client)

This function will be called after the client has successfully connected by calling start_wss_client or connect_wss_client.

on_message(WSS_Client *client, void *data, unsigned long len)

This function is called when a message is received from the socket.

The data received is not null-terminated. len is the length of data received.

on_close(WSS_Client *client)

This function will be after the client has disconnected from the socket.

Functions

connect_wss_client

/**
 * @brief Just connects to the web socket.
 * @param client
 * @return int - 0 if success
 */
int connect_wss_client(WSS_Client *client);

This function will open a new connection and call client->on_open if successful. After you are done with the connection, call close_wss_client. At the end of the program call curl_global_cleanup to avoid any memory leaks.

listen_wss_client

/**
 * @brief Create a new thread if not done already to read from sockets.
 * @param client
 * @return int - 0 if success
 */
int listen_wss_client(WSS_Client *client);

A list of all open connections is maintained by CWebSockets, this is used with poll to wait for any new data in any connection.

If listen_wss_client is called for the first time, it will create a new thread using pthread_create which will use poll to wait for any data. On subsequent calls, only the list is updated to include the new client's socket.

send_wss_client

/**
 * @brief Sends the data through the socket.
 * @param client
 * @param data
 * @param size
 * @param flags - for curl_ws_send
 * @return int - 0 if success
 */
int send_wss_client(WSS_Client *client, void *data, unsigned long size, unsigned int flags);

This function sends the data and returns 0 on success. For more info on flags, refer to curl_ws_send.

close_wss_client

/**
 * @brief Closes the connection
 * @param client
 */
void close_wss_client(WSS_Client *client);

This closes the connection and frees the memory allocated for it.

start_wss_client

/**
 * @brief Connects to the socket and starts listening
 * @param client
 * @return int
 */
int start_wss_client(WSS_Client *client);

This function just calls connect and listen together and returns 0 if no error occurs.

join_thread_wss_client

This function joins the thread created for reading new data. This will block further execution.