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Real-time trades stream using WebSocket with different languages

Introduction​

This tutorial will guide you on how to subscribe to real-time cryptocurrency market data using CoinAPI.
We will explore using the WebSocket protocol in Python, JavaScript, and Java to get live market data updates.

Understanding WebSocket Protocol​

CoinAPI provides real-time data through the WebSocket protocol.
WebSocket allows for full-duplex communication channels over a single TCP connection, making it an excellent choice for live data updates.
The key endpoint for real-time data is wss://ws.coinapi.io/v1/.
To subscribe to a specific type of data, you need to send a subscription message after the connection is established.

Python Example​

In Python, we can use the websocket-client library to connect to CoinAPI's WebSocket API.
If you don't have the websocket-client library installed, you can add it using pip:

pip install websocket-client

Here's an example of real time trade data retrieval:

import websocket
import json
 
def on_message(ws, message):
    print(message)
 
def on_error(ws, error):
    print(error)
 
def on_close(ws):
    print("### closed ###")
 
def on_open(ws):

    ws.send(json.dumps({
        "type": "hello",
        "apikey": "YOUR_API_KEY",
        "subscribe_data_type": ["trade"],
        "subscribe_filter_symbol_id": [ "BITSTAMP_SPOT_BTC_USD$", "BITFINEX_SPOT_BTC_USD$" ]
    }))
 
ws = websocket.WebSocketApp("wss://ws.coinapi.io/v1",
                              on_message = on_message,
                              on_error = on_error,
                              on_close = on_close)
ws.on_open = on_open
ws.run_forever()

This script:

  • Opens WebSocket connection
  • Subscribes to real-time data for BTC/USD trading on Bitstamp and Bitfinex (you may replace with your desired cryptocurrency pair)
  • Prints incoming real-time messages

Note: If subscribe_filter_symbol_id is ended with $ character then the exact match is used instead of prefix match.

You can check out more message examples and hello message parameters.

JavaScript Example​

Make sure to install nodejs runtime environment before.
First, add package.json with node-fetch dependency:

{
  "type": "module",
  "dependencies": {
    "ws": "^8.13.0"
  }
}

In JavaScript, you can use WebSocket API:

import WebSocket from 'ws';

const socket = new WebSocket('wss://ws.coinapi.io/v1/');
 
socket.onopen = function (event) {
  socket.send(JSON.stringify({
      "type": "hello",
      "apikey": "YOUR_API_KEY",
      "subscribe_data_type": ["trade"],
      "subscribe_filter_symbol_id": [ "BITSTAMP_SPOT_BTC_USD$", "BITFINEX_SPOT_BTC_LTC$" ]
  }));
};
 
socket.onmessage = function (event) {
  console.log(event.data);
};
 
socket.onerror = function (error) {
  console.log(`WebSocket error: ${error}`);
};

This script:

  • Opens WebSocket connection
  • Subscribes to real-time data for BTC/USD trading on Bitstamp and Bitfinex (you may replace with your desired cryptocurrency pair)
  • Prints incoming real-time messages

Install dependencies via npm install command.
Execute your program in nodejs runtime environment with node your-script-name.js command.

Note: If subscribe_filter_symbol_id is ended with $ character then the exact match is used instead of prefix match.

You can check out more message examples and hello message parameters.

JavaScript in a web browser​

Here's an example that works directly in a web browser, create index.html file, paste the code, and start in a web browser:

<!DOCTYPE html>
<html>
<head>
    <title>Realtime Crypto Market Data Example</title>
</head>
<body>
    <script>
        const socket = new WebSocket('wss://ws.coinapi.io/v1/');

        socket.onopen = function (event) {
            socket.send(JSON.stringify({
                "type": "hello",
                "apikey": "YOUR_API_KEY",
                "subscribe_data_type": ["trade"],
                "subscribe_filter_symbol_id": ["BITSTAMP_SPOT_BTC_USD$", "BITFINEX_SPOT_BTC_LTC$"]
            }));
        };

        socket.onmessage = function (event) {
            console.log(event.data);
            const contentDiv = document.getElementById('content');
            contentDiv.textContent += event.data;
        };

        socket.onerror = function (error) {
            console.log(`WebSocket error: ${error}`);
        };
    </script>
    
    <div id="content">
    
</body>
</html>

Java Example​

If you're using a Maven project, include Java-WebSocket and JSON dependencies in your pom.xml file:

<dependencies>

    <dependency>
        <groupId>org.java-websocket</groupId>
        <artifactId>Java-WebSocket</artifactId>
        <version>1.5.1</version>
    </dependency>

    <dependency>
        <groupId>org.json</groupId>
        <artifactId>json</artifactId>
        <version>20210307</version>
    </dependency>
    
</dependencies>

Here's a Java example that uses WebSocketClient and JSONObject classes:

import org.java_websocket.client.WebSocketClient;
import org.java_websocket.handshake.ServerHandshake;
import org.json.JSONArray;
import org.json.JSONObject;
import java.net.URI;
import java.net.URISyntaxException;

public class Main {

    public static void main(String[] args) {
        try {
            WebSocketClient socket = new WebSocketClient(new URI("wss://ws.coinapi.io/v1/")) {
                
                @Override
                public void onOpen(ServerHandshake serverHandshake) {
                    JSONObject message = new JSONObject();
                    message.put("type", "hello");
                    message.put("apikey", "YOUR_API_KEY");

                    JSONArray subscribeDataType = new JSONArray();
                    subscribeDataType.put("trade");
                    message.put("subscribe_data_type", subscribeDataType);

                    JSONArray subscribeFilterSymbolId = new JSONArray();
                    subscribeFilterSymbolId.put("BITSTAMP_SPOT_BTC_USD$");
                    subscribeFilterSymbolId.put("BITFINEX_SPOT_BTC_LTC$");
                    message.put("subscribe_filter_symbol_id", subscribeFilterSymbolId);

                    this.send(message.toString());
                }

                @Override
                public void onMessage(String message) {
                    System.out.println(message);
                }

                @Override
                public void onClose(int code, String reason, boolean remote) {
                    System.out.println("WebSocket closed");
                }

                @Override
                public void onError(Exception ex) {
                    System.out.println("WebSocket error: " + ex.getMessage());
                }
            };

            socket.connect();
        } catch (URISyntaxException e) {
            e.printStackTrace();
        }
    }
}

This Java program:

  • Opens WebSocket connection
  • Subscribes to real-time data for BTC/USD trading on Bitstamp and Bitfinex (you may replace with your desired cryptocurrency pair)
  • Prints incoming real-time messages

Best Practices​

  • Handle connection issues: internet connections aren't always stable. Implement reconnection logic for robustness.
  • Handle rate limiting: even for WebSocket connections, CoinAPI has rate limits. Keep track of your message rate.
  • Secure your API Key: do not hardcode your API key. Make sure it is kept secure, consider using environment variables or secure config files which are not committed to your version control system.

Note: If subscribe_filter_symbol_id is ended with $ character then the exact match is used instead of prefix match.

You can check out more message examples and hello message parameters.

Troubleshooting​

If you're having issues, double-check the following:

  • The API key is correct and has the required permissions.
  • The WebSocket endpoint URL is correctly formatted.
  • The subscription message contains a valid symbol_id.
  • You have the correct libraries or dependencies installed, and you're using a supported version of the language.

Stay tuned for more tutorials on advanced uses of CoinAPI!