export SubscriptionFilter type, add comments to WebSocket functions a…

…nd allow to pass custom RPC URL on PushChain.initialize (#75)

* export SubscriptionFilter type and add comments to WebSocket functions

* add websocket example and allow RPCURL at PushChain.initialize for custom RPC URLs

examples/websocket/index.js

@@ -0,0 +1,41 @@
+import { PushChain } from '@pushchain/devnet';
+
+const pushChain = await PushChain.initialize();
+
+// Connect to the WebSocket server
+await pushChain.ws.connect();
+console.log('WebSocket connected.');
+
+// Define a custom filter to only subscribe to blocks that include transactions with the category 'CUSTOM:SAMPLE_TX'
+const customFilters = [{ type: 'CATEGORY', value: ['CUSTOM:SAMPLE_TX'] }];
+
+// Subscribe to block updates using the custom filter
+await pushChain.ws.subscribe(async (block) => {
+  console.log('New block received:', block.blockHash);
+
+  // Iterate over each transaction in the block
+  for (const tx of block.transactions) {
+    // Check if the transaction category matches our filter
+    if (tx.category === 'CUSTOM:SAMPLE_TX') {
+      console.log(
+        `Found transaction with hash ${tx.hash} and category ${tx.category}`
+      );
+
+      try {
+        // Fetch the full transaction details using the transaction hash
+        const txDetails = await pushChain.tx.get(tx.hash);
+
+        // Assume the fetched result contains a list of blocks and each block contains an array of transactions
+        if (txDetails.blocks && txDetails.blocks.length > 0) {
+          const fetchedTx = txDetails.blocks[0].transactions[0];
+          // Log the transaction data from the fetched transaction details
+          console.log('Transaction Data:', fetchedTx.data);
+        } else {
+          console.log(`No details found for transaction hash ${tx.hash}`);
+        }
+      } catch (error) {
+        console.error('Error fetching transaction details:', error);
+      }
+    }
+  }
+}, customFilters);