Resolve "feat(blockchain): Add method to get the current blockheight"

packages/stack/src/blockchain/base-blockchain.ts

@@ -5,6 +5,7 @@ import {
   type BlockchainUTXOs,
   type BlockchainTransactions,
   type BlockchainUnsubscribeCallback,
+  type BlockchainChainTip,
 } from './types.js';
 
 import { BlockHeader, Transaction, TransactionHash } from '@xocash/primitives';
@@ -89,6 +90,14 @@ export abstract class BaseBlockchain<
    */
   abstract fetchBlockHeader(blockHeight: number): Promise<BlockHeader>;
 
+  /**
+   * Retrieves the current chain tip block.
+   *
+   * @returns {Promise<BlockchainChainTip>} A promise that resolves with the current chain tip
+   * @throws {Error} If the chain tip cannot be retrieved
+   */
+  abstract fetchChainTip(): Promise<BlockchainChainTip>;
+
   /**
    * Retrieves detailed information about a specific transaction.
    *

packages/stack/src/blockchain/blockchain-electrum.ts

@@ -32,6 +32,7 @@ import {
   fetchHistory,
   fetchTransaction,
   subscribeToBlockheaderUpdates,
+  fetchCurrentChainTip,
 } from '@electrum-cash/protocol';
 
 import { hexToBin } from '@bitauth/libauth';
@@ -181,8 +182,11 @@ export class BlockchainElectrum extends BaseBlockchain<
         this.handleTransactionStatusUpdates.bind(this),
       );
 
-      // Subscribe to block header notifications.
-      await subscribeToBlockheaderUpdates(this.electrumClient);
+      // Subscribe to block header notifications and fetch the chain tip.
+      await Promise.all([
+        subscribeToBlockheaderUpdates(this.electrumClient),
+        this.fetchChainTip(),
+      ]);
 
       // Return to prevent further execution.
       return;
@@ -338,6 +342,37 @@ export class BlockchainElectrum extends BaseBlockchain<
     return blockHeader;
   }
 
+  // TODO: ElectrumClient provides a chainHeight property that is populated after a `blockchain.headers.subscribe` call.
+  //       We may be able to leverage this side-effect to avoid fetching the chain tip.
+  async fetchChainTip() {
+    // Wait for connection to be established before attempting to subscribe.
+    // TODO: Consider doing this at a higher level.
+    if (!this.isConnected) {
+      await this.waitFor('isConnectedUpdated', (isConnected) => isConnected);
+    }
+
+    // If we don't currently have a block height, fetch the current chain tip.
+    // NOTE: We don't use our cache here because the key will be the same and so on-boot, we will have a stale value.
+    if (!this.blockHeight) {
+      const chainTip = await fetchCurrentChainTip(this.electrumClient);
+
+      this.blockHeight = chainTip.height;
+    }
+
+    // Get the block header
+    // NOTE: If we didn't have the block height, we are performing double-fetch here
+    const blockHeader = await this.fetchBlockHeader(this.blockHeight);
+
+    // Create a chain tip object.
+    const chainTip = {
+      height: this.blockHeight,
+      blockHeader: blockHeader,
+    };
+
+    // Return the chain tip.
+    return chainTip;
+  }
+
   async broadcastTransaction(
     tx: Transaction | Uint8Array | string,
     opts: BroadcastOpts = { timeoutMs: 10_000, waitUntilSeen: true },
@@ -546,13 +581,19 @@ export class BlockchainElectrum extends BaseBlockchain<
     return response;
   }
 
-  protected handleNewBlockchainHeaders(
+  protected async handleNewBlockchainHeaders(
     notification: HeadersSubscribeNotification,
   ) {
-    // Extract height from the first param.
+    // Extract height and hex from the first param.
     // NOTE: This is an object.
     //       https://electrum-cash-protocol.readthedocs.io/en/latest/protocol-methods.html#blockchain-headers-subscribe
-    const { height } = notification.params[0];
+    const { height, hex } = notification.params[0];
+
+    // Decode the raw data into our Block Header primitive.
+    const blockHeader = BlockHeader.fromHex(hex);
+
+    // Update the cache with the new block header.
+    await this.store.set(`blockHeader.${height}`, blockHeader.toRaw());
 
     // Assign the block height.
     this.blockHeight = height;

packages/stack/src/blockchain/blockchain-inmemory.ts

@@ -5,6 +5,7 @@ import {
   type BlockchainTransactions,
   type BlockchainUTXO,
   type BlockchainUTXOs,
+  type BlockchainChainTip,
 } from './types.js';
 
 import {
@@ -103,6 +104,12 @@ export class BlockchainInMemory extends BaseBlockchain {
     return blockHeader;
   }
 
+  // TODO: Implement a method for fetching the chain tip.
+  //       This is a placeholder for now.
+  async fetchChainTip(): Promise<BlockchainChainTip> {
+    throw new Error('Not implemented yet');
+  }
+
   async broadcastTransaction(
     tx: Transaction | Uint8Array | string,
     opts: { skipValidation: boolean } = { skipValidation: false },

packages/stack/src/blockchain/types.ts

@@ -1,4 +1,10 @@
-import { Transaction, TransactionHash, UTXO, ExtMap } from '@xocash/primitives';
+import {
+  Transaction,
+  TransactionHash,
+  UTXO,
+  ExtMap,
+  BlockHeader,
+} from '@xocash/primitives';
 
 export type BlockchainCallback<Payload = undefined> = (
   /** The transaction hash, address, lockscript or scriptHash of this subscription. */
@@ -43,3 +49,8 @@ export type BlockHeightPayload = {
   type: 'block-height';
   height: number | null;
 };
+
+export type BlockchainChainTip = {
+  height: number;
+  blockHeader: BlockHeader;
+};