feat: add support for getFirstAvailableBlock method

web3.js/module.d.ts

@@ -219,6 +219,7 @@ declare module '@solana/web3.js' {
     getBalance(publicKey: PublicKey, commitment?: Commitment): Promise<number>;
     getBlockTime(slot: number): Promise<number | null>;
     getMinimumLedgerSlot(): Promise<number>;
+    getFirstAvailableBlock(): Promise<number>;
     getSupply(commitment?: Commitment): Promise<RpcResponseAndContext<Supply>>;
     getLargestAccounts(
       config?: GetLargestAccountsConfig,

web3.js/module.flow.js

@@ -232,6 +232,7 @@ declare module '@solana/web3.js' {
     getBalance(publicKey: PublicKey, commitment: ?Commitment): Promise<number>;
     getBlockTime(slot: number): Promise<number | null>;
     getMinimumLedgerSlot(): Promise<number>;
+    getFirstAvailableBlock(): Promise<number>;
     getSupply(commitment: ?Commitment): Promise<RpcResponseAndContext<Supply>>;
     getLargestAccounts(
       config: ?GetLargestAccountsConfig,

web3.js/src/connection.js

@@ -417,9 +417,9 @@ const GetBlockTimeRpcResult = struct({
 });
 
 /**
- * Expected JSON RPC response for the "minimumLedgerSlot" message
+ * Expected JSON RPC response for the "minimumLedgerSlot" and "getFirstAvailableBlock" messages
  */
-const MinimumLedgerSlotRpcResult = struct({
+const SlotRpcResult = struct({
   jsonrpc: struct.literal('2.0'),
   id: 'string',
   error: 'any?',
@@ -1081,7 +1081,7 @@ export class Connection {
    */
   async getMinimumLedgerSlot(): Promise<number> {
     const unsafeRes = await this._rpcRequest('minimumLedgerSlot', []);
-    const res = MinimumLedgerSlotRpcResult(unsafeRes);
+    const res = SlotRpcResult(unsafeRes);
     if (res.error) {
       throw new Error(
         'failed to get minimum ledger slot: ' + res.error.message,
@@ -1091,6 +1091,21 @@ export class Connection {
     return res.result;
   }
 
+  /**
+   * Fetch the slot of the lowest confirmed block that has not been purged from the ledger
+   */
+  async getFirstAvailableBlock(): Promise<number> {
+    const unsafeRes = await this._rpcRequest('getFirstAvailableBlock', []);
+    const res = SlotRpcResult(unsafeRes);
+    if (res.error) {
+      throw new Error(
+        'failed to get first available block: ' + res.error.message,
+      );
+    }
+    assert(typeof res.result !== 'undefined');
+    return res.result;
+  }
+
   /**
    * Fetch information about the current supply
    */

web3.js/test/connection.test.js

@@ -1109,6 +1109,25 @@ test('get minimum ledger slot', async () => {
   expect(minimumLedgerSlot).toBeGreaterThanOrEqual(0);
 });
 
+test('get first available block', async () => {
+  const connection = new Connection(url);
+
+  mockRpc.push([
+    url,
+    {
+      method: 'getFirstAvailableBlock',
+      params: [],
+    },
+    {
+      error: null,
+      result: 0,
+    },
+  ]);
+
+  const firstAvailableBlock = await connection.getFirstAvailableBlock();
+  expect(firstAvailableBlock).toBeGreaterThanOrEqual(0);
+});
+
 test('get supply', async () => {
   const connection = new Connection(url);