feat: Add max pending txs to bot

Adds a config to txs bot so it does not send more txs if there are more
than N pending txs. Adds a requirement for an AZTEC_NODE_URL to be
passed into the bot runner.

yarn-project/aztec-node/src/aztec-node/server.ts

@@ -385,6 +385,10 @@ export class AztecNodeService implements AztecNode {
     return Promise.resolve(this.p2pClient!.getTxs('pending'));
   }
 
+  public getPendingTxCount() {
+    return Promise.resolve(this.p2pClient!.getTxs('pending').length);
+  }
+
   /**
    * Method to retrieve a single tx from the mempool or unfinalised chain.
    * @param txHash - The transaction hash to return.

yarn-project/aztec/src/cli/cmds/start_bot.ts

@@ -1,5 +1,5 @@
 import { type BotConfig, BotRunner, botConfigMappings, createBotRunnerRpcServer } from '@aztec/bot';
-import { type PXE } from '@aztec/circuit-types';
+import { type AztecNode, type PXE } from '@aztec/circuit-types';
 import { type ServerList } from '@aztec/foundation/json-rpc/server';
 import { type LogFn } from '@aztec/foundation/log';
 
@@ -35,11 +35,11 @@ export function addBot(
   options: any,
   services: ServerList,
   signalHandlers: (() => Promise<void>)[],
-  deps: { pxe?: PXE } = {},
+  deps: { pxe?: PXE; node?: AztecNode } = {},
 ) {
   const config = extractRelevantOptions<BotConfig>(options, botConfigMappings);
 
-  const botRunner = new BotRunner(config, { pxe: deps.pxe });
+  const botRunner = new BotRunner(config, deps);
   const botServer = createBotRunnerRpcServer(botRunner);
   if (!config.noStart) {
     void botRunner.start(); // Do not block since bot setup takes time

yarn-project/aztec/src/cli/cmds/start_node.ts

@@ -113,7 +113,7 @@ export const startNode = async (
   // Add a txs bot if requested
   if (options.bot) {
     const { addBot } = await import('./start_bot.js');
-    await addBot(options, services, signalHandlers, { pxe });
+    await addBot(options, services, signalHandlers, { pxe, node });
   }
 
   return services;

yarn-project/bot/src/config.ts

@@ -8,6 +8,8 @@ import {
 } from '@aztec/foundation/config';
 
 export type BotConfig = {
+  /** The URL to the Aztec node to check for tx pool status. */
+  nodeUrl: string | undefined;
   /** URL to the PXE for sending txs, or undefined if an in-proc PXE is used. */
   pxeUrl: string | undefined;
   /** Signing private key for the sender account. */
@@ -30,9 +32,15 @@ export type BotConfig = {
   txMinedWaitSeconds: number;
   /** Don't wait for transfer transactions. */
   noWaitForTransfers: boolean;
+  /** Do not send a tx if the node's tx pool already has this many pending txs. */
+  maxPendingTxs: number;
 };
 
 export const botConfigMappings: ConfigMappingsType<BotConfig> = {
+  nodeUrl: {
+    env: 'AZTEC_NODE_URL',
+    description: 'The URL to the Aztec node to check for tx pool status.',
+  },
   pxeUrl: {
     env: 'BOT_PXE_URL',
     description: 'URL to the PXE for sending txs, or undefined if an in-proc PXE is used.',
@@ -91,6 +99,11 @@ export const botConfigMappings: ConfigMappingsType<BotConfig> = {
     description: "Don't wait for transfer transactions.",
     ...booleanConfigHelper(),
   },
+  maxPendingTxs: {
+    env: 'BOT_MAX_PENDING_TXS',
+    description: "Do not send a tx if the node's tx pool already has this many pending txs.",
+    ...numberConfigHelper(128),
+  },
 };
 
 export function getBotConfigFromEnv(): BotConfig {

yarn-project/bot/src/runner.ts

@@ -1,4 +1,4 @@
-import { type PXE, createDebugLogger } from '@aztec/aztec.js';
+import { type AztecNode, type PXE, createAztecNodeClient, createDebugLogger } from '@aztec/aztec.js';
 import { RunningPromise } from '@aztec/foundation/running-promise';
 
 import { Bot } from './bot.js';
@@ -8,11 +8,16 @@ export class BotRunner {
   private log = createDebugLogger('aztec:bot');
   private bot?: Promise<Bot>;
   private pxe?: PXE;
+  private node: AztecNode;
   private runningPromise: RunningPromise;
 
-  public constructor(private config: BotConfig, dependencies: { pxe?: PXE } = {}) {
+  public constructor(private config: BotConfig, dependencies: { pxe?: PXE; node?: AztecNode }) {
     this.pxe = dependencies.pxe;
-    this.runningPromise = new RunningPromise(() => this.#safeRun(), config.txIntervalSeconds * 1000);
+    if (!dependencies.node && !config.nodeUrl) {
+      throw new Error(`Missing node URL in config or dependencies`);
+    }
+    this.node = dependencies.node ?? createAztecNodeClient(config.nodeUrl!);
+    this.runningPromise = new RunningPromise(() => this.#work(), config.txIntervalSeconds * 1000);
   }
 
   /** Initializes the bot if needed. Blocks until the bot setup is finished. */
@@ -112,7 +117,15 @@ export class BotRunner {
     }
   }
 
-  async #safeRun() {
+  async #work() {
+    if (this.config.maxPendingTxs > 0) {
+      const pendingTxs = await this.node.getPendingTxs();
+      if (pendingTxs.length >= this.config.maxPendingTxs) {
+        this.log.verbose(`Not sending bot tx since node has ${pendingTxs.length} pending txs`);
+        return;
+      }
+    }
+
     try {
       await this.run();
     } catch (err) {

yarn-project/circuit-types/src/interfaces/aztec-node.ts

@@ -283,6 +283,12 @@ export interface AztecNode {
    */
   getPendingTxs(): Promise<Tx[]>;
 
+  /**
+   * Retrieves the number of pending txs
+   * @returns The number of pending txs.
+   */
+  getPendingTxCount(): Promise<number>;
+
   /**
    * Method to retrieve a single pending tx.
    * @param txHash - The transaction hash to return.

yarn-project/foundation/src/config/env_var.ts

@@ -89,6 +89,7 @@ export type EnvVar =
   | 'BOT_NO_START'
   | 'BOT_TX_MINED_WAIT_SECONDS'
   | 'BOT_NO_WAIT_FOR_TRANSFERS'
+  | 'BOT_MAX_PENDING_TXS'
   | 'PXE_BLOCK_POLLING_INTERVAL_MS'
   | 'PXE_L2_STARTING_BLOCK'
   | 'PXE_DATA_DIRECTORY'