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/**
* @license
* Copyright 2025 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
import { createHash } from 'crypto';
import { GeminiEventType, ServerGeminiStreamEvent } from '../core/turn.js';
import { logLoopDetected } from '../telemetry/loggers.js';
import { LoopDetectedEvent, LoopType } from '../telemetry/types.js';
import { Config } from '../config/config.js';
const TOOL_CALL_LOOP_THRESHOLD = 5;
const CONTENT_LOOP_THRESHOLD = 10;
const SENTENCE_ENDING_PUNCTUATION_REGEX = /[.!?]+(?=\s|$)/;
/**
* Service for detecting and preventing infinite loops in AI responses.
* Monitors tool call repetitions and content sentence repetitions.
*/
export class LoopDetectionService {
// Tool call tracking
private lastToolCallKey: string | null = null;
private toolCallRepetitionCount: number = 0;
// Content streaming tracking
private lastRepeatedSentence: string = '';
private sentenceRepetitionCount: number = 0;
private partialContent: string = '';
private config: Config;
constructor(config: Config) {
this.config = config;
}
private getToolCallKey(toolCall: { name: string; args: object }): string {
const argsString = JSON.stringify(toolCall.args);
const keyString = `${toolCall.name}:${argsString}`;
return createHash('sha256').update(keyString).digest('hex');
}
/**
* Processes a stream event and checks for loop conditions.
* @param event - The stream event to process
* @returns true if a loop is detected, false otherwise
*/
addAndCheck(event: ServerGeminiStreamEvent): boolean {
switch (event.type) {
case GeminiEventType.ToolCallRequest:
// content chanting only happens in one single stream, reset if there
// is a tool call in between
this.resetSentenceCount();
return this.checkToolCallLoop(event.value);
case GeminiEventType.Content:
return this.checkContentLoop(event.value);
default:
this.reset();
return false;
}
}
private checkToolCallLoop(toolCall: { name: string; args: object }): boolean {
const key = this.getToolCallKey(toolCall);
if (this.lastToolCallKey === key) {
this.toolCallRepetitionCount++;
} else {
this.lastToolCallKey = key;
this.toolCallRepetitionCount = 1;
}
if (this.toolCallRepetitionCount >= TOOL_CALL_LOOP_THRESHOLD) {
logLoopDetected(
this.config,
new LoopDetectedEvent(LoopType.CONSECUTIVE_IDENTICAL_TOOL_CALLS),
);
return true;
}
return false;
}
private checkContentLoop(content: string): boolean {
this.partialContent += content;
if (!SENTENCE_ENDING_PUNCTUATION_REGEX.test(this.partialContent)) {
return false;
}
const completeSentences =
this.partialContent.match(/[^.!?]+[.!?]+(?=\s|$)/g) || [];
if (completeSentences.length === 0) {
return false;
}
const lastSentence = completeSentences[completeSentences.length - 1];
const lastCompleteIndex = this.partialContent.lastIndexOf(lastSentence);
const endOfLastSentence = lastCompleteIndex + lastSentence.length;
this.partialContent = this.partialContent.slice(endOfLastSentence);
for (const sentence of completeSentences) {
const trimmedSentence = sentence.trim();
if (trimmedSentence === '') {
continue;
}
if (this.lastRepeatedSentence === trimmedSentence) {
this.sentenceRepetitionCount++;
} else {
this.lastRepeatedSentence = trimmedSentence;
this.sentenceRepetitionCount = 1;
}
if (this.sentenceRepetitionCount >= CONTENT_LOOP_THRESHOLD) {
logLoopDetected(
this.config,
new LoopDetectedEvent(LoopType.CHANTING_IDENTICAL_SENTENCES),
);
return true;
}
}
return false;
}
/**
* Resets all loop detection state.
*/
reset(): void {
this.resetToolCallCount();
this.resetSentenceCount();
}
private resetToolCallCount(): void {
this.lastToolCallKey = null;
this.toolCallRepetitionCount = 0;
}
private resetSentenceCount(): void {
this.lastRepeatedSentence = '';
this.sentenceRepetitionCount = 0;
this.partialContent = '';
}
}
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