PromptTuner MCP

// Shared utilities for parsing JSON from LLM responses // Handles common wrapping patterns like ```json code blocks``` and surrounding text. import { LLM_ERROR_PREVIEW_CHARS, LLM_MAX_RESPONSE_LENGTH, } from '../config/constants.js'; import type { ErrorCodeType } from '../config/types.js'; import { logger, McpError } from './errors.js'; // Matches opening code block: ```json or ``` at start (with optional whitespace/newlines before) const CODE_BLOCK_START_RE = /^[\s\n]*```(?:json)?[\s\n]*/i; // Matches closing code block at end (with optional whitespace/newlines after) const CODE_BLOCK_END_RE = /[\s\n]*```[\s\n]*$/; /** * Strips code block markers from the start and end of a string. */ function stripCodeBlockMarkers(text: string): string { let result = text; // Remove opening code block marker const startMatch = CODE_BLOCK_START_RE.exec(result); if (startMatch) { result = result.slice(startMatch[0].length); } // Remove closing code block marker const endMatch = CODE_BLOCK_END_RE.exec(result); if (endMatch) { result = result.slice(0, result.length - endMatch[0].length); } return result.trim(); } export function parseJsonFromLlmResponse<T>( llmResponseText: string, parse: (value: unknown) => T, options: { errorCode: ErrorCodeType; maxPreviewChars?: number; maxInputLength?: number; debugLabel?: string; } ): T { // Input validation: prevent DoS attacks with excessively large responses const maxInputLength = options.maxInputLength ?? LLM_MAX_RESPONSE_LENGTH; if (llmResponseText.length > maxInputLength) { throw new McpError( options.errorCode, `LLM response too large: ${llmResponseText.length} chars (max: ${maxInputLength})`, undefined, { responseLength: llmResponseText.length, maxLength: maxInputLength } ); } const jsonStr = llmResponseText.trim(); const maxPreviewChars = options.maxPreviewChars ?? LLM_ERROR_PREVIEW_CHARS; // Try raw parse first try { const parsed: unknown = JSON.parse(jsonStr); const result = parse(parsed); if (options.debugLabel) { logger.debug(`${options.debugLabel}: parsed JSON successfully (raw)`); } return result; } catch (error) { logger.debug( `${options.debugLabel ?? 'JSON parse'}: raw parse failed: ${error instanceof Error ? error.message : String(error)}` ); } // Try with code block markers stripped try { const stripped = stripCodeBlockMarkers(jsonStr); const parsed: unknown = JSON.parse(stripped); const result = parse(parsed); if (options.debugLabel) { logger.debug( `${options.debugLabel}: parsed JSON successfully (stripped markers)` ); } return result; } catch (error) { logger.debug( `${options.debugLabel ?? 'JSON parse'}: stripped parse failed: ${error instanceof Error ? error.message : String(error)}` ); } // Both strategies failed - throw error with helpful context const debugEnabled = process.env.DEBUG === 'true'; const contextLabel = options.debugLabel ?? 'LLM response'; throw new McpError( options.errorCode, `Failed to parse ${contextLabel} as JSON`, undefined, { strategiesAttempted: ['raw', 'codeblock-stripped'], ...(debugEnabled && { rawResponse: llmResponseText.slice(0, maxPreviewChars), }), } ); }