# All files / src/tools/shared errorClassifier.ts

98.14% Statements 53/54
96.07% Branches 49/51
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     /**
     * Error classification utilities for MCP tool error responses.
     *
     * Extracted from `errorHandler.ts` so that both `errorHandler.ts` and
     * `responseBuilder.ts` can import classification logic without creating
     * a circular dependency.
     *
     * ISMS Policy: SC-002 (Input Validation), AC-003 (Least Privilege)
     */

    import { z } from 'zod';
    import { ToolError } from './errors.js';
    import type { ErrorCode, ErrorCategory } from './errors.js';

    /**
     * Structured error classification result for MCP responses.
     */
    export interface ErrorClassification {
      errorCode: ErrorCode;
      errorCategory: ErrorCategory;
      httpStatus?: number;
      retryable: boolean;
    }

    /**
     * Extract an HTTP status code from an error via duck typing.
     * Works with both `APIError` (from `clients/ep/baseClient`) and any error
     * carrying a numeric `statusCode` property (avoids circular imports).
     */
    export function extractHttpStatus(error: unknown): number | undefined {
      if (
        error !== null &&
        error !== undefined &&
        typeof error === 'object' &&
        'statusCode' in error &&
        typeof (error as { statusCode?: unknown }).statusCode === 'number'
      ) {
        return (error as { statusCode: number }).statusCode;
      }
      return undefined;
    }

    /**
     * Classify an error into a structured error code, category, and retryability.
     *
     * Priority:
     * 1. If the error is a `ToolError` with explicit `errorCode` already set, use it.
     *    Retryability is derived from the error code's standard meaning (via
     *    {@link retryableForCode}) rather than `ToolError.isRetryable`, ensuring
     *    consistency even when callers set `errorCode` without a matching
     *    `isRetryable`. **Note:** `ToolError.isRetryable` is ignored when
     *    `errorCode` is present.
     * 2. Inspect the error and its cause chain for HTTP status codes (for example
     *    from `APIError`) and classify from the resolved status.
     * 3. If the error is a `ToolError` without an explicit `errorCode`, apply
     *    heuristic classification, including operation-based mappings
     *    (`validateInput` → `INVALID_PARAMS`) and message-based timeout detection.
     * 4. If the error is a `ZodError` (validation failure), classify as
     *    `INVALID_PARAMS` / `CLIENT_ERROR`.
     * 5. If the error is a plain `Error`, apply message-based timeout detection
     *    (`timed out` → `UPSTREAM_TIMEOUT`).
     * 6. Default to `INTERNAL_ERROR`.
     *
     * @param error - The caught error value
     * @returns Structured classification with code, category, httpStatus, and retryable flag
     */
    export function classifyError(error: unknown): ErrorClassification {
      if (error instanceof ToolError && error.errorCode !== undefined) {
        const code = error.errorCode;
        return {
          errorCode: code,
          errorCategory: error.errorCategory ?? categoryForCode(code),
          ...(error.httpStatus !== undefined ? { httpStatus: error.httpStatus } : {}),
          retryable: retryableForCode(code),
        };
      }

      const httpStatus = resolveHttpStatus(error);
      if (httpStatus !== undefined) {
        return classifyHttpStatus(httpStatus);
      }

      if (error instanceof ToolError) {
        return classifyToolErrorHeuristic(error);
      }

      return classifyPlainErrorHeuristic(error);
    }

    /**
     * Resolve HTTP status by walking the error's cause chain (duck-typed).
     * Stops after 10 levels or on a cycle to prevent infinite loops.
     * @internal
     */
    function resolveHttpStatus(error: unknown): number | undefined {
      const maxDepth = 10;
      const visited = new Set<object>();

      let current: unknown = error;
      for (let depth = 0; depth < maxDepth && current != null; depth += 1) {
        const status = extractHttpStatus(current);
        if (status !== undefined) {
          return status;
        }

        if (typeof current !== 'object') {
          return undefined;
        }
        if (visited.has(current)) {
          return undefined;
        }
        visited.add(current);

        current =
          current instanceof Error ? current.cause : undefined;
      }

      return undefined;
    }

    /**
     * Classify a ToolError using operation name and message heuristics.
     * @internal
     */
    function classifyToolErrorHeuristic(error: ToolError): ErrorClassification {
      if (error.operation === 'validateInput') {
        return { errorCode: 'INVALID_PARAMS', errorCategory: 'CLIENT_ERROR', retryable: false };
      }
      if (error.message.includes('timed out')) {
        return { errorCode: 'UPSTREAM_TIMEOUT', errorCategory: 'TIMEOUT', retryable: true };
      }
      return { errorCode: 'INTERNAL_ERROR', errorCategory: 'INTERNAL', retryable: error.isRetryable };
    }

    /**
     * Classify a plain Error (non-ToolError) using name and message heuristics.
     * Detects ZodError (validation) and timeout patterns before falling back to INTERNAL_ERROR.
     * @internal
     */
    function classifyPlainErrorHeuristic(error: unknown): ErrorClassification {
      if (error instanceof z.ZodError) {
        return { errorCode: 'INVALID_PARAMS', errorCategory: 'CLIENT_ERROR', retryable: false };
      }
      if (error instanceof Error && error.message.includes('timed out')) {
        return { errorCode: 'UPSTREAM_TIMEOUT', errorCategory: 'TIMEOUT', retryable: true };
      }
      return { errorCode: 'INTERNAL_ERROR', errorCategory: 'INTERNAL', retryable: false };
    }

    /**
     * Map an HTTP status code to a structured error classification.
     * @internal
     */
    function classifyHttpStatus(status: number): ErrorClassification {
      if (status === 404) {
        return {
          errorCode: 'UPSTREAM_404',
          errorCategory: 'DATA_UNAVAILABLE',
          httpStatus: status,
          retryable: false,
        };
      }
      if (status === 429) {
        return {
          errorCode: 'RATE_LIMITED',
          errorCategory: 'RATE_LIMIT',
          httpStatus: status,
          retryable: true,
        };
      }
      if (status === 408) {
        return {
          errorCode: 'UPSTREAM_TIMEOUT',
          errorCategory: 'TIMEOUT',
          httpStatus: status,
          retryable: true,
        };
      }
      if (status === 503) {
        return {
          errorCode: 'UPSTREAM_503',
          errorCategory: 'SERVER_ERROR',
          httpStatus: status,
          retryable: true,
        };
      }
      if (status >= 500) {
        return {
          errorCode: 'UPSTREAM_500',
          errorCategory: 'SERVER_ERROR',
          httpStatus: status,
          retryable: true,
        };
      }
      Eif (status >= 400) {
        return {
          errorCode: 'INVALID_PARAMS',
          errorCategory: 'CLIENT_ERROR',
          httpStatus: status,
          retryable: false,
        };
      }
      return {
        errorCode: 'INTERNAL_ERROR',
        errorCategory: 'INTERNAL',
        httpStatus: status,
        retryable: false,
      };
    }

    /**
     * Derive default category from error code.
     * @internal
     */
    function categoryForCode(code: ErrorCode): ErrorCategory {
      const map: Record<ErrorCode, ErrorCategory> = {
        UPSTREAM_404: 'DATA_UNAVAILABLE',
        UPSTREAM_500: 'SERVER_ERROR',
        UPSTREAM_503: 'SERVER_ERROR',
        UPSTREAM_TIMEOUT: 'TIMEOUT',
        RATE_LIMITED: 'RATE_LIMIT',
        INVALID_PARAMS: 'CLIENT_ERROR',
        FEED_FALLBACK: 'DATA_QUALITY',
        UNKNOWN_TOOL: 'CLIENT_ERROR',
        INTERNAL_ERROR: 'INTERNAL',
      };
      return map[code];
    }

    /**
     * Derive standard retryability from an error code.
     *
     * Ensures callers who set `errorCode` on a `ToolError` get consistent
     * retryable metadata without needing to also set `isRetryable`.
     * @internal
     */
    function retryableForCode(code: ErrorCode): boolean {
      const map: Record<ErrorCode, boolean> = {
        UPSTREAM_404: false,
        UPSTREAM_500: true,
        UPSTREAM_503: true,
        UPSTREAM_TIMEOUT: true,
        RATE_LIMITED: true,
        INVALID_PARAMS: false,
        FEED_FALLBACK: false,
        UNKNOWN_TOOL: false,
        INTERNAL_ERROR: false,
      };
      return map[code];
    }