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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 {
// 1. ToolError with explicit classification
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),
};
}
// 2. Extract HTTP status from error or its cause chain
const httpStatus = resolveHttpStatus(error);
if (httpStatus !== undefined) {
return classifyHttpStatus(httpStatus);
}
// 3. ToolError operation-based and message-based heuristics
if (error instanceof ToolError) {
return classifyToolErrorHeuristic(error);
}
// 4–6. Plain Error heuristics (ZodError, timeout, default)
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];
}
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