api-utils

name	api-utils
description	API reference for all utilities exported from `@cyanheads/mcp-ts-core/utils`. Use when looking up utility method signatures, options, peer dependencies, or usage patterns.
metadata	{"author":"cyanheads","version":"2.9","audience":"external","type":"reference"}

Overview

Utility exports from @cyanheads/mcp-ts-core/utils. Utilities with complex APIs have dedicated reference files; simpler utilities are documented inline below.

Tier 3 = optional peer dependency. Install as needed (e.g., bun add js-yaml). All Tier 3 methods are async (lazy-load deps on first call).

Context parameters. Every helper below that takes a context accepts the handler Context as well as a RequestContext bag — pass ctx straight through, no slicing.

References

Reference	Path	Covers
Formatting	references/formatting.md	markdown(), MarkdownBuilder, diffFormatter, tableFormatter, treeFormatter — builder patterns, option types, style variants, usage examples
Parsing	references/parsing.md	yamlParser, xmlParser, csvParser, jsonParser, pdfParser, dateParser, frontmatterParser — method signatures, option types, peer deps, Allow flags, PDF workflows
Security	references/security.md	sanitization, RateLimiter, IdGenerator — config types, method details, sensitive fields, usage examples

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@cyanheads/mcp-ts-core/utils — network

Export	API	Notes
fetchWithTimeout	(url, timeoutMs, context, options?: FetchWithTimeoutOptions) -> Promise<Response>	Wraps fetch with AbortController timeout. timeoutMs bounds the whole exchange: on a 2xx carrying a body the returned Response is a passthrough wrapper that keeps the deadline armed until the body closes, errors, or is cancelled, so a stalled stream rejects the caller's .text()/.json() with the same Timeout error the header phase raises. status, statusText, headers, url, redirected, and type carry across the wrapper; the original body is locked by it, and bodyless/null-body responses (HEAD, 204/205/304) come back untouched. FetchWithTimeoutOptions extends RequestInit (minus signal) and adds rejectPrivateIPs?: boolean, expectedStatuses?: number[] (listed non-2xx statuses logged at debug not error, still thrown), errorBodyLimit?: number (bytes of a non-2xx body kept, default 500), and signal?: AbortSignal (external cancellation — an abort on it throws RequestCancelled (-32011), logged at info and outside withRetry's transient set, since the caller is gone and no retry can reach them). On a non-2xx, error.data carries status/body plus the legacy statusCode/responseBody aliases (identical values; consolidating in a future major); a body over errorBodyLimit is captured from both ends — 40% head, 60% tail, joined by …[N bytes elided]… — so a diagnostic behind a boilerplate preamble survives the cap, while a body still streaming at the 16 KiB scan ceiling stays head-only with a trailing …. SSRF guard (best-effort, not hard isolation): blocks RFC 1918, loopback, link-local, CGNAT, cloud metadata. DNS validation on Node, Bun, and Cloudflare Workers under nodejs_compat; hostname-only fallback otherwise. Both resolvers are queried — resolve4/resolve6 (c-ares) and lookup (the system resolver, which is what reads /etc/hosts, split DNS, and NSS modules) — and a non-global answer from either rejects. Runtimes differ in which resolver the connection uses (Bun 1.4 moved net.connect() on Linux to getaddrinfo while leaving dns.resolve*() on c-ares), so checking one alone leaves a name the other can see unguarded; each probe settles independently, so a resolver absent from the runtime is skipped rather than fatal. Manual redirect following (max 5) with per-hop SSRF check. DNS rebinding / TOCTOU gap — the validation lookup and fetch's own resolution are independent; pair with egress controls or a DNS-pinning fetch proxy for strong isolation. Error/log redaction: URLs written into thrown errors and log lines are reduced to origin + pathname — the query string (where API keys commonly ride: ?api-key=…, ?api_key=…) never reaches the client or the logs. The actual request still uses the full URL.
withRetry	<T>(fn: () => Promise<T>, options?: RetryOptions) -> Promise<T>	Executes fn with exponential backoff. Retries on transient errors (ServiceUnavailable, Timeout, RateLimited); non-transient errors fail immediately. Honors an upstream Retry-After on data.retryAfter (delta-seconds or HTTP-date) over exponential backoff, capped at maxDelayMs; a requested wait beyond the cap fails fast rather than sleeping. On exhaustion, enriches the final error with attempt count in message and data.retryAttempts. Place the retry boundary around the full pipeline (fetch + parse), not just the network call. RetryOptions: maxRetries (default 3), baseDelayMs (default 1000), maxDelayMs (default 30000), jitter (default 0.25), operation (log label), context (RequestContext), signal (AbortSignal), isTransient (custom predicate).
httpErrorFromResponse	(response: Response, options?: HttpErrorFromResponseOptions) -> Promise<McpError>	Maps an HTTP Response to a properly classified McpError — full status table including 401/403/408/422/429/5xx, body capture (truncated), retry-after header, optional cause. error.data carries status/body plus the legacy statusCode/responseBody aliases (identical values), so a consumer can classify either helper's error without knowing which raised it. Use this instead of hand-rolling if (status === 429) ... ladders. Reads the response body — clone() first if you need it elsewhere. HttpErrorFromResponseOptions: service? (logical name in message, e.g. 'NCBI'), captureBody? (default true), bodyLimit? (default 500), data? (extra fields merged into error.data), cause?, codeOverride? (per-status mapping override). Pairs naturally with withRetry — both classify codes the same way. A 501 also carries data.retryable: false, so retry fails it fast instead of re-asking for a method the upstream does not implement.
httpStatusToErrorCode	(status: number) -> JsonRpcErrorCode | undefined	Sync status → code lookup. Returns undefined for 1xx/2xx/3xx. Use when you need just the code without a Response object handy. No status maps to InternalError — that code means this server failed, which a remote status cannot establish; every 5xx is ServiceUnavailable (or Timeout for 504) and so picks up withRetry's default transient policy.

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@cyanheads/mcp-ts-core/utils — pagination

Export	API	Notes
extractCursor	(params?) -> string | undefined	Extracts opaque cursor string from MCP request params. Checks params.cursor then params._meta.cursor. Returns undefined when no cursor is present. Does not decode.
paginateArray	<T>(items, cursorStr, defaultPageSize, maxPageSize, context: RequestContext) -> PaginatedResult<T>	Decodes cursor, slices array, returns { items, nextCursor?, totalCount }. nextCursor omitted on last page. Throws McpError(InvalidParams) on invalid cursor.
encodeCursor	(state: PaginationState) -> string	Encodes { offset, limit, ...extra } to opaque base64url string.
decodeCursor	(cursor, context: RequestContext) -> PaginationState	Decodes opaque base64url cursor. Throws McpError(InvalidParams) if malformed.

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@cyanheads/mcp-ts-core/utils — runtime

Export	API	Notes
runtimeCaps	RuntimeCapabilities object	Snapshot at import time. Fields: isNode, isBun, isWorkerLike, isBrowserLike, hasProcess, hasBuffer, hasTextEncoder, hasPerformanceNow. All booleans. Never throws.

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@cyanheads/mcp-ts-core/utils — scheduling

Export	API	Notes
schedulerService	.schedule(id, schedule, taskFunction, description) -> Promise<Job> .start(id) -> void .stop(id) -> void .remove(id) -> void .listJobs() -> Job[]	Async schedule() — Tier 3 peer: node-cron. Node-only (throws ConfigurationError in Workers). Jobs start in stopped state; call start(id) to activate. Skips overlapping executions. Each tick gets fresh RequestContext. Job: { id, schedule, description, isRunning, task }. taskFunction: (context: RequestContext) => void | Promise<void>.

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@cyanheads/mcp-ts-core/utils — types

The utils export includes two type guards. The full set of guards lives in the internal module and is not part of the public API.

Export	Signature	Notes
isErrorWithCode	(error: unknown) -> error is Error & { code: unknown }	Type guard — true when value is an Error instance with a code property
isRecord	(value: unknown) -> value is Record<string, unknown>	Type guard for plain objects (non-null, non-array)

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@cyanheads/mcp-ts-core/utils — logger

Export	API	Notes
Logger	Class	The Logger class itself. Use Logger.getInstance() if needed; most consumers use the logger singleton.
logger	Logger instance (wraps Pino). .debug(msg, ctx?) .info(msg, ctx?) .notice(msg, ctx?) .warning(msg, ctx?) .error(msg, errorOrCtx, ctx?) .crit(msg, errorOrCtx, ctx?) .alert(msg, errorOrCtx, ctx?) .emerg(msg, errorOrCtx, ctx?) .fatal(msg, errorOrCtx, ctx?)	Global structured logger. Use ctx.log in handlers instead. logger is for lifecycle/background contexts (startup, shutdown, setup()). Auto-redacts sensitive fields. Records logged before the framework initializes the logger — anything in setup() — are held in a 250-record buffer and replayed once the sinks exist, filtered against the level the logger starts with. Note: .error() and higher accept (msg, Error, ctx?) or (msg, ctx?) — the second arg is overloaded. .fatal() is an alias for .emerg(). Full RFC 5424 severity set.
McpLogLevel	Type	Log level union type for typing level variables.

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@cyanheads/mcp-ts-core/utils — requestContext

Export	API	Notes
requestContextService	.createRequestContext(params?) -> RequestContext .withAuthInfo(authInfo, parentContext?) -> RequestContext	Creates tracing context with requestId, timestamp, traceId, spanId, tenantId, auth. Internal — most consumers use ctx from handlers.
RequestContext	Type: { requestId, timestamp, operation?, traceId?, spanId?, tenantId?, auth?, [key: string]: unknown }	Request tracing metadata.
CreateRequestContextParams	Type: { parentContext?, additionalContext?, operation?, [key: string]: unknown }	Params accepted by createRequestContext. Named fields get special merge handling; other properties spread directly onto the context.
AuthContext	Type: { clientId, scopes, sub, token, tenantId?, [key: string]: unknown }	Structured auth data attached to RequestContext.auth after token verification.

createRequestContext merge order (later wins, except requestId/timestamp): parentContext → spread rest params → additionalContext (strips requestId/timestamp) → pinned requestId/timestamp → resolved tenantId → operation → OTel traceId/spanId.

withAuthInfo(authInfo, parentContext?) builds a context and populates auth from a validated token. Does not write to AsyncLocalStorage — ALS propagation is the auth middleware's responsibility.

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@cyanheads/mcp-ts-core/utils — errorHandler

Export	API	Notes
ErrorHandler	.tryCatch<T>(fn, opts) -> Promise<T> .handleError(error, opts) -> Error .classifyOnly(error) -> { code, message, data? } .determineErrorCode(error) -> JsonRpcErrorCode .mapError(error, mappings, defaultFactory?) -> T | Error .formatError(error) -> Record<string, unknown>	Service-level error handling. tryCatch wraps async or sync fn, logs via handleError, and always rethrows. No .tryCatchSync(). Use in services, NOT in tool handlers (those throw raw McpError). tryCatch accepts Omit<ErrorHandlerOptions, 'rethrow'> — required: operation. Optional: context, errorCode, input, includeStack, critical, errorMapper. handleError accepts the full ErrorHandlerOptions including rethrow.

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@cyanheads/mcp-ts-core/utils — encoding

Cross-platform encoding utilities. No peer deps.

Export	Signature	Notes
arrayBufferToBase64	(buffer: ArrayBuffer) -> string	Encodes an ArrayBuffer to base64. Uses Buffer on Node/Bun; chunked btoa on Workers/browsers to avoid stack overflow on large buffers.
stringToBase64	(str: string) -> string	UTF-8 string → base64. Uses Buffer.from(str, 'utf-8') on Node/Bun; TextEncoder + arrayBufferToBase64 on Workers.
base64ToString	(base64: string) -> string	base64 → UTF-8 string. Uses Buffer on Node/Bun; atob + TextDecoder on Workers. Throws if input is not valid base64.

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@cyanheads/mcp-ts-core/utils — token counting

Dependency-free heuristic token estimation. No native/WASM deps.

Export	Signature	Notes
countTokens	async (text: string, context?: RequestContext, model?: string) -> Promise<number>	Estimates tokens in a plain string. Normalizes whitespace, divides by charsPerToken. Returns 0 for empty/whitespace input. Falls back to gpt-4o heuristics when model is omitted or unrecognized.
countChatTokens	async (messages: ReadonlyArray<ChatMessage>, context?: RequestContext, model?: string) -> Promise<number>	Estimates total tokens for a chat message array. Adds per-message overhead (tokensPerMessage), counts string/array content, name, assistant tool_calls, and tool tool_call_id. Adds replyPrimer once.
ChatMessage	Type	{ role: string, content: string | Array<{type, text?, ...}> | null, name?, tool_calls?, tool_call_id? } — provider-agnostic chat message shape.
ModelHeuristics	Interface	{ charsPerToken, replyPrimer, tokensPerMessage, tokensPerName } — heuristic parameters; built-in entries for gpt-4o, gpt-4o-mini, default.

Both functions throw McpError(InternalError) only on unexpected heuristic failure.

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@cyanheads/mcp-ts-core/utils — Telemetry

Helper API only. For the catalog of what the framework auto-emits (span names, metric names, attributes, completion log fields, env config, runtime support, cardinality rules), see the api-telemetry skill.

telemetry/instrumentation

Export	Signature	Notes
initializeOpenTelemetry	() -> Promise<void>	Idempotent. Initializes NodeSDK with OTLP trace + metrics exporters, TraceIdRatioBasedSampler, HTTP instrumentation, and Pino log injection. No-ops when OTEL_ENABLED=false or in Worker/Edge runtimes where NodeSDK is unavailable. Safe to call multiple times.
shutdownOpenTelemetry	(timeoutMs?: number) -> Promise<void>	Gracefully flushes and shuts down the SDK. timeoutMs defaults to 5000. Resets internal state so the next initializeOpenTelemetry() call can reinitialize. No-op when SDK was never started.
sdk	NodeSDK | null	The live SDK instance, or null when telemetry is disabled, in a Worker runtime, or after shutdown.

telemetry/metrics

Export	Signature	Notes
getMeter	(name?: string) -> Meter	Returns an OTel Meter. Defaults to service name + version from config.
createCounter	(name: string, description: string, unit?: string) -> Counter	Monotonically increasing counter. unit defaults to '1'.
createUpDownCounter	(name: string, description: string, unit?: string) -> UpDownCounter	Bidirectional counter (active connections, queue depth, etc.). unit defaults to '1'.
createHistogram	(name: string, description: string, unit?: string) -> Histogram	Distribution recording (latency, sizes). unit optional.
createObservableGauge	(name: string, description: string, callback: () => Promise<number> | number, unit?: string) -> ObservableGauge	Polled gauge. callback is registered via addCallback; invoked on each SDK collection cycle. unit optional. For other observable instrument types, use getMeter() directly.

telemetry/trace

Export	Signature	Notes
withSpan	async <T>(operationName: string, fn: (span: Span) => Promise<T>, attributes?: Record<string, string | number | boolean>) -> Promise<T>	Creates an active span, calls fn(span), sets OK on success or records exception + sets ERROR on throw, then ends the span. Always rethrows.
runInContext	(ctx: RequestContext | undefined, fn: () => T) -> T	Runs fn with the span ctx names (traceId/spanId) re-established as the active OTel span, so spans opened inside fn parent to it. When ctx has no traceId/spanId, calls fn directly. Use for carrying a request's trace across async boundaries (setTimeout, queueMicrotask).
buildTraceparent	(ctx?: RequestContext) -> string | undefined	Builds a W3C traceparent header (00-<traceId>-<spanId>-01) from ctx or the active span. Returns undefined when neither source yields both IDs.
extractTraceparent	(headers: Headers | Record<string, string | undefined>) -> TraceparentInfo | undefined	Parses a W3C traceparent header. Returns undefined when absent or malformed. TraceparentInfo: { traceId, spanId, sampled }.
createContextWithParentTrace	(parentHeaders: Headers | Record<string, string | undefined>, operation: string) -> RequestContext	Extracts traceparent from headers and creates a child RequestContext inheriting traceId/parentSpanId.
injectCurrentContextInto	<T extends Record<string, unknown>>(carrier: T) -> T	Injects the active OTel context (traceparent, tracestate, etc.) into carrier via propagation.inject. Returns the same object.

telemetry/attributes

MCP-specific ATTR_* constant exports for span and metric attributes. Covers: code execution (code.function.name, code.namespace), MCP tool execution (name, input/output bytes, duration, success, error code, error category, partial success, batch succeeded/failed counts), MCP resource (URI, name, MIME type, size, duration, success, error code), MCP request context (tenant ID, client ID), MCP session events, MCP storage, GenAI semantic conventions, speech, graph, auth, task, and error classification attributes.

Batch/partial success attributes (mcp.tool.partial_success, mcp.tool.batch.succeeded_count, mcp.tool.batch.failed_count) are set automatically by the framework when a tool handler returns a result containing a non-empty failed array — matching the batch response pattern from the design skill.

Standard OTel semantic conventions (HTTP, cloud, service, network, etc.) are NOT re-exported — import those directly from @opentelemetry/semantic-conventions if needed.