1---2name: api-utils3description: 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.4---5
6## Overview
7
8Utility exports from `@cyanheads/mcp-ts-core/utils`. Utilities with complex APIs have dedicated reference files; simpler utilities are documented inline below.
9
10**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).
11
12**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.
13
14## References
15
16| Reference | Path | Covers |
17|:----------|:-----|:-------|
18| Formatting | `references/formatting.md` | `markdown()`, `MarkdownBuilder`, `diffFormatter`, `tableFormatter`, `treeFormatter` — builder patterns, option types, style variants, usage examples |
19| Parsing | `references/parsing.md` | `yamlParser`, `xmlParser`, `csvParser`, `jsonParser`, `pdfParser`, `dateParser`, `frontmatterParser` — method signatures, option types, peer deps, `Allow` flags, PDF workflows |
20| Security | `references/security.md` | `sanitization`, `RateLimiter`, `IdGenerator` — config types, method details, sensitive fields, usage examples |
21
22---
23
24## `@cyanheads/mcp-ts-core/utils` — network
25
26| Export | API | Notes |
27|:-------|:----|:------|
28| `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. |
29| `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). |
30| `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. |
31| `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. |
32
33---
34
35## `@cyanheads/mcp-ts-core/utils` — pagination
36
37| Export | API | Notes |
38|:-------|:----|:------|
39| `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. |
40| `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. |
41| `encodeCursor` | `(state: PaginationState) -> string` | Encodes `{ offset, limit, ...extra }` to opaque base64url string. |
42| `decodeCursor` | `(cursor, context: RequestContext) -> PaginationState` | Decodes opaque base64url cursor. Throws `McpError(InvalidParams)` if malformed. |
43
44---
45
46## `@cyanheads/mcp-ts-core/utils` — runtime
47
48| Export | API | Notes |
49|:-------|:----|:------|
50| `runtimeCaps` | `RuntimeCapabilities` object | Snapshot at import time. Fields: `isNode`, `isBun`, `isWorkerLike`, `isBrowserLike`, `hasProcess`, `hasBuffer`, `hasTextEncoder`, `hasPerformanceNow`. All booleans. Never throws. |
51
52---
53
54## `@cyanheads/mcp-ts-core/utils` — scheduling
55
56| Export | API | Notes |
57|:-------|:----|:------|
58| `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>`. |
59
60---
61
62## `@cyanheads/mcp-ts-core/utils` — types
63
64The `utils` export includes two type guards. The full set of guards lives in the internal module and is not part of the public API.
65
66| Export | Signature | Notes |
67|:-------|:----------|:------|
68| `isErrorWithCode` | `(error: unknown) -> error is Error & { code: unknown }` | Type guard — `true` when value is an `Error` instance with a `code` property |
69| `isRecord` | `(value: unknown) -> value is Record<string, unknown>` | Type guard for plain objects (non-null, non-array) |
70
71---
72
73## `@cyanheads/mcp-ts-core/utils` — logger
74
75| Export | API | Notes |
76|:-------|:----|:------|
77| `Logger` | Class | The `Logger` class itself. Use `Logger.getInstance()` if needed; most consumers use the `logger` singleton. |
78| `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. |
79| `McpLogLevel` | Type | Log level union type for typing level variables. |
80
81---
82
83## `@cyanheads/mcp-ts-core/utils` — requestContext
84
85| Export | API | Notes |
86|:-------|:----|:------|
87| `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. |
88| `RequestContext` | Type: `{ requestId, timestamp, operation?, traceId?, spanId?, tenantId?, auth?, [key: string]: unknown }` | Request tracing metadata. |
89| `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. |
90| `AuthContext` | Type: `{ clientId, scopes, sub, token, tenantId?, [key: string]: unknown }` | Structured auth data attached to `RequestContext.auth` after token verification. |
91
92`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`.
93
94`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.
95
96---
97
98## `@cyanheads/mcp-ts-core/utils` — errorHandler
99
100| Export | API | Notes |
101|:-------|:----|:------|
102| `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`. |
103
104---
105
106## `@cyanheads/mcp-ts-core/utils` — encoding
107
108Cross-platform encoding utilities. No peer deps.
109
110| Export | Signature | Notes |
111|:-------|:----------|:------|
112| `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. |
113| `stringToBase64` | `(str: string) -> string` | UTF-8 string → base64. Uses `Buffer.from(str, 'utf-8')` on Node/Bun; `TextEncoder` + `arrayBufferToBase64` on Workers. |
114| `base64ToString` | `(base64: string) -> string` | base64 → UTF-8 string. Uses `Buffer` on Node/Bun; `atob` + `TextDecoder` on Workers. Throws if input is not valid base64. |
115
116---
117
118## `@cyanheads/mcp-ts-core/utils` — token counting
119
120Dependency-free heuristic token estimation. No native/WASM deps.
121
122| Export | Signature | Notes |
123|:-------|:----------|:------|
124| `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. |
125| `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. |
126| `ChatMessage` | Type | `{ role: string, content: string \| Array<{type, text?, ...}> \| null, name?, tool_calls?, tool_call_id? }` — provider-agnostic chat message shape. |
127| `ModelHeuristics` | Interface | `{ charsPerToken, replyPrimer, tokensPerMessage, tokensPerName }` — heuristic parameters; built-in entries for `gpt-4o`, `gpt-4o-mini`, `default`. |
128
129Both functions throw `McpError(InternalError)` only on unexpected heuristic failure.
130
131---
132
133## `@cyanheads/mcp-ts-core/utils` — Telemetry
134
135Helper 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.
136
137### `telemetry/instrumentation`
138
139| Export | Signature | Notes |
140|:-------|:----------|:------|
141| `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. |
142| `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. |
143| `sdk` | `NodeSDK \| null` | The live SDK instance, or `null` when telemetry is disabled, in a Worker runtime, or after shutdown. |
144
145### `telemetry/metrics`
146
147| Export | Signature | Notes |
148|:-------|:----------|:------|
149| `getMeter` | `(name?: string) -> Meter` | Returns an OTel `Meter`. Defaults to service name + version from config. |
150| `createCounter` | `(name: string, description: string, unit?: string) -> Counter` | Monotonically increasing counter. `unit` defaults to `'1'`. |
151| `createUpDownCounter` | `(name: string, description: string, unit?: string) -> UpDownCounter` | Bidirectional counter (active connections, queue depth, etc.). `unit` defaults to `'1'`. |
152| `createHistogram` | `(name: string, description: string, unit?: string) -> Histogram` | Distribution recording (latency, sizes). `unit` optional. |
153| `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. |
154
155### `telemetry/trace`
156
157| Export | Signature | Notes |
158|:-------|:----------|:------|
159| `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. |
160| `runInContext` | `(ctx: RequestContext \| undefined, fn: () => T) -> T` | Runs `fn` inside the currently active OTel context. When `ctx` has no `traceId`/`spanId`, calls `fn` directly. Does not restore a specific span — use for carrying context across async boundaries (`setTimeout`, `queueMicrotask`). |
161| `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. |
162| `extractTraceparent` | `(headers: Headers \| Record<string, string \| undefined>) -> TraceparentInfo \| undefined` | Parses a W3C `traceparent` header. Returns `undefined` when absent or malformed. `TraceparentInfo: { traceId, spanId, sampled }`. |
163| `createContextWithParentTrace` | `(parentHeaders: Headers \| Record<string, string \| undefined>, operation: string) -> RequestContext` | Extracts `traceparent` from headers and creates a child `RequestContext` inheriting `traceId`/`parentSpanId`. |
164| `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. |
165
166### `telemetry/attributes`
167
168MCP-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.
169
170Batch/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.
171
172Standard OTel semantic conventions (HTTP, cloud, service, network, etc.) are NOT re-exported — import those directly from `@opentelemetry/semantic-conventions` if needed.
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