[V0_FILE]typescriptreact:file="app/components/demo.tsx" "use client"; import { useCallback, useEffect, useMemo, useRef, useState } from "react"; import type { RequestSnapshot, MockCircuitSnapshot, CircuitLogEvent, CircuitStateKind, } from "@/app/api/mock/store"; import { CircuitCodeWorkbench } from "./circuit-code-workbench"; type LifecycleState = "idle" | "running" | "completed" | "failed"; type HighlightTone = "amber" | "cyan" | "green" | "red"; type StartResponse = { runId: string; status: "running" | "completed" | "failed"; snapshot: MockCircuitSnapshot; }; type CircuitWorkflowLineMap = { callService: number[]; sleep: number[]; successReturn: number[]; failureReturn: number[]; circuitOpen: number[]; circuitClosed: number[]; }; type CircuitStepLineMap = { callService: number[]; successReturn: number[]; }; type CircuitBreakerDemoProps = { workflowCode: string; workflowHtmlLines: string[]; workflowLineMap: CircuitWorkflowLineMap; stepCode: string; stepHtmlLines: string[]; stepLineMap: CircuitStepLineMap; }; const POLL_INTERVAL_MS = 120; const MAX_REQUESTS = 10; type FailPreset = { label: string; range: [number, number] | null; }; const FAIL_PRESETS: FailPreset[] = [ { label: "4-6", range: [4, 6] }, { label: "3-5", range: [3, 5] }, { label: "None", range: null }, ]; function formatDurationLabel(durationMs: number): string { if (durationMs >= 1000 && durationMs % 1000 === 0) { return `${durationMs / 1000}s`; } return `${durationMs}ms`; } function formatElapsedLabel(durationMs: number): string { const seconds = (durationMs / 1000).toFixed(2); return `${seconds}s`; } async function postJson( url: string, body: Record, signal: AbortSignal ): Promise { const response = await fetch(url, { method: "POST", headers: { "Content-Type": "application/json", }, body: JSON.stringify(body), signal, }); const payload = (await response .json() .catch(() => ({ error: "Failed to parse JSON response" }))) as | T | { error?: string }; if (signal.aborted) { throw new DOMException("Request aborted", "AbortError"); } if (!response.ok) { const message = typeof payload === "object" && payload && "error" in payload ? (payload.error ?? `Request failed (${response.status})`) : `Request failed (${response.status})`; throw new Error(message); } return payload as T; } export function CircuitBreakerDemo({ workflowCode, workflowHtmlLines, workflowLineMap, stepCode, stepHtmlLines, stepLineMap, }: CircuitBreakerDemoProps) { const [failPresetIndex, setFailPresetIndex] = useState(0); const [lifecycle, setLifecycle] = useState("idle"); const [runId, setRunId] = useState(null); const [snapshot, setSnapshot] = useState(null); const [error, setError] = useState(null); const pollTimerRef = useRef | null>(null); const inFlightRef = useRef(false); const abortRef = useRef(null); const startButtonRef = useRef(null); const stopPolling = useCallback(() => { if (pollTimerRef.current) { clearInterval(pollTimerRef.current); pollTimerRef.current = null; } inFlightRef.current = false; }, []); const ensureAbortController = useCallback((): AbortController => { if (!abortRef.current || abortRef.current.signal.aborted) { abortRef.current = new AbortController(); } return abortRef.current; }, []); useEffect(() => { return () => { stopPolling(); abortRef.current?.abort(); abortRef.current = null; }; }, [stopPolling]); const fetchStatusSnapshot = useCallback(async (targetRunId: string, signal: AbortSignal) => { const response = await fetch( `/api/mock/status?runId=${encodeURIComponent(targetRunId)}`, { cache: "no-store", signal, } ); const payload = (await response .json() .catch(() => ({ error: "Failed to parse status response" }))) as | MockCircuitSnapshot | { error?: string }; if (signal.aborted) { throw new DOMException("Request aborted", "AbortError"); } if (!response.ok) { const message = typeof payload === "object" && payload && "error" in payload ? payload.error ?? `Status request failed (${response.status})` : `Status request failed (${response.status})`; throw new Error(message); } return payload as MockCircuitSnapshot; }, []); const beginPolling = useCallback( (targetRunId: string) => { stopPolling(); const poll = async () => { if (inFlightRef.current) { return; } inFlightRef.current = true; let signal: AbortSignal | null = null; try { const controller = ensureAbortController(); signal = controller.signal; const nextSnapshot = await fetchStatusSnapshot(targetRunId, signal); if (signal.aborted) { return; } setSnapshot(nextSnapshot); if (nextSnapshot.status === "completed") { if (signal.aborted) { return; } setLifecycle("completed"); stopPolling(); return; } if (nextSnapshot.status === "failed") { if (signal.aborted) { return; } setLifecycle("failed"); stopPolling(); return; } if (signal.aborted) { return; } setLifecycle("running"); } catch (pollError) { if ((signal && signal.aborted) || (pollError instanceof Error && pollError.name === "AbortError")) { return; } stopPolling(); setLifecycle("failed"); const message = pollError instanceof Error ? pollError.message : "Failed to read circuit breaker status"; setError(message); } finally { inFlightRef.current = false; } }; void poll(); pollTimerRef.current = setInterval(() => { void poll(); }, POLL_INTERVAL_MS); }, [ensureAbortController, fetchStatusSnapshot, stopPolling] ); const hasScrolledRef = useRef(false); useEffect(() => { if (lifecycle !== "idle" && !hasScrolledRef.current) { hasScrolledRef.current = true; const heading = document.getElementById("try-it-heading"); if (heading) { const top = heading.getBoundingClientRect().top + window.scrollY; window.scrollTo({ top, behavior: "smooth" }); } } if (lifecycle === "idle") { hasScrolledRef.current = false; } }, [lifecycle]); const handleStart = useCallback(async () => { setError(null); stopPolling(); abortRef.current?.abort(); abortRef.current = null; const controller = ensureAbortController(); const signal = controller.signal; const preset = FAIL_PRESETS[failPresetIndex]; const failRange = preset.range ?? [0, 0]; try { const payload = await postJson("/api/mock/start", { serviceId: "payment-api", maxRequests: MAX_REQUESTS, failRange: preset.range ? failRange : undefined, }, signal); if (signal.aborted) { return; } setRunId(payload.runId); if (signal.aborted) { return; } setSnapshot(payload.snapshot); if (signal.aborted) { return; } setLifecycle(payload.status === "running" ? "running" : payload.status); if (payload.status === "running") { if (signal.aborted) { return; } beginPolling(payload.runId); } } catch (startError) { if (signal.aborted || (startError instanceof Error && startError.name === "AbortError")) { return; } const message = startError instanceof Error ? startError.message : "Failed to start mock circuit breaker run"; setError(message); setLifecycle("idle"); } }, [beginPolling, ensureAbortController, failPresetIndex, stopPolling]); const handleReset = useCallback(() => { stopPolling(); abortRef.current?.abort(); abortRef.current = null; setLifecycle("idle"); setRunId(null); setSnapshot(null); setError(null); setTimeout(() => { startButtonRef.current?.focus(); }, 0); }, [stopPolling]); const isRunning = lifecycle === "running"; const phaseExplainer = useMemo(() => { if (!snapshot) { return "Waiting to start a run."; } if (snapshot.status === "running" && snapshot.currentPhase.phase === "request") { const state = snapshot.currentPhase.circuitState; const prefix = state === "half-open" ? "Half-open test: " : ""; return `${prefix}Request ${snapshot.currentPhase.requestNum} executing callPaymentService() in a step. Circuit: ${state}.`; } if (snapshot.status === "running" && snapshot.currentPhase.phase === "cooldown") { return `Circuit OPEN — sleep('${formatDurationLabel(snapshot.currentPhase.cooldownMs ?? 0)}') cooldown in progress. Zero compute while waiting.`; } if (snapshot.status === "completed" && snapshot.result) { if (snapshot.result.outcome === "recovered") { return `Circuit recovered. ${snapshot.result.totalRequests} requests, ${snapshot.result.totalFailures} failures, circuit opened ${snapshot.result.circuitOpened} time(s).`; } return `Run completed. ${snapshot.result.totalRequests} requests, ${snapshot.result.totalFailures} failures.`; } if (snapshot.status === "failed") { return `Run failed.`; } return "Run is active."; }, [snapshot]); type GutterMarkKind = "success" | "fail"; const codeState = useMemo(() => { const wfMarks: Record = {}; const stepMarks: Record = {}; if (snapshot) { const lastSuccess = [...snapshot.executionLog].reverse().find((e) => e.kind === "success"); const lastFailure = [...snapshot.executionLog].reverse().find((e) => e.kind === "failure"); let lastRequestIdx = -1; let lastFailIdx = -1; for (let i = snapshot.executionLog.length - 1; i >= 0; i--) { if (lastRequestIdx === -1 && snapshot.executionLog[i].kind === "request") lastRequestIdx = i; if (lastFailIdx === -1 && snapshot.executionLog[i].kind === "failure") lastFailIdx = i; if (lastRequestIdx !== -1 && lastFailIdx !== -1) break; } // Mark call service lines based on most recent outcome if (lastSuccess && (!lastFailure || lastSuccess.atMs > lastFailure.atMs)) { for (const ln of workflowLineMap.callService) wfMarks[ln] = "success"; for (const ln of stepLineMap.callService) stepMarks[ln] = "success"; } else if (lastFailIdx > lastRequestIdx) { for (const ln of workflowLineMap.callService) wfMarks[ln] = "fail"; for (const ln of stepLineMap.callService) stepMarks[ln] = "fail"; } // Mark sleep lines if cooldown has occurred const hasCooldown = snapshot.executionLog.some( (e) => e.kind === "cooldown_start" || e.kind === "cooldown_end" ); if (hasCooldown) { for (const ln of workflowLineMap.sleep) wfMarks[ln] = "success"; } // Mark circuit state transition lines const hasCircuitOpen = snapshot.executionLog.some((e) => e.kind === "circuit_open"); if (hasCircuitOpen) { for (const ln of workflowLineMap.circuitOpen) wfMarks[ln] = "fail"; } const hasCircuitClosed = snapshot.executionLog.some((e) => e.kind === "circuit_closed"); if (hasCircuitClosed) { for (const ln of workflowLineMap.circuitClosed) wfMarks[ln] = "success"; } if (snapshot.status === "completed") { if (snapshot.result?.outcome === "recovered") { for (const ln of workflowLineMap.successReturn) wfMarks[ln] = "success"; for (const ln of stepLineMap.successReturn) stepMarks[ln] = "success"; } else { for (const ln of workflowLineMap.failureReturn) wfMarks[ln] = "fail"; } } } if (!snapshot) { return { tone: "amber" as HighlightTone, workflowActiveLines: [] as number[], stepActiveLines: [] as number[], workflowGutterMarks: wfMarks, stepGutterMarks: stepMarks, }; } if (snapshot.status === "running" && snapshot.currentPhase.phase === "request") { return { tone: "amber" as HighlightTone, workflowActiveLines: workflowLineMap.callService, stepActiveLines: stepLineMap.callService, workflowGutterMarks: wfMarks, stepGutterMarks: stepMarks, }; } if (snapshot.status === "running" && snapshot.currentPhase.phase === "cooldown") { return { tone: "cyan" as HighlightTone, workflowActiveLines: workflowLineMap.sleep, stepActiveLines: [] as number[], workflowGutterMarks: wfMarks, stepGutterMarks: stepMarks, }; } if (snapshot.status === "completed") { if (snapshot.result?.outcome === "recovered") { return { tone: "green" as HighlightTone, workflowActiveLines: workflowLineMap.successReturn, stepActiveLines: stepLineMap.successReturn, workflowGutterMarks: wfMarks, stepGutterMarks: stepMarks, }; } return { tone: "red" as HighlightTone, workflowActiveLines: workflowLineMap.failureReturn, stepActiveLines: [] as number[], workflowGutterMarks: wfMarks, stepGutterMarks: stepMarks, }; } return { tone: "red" as HighlightTone, workflowActiveLines: workflowLineMap.failureReturn, stepActiveLines: [] as number[], workflowGutterMarks: wfMarks, stepGutterMarks: stepMarks, }; }, [snapshot, stepLineMap, workflowLineMap]); return (

{error && (

{error}

)}

{lifecycle !== "idle" && ( )} Fail requests

{phaseExplainer}

{runId && ( run: {runId} )}

sleep() → durable cooldown with zero compute while circuit is open

); } function CircuitStateIndicator({ circuitState, isRunning, }: { circuitState: CircuitStateKind; isRunning: boolean; }) { const stateConfig = { closed: { bg: "bg-green-700/20", border: "border-green-700/40", dot: "bg-green-700", text: "text-green-700", label: "CLOSED", icon: ( ), }, open: { bg: "bg-red-700/20", border: "border-red-700/40", dot: "bg-red-700", text: "text-red-700", label: "OPEN", icon: ( ), }, "half-open": { bg: "bg-amber-700/20", border: "border-amber-700/40", dot: "bg-amber-700", text: "text-amber-700", label: "HALF-OPEN", icon: ( ), }, } as const; const config = stateConfig[circuitState]; return (

{config.icon}

{config.label}

); } function RequestLadder({ requests, currentPhase, }: { requests: RequestSnapshot[]; currentPhase: MockCircuitSnapshot["currentPhase"]["phase"] | null; }) { if (requests.length === 0) { return (

No requests yet.

); } return (

{requests.map((req) => { const statusTone = requestTone(req.state); const stateLabel = req.circuitStateBefore !== "closed" ? ` (${req.circuitStateBefore})` : ""; return (

Req {req.requestNum}{stateLabel}

{req.state} {req.cooldownMs > 0 && (

cooldown({formatDurationLabel(req.cooldownMs)}) {req.state === "cooldown" && req.remainingCooldownMs > 0 ? ` (${formatDurationLabel(req.remainingCooldownMs)} left)` : ""} {req.state === "cooldown" && currentPhase === "cooldown" ? " *" : ""}

)}

); })}

); } function ExecutionLog({ events, elapsedMs, }: { events: CircuitLogEvent[]; elapsedMs: number; }) { const scrollRef = useRef(null); useEffect(() => { const el = scrollRef.current; if (el) { el.scrollTop = el.scrollHeight; } }, [events.length]); return (

Execution log

{formatElapsedLabel(elapsedMs)}

{events.length === 0 && (

No events yet.

)} {events.map((event, index) => { const tone = eventTone(event.kind); return (

); })}

); } function requestTone(state: RequestSnapshot["state"]): { dotClass: string; badgeClass: string; cardClass: string; } { switch (state) { case "running": return { dotClass: "bg-amber-700 animate-pulse", badgeClass: "border-amber-700/40 bg-amber-700/10 text-amber-700", cardClass: "border-amber-700/40 bg-amber-700/10", }; case "cooldown": return { dotClass: "bg-cyan-700 animate-pulse", badgeClass: "border-cyan-700/40 bg-cyan-700/10 text-cyan-700", cardClass: "border-cyan-700/40 bg-cyan-700/10", }; case "failed": case "fast-failed": return { dotClass: "bg-red-700", badgeClass: "border-red-700/40 bg-red-700/10 text-red-700", cardClass: "border-red-700/40 bg-red-700/10", }; case "succeeded": return { dotClass: "bg-green-700", badgeClass: "border-green-700/40 bg-green-700/10 text-green-700", cardClass: "border-green-700/40 bg-green-700/10", }; case "pending": default: return { dotClass: "bg-gray-500", badgeClass: "border-gray-400/70 bg-background-100 text-gray-900", cardClass: "border-gray-400/40 bg-background-100", }; } } function eventTone(kind: CircuitLogEvent["kind"]): { dotClass: string; labelClass: string; } { switch (kind) { case "request": return { dotClass: "bg-blue-700", labelClass: "text-blue-700", }; case "success": return { dotClass: "bg-green-700", labelClass: "text-green-700", }; case "failure": return { dotClass: "bg-red-700", labelClass: "text-red-700", }; case "circuit_open": return { dotClass: "bg-red-700", labelClass: "text-red-700", }; case "cooldown_start": return { dotClass: "bg-cyan-700", labelClass: "text-cyan-700", }; case "cooldown_end": return { dotClass: "bg-amber-700", labelClass: "text-amber-700", }; case "half_open_test": return { dotClass: "bg-amber-700", labelClass: "text-amber-700", }; case "circuit_closed": return { dotClass: "bg-green-700", labelClass: "text-green-700", }; case "completed": return { dotClass: "bg-green-700", labelClass: "text-green-700", }; case "exhausted": return { dotClass: "bg-red-700", labelClass: "text-red-700", }; default: return { dotClass: "bg-gray-500", labelClass: "text-gray-900", }; } } [V0_FILE]typescriptreact:file="app/components/circuit-code-workbench.tsx" "use client"; import { useEffect, useMemo, useRef, useState } from "react"; type HighlightTone = "amber" | "cyan" | "green" | "red"; type CopyState = "idle" | "copied" | "failed"; type HighlightStyle = { border: string; bg: string; text: string; }; const HIGHLIGHT_STYLES: Record = { amber: { border: "border-amber-700", bg: "bg-amber-700/15", text: "text-amber-700", }, cyan: { border: "border-cyan-700", bg: "bg-cyan-700/15", text: "text-cyan-700", }, green: { border: "border-green-700", bg: "bg-green-700/15", text: "text-green-700", }, red: { border: "border-red-700", bg: "bg-red-700/15", text: "text-red-700", }, }; const CHECKMARK_POINTS = "3,8.5 7,12.5 14,4.5"; type GutterMarkKind = "success" | "fail"; type CodePaneProps = { code: string; htmlLines: string[]; activeLines: number[]; gutterMarks: Record; filename: string; subtitle: string; tone: HighlightTone; }; function CodePane({ code, htmlLines, activeLines, gutterMarks, filename, subtitle, tone, }: CodePaneProps) { const [copyState, setCopyState] = useState("idle"); const activeLineSet = useMemo(() => new Set(activeLines), [activeLines]); const gutterMarkMap = useMemo(() => new Map(Object.entries(gutterMarks).map(([k, v]) => [Number(k), v])), [gutterMarks]); const prevMarkRef = useRef>(new Map()); const isFullReset = gutterMarkMap.size === 0 && activeLines.length === 0; useEffect(() => { if (isFullReset) { prevMarkRef.current.clear(); return; } gutterMarkMap.forEach((kind, line) => { prevMarkRef.current.set(line, kind); }); }, [gutterMarkMap, isFullReset]); const highlightStyle = HIGHLIGHT_STYLES[tone]; const handleCopy = async () => { try { await navigator.clipboard.writeText(code); setCopyState("copied"); window.setTimeout(() => setCopyState("idle"), 1200); } catch { setCopyState("failed"); window.setTimeout(() => setCopyState("idle"), 1200); } }; return (

{filename}

{subtitle}

          
            {htmlLines.map((lineHtml, index) => {
              const lineNumber = index + 1;
              const isActive = activeLineSet.has(lineNumber);
              const markKind = gutterMarkMap.get(lineNumber);
              const displayKind = isFullReset
                ? undefined
                : markKind ?? prevMarkRef.current.get(lineNumber);

              return (
                
                  
                    
                  
                  
                    {lineNumber}
                  
                   0 ? lineHtml : " ",
                    }}
                  />
                
              );
            })}

); } export type CircuitCodeWorkbenchProps = { workflowCode: string; workflowHtmlLines: string[]; workflowActiveLines: number[]; workflowGutterMarks: Record; stepCode: string; stepHtmlLines: string[]; stepActiveLines: number[]; stepGutterMarks: Record; tone: HighlightTone; }; export function CircuitCodeWorkbench({ workflowCode, workflowHtmlLines, workflowActiveLines, workflowGutterMarks, stepCode, stepHtmlLines, stepActiveLines, stepGutterMarks, tone, }: CircuitCodeWorkbenchProps) { return (

); } [V0_FILE]typescript:file="app/components/code-highlight-server.ts" import { highlight } from "sugar-high"; export function highlightCodeToHtmlLines(code: string): string[] { return highlight(code).split("\n"); } [V0_FILE]typescriptreact:file="app/layout.tsx" import type { Metadata } from "next"; import { Geist, Geist_Mono } from "next/font/google"; import "./globals.css"; const geistSans = Geist({ variable: "--font-geist-sans", subsets: ["latin"], }); const geistMono = Geist_Mono({ variable: "--font-geist-mono", subsets: ["latin"], }); export const metadata: Metadata = { title: "Circuit Breaker - Workflow DevKit Example", description: "Demonstrates durable circuit breaker pattern with sleep() cooldowns in Workflow DevKit", }; export default function RootLayout({ children, }: Readonly<{ children: React.ReactNode; }>) { return ( Skip to main content {children} ); } [V0_FILE]typescript:file="app/api/mock/start/route.ts" import { createApiErrorResponse, createApiSuccessResponse } from "../api"; import { buildMockCircuitSnapshot, createMockCircuitRun, } from "../store"; type StartRequestBody = { serviceId?: unknown; maxRequests?: unknown; failRange?: unknown; }; const DEFAULT_SERVICE_ID = "payment-api"; const DEFAULT_MAX_REQUESTS = 10; const DEFAULT_FAIL_RANGE: [number, number] = [4, 6]; function generateRunId(): string { return `cb_${Date.now().toString(36)}_${Math.random().toString(36).slice(2, 8)}`; } function parseServiceId(value: unknown): { value: string } | { error: string } { if (value === undefined) { return { value: DEFAULT_SERVICE_ID }; } if (typeof value !== "string") { return { error: "serviceId must be a string" }; } const normalized = value.trim(); if (!normalized) { return { error: "serviceId cannot be empty" }; } return { value: normalized }; } function parseFailRange( value: unknown, maxRequests: number ): { value: [number, number] } | { error: string } { if (value === undefined) { return { value: DEFAULT_FAIL_RANGE }; } if (!Array.isArray(value) || value.length !== 2) { return { error: "failRange must be a [start, end] array" }; } const [start, end] = value; if ( typeof start !== "number" || typeof end !== "number" || !Number.isInteger(start) || !Number.isInteger(end) ) { return { error: "failRange values must be integers" }; } if (start < 1 || end > maxRequests || start > end) { return { error: `failRange must be within [1, ${maxRequests}] with start <= end`, }; } return { value: [start, end] }; } function parseBoundedInteger(input: { field: string; value: unknown; min: number; max: number; fallback: number; }): { value: number } | { error: string } { if (input.value === undefined) { return { value: input.fallback }; } if ( typeof input.value !== "number" || !Number.isFinite(input.value) || !Number.isInteger(input.value) ) { return { error: `${input.field} must be an integer between ${input.min} and ${input.max}`, }; } if (input.value < input.min || input.value > input.max) { return { error: `${input.field} must be between ${input.min} and ${input.max}`, }; } return { value: input.value }; } function validationErrorResponse( attempted: string, reason: string, body: StartRequestBody ): Response { console.warn("[mock-circuit-breaker] start_validation_failed", { attempted, reason, body, }); return createApiErrorResponse( { code: "INVALID_REQUEST", message: reason, }, { status: 400 } ); } export async function POST(request: Request): Promise { let body: StartRequestBody; try { body = (await request.json()) as StartRequestBody; } catch { return createApiErrorResponse( { code: "INVALID_REQUEST", message: "Invalid JSON body", }, { status: 400 } ); } const serviceIdResult = parseServiceId(body.serviceId); if ("error" in serviceIdResult) { return validationErrorResponse( "validate_service_id", serviceIdResult.error, body ); } const maxRequestsResult = parseBoundedInteger({ field: "maxRequests", value: body.maxRequests, min: 4, max: 20, fallback: DEFAULT_MAX_REQUESTS, }); if ("error" in maxRequestsResult) { return validationErrorResponse( "validate_max_requests", maxRequestsResult.error, body ); } const failRangeResult = parseFailRange( body.failRange, maxRequestsResult.value ); if ("error" in failRangeResult) { return validationErrorResponse( "validate_fail_range", failRangeResult.error, body ); } const run = createMockCircuitRun({ runId: generateRunId(), serviceId: serviceIdResult.value, maxRequests: maxRequestsResult.value, failureThreshold: 3, cooldownMs: 3_000, failRange: failRangeResult.value, }); const snapshot = buildMockCircuitSnapshot(run, run.startedAtMs); return createApiSuccessResponse({ runId: run.id, serviceId: run.serviceId, status: snapshot.status, maxRequests: run.maxRequests, failRange: run.failRange, snapshot, }); } [V0_FILE]typescript:file="app/api/mock/api.ts" import { NextResponse } from "next/server"; type ApiError = { code: string; message: string; }; export function createApiSuccessResponse>( fields: T, init?: ResponseInit ) { return NextResponse.json( { ok: true, ...fields, }, init ); } export function createApiErrorResponse(error: ApiError, init?: ResponseInit) { return NextResponse.json( { ok: false, error, }, init ); } [V0_FILE]typescript:file="app/api/mock/status/route.ts" import { createApiErrorResponse, createApiSuccessResponse } from "../api"; import { buildMockCircuitSnapshot, getMockCircuitRun } from "../store"; export async function GET(request: Request): Promise { const searchParams = new URL(request.url).searchParams; const runId = searchParams.get("runId"); if (!runId) { return createApiErrorResponse( { code: "INVALID_REQUEST", message: "runId is required", }, { status: 400 } ); } const run = getMockCircuitRun(runId); if (!run) { console.warn("[mock-circuit-breaker] status_lookup_failed", { attempted: "mock_circuit_status_lookup", reason: "run_not_found", runId, }); return createApiErrorResponse( { code: "NOT_FOUND", message: "Run not found", }, { status: 404 } ); } return createApiSuccessResponse({ ...buildMockCircuitSnapshot(run) }); } [V0_FILE]typescript:file="app/api/mock/store.ts" export const REQUEST_WORK_MS = 500; export const COOLDOWN_MS = 3_000; export const FAILURE_THRESHOLD = 3; export type MockRunStatus = "running" | "completed" | "failed"; export type RequestOutcome = "success" | "fail" | "fast-fail"; export type RequestRuntimeState = | "pending" | "running" | "succeeded" | "failed" | "fast-failed" | "cooldown"; export type CircuitPhaseKind = "request" | "cooldown" | "done"; export type CircuitStateKind = "closed" | "open" | "half-open"; export interface RequestPlan { requestNum: number; startMs: number; endMs: number; cooldownMs: number; outcome: RequestOutcome; circuitStateBefore: CircuitStateKind; circuitStateAfter: CircuitStateKind; } export interface MockCircuitRun { id: string; serviceId: string; maxRequests: number; failureThreshold: number; cooldownMs: number; failRange: [number, number]; startedAt: string; startedAtMs: number; status: MockRunStatus; plan: RequestPlan[]; } export interface RequestSnapshot extends RequestPlan { state: RequestRuntimeState; cooldownEndMs: number; remainingCooldownMs: number; } export interface CircuitPhase { phase: CircuitPhaseKind; requestNum: number | null; circuitState: CircuitStateKind; cooldownMs: number | null; } export type CircuitLogEventKind = | "request" | "success" | "failure" | "circuit_open" | "cooldown_start" | "cooldown_end" | "half_open_test" | "circuit_closed" | "completed" | "exhausted"; export interface CircuitLogEvent { atMs: number; requestNum: number; kind: CircuitLogEventKind; message: string; } export interface MockCircuitSnapshot { runId: string; serviceId: string; status: MockRunStatus; maxRequests: number; failureThreshold: number; cooldownMs: number; failRange: [number, number]; requestWorkMs: number; startedAt: string; startedAtMs: number; elapsedMs: number; totalDurationMs: number; requests: RequestSnapshot[]; currentPhase: CircuitPhase; executionLog: CircuitLogEvent[]; result: { totalRequests: number; totalFailures: number; circuitOpened: number; outcome: "recovered" | "failed"; } | null; } declare global { // eslint-disable-next-line no-var var __mockCircuitBreakerRuns: Map | undefined; } function toIso(timestampMs: number): string { return new Date(timestampMs).toISOString(); } export function getRunStore(): Map { return ( globalThis.__mockCircuitBreakerRuns ?? (globalThis.__mockCircuitBreakerRuns = new Map()) ); } function runStatusTransition( run: MockCircuitRun, nextStatus: MockRunStatus, reason: string, context: Record ): void { if (run.status === nextStatus) { return; } console.info("[mock-circuit-breaker] run_status_transition", { runId: run.id, from: run.status, to: nextStatus, reason, ...context, }); run.status = nextStatus; } export function buildRequestPlan(input: { maxRequests: number; failureThreshold: number; cooldownMs: number; failRange: [number, number]; }): RequestPlan[] { const { maxRequests, failureThreshold, cooldownMs, failRange } = input; const [failStart, failEnd] = failRange; const plan: RequestPlan[] = []; let cursorMs = 0; let circuitState: CircuitStateKind = "closed"; let consecutiveFailures = 0; for (let reqNum = 1; reqNum <= maxRequests; reqNum += 1) { const stateBefore = circuitState; // If circuit is open, we need a cooldown before we can do a half-open test let thisCooldownMs = 0; if (circuitState === "open") { thisCooldownMs = cooldownMs; cursorMs += thisCooldownMs; circuitState = "half-open"; } const startMs = cursorMs; const endMs = startMs + REQUEST_WORK_MS; // Determine outcome const isFailing = reqNum >= failStart && reqNum <= failEnd; let outcome: RequestOutcome; if (isFailing) { outcome = "fail"; } else { outcome = "success"; } // Compute state transitions let stateAfter: CircuitStateKind = circuitState; if (outcome === "success") { consecutiveFailures = 0; if (circuitState === "half-open") { stateAfter = "closed"; } } else { consecutiveFailures += 1; if (consecutiveFailures >= failureThreshold) { stateAfter = "open"; consecutiveFailures = 0; } } plan.push({ requestNum: reqNum, startMs, endMs, cooldownMs: thisCooldownMs, outcome, circuitStateBefore: stateBefore === "open" ? "half-open" : stateBefore, circuitStateAfter: stateAfter, }); cursorMs = endMs; circuitState = stateAfter; } return plan; } export function createMockCircuitRun(input: { runId: string; serviceId: string; maxRequests: number; failureThreshold: number; cooldownMs: number; failRange: [number, number]; nowMs?: number; }): MockCircuitRun { const nowMs = input.nowMs ?? Date.now(); const run: MockCircuitRun = { id: input.runId, serviceId: input.serviceId, maxRequests: input.maxRequests, failureThreshold: input.failureThreshold, cooldownMs: input.cooldownMs, failRange: input.failRange, startedAt: toIso(nowMs), startedAtMs: nowMs, status: "running", plan: buildRequestPlan({ maxRequests: input.maxRequests, failureThreshold: input.failureThreshold, cooldownMs: input.cooldownMs, failRange: input.failRange, }), }; console.info("[mock-circuit-breaker] run_created", { runId: run.id, serviceId: run.serviceId, maxRequests: run.maxRequests, failureThreshold: run.failureThreshold, cooldownMs: run.cooldownMs, failRange: run.failRange, planLength: run.plan.length, totalDurationMs: run.plan.at(-1)?.endMs ?? 0, }); getRunStore().set(run.id, run); return run; } export function getMockCircuitRun(runId: string): MockCircuitRun | undefined { return getRunStore().get(runId); } function buildExecutionTimeline(plan: RequestPlan[]): CircuitLogEvent[] { const events: CircuitLogEvent[] = []; for (const req of plan) { // Cooldown events if (req.cooldownMs > 0) { events.push({ atMs: req.startMs - req.cooldownMs, requestNum: req.requestNum, kind: "cooldown_start", message: `Circuit OPEN — cooldown sleep('${req.cooldownMs}ms') started`, }); events.push({ atMs: req.startMs, requestNum: req.requestNum, kind: "cooldown_end", message: `Cooldown ended — circuit HALF-OPEN`, }); events.push({ atMs: req.startMs, requestNum: req.requestNum, kind: "half_open_test", message: `Half-open test: request ${req.requestNum}`, }); } // Request start events.push({ atMs: req.startMs, requestNum: req.requestNum, kind: "request", message: `Request ${req.requestNum} started (circuit: ${req.circuitStateBefore})`, }); // Request outcome if (req.outcome === "success") { events.push({ atMs: req.endMs, requestNum: req.requestNum, kind: "success", message: `Request ${req.requestNum} succeeded`, }); if (req.circuitStateBefore === "half-open" && req.circuitStateAfter === "closed") { events.push({ atMs: req.endMs, requestNum: req.requestNum, kind: "circuit_closed", message: `Circuit CLOSED — service recovered`, }); } } else { events.push({ atMs: req.endMs, requestNum: req.requestNum, kind: "failure", message: `Request ${req.requestNum} failed`, }); if (req.circuitStateAfter === "open") { events.push({ atMs: req.endMs, requestNum: req.requestNum, kind: "circuit_open", message: `Circuit OPEN — ${plan[0] ? plan.filter((p) => p.requestNum <= req.requestNum).length : 0} consecutive failures hit threshold`, }); } } } // Completion const lastReq = plan.at(-1); if (lastReq) { events.push({ atMs: lastReq.endMs, requestNum: lastReq.requestNum, kind: "completed", message: `All ${plan.length} requests processed`, }); } return events.sort((a, b) => a.atMs - b.atMs || 0); } export function buildMockCircuitSnapshot( run: MockCircuitRun, nowMs: number = Date.now() ): MockCircuitSnapshot { const elapsedMs = Math.max(0, nowMs - run.startedAtMs); const requests: RequestSnapshot[] = run.plan.map((req) => ({ ...req, state: "pending" as RequestRuntimeState, cooldownEndMs: req.startMs, remainingCooldownMs: 0, })); let status: MockRunStatus = "running"; let currentPhase: CircuitPhase = { phase: "done", requestNum: null, circuitState: "closed", cooldownMs: null, }; let result: MockCircuitSnapshot["result"] = null; for (let index = 0; index < requests.length; index += 1) { const req = requests[index]; // Check if we're in cooldown before this request const cooldownStartMs = req.startMs - req.cooldownMs; if (req.cooldownMs > 0 && elapsedMs >= cooldownStartMs && elapsedMs < req.startMs) { req.state = "cooldown"; req.remainingCooldownMs = Math.max(0, req.startMs - elapsedMs); currentPhase = { phase: "cooldown", requestNum: req.requestNum, circuitState: "open", cooldownMs: req.cooldownMs, }; // Mark all previous requests as resolved for (let prev = 0; prev < index; prev++) { const p = requests[prev]; if (p.state === "pending") { p.state = p.outcome === "success" ? "succeeded" : "failed"; } } break; } // Check if request is currently running if (elapsedMs >= req.startMs && elapsedMs < req.endMs) { req.state = "running"; currentPhase = { phase: "request", requestNum: req.requestNum, circuitState: req.circuitStateBefore, cooldownMs: null, }; // Mark all previous requests as resolved for (let prev = 0; prev < index; prev++) { const p = requests[prev]; if (p.state === "pending") { p.state = p.outcome === "success" ? "succeeded" : "failed"; } } break; } // Request has completed if (elapsedMs >= req.endMs) { req.state = req.outcome === "success" ? "succeeded" : "failed"; // Last request — run is done if (index === requests.length - 1) { const totalFailures = requests.filter((r) => r.outcome !== "success").length; const circuitOpened = requests.filter((r) => r.circuitStateAfter === "open").length; const lastState = req.circuitStateAfter; status = "completed"; currentPhase = { phase: "done", requestNum: req.requestNum, circuitState: lastState, cooldownMs: null, }; result = { totalRequests: requests.length, totalFailures, circuitOpened, outcome: lastState === "closed" ? "recovered" : "failed", }; break; } continue; } } runStatusTransition(run, status, "snapshot_recomputed", { elapsedMs, currentPhase, }); return { runId: run.id, serviceId: run.serviceId, status, maxRequests: run.maxRequests, failureThreshold: run.failureThreshold, cooldownMs: run.cooldownMs, failRange: run.failRange, requestWorkMs: REQUEST_WORK_MS, startedAt: run.startedAt, startedAtMs: run.startedAtMs, elapsedMs, totalDurationMs: run.plan.at(-1)?.endMs ?? 0, requests, currentPhase, executionLog: buildExecutionTimeline(run.plan).filter( (event) => event.atMs <= elapsedMs ), result, }; } [V0_FILE]typescriptreact:file="app/page.tsx" import { highlightCodeToHtmlLines } from "./components/code-highlight-server"; import { CircuitBreakerDemo } from "./components/demo"; const directiveUseWorkflow = `"use ${"workflow"}"`; const directiveUseStep = `"use ${"step"}"`; const workflowCode = `import { sleep } from "workflow"; export async function circuitBreakerFlow(serviceId: string) { ${directiveUseWorkflow}; let state: CircuitState = "closed"; let consecutiveFailures = 0; const failureThreshold = 3; for (let i = 1; i <= maxRequests; i++) { if (state === "open") { await sleep(\`${"${cooldownMs}"}ms\`); state = "half-open"; } const success = await callPaymentService(serviceId, i, state); if (success) { consecutiveFailures = 0; if (state === "half-open") { state = "closed"; } } else { consecutiveFailures++; if (consecutiveFailures >= failureThreshold) { state = "open"; consecutiveFailures = 0; } } } return { serviceId, status: state === "closed" ? "recovered" : "failed" }; }`; const stepCode = `async function callPaymentService( serviceId: string, requestNum: number, circuitState: CircuitState ): Promise { ${directiveUseStep}; const response = await fetch(\`https://payments.example.com/charge\`, { method: "POST", headers: { "x-circuit-state": circuitState }, body: JSON.stringify({ serviceId, requestNum }), }); if (!response.ok) { throw new Error(\`Payment service returned \${response.status}\`); } return true; }`; function buildWorkflowLineMap(code: string) { const lines = code.split("\n"); const callService = lines .map((line, index) => line.includes("await callPaymentService(") ? index + 1 : null ) .filter((line): line is number => line !== null); const sleep = lines .map((line, index) => (line.includes("await sleep(") ? index + 1 : null)) .filter((line): line is number => line !== null); const successReturn = lines .map((line, index) => line.includes('"recovered"') ? index + 1 : null ) .filter((line): line is number => line !== null); const failureReturn = lines .map((line, index) => line.includes('"failed"') && line.includes("status:") ? index + 1 : null ) .filter((line): line is number => line !== null); const circuitOpen = lines .map((line, index) => line.includes('"open"') && line.includes("state =") ? index + 1 : null ) .filter((line): line is number => line !== null); const circuitClosed = lines .map((line, index) => line.includes('"closed"') && line.includes("state =") ? index + 1 : null ) .filter((line): line is number => line !== null); return { callService, sleep, successReturn, failureReturn, circuitOpen, circuitClosed, }; } function buildStepLineMap(code: string) { const lines = code.split("\n"); const callService = lines .map((line, index) => line.includes("const response = await fetch(") ? index + 1 : null ) .filter((line): line is number => line !== null); const successReturn = lines .map((line, index) => (line.includes("return true;") ? index + 1 : null)) .filter((line): line is number => line !== null); return { callService, successReturn }; } const workflowHtmlLines = highlightCodeToHtmlLines(workflowCode); const stepHtmlLines = highlightCodeToHtmlLines(stepCode); const workflowLineMap = buildWorkflowLineMap(workflowCode); const stepLineMap = buildStepLineMap(stepCode); export default function Home() { return (

Workflow DevKit Example

Circuit Breaker

When a downstream service starts failing, a circuit breaker prevents cascading failures by fast-failing requests until the service recovers. This workflow tracks failures in a local variable, opens the circuit after a threshold, and uses durable{" "} sleep(){" "} for the cooldown period — zero compute while waiting, no Redis needed.

Try It

{/* ── Why this matters ────────────────────────────────────── */}

Why Not Just Use Redis?

Traditional

You need Redis or Memcached{" "} for shared circuit state, custom middleware to intercept requests, health-check endpoints, and a state machine spread across multiple services. The failure counter, cooldown timer, and half-open probe logic live in different codebases.

Workflow Circuit Breaker

A for loop with a let state{" "} variable is the circuit breaker. Each{" "} sleep() is a durable cooldown at zero compute. The consecutive failure counter and state transitions are plain local variables that survive across restarts.

No Redis. No external state store. No health-check endpoints. The workflow is the circuit breaker.

); } [V0_FILE]css:file="app/globals.css" @import "tailwindcss"; @theme { --color-background-100: #0a0a0a; --color-background-200: #171717; --color-gray-100: #1a1a1a; --color-gray-200: #1f1f1f; --color-gray-300: #292929; --color-gray-400: #737373; --color-gray-500: #525252; --color-gray-600: #404040; --color-gray-700: #262626; --color-gray-800: #171717; --color-gray-900: #a1a1a1; --color-gray-1000: #ededed; --color-blue-700: #0070F3; --color-red-700: #E5484D; --color-amber-700: #FFB224; --color-green-700: #46A758; --color-violet-700: #8B5CF6; --color-cyan-700: #06B6D4; --font-sans: var(--font-geist-sans); --font-mono: var(--font-geist-mono); } body { background: #0a0a0a; color: #ededed; font-family: var(--font-sans), -apple-system, BlinkMacSystemFont, sans-serif; } /* sugar-high syntax tokens */ :root, .dark { --sh-class: #52a8ff; --sh-identifier: #ededed; --sh-sign: #a1a1a1; --sh-property: #ff6166; --sh-entity: #62c073; --sh-jsxliterals: #ededed; --sh-string: #62c073; --sh-keyword: #f75f8f; --sh-comment: #a1a1a1; } /* Prism token colors - Geist dark-mode palette */ .token.keyword, .token.keyword.control-flow { color: #f75f8f; } .token.plain, .token.parameter, .token.punctuation, .token.plain-text, .token.property-access, .token.operator, .token.tag.punctuation { color: #ededed; } .token.function, .token.function.maybe-class-name { color: #bf7af0; } .token.tag { color: #62c073; } .token.literal-property.property { color: #ff6166; } .token.string, .token.boolean { color: #62c073; } .token.comment { color: #a1a1a1; } .token.class-name { color: #52a8ff; } .token.number { color: #62c073; } .token.attr-name { color: #ff6166; } .token.attr-value { color: #62c073; } .token.builtin { color: #52a8ff; } .token.template-string { color: #62c073; } .token.interpolation { color: #ededed; } [V0_FILE]javascript:file="postcss.config.mjs" export default { plugins: { "@tailwindcss/postcss": {}, }, }; [V0_FILE]typescript:file="workflows/circuit-breaker.ts" import { sleep } from "workflow"; export type CircuitState = "closed" | "open" | "half-open"; export interface CircuitBreakerResult { serviceId: string; status: "recovered" | "failed"; totalRequests: number; totalFailures: number; circuitOpened: number; } export async function circuitBreakerFlow( serviceId: string, maxRequests: number = 12, failureThreshold: number = 3, cooldownMs: number = 3000 ): Promise { "use workflow"; let state: CircuitState = "closed"; let consecutiveFailures = 0; let totalRequests = 0; let totalFailures = 0; let circuitOpened = 0; for (let i = 1; i <= maxRequests; i++) { if (state === "open") { await sleep(`${cooldownMs}ms`); state = "half-open"; } const success = await callPaymentService(serviceId, i, state); totalRequests++; if (success) { consecutiveFailures = 0; if (state === "half-open") { state = "closed"; } } else { totalFailures++; consecutiveFailures++; if (consecutiveFailures >= failureThreshold) { state = "open"; circuitOpened++; consecutiveFailures = 0; } } } return { serviceId, status: state === "closed" ? "recovered" : "failed", totalRequests, totalFailures, circuitOpened, }; } async function callPaymentService( serviceId: string, requestNum: number, circuitState: CircuitState ): Promise { "use step"; console.info("[circuit-breaker] call_service", { serviceId, requestNum, circuitState, }); return true; } [V0_FILE]json:file="package.json" { "name": "circuit-breaker", "version": "0.1.0", "private": true, "scripts": { "dev": "next dev", "build": "next build", "start": "next start", "lint": "next lint" }, "dependencies": { "next": "16.0.10", "react": "19.2.3", "react-dom": "19.2.3", "sugar-high": "^0.9.5", "workflow": "4.1.0-beta.53" }, "devDependencies": { "@tailwindcss/postcss": "^4", "@types/node": "^20", "@types/react": "^19", "@types/react-dom": "^19", "tailwindcss": "^4", "typescript": "^5" } } [V0_FILE]json:file="tsconfig.json" { "compilerOptions": { "target": "ES2017", "lib": ["dom", "dom.iterable", "esnext"], "allowJs": true, "skipLibCheck": true, "strict": true, "noEmit": true, "esModuleInterop": true, "module": "esnext", "moduleResolution": "bundler", "resolveJsonModule": true, "isolatedModules": true, "jsx": "react-jsx", "incremental": true, "plugins": [ { "name": "next" }, { "name": "workflow" } ], "paths": { "@/*": ["./*"] } }, "include": [ "next-env.d.ts", "**/*.ts", "**/*.tsx", ".next/types/**/*.ts", ".next/dev/types/**/*.ts", "**/*.mts" ], "exclude": ["node_modules"] } [V0_FILE]typescript:file="next.config.ts" import { withWorkflow } from "workflow/next"; import type { NextConfig } from "next"; const nextConfig: NextConfig = {}; export default withWorkflow(nextConfig);