miniflare

🔥 Miniflare

Miniflare 3 is a simulator for developing and testing Cloudflare Workers, powered by workerd.

:warning: Miniflare 3 is API-only, and does not expose a CLI. Use Wrangler with wrangler dev to develop your Workers locally with Miniflare 3.

Quick Start

$ npm install miniflare --save-dev

import { Miniflare } from "miniflare";

// Create a new Miniflare instance, starting a workerd server
const mf = new Miniflare({
	script: `addEventListener("fetch", (event) => {
    event.respondWith(new Response("Hello Miniflare!"));
  })`,
});

// Send a request to the workerd server, the host is ignored
const response = await mf.dispatchFetch("http://localhost:8787/");
console.log(await response.text()); // Hello Miniflare!

// Cleanup Miniflare, shutting down the workerd server
await mf.dispose();

API

type Awaitable<T>

T | Promise<T>

Represents a value that can be awaited. Used in callback types to allow Promises to be returned if necessary.

type Json

string | number | boolean | null | Record<string, Json> | Json[]

Represents a JSON-serialisable value.

type ModuleRuleType

"ESModule" | "CommonJS" | "Text" | "Data" | "CompiledWasm"

Represents how a module's contents should be interpreted.

• "ESModule": interpret as ECMAScript module
• "CommonJS": interpret as CommonJS module
• "Text": interpret as UTF8-encoded data, expose in runtime with string-typed default export
• "Data": interpret as arbitrary binary data, expose in runtime with ArrayBuffer-typed default export
• "CompiledWasm": interpret as binary WebAssembly module data, expose in runtime with WebAssembly.Module-typed default export

interface ModuleDefinition

Represents a manually defined module.

• type: ModuleRuleType

  How this module's contents should be interpreted.

• path: string

  Path of this module. The module's "name" will be obtained by converting this to a relative path. The original path will be used to read contents if it's omitted.

• contents?: string | Uint8Array

  Contents override for this module. Binary data should be passed as Uint8Arrays. If omitted, will be read from path.

interface ModuleRule

Represents a rule for identifying the ModuleRuleType of automatically located modules.

• type: ModuleRuleType

  How to interpret modules that match the include patterns.

• include: string[]

  Glob patterns to match located module paths against (e.g. ["**/*.txt"]).

• fallthrough?: boolean

  If true, ignore any further rules of this type. This is useful for disabling the built-in ESModule and CommonJS rules that match *.mjs and *.js/*.cjs files respectively.

type Persistence

boolean | string | undefined

Represents where data should be persisted, if anywhere.

• If this is undefined or false, data will be stored in-memory and only persist between Miniflare#setOptions() calls, not restarts nor new Miniflare instances.
• If this is true, data will be stored on the file-system, in the $PWD/.mf directory.
• If this looks like a URL, then:
  • If the protocol is memory:, data will be stored in-memory as above.
  • If the protocol is file:, data will be stored on the file-system, in the specified directory (e.g. file:///path/to/directory).
• Otherwise, if this is just a regular string, data will be stored on the file-system, using the value as the directory path.

enum LogLevel

NONE, ERROR, WARN, INFO, DEBUG, VERBOSE

Controls which messages Miniflare logs. All messages at or below the selected level will be logged.

interface LogOptions

• prefix?: string

  String to add before the level prefix when logging messages. Defaults to mf.

• suffix?: string

  String to add after the level prefix when logging messages.

class Log

• constructor(level?: LogLevel, opts?: LogOptions)

  Creates a new logger that logs all messages at or below the specified level to the console.

• error(message: Error)

  Logs a message at the ERROR level. If the constructed log level is less than ERROR, throws the message instead.

• warn(message: string)

  Logs a message at the WARN level.

• info(message: string)

  Logs a message at the INFO level.

• debug(message: string)

  Logs a message at the DEBUG level.

• verbose(message: string)

  Logs a message at the VERBOSE level.

class NoOpLog extends Log

• constructor()

  Creates a new logger that logs nothing to the console, and always throws messages logged at the ERROR level.

interface QueueProducerOptions

• queueName: string

  The name of the queue where messages will be sent by the producer.

• deliveryDelay?: number

  Default number of seconds to delay the delivery of messages to consumers. Value between 0 (no delay) and 42300 (12 hours).

interface QueueConsumerOptions

• maxBatchSize?: number

  Maximum number of messages allowed in each batch. Defaults to 5.

• maxBatchTimeout?: number

  Maximum number of seconds to wait for a full batch. If a message is sent, and this timeout elapses, a partial batch will be dispatched. Defaults to 1.

• maxRetries?: number

  Maximum number of times to retry dispatching a message, if handling it throws, or it is explicitly retried. Defaults to 2.

• deadLetterQueue?: string

  Name of another Queue to send a message on if it fails processing after maxRetries. If this isn't specified, failed messages will be discarded.

• retryDelay?: number

  Number of seconds to delay the (re-)delivery of messages by default. Value between 0 (no delay) and 42300 (12 hours).

interface WorkerOptions

Options for an individual Worker/"nanoservice". All bindings are accessible on the global scope in service-worker format Workers, or via the 2nd env parameter in module format Workers.

Core

• name?: string

  Unique name for this worker. Only required if multiple workers are specified.

• rootPath?: string

  Path against which all other path options for this Worker are resolved relative to. This path is itself resolved relative to the rootPath from SharedOptions if multiple workers are specified. Defaults to the current working directory.

• script?: string

  JavaScript code for this worker. If this is a service worker format Worker, it must not have any imports. If this is a modules format Worker, it must not have any npm imports, and modules: true must be set. If it does have imports, scriptPath must also be set so Miniflare knows where to resolve them relative to.

• scriptPath?: string

  Path of JavaScript entrypoint. If this is a service worker format Worker, it must not have any imports. If this is a modules format Worker, it must not have any npm imports, and modules: true must be set.

• modules?: boolean | ModuleDefinition[]

  • If true, Miniflare will treat script/scriptPath as an ES Module and automatically locate transitive module dependencies according to modulesRules. Note that automatic location is not perfect: if the specifier to a dynamic import() or require() is not a string literal, an exception will be thrown.

  • If set to an array, modules can be defined manually. Transitive dependencies must also be defined. Note the first module must be the entrypoint and have type "ESModule".

• modulesRoot?: string

  If modules is set to true or an array, modules' "name"s will be their paths relative to this value. This ensures file paths in stack traces are correct.

• modulesRules?: ModuleRule[]

  Rules for identifying the ModuleRuleType of automatically located modules when modules: true is set. Note the following default rules are always included at the end:

  [
    { type: "ESModule", include: ["**/*.mjs"] },
    { type: "CommonJS", include: ["**/*.js", "**/*.cjs"] },
  ]
  

  If script and scriptPath are set, and modules is set to an array, modules takes priority for a Worker's code, followed by script, then scriptPath.

• compatibilityDate?: string

  Compatibility date to use for this Worker. Defaults to a date far in the past.

• compatibilityFlags?: string[]

  Compatibility flags to use for this Worker.

• bindings?: Record<string, Json>

  Record mapping binding name to arbitrary JSON-serialisable values to inject as bindings into this Worker.

• wasmBindings?: Record<string, string>

  Record mapping binding name to paths containing binary WebAssembly module data to inject as WebAssembly.Module bindings into this Worker.

• textBlobBindings?: Record<string, string>

  Record mapping binding name to paths containing UTF8-encoded data to inject as string bindings into this Worker.

• dataBlobBindings?: Record<string, string>

  Record mapping binding name to paths containing arbitrary binary data to inject as ArrayBuffer bindings into this Worker.

• serviceBindings?: Record<string, string | typeof kCurrentWorker | { name: string | typeof kCurrentWorker, entrypoint?: string } | { network: Network } | { external: ExternalServer } | { disk: DiskDirectory } | (request: Request, instance: Miniflare) => Awaitable<Response>>

  Record mapping binding name to service designators to inject as { fetch: typeof fetch } service bindings into this Worker.

  • If the designator is a string, requests will be dispatched to the Worker with that name.
  • If the designator is (await import("miniflare")).kCurrentWorker, requests will be dispatched to the Worker defining the binding.
  • If the designator is an object of the form { name: ..., entrypoint: ... }, requests will be dispatched to the entrypoint named entrypoint in the Worker named name. The entrypoint defaults to default, meaning { name: "a" } is the same as "a". If name is (await import("miniflare")).kCurrentWorker, requests will be dispatched to the Worker defining the binding.
  • If the designator is an object of the form { network: { ... } }, where network is a workerd Network struct, requests will be dispatched according to the fetched URL.
  • If the designator is an object of the form { external: { ... } } where external is a workerd ExternalServer struct, requests will be dispatched to the specified remote server.
  • If the designator is an object of the form { disk: { ... } } where disk is a workerd DiskDirectory struct, requests will be dispatched to an HTTP service backed by an on-disk directory.
  • If the designator is a function, requests will be dispatched to your custom handler. This allows you to access data and functions defined in Node.js from your Worker. Note instance will be the Miniflare instance dispatching the request.

• wrappedBindings?: Record<string, string | { scriptName: string, entrypoint?: string, bindings?: Record<string, Json> }>

  Record mapping binding name to designators to inject as wrapped bindings into this Worker. Wrapped bindings allow custom bindings to be written as JavaScript functions accepting an env parameter of "inner bindings" and returning the value to bind. A string designator is equivalent to { scriptName: <string> }. scriptName's bindings will be used as "inner bindings". JSON bindings in the designator also become "inner bindings" and will override any of scriptName bindings with the same name. The Worker named scriptName...

  • Must define a single ESModule as its source, using { modules: true, script: "..." }, { modules: true, scriptPath: "..." }, or { modules: [...] }
  • Must provide the function to use for the wrapped binding as an entrypoint named export or a default export if entrypoint is omitted
  • Must not be the first/entrypoint worker
  • Must not be bound to with service or Durable Object bindings
  • Must not define compatibilityDate or compatibilityFlags
  • Must not define outboundService
  • Must not directly or indirectly have a wrapped binding to itself
  • Must not be used as an argument to Miniflare#getWorker()
  Wrapped Bindings Example

  import { Miniflare } from "miniflare";
  const store = new Map<string, string>();
  const mf = new Miniflare({
    workers: [
      {
        wrappedBindings: {
          MINI_KV: {
            scriptName: "mini-kv", // Use Worker named `mini-kv` for implementation
            bindings: { NAMESPACE: "ns" }, // Override `NAMESPACE` inner binding
          },
        },
        modules: true,
        script: `export default {
          async fetch(request, env, ctx) {
            // Example usage of wrapped binding
            await env.MINI_KV.set("key", "value");
            return new Response(await env.MINI_KV.get("key"));
          }
        }`,
      },
      {
        name: "mini-kv",
        serviceBindings: {
          // Function-valued service binding for accessing Node.js state
          async STORE(request) {
            const { pathname } = new URL(request.url);
            const key = pathname.substring(1);
            if (request.method === "GET") {
              const value = store.get(key);
              const status = value === undefined ? 404 : 200;
              return new Response(value ?? null, { status });
            } else if (request.method === "PUT") {
              const value = await request.text();
              store.set(key, value);
              return new Response(null, { status: 204 });
            } else if (request.method === "DELETE") {
              store.delete(key);
              return new Response(null, { status: 204 });
            } else {
              return new Response(null, { status: 405 });
            }
          },
        },
        modules: true,
        script: `
        // Implementation of binding
        class MiniKV {
          constructor(env) {
            this.STORE = env.STORE;
            this.baseURL = "http://x/" + (env.NAMESPACE ?? "") + ":";
          }
          async get(key) {
            const res = await this.STORE.fetch(this.baseURL + key);
            return res.status === 404 ? null : await res.text();
          }
          async set(key, body) {
            await this.STORE.fetch(this.baseURL + key, { method: "PUT", body });
          }
          async delete(key) {
            await this.STORE.fetch(this.baseURL + key, { method: "DELETE" });
          }
        }
  
        // env has the type { STORE: Fetcher, NAMESPACE?: string }
        export default function (env) {
          return new MiniKV(env);
        }
        `,
      },
    ],
  });
  

  :warning: wrappedBindings are only supported in modules format Workers.

• outboundService?: string | { network: Network } | { external: ExternalServer } | { disk: DiskDirectory } | (request: Request) => Awaitable<Response>

  Dispatch this Worker's global fetch() and connect() requests to the configured service. Service designators follow the same rules above for serviceBindings.

• fetchMock?: import("undici").MockAgent

  An undici MockAgent to dispatch this Worker's global fetch() requests through.

  :warning: outboundService and fetchMock are mutually exclusive options. At most one of them may be specified per Worker.

• routes?: string[]

  Array of route patterns for this Worker. These follow the same routing rules as deployed Workers. If no routes match, Miniflare will fallback to the Worker defined first.

Cache

• cache?: boolean

  If false, default and named caches will be disabled. The Cache API will still be available, it just won't cache anything.

• cacheWarnUsage?: boolean

  If true, the first use of the Cache API will log a warning stating that the Cache API is unsupported on workers.dev subdomains.

Durable Objects

• durableObjects?: Record<string, string | { className: string, scriptName?: string }>

  Record mapping binding name to Durable Object class designators to inject as DurableObjectNamespace bindings into this Worker.

  • If the designator is a string, it should be the name of a class exported by this Worker.
  • If the designator is an object, and scriptName is undefined, className should be the name of a class exported by this Worker.
  • Otherwise, className should be the name of a class exported by the Worker with a name of scriptName.

KV

• kvNamespaces?: Record<string, string> | string[]

  Record mapping binding name to KV namespace IDs to inject as KVNamespace bindings into this Worker. Different Workers may bind to the same namespace ID with different binding names. If a string[] of binding names is specified, the binding name and KV namespace ID are assumed to be the same.

• sitePath?: string

  Path to serve Workers Sites files from. If set, __STATIC_CONTENT and __STATIC_CONTENT_MANIFEST bindings will be injected into this Worker. In modules mode, __STATIC_CONTENT_MANIFEST will also be exposed as a module with a string-typed default export, containing the JSON-stringified manifest. Note Workers Sites files are never cached in Miniflare.

• siteInclude?: string[]

  If set, only files with paths matching these glob patterns will be served.

• siteExclude?: string[]

  If set, only files with paths not matching these glob patterns will be served.

  • assetsPath?: string

  Path to serve Workers assets from.

  • assetsKVBindingName?: string Name of the binding to the KV namespace that the assets are in. If assetsPath is set, this binding will be injected into this Worker.

  • assetsManifestBindingName?: string Name of the binding to an ArrayBuffer containing the binary-encoded assets manifest. If assetsPath is set, this binding will be injected into this Worker.

R2

• r2Buckets?: Record<string, string> | string[]

  Record mapping binding name to R2 bucket names to inject as R2Bucket bindings into this Worker. Different Workers may bind to the same bucket name with different binding names. If a string[] of binding names is specified, the binding name and bucket name are assumed to be the same.

D1

• d1Databases?: Record<string, string> | string[]

  Record mapping binding name to D1 database IDs to inject as D1Database bindings into this Worker. Note binding names starting with __D1_BETA__ are injected as Fetcher bindings instead, and must be wrapped with a facade to provide the expected D1Database API. Different Workers may bind to the same database ID with different binding names. If a string[] of binding names is specified, the binding name and database ID are assumed to be the same.

Queues

• queueProducers?: Record<string, QueueProducerOptions> | string[]

  Record mapping binding name to queue options to inject as WorkerQueue bindings into this Worker. Different Workers may bind to the same queue name with different binding names. If a string[] of binding names is specified, the binding name and queue name (part of the queue options) are assumed to be the same.

• queueConsumers?: Record<string, QueueConsumerOptions> | string[]

  Record mapping queue name to consumer options. Messages enqueued on the corresponding queues will be dispatched to this Worker. Note each queue can have at most one consumer. If a string[] of queue names is specified, default consumer options will be used.

Analytics Engine, Sending Email, Vectorize and Workers for Platforms

Not yet supported

If you need support for these locally, consider using the wrappedBindings option to mock them out.

Browser Rendering and Workers AI

Not yet supported

If you need support for these locally, consider using the serviceBindings option to mock them out.

interface SharedOptions

Options shared between all Workers/"nanoservices".

Core

• rootPath?: string

  Path against which all other path options for this instance are resolved relative to. Defaults to the current working directory.

• host?: string

  Hostname that the workerd server should listen on. Defaults to 127.0.0.1.

• port?: number

  Port that the workerd server should listen on. Tries to default to 8787, but falls back to a random free port if this is in use. Note if a manually specified port is in use, Miniflare throws an error, rather than attempting to find a free port.

• https?: boolean

  If true, start an HTTPS server using a pre-generated self-signed certificate for localhost. Note this certificate is not valid for any other hostnames or IP addresses. If you need to access the HTTPS server from another device, you'll need to generate your own certificate and use the other https* options below.

  $ openssl req -newkey rsa:2048 -nodes -keyout key.pem -x509 -days 365 -out cert.pem
  

  new Miniflare({
  	httpsKeyPath: "key.pem",
  	httpsCertPath: "cert.pem",
  });
  

• httpsKey?: string

  When one of httpsCert or httpCertPath is also specified, starts an HTTPS server using the value of this option as the PEM encoded private key.

• httpsKeyPath?: string

  When one of httpsCert or httpCertPath is also specified, starts an HTTPS server using the PEM encoded private key stored at this file path.

• httpsCert?: string

  When one of httpsKey or httpsKeyPath is also specified, starts an HTTPS server using the value of this option as the PEM encoded certificate chain.

• httpsCertPath?: string

  When one of httpsKey or httpsKeyPath is also specified, starts an HTTPS server using the PEM encoded certificate chain stored at this file path.

• inspectorPort?: number

  Port that workerd should start a DevTools inspector server on. Visit chrome://inspect in a Chromium-based browser to connect to this. This can be used to see detailed console.logs, profile CPU usage, and will eventually allow step-through debugging.

• verbose?: boolean

  Enable workerd's --verbose flag for verbose logging. This can be used to see simplified console.logs.

• log?: Log

  Logger implementation for Miniflare's errors, warnings and informative messages.

• upstream?: string

  URL to use as the origin for incoming requests. If specified, all incoming request.urls will be rewritten to start with this string. This is especially useful when testing Workers that act as a proxy, and not as origins themselves.

• cf?: boolean | string | Record<string, any>

  Controls the object returned from incoming Request's cf property.

  • If set to a falsy value, an object with default placeholder values will be used
  • If set to an object, that object will be used
  • If set to true, a real cf object will be fetched from a trusted Cloudflare endpoint and cached in node_modules/.mf for 30 days
  • If set to a string, a real cf object will be fetched and cached at the provided path for 30 days

• liveReload?: boolean

  If true, Miniflare will inject a script into HTML responses that automatically reloads the page in-browser whenever the Miniflare instance's options are updated.

Cache, Durable Objects, KV, R2 and D1

• cachePersist?: Persistence

  Where to persist data cached in default or named caches. See docs for Persistence.

• durableObjectsPersist?: Persistence

  Where to persist data stored in Durable Objects. See docs for Persistence.

• kvPersist?: Persistence

  Where to persist data stored in KV namespaces. See docs for Persistence.

• r2Persist?: Persistence

  Where to persist data stored in R2 buckets. See docs for Persistence.

• d1Persist?: Persistence

  Where to persist data stored in D1 databases. See docs for Persistence.

Analytics Engine, Browser Rendering, Sending Email, Vectorize, Workers AI and Workers for Platforms

Not yet supported

type MiniflareOptions

SharedOptions & (WorkerOptions | { workers: WorkerOptions[] })

Miniflare accepts either a single Worker configuration or multiple Worker configurations in the workers array. When specifying an array of Workers, the first Worker is designated the entrypoint and will receive all incoming HTTP requests. Some options are shared between all workers and should always be defined at the top-level.

class Miniflare

• constructor(opts: MiniflareOptions)

  Creates a Miniflare instance and starts a new workerd server. Note unlike Miniflare 2, Miniflare 3 always starts a HTTP server listening on the configured host and port: there are no createServer/startServer functions.

• setOptions(opts: MiniflareOptions)

  Updates the configuration for this Miniflare instance and restarts the workerd server. Note unlike Miniflare 2, this does not merge the new configuration with the old configuration. Note that calling this function will invalidate any existing values returned by the Miniflare#get*() methods, preventing them from being used.

• ready: Promise<URL>

  Returns a Promise that resolves with a http URL to the workerd server once it has started and is able to accept requests.

• dispatchFetch(input: RequestInfo, init?: RequestInit): Promise<Response>

  Sends a HTTP request to the workerd server, dispatching a fetch event in the entrypoint Worker. Returns a Promise that resolves with the response. Note that this implicitly waits for the ready Promise to resolve, there's no need to do that yourself first. Additionally, the host of the request's URL is always ignored and replaced with the workerd server's.

• getBindings<Env extends Record<string, unknown> = Record<string, unknown>>(workerName?: string): Promise<Env>

  Returns a Promise that resolves with a record mapping binding names to bindings, for all bindings in the Worker with the specified workerName. If workerName is not specified, defaults to the entrypoint Worker.

• getWorker(workerName?: string): Promise<Fetcher>

  Returns a Promise that resolves with a Fetcher pointing to the specified workerName. If workerName is not specified, defaults to the entrypoint Worker. Note this Fetcher uses the experimental service_binding_extra_handlers compatibility flag to expose scheduled() and queue() methods for dispatching scheduled and queue events.

• getCaches(): Promise<CacheStorage>

  Returns a Promise that resolves with the CacheStorage instance of the entrypoint Worker. This means if cache: false is set on the entrypoint, calling methods on the resolved value won't do anything.

• getD1Database(bindingName: string, workerName?: string): Promise<D1Database>

  Returns a Promise that resolves with the D1Database instance corresponding to the specified bindingName of workerName. Note bindingName must not begin with __D1_BETA__. If workerName is not specified, defaults to the entrypoint Worker.

• getDurableObjectNamespace(bindingName: string, workerName?: string): Promise<DurableObjectNamespace>

  Returns a Promise that resolves with the DurableObjectNamespace instance corresponding to the specified bindingName of workerName. If workerName is not specified, defaults to the entrypoint Worker.

• getKVNamespace(bindingName: string, workerName?: string): Promise<KVNamespace>

  Returns a Promise that resolves with the KVNamespace instance corresponding to the specified bindingName of workerName. If workerName is not specified, defaults to the entrypoint Worker.

• getQueueProducer<Body>(bindingName: string, workerName?: string): Promise<Queue<Body>>

  Returns a Promise that resolves with the Queue producer instance corresponding to the specified bindingName of workerName. If workerName is not specified, defaults to the entrypoint Worker.

• getR2Bucket(bindingName: string, workerName?: string): Promise<R2Bucket>

  Returns a Promise that resolves with the R2Bucket producer instance corresponding to the specified bindingName of workerName. If workerName is not specified, defaults to the entrypoint Worker.

• dispose(): Promise<void>

  Cleans up the Miniflare instance, and shuts down the workerd server. Note that after this is called, Miniflare#setOptions() and Miniflare#dispatchFetch() cannot be called. Additionally, calling this function will invalidate any values returned by the Miniflare#get*() methods, preventing them from being used.

• getCf(): Promise<Record<string, any>>

  Returns the same object returned from incoming Request's cf property. This object depends on the cf property from SharedOptions.

Configuration

Local workerd

You can override the workerd binary being used by miniflare with a your own local build by setting the MINIFLARE_WORKERD_PATH environment variable.

For example:

$ export MINIFLARE_WORKERD_PATH="<WORKERD_REPO_DIR>/bazel-bin/src/workerd/server/workerd"

Similar packages

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wrangler

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worktop

Worktop is a lightweight framework for building Cloudflare Workers. It provides utilities for routing, handling requests, and managing responses. While it simplifies the development of Workers, it does not offer the local simulation capabilities that Miniflare provides.