Add native support for warmup trigger (#180)

* Add warmup trigger

* Additional changes to types

* Add back trigger property

* Minor changes to docs, types, signatures

* Revert a few minor edits

* PR review suggestions

* Add interface for warmupContext

src/addBindingName.ts

@@ -1,13 +1,13 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT License.
 
+export { InvocationContext } from './InvocationContext';
 export { HttpRequest } from './http/HttpRequest';
 export { HttpResponse } from './http/HttpResponse';
-export { InvocationContext } from './InvocationContext';
 
 const bindingCounts: Record<string, number> = {};
 /**
- * If the host spawns multiple workers, it expects the metadata (including binding name) to be the same accross workers
+ * If the host spawns multiple workers, it expects the metadata (including binding name) to be the same across workers.
  * That means we need to generate binding names in a deterministic fashion, so we'll do that using a count
  * There's a tiny risk users register bindings in a non-deterministic order (i.e. async race conditions), but it's okay considering the following:
  * 1. We will track the count individually for each binding type. This makes the names more readable and reduces the chances a race condition will matter

src/app.ts

@@ -19,6 +19,7 @@ import {
     StorageBlobFunctionOptions,
     StorageQueueFunctionOptions,
     TimerFunctionOptions,
+    WarmupFunctionOptions,
 } from '@azure/functions';
 import * as coreTypes from '@azure/functions-core';
 import { CoreInvocationContext, FunctionCallback } from '@azure/functions-core';
@@ -145,6 +146,10 @@ export function cosmosDB(name: string, options: CosmosDBFunctionOptions): void {
     generic(name, convertToGenericOptions(options, <any>trigger.cosmosDB));
 }
 
+export function warmup(name: string, options: WarmupFunctionOptions): void {
+    generic(name, convertToGenericOptions(options, trigger.warmup));
+}
+
 export function generic(name: string, options: GenericFunctionOptions): void {
     if (!hasSetup) {
         setup();

src/trigger.ts

@@ -22,6 +22,8 @@ import {
     StorageQueueTriggerOptions,
     TimerTrigger,
     TimerTriggerOptions,
+    WarmupTrigger,
+    WarmupTriggerOptions,
 } from '@azure/functions';
 import { addBindingName } from './addBindingName';
 
@@ -90,6 +92,13 @@ export function cosmosDB(options: CosmosDBTriggerOptions): CosmosDBTrigger {
     });
 }
 
+export function warmup(options: WarmupTriggerOptions): WarmupTrigger {
+    return addTriggerBindingName({
+        ...options,
+        type: 'warmupTrigger',
+    });
+}
+
 export function generic(options: GenericTriggerOptions): FunctionTrigger {
     return addTriggerBindingName(options);
 }

types/app.d.ts

@@ -9,6 +9,7 @@ import { HttpFunctionOptions, HttpHandler, HttpMethodFunctionOptions } from './h
 import { ServiceBusQueueFunctionOptions, ServiceBusTopicFunctionOptions } from './serviceBus';
 import { StorageBlobFunctionOptions, StorageQueueFunctionOptions } from './storage';
 import { TimerFunctionOptions } from './timer';
+import { WarmupFunctionOptions } from './warmup';
 
 /**
  * Registers an http function in your app that will be triggered by making a request to the function url
@@ -143,6 +144,18 @@ export function eventGrid(name: string, options: EventGridFunctionOptions): void
  */
 export function cosmosDB(name: string, options: CosmosDBFunctionOptions): void;
 
+/**
+ * Registers a function in your app that will be triggered when an instance is added to scale a running function app.
+ * The warmup trigger is only called during scale-out operations, not during restarts or other non-scale startups.
+ * Make sure your logic can load all required dependencies without relying on the warmup trigger.
+ * Lazy loading is a good pattern to achieve this goal.
+ * The warmup trigger isn't available to apps running on the Consumption plan.
+ * For more information, please see the [Azure Functions warmup trigger documentation](https://learn.microsoft.com/azure/azure-functions/functions-bindings-warmup?tabs=isolated-process&pivots=programming-language-javascript).
+ * @param name The name of the function. The name must be unique within your app and will mostly be used for your own tracking purposes
+ * @param options Configuration options describing the inputs, outputs, and handler for this function
+ */
+export function warmup(name: string, options: WarmupFunctionOptions): void;
+
 /**
  * Registers a generic function in your app that will be triggered based on the type specified in `options.trigger.type`
  * Use this method if your desired trigger type does not already have its own method

types/index.d.ts

@@ -20,6 +20,7 @@ export * from './storage';
 export * from './table';
 export * from './timer';
 export * as trigger from './trigger';
+export * from './warmup';
 
 /**
  * Void if no `return` output is registered

types/trigger.d.ts

@@ -20,6 +20,7 @@ import {
     StorageQueueTriggerOptions,
 } from './storage';
 import { TimerTrigger, TimerTriggerOptions } from './timer';
+import { WarmupTrigger, WarmupTriggerOptions } from './warmup';
 
 /**
  * [Link to docs and examples](https://docs.microsoft.com/azure/azure-functions/functions-bindings-http-webhook-trigger?&pivots=programming-language-javascript)
@@ -66,6 +67,11 @@ export function eventGrid(options: EventGridTriggerOptions): EventGridTrigger;
  */
 export function cosmosDB(options: CosmosDBTriggerOptions): CosmosDBTrigger;
 
+/**
+ * [Link to docs and examples](https://learn.microsoft.com/azure/azure-functions/functions-bindings-warmup?tabs=isolated-process&pivots=programming-language-javascript)
+ */
+export function warmup(options: WarmupTriggerOptions): WarmupTrigger;
+
 /**
  * A generic option that can be used for any trigger type
  * Use this method if your desired trigger type does not already have its own method

types/warmup.d.ts

@@ -0,0 +1,17 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT License.
+
+import { FunctionOptions, FunctionResult, FunctionTrigger } from './index';
+import { InvocationContext } from './InvocationContext';
+
+export interface WarmupContextOptions {}
+export type WarmupHandler = (warmupContext: WarmupContextOptions, context: InvocationContext) => FunctionResult;
+
+export interface WarmupFunctionOptions extends WarmupTriggerOptions, Partial<FunctionOptions> {
+    handler: WarmupHandler;
+
+    trigger?: WarmupTrigger;
+}
+
+export interface WarmupTriggerOptions {}
+export type WarmupTrigger = FunctionTrigger & WarmupTriggerOptions;