Support log hooks

src/hooks/LogHookContext.ts

@@ -0,0 +1,51 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT License.
+
+import * as types from '@azure/functions';
+import { ReadOnlyError } from '../errors';
+import { nonNullProp } from '../utils/nonNull';
+import { HookContext } from './HookContext';
+
+export class LogHookContext extends HookContext implements types.LogHookContext {
+    #init: types.LogHookContextInit;
+
+    constructor(init?: types.LogHookContextInit) {
+        super(init);
+        this.#init = init ?? {};
+        this.#init.level ??= 'information';
+        this.#init.message ??= 'unknown';
+        this.#init.category ??= 'user';
+    }
+
+    get level(): types.LogLevel {
+        return nonNullProp(this.#init, 'level');
+    }
+
+    set level(value: types.LogLevel) {
+        this.#init.level = value;
+    }
+
+    get message(): string {
+        return nonNullProp(this.#init, 'message');
+    }
+
+    set message(value: string) {
+        this.#init.message = value;
+    }
+
+    get category(): types.LogCategory {
+        return nonNullProp(this.#init, 'category');
+    }
+
+    set category(_value: types.LogCategory) {
+        throw new ReadOnlyError('category');
+    }
+
+    get invocationContext(): types.InvocationContext | undefined {
+        return this.#init.invocationContext;
+    }
+
+    set invocationContext(_value: types.InvocationContext | undefined) {
+        throw new ReadOnlyError('invocationContext');
+    }
+}

src/hooks/registerHook.ts

@@ -1,12 +1,19 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT License.
 
-import { AppStartHandler, AppTerminateHandler, PostInvocationHandler, PreInvocationHandler } from '@azure/functions';
+import {
+    AppStartHandler,
+    AppTerminateHandler,
+    LogHookHandler,
+    PostInvocationHandler,
+    PreInvocationHandler,
+} from '@azure/functions';
 import * as coreTypes from '@azure/functions-core';
 import { Disposable } from '../utils/Disposable';
 import { tryGetCoreApiLazy } from '../utils/tryGetCoreApiLazy';
 import { AppStartContext } from './AppStartContext';
 import { AppTerminateContext } from './AppTerminateContext';
+import { LogHookContext } from './LogHookContext';
 import { PostInvocationContext } from './PostInvocationContext';
 import { PreInvocationContext } from './PreInvocationContext';
 
@@ -49,3 +56,9 @@ export function postInvocation(handler: PostInvocationHandler): Disposable {
         return handler(new PostInvocationContext(coreContext));
     });
 }
+
+export function log(handler: LogHookHandler): Disposable {
+    return registerHook('log', (coreContext) => {
+        return handler(new LogHookContext(coreContext));
+    });
+}

types-core/index.d.ts

@@ -58,13 +58,15 @@ declare module '@azure/functions-core' {
     function registerHook(hookName: 'postInvocation', callback: PostInvocationCallback): Disposable;
     function registerHook(hookName: 'appStart', callback: AppStartCallback): Disposable;
     function registerHook(hookName: 'appTerminate', callback: AppTerminateCallback): Disposable;
+    function registerHook(hookName: 'log', callback: LogHookCallback): Disposable;
     function registerHook(hookName: string, callback: HookCallback): Disposable;
 
-    type HookCallback = (context: HookContext) => void | Promise<void>;
+    type HookCallback = (context: HookContext) => unknown;
     type PreInvocationCallback = (context: PreInvocationContext) => void | Promise<void>;
     type PostInvocationCallback = (context: PostInvocationContext) => void | Promise<void>;
     type AppStartCallback = (context: AppStartContext) => void | Promise<void>;
     type AppTerminateCallback = (context: AppTerminateContext) => void | Promise<void>;
+    type LogHookCallback = (context: LogHookContext) => void;
 
     type HookData = { [key: string]: any };
 
@@ -146,6 +148,29 @@ declare module '@azure/functions-core' {
 
     type AppTerminateContext = HookContext;
 
+    interface LogHookContext extends HookContext {
+        /**
+         * If the log occurs during a function execution, the context object passed to the function handler.
+         * Otherwise, undefined.
+         */
+        readonly invocationContext?: unknown;
+
+        /**
+         * 'system' if the log is generated by Azure Functions, 'user' if the log is generated by your own app.
+         */
+        readonly category: RpcLogCategory;
+
+        /**
+         * Changes to this value _will_ affect the resulting log, but only for user-generated logs.
+         */
+        level: RpcLogLevel;
+
+        /**
+         * Changes to this value _will_ affect the resulting log, but only for user-generated logs.
+         */
+        message: string;
+    }
+
     /**
      * Represents a type which can release resources, such as event listening or a timer.
      */

types/InvocationContext.d.ts

@@ -5,7 +5,7 @@ import { CosmosDBInput, CosmosDBOutput } from './cosmosDB';
 import { EventGridOutput, EventGridPartialEvent } from './eventGrid';
 import { EventHubOutput } from './eventHub';
 import { HttpOutput, HttpResponse } from './http';
-import { FunctionInput, FunctionOutput, FunctionTrigger } from './index';
+import { FunctionInput, FunctionOutput, FunctionTrigger, LogLevel } from './index';
 import { ServiceBusQueueOutput, ServiceBusTopicOutput } from './serviceBus';
 import { SqlInput, SqlOutput } from './sql';
 import { StorageBlobInput, StorageBlobOutput, StorageQueueOutput } from './storage';
@@ -342,5 +342,3 @@ export interface InvocationContextInit {
 }
 
 export type LogHandler = (level: LogLevel, ...args: unknown[]) => void;
-
-export type LogLevel = 'trace' | 'debug' | 'information' | 'warning' | 'error' | 'critical' | 'none';

types/hooks/logHooks.d.ts

@@ -0,0 +1,58 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the MIT License.
+
+import { LogLevel } from '../index';
+import { InvocationContext } from '../InvocationContext';
+import { HookContext, HookContextInit } from './HookContext';
+
+/**
+ * Handler for log hooks.
+ */
+export type LogHookHandler = (context: LogHookContext) => void;
+
+/**
+ * Context on a log
+ */
+export declare class LogHookContext extends HookContext {
+    /**
+     * For testing purposes only. This will always be constructed for you when run in the context of the Azure Functions runtime
+     */
+    constructor(init?: LogHookContextInit);
+
+    /**
+     * If the log occurs during a function execution, the context object passed to the function handler.
+     * Otherwise, undefined.
+     */
+    readonly invocationContext: InvocationContext | undefined;
+
+    /**
+     * 'system' if the log is generated by Azure Functions, 'user' if the log is generated by your own app.
+     */
+    readonly category: LogCategory;
+
+    /**
+     * Changes to this value _will_ affect the resulting log, but only for user-generated logs.
+     */
+    level: LogLevel;
+
+    /**
+     * Changes to this value _will_ affect the resulting log, but only for user-generated logs.
+     */
+    message: string;
+}
+
+/**
+ * Object passed to LogHookContext constructors.
+ * For testing purposes only
+ */
+export interface LogHookContextInit extends HookContextInit {
+    invocationContext?: InvocationContext;
+
+    level?: LogLevel;
+
+    category?: LogCategory;
+
+    message?: string;
+}
+
+export type LogCategory = 'user' | 'system' | 'customMetric';

types/hooks/registerHook.d.ts

@@ -4,6 +4,7 @@
 import { Disposable } from '../index';
 import { AppStartHandler, AppTerminateHandler } from './appHooks';
 import { PostInvocationHandler, PreInvocationHandler } from './invocationHooks';
+import { LogHookHandler } from './logHooks';
 
 /**
  * Register a hook to be run at the start of your application
@@ -38,3 +39,12 @@ export function preInvocation(handler: PreInvocationHandler): Disposable;
  * @returns a `Disposable` object that can be used to unregister the hook
  */
 export function postInvocation(handler: PostInvocationHandler): Disposable;
+
+/**
+ * PREVIEW: Register a hook to be run for each log.
+ * This functionality requires Azure Functions Host v4.34+.
+ *
+ * @param handler the handler for the hook
+ * @returns a `Disposable` object that can be used to unregister the hook
+ */
+export function log(handler: LogHookHandler): Disposable;

types/index.d.ts

@@ -13,6 +13,7 @@ export * from './generic';
 export * from './hooks/appHooks';
 export * from './hooks/HookContext';
 export * from './hooks/invocationHooks';
+export * from './hooks/logHooks';
 export * from './http';
 export * as input from './input';
 export * from './InvocationContext';
@@ -198,3 +199,5 @@ export declare class Disposable {
      */
     dispose(): any;
 }
+
+export type LogLevel = 'trace' | 'debug' | 'information' | 'warning' | 'error' | 'critical' | 'none';