Adding package.json warning when using AzureFiles

src/WorkerChannel.ts

@@ -2,6 +2,8 @@
 // Licensed under the MIT License.
 
 import { Context } from '@azure/functions';
+import { access, constants } from 'fs';
+import * as path from 'path';
 import { format, isFunction } from 'util';
 import { AzureFunctionsRpcMessages as rpc } from '../azure-functions-language-worker-protobuf/src/rpc';
 import { CreateContextAndInputs, LogCallback, ResultCallback } from './Context';
@@ -129,6 +131,8 @@ export class WorkerChannel implements IWorkerChannel {
             throw new InternalException(msg);
         }
 
+        this.logColdStartWarning();
+
         const workerCapabilities = {
             RpcHttpTriggerMetadataRemoved: 'true',
             RpcHttpBodyOnly: 'true',
@@ -407,4 +411,31 @@ export class WorkerChannel implements IWorkerChannel {
             after(context);
         }
     }
+
+    private logColdStartWarning(delayInMs?: number): void {
+        // On reading a js file with function code('require') NodeJs tries to find 'package.json' all the way up to the file system root.
+        // In Azure files it causes a delay during cold start as connection to Azure Files is an expensive operation.
+        if (
+            process.env.WEBSITE_CONTENTAZUREFILECONNECTIONSTRING &&
+            process.env.WEBSITE_CONTENTSHARE &&
+            process.env.AzureWebJobsScriptRoot
+        ) {
+            // Add delay to avoid affecting coldstart
+            if (!delayInMs) {
+                delayInMs = 5000;
+            }
+            setTimeout(() => {
+                access(path.join(process.env.AzureWebJobsScriptRoot!, 'package.json'), constants.F_OK, (e) => {
+                    if (e) {
+                        this.log({
+                            message:
+                                'package.json is not found at the root of the Function App in Azure Files - cold start for NodeJs can be affected.',
+                            level: LogLevel.Debug,
+                            logCategory: LogCategory.System,
+                        });
+                    }
+                });
+            }, delayInMs);
+        }
+    }
 }

test/WorkerChannelTests.ts

@@ -9,6 +9,8 @@ import { FunctionInfo } from '../src/FunctionInfo';
 import { FunctionLoader } from '../src/FunctionLoader';
 import { WorkerChannel } from '../src/WorkerChannel';
 import { TestEventStream } from './TestEventStream';
+import LogCategory = rpc.RpcLog.RpcLogCategory;
+import LogLevel = rpc.RpcLog.Level;
 
 describe('WorkerChannel', () => {
     let channel: WorkerChannel;
@@ -662,5 +664,25 @@ describe('WorkerChannel', () => {
             };
             assertInvocationSuccess(expectedOutput, expectedReturnValue);
         });
+
+        it('logs AzureFiles cold start warning', async () => {
+            process.env.WEBSITE_CONTENTAZUREFILECONNECTIONSTRING = 'test';
+            process.env.WEBSITE_CONTENTSHARE = 'test';
+            process.env.AzureWebJobsScriptRoot = 'test';
+
+            // Accesing private method
+            (channel as any).logColdStartWarning(100);
+
+            // Set slight delay
+            await new Promise((resolve) => setTimeout(resolve, 200));
+            sinon.assert.calledWith(stream.written, <rpc.IStreamingMessage>{
+                rpcLog: {
+                    message:
+                        'package.json is not found at the root of the Function App in Azure Files - cold start for NodeJs can be affected.',
+                    level: LogLevel.Debug,
+                    logCategory: LogCategory.System,
+                },
+            });
+        });
     });
 });