From fe1dfee7bb5a34421dfc9ee591f968461d5568e1 Mon Sep 17 00:00:00 2001
From: Marie Hoeger <marie.hoeger@gmail.com>
Date: Tue, 3 Dec 2019 19:12:22 -0800
Subject: [PATCH] do not use placeholder worker if ~3 and v2 compatability
 enabled (#5328)

* do not use placeholder worker if ~3 and v2 compatability enabled

* delete irrelevant comment
---
 .../Environment/EnvironmentExtensions.cs      | 11 +++++++++
 .../Rpc/WebHostRpcWorkerChannelManager.cs     |  4 +++-
 .../WebHostRpcWorkerChannelManagerTests.cs    | 23 +++++++++++++++++++
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/src/WebJobs.Script/Environment/EnvironmentExtensions.cs b/src/WebJobs.Script/Environment/EnvironmentExtensions.cs
index 4f2f43fe6e..a6b43bef91 100644
--- a/src/WebJobs.Script/Environment/EnvironmentExtensions.cs
+++ b/src/WebJobs.Script/Environment/EnvironmentExtensions.cs
@@ -108,6 +108,17 @@ public static bool IsV2CompatibilityMode(this IEnvironment environment)
             return isFunctionsV2CompatibilityMode || isV2ExtensionVersion;
         }
 
+        public static bool IsV2CompatabileOnV3Extension(this IEnvironment environment)
+        {
+            string compatModeString = environment.GetEnvironmentVariable(FunctionsV2CompatibilityModeKey);
+            bool.TryParse(compatModeString, out bool isFunctionsV2CompatibilityMode);
+
+            string extensionVersion = environment.GetEnvironmentVariable(FunctionsExtensionVersion);
+            bool isV3ExtensionVersion = string.Compare(extensionVersion, "~3", CultureInfo.InvariantCulture, CompareOptions.OrdinalIgnoreCase) == 0;
+
+            return isFunctionsV2CompatibilityMode && isV3ExtensionVersion;
+        }
+
         public static bool IsContainer(this IEnvironment environment)
         {
             var runningInContainer = environment.GetEnvironmentVariable(RunningInContainer);
diff --git a/src/WebJobs.Script/Workers/Rpc/WebHostRpcWorkerChannelManager.cs b/src/WebJobs.Script/Workers/Rpc/WebHostRpcWorkerChannelManager.cs
index cf47f9db10..08ccc13036 100644
--- a/src/WebJobs.Script/Workers/Rpc/WebHostRpcWorkerChannelManager.cs
+++ b/src/WebJobs.Script/Workers/Rpc/WebHostRpcWorkerChannelManager.cs
@@ -133,10 +133,12 @@ private bool UsePlaceholderChannel(string workerRuntime)
             if (!string.IsNullOrEmpty(workerRuntime))
             {
                 // Special case: node apps must be read-only to use the placeholder mode channel
+                // Also cannot use placeholder worker that is targeting ~3 but has backwards compatibility with V2 enabled
                 // TODO: Remove special casing when resolving https://github.com/Azure/azure-functions-host/issues/4534
                 if (string.Equals(workerRuntime, RpcWorkerConstants.NodeLanguageWorkerName, StringComparison.OrdinalIgnoreCase))
                 {
-                    return _environment.IsFileSystemReadOnly();
+                    // Use if readonly and not v2 compatible on ~3 extension
+                    return _environment.IsFileSystemReadOnly() && !_environment.IsV2CompatabileOnV3Extension();
                 }
                 return true;
             }
diff --git a/test/WebJobs.Script.Tests/Workers/Rpc/WebHostRpcWorkerChannelManagerTests.cs b/test/WebJobs.Script.Tests/Workers/Rpc/WebHostRpcWorkerChannelManagerTests.cs
index 9954f59ce4..c69fd961c3 100644
--- a/test/WebJobs.Script.Tests/Workers/Rpc/WebHostRpcWorkerChannelManagerTests.cs
+++ b/test/WebJobs.Script.Tests/Workers/Rpc/WebHostRpcWorkerChannelManagerTests.cs
@@ -258,6 +258,29 @@ public async Task SpecializeAsync_Node_NotReadOnly_KillsProcess()
             Assert.Null(initializedChannel);
         }
 
+        [Fact]
+        public async Task SpecializeAsync_Node_V2CompatibilityWithV3Extension_KillsProcess()
+        {
+            var testMetricsLogger = new TestMetricsLogger();
+            _testEnvironment.SetEnvironmentVariable(RpcWorkerConstants.FunctionWorkerRuntimeSettingName, RpcWorkerConstants.NodeLanguageWorkerName);
+            _testEnvironment.SetEnvironmentVariable(EnvironmentSettingNames.FunctionsV2CompatibilityModeKey, "true");
+            _testEnvironment.SetEnvironmentVariable(EnvironmentSettingNames.FunctionsExtensionVersion, "~3");
+
+            _rpcWorkerChannelManager = new WebHostRpcWorkerChannelManager(_eventManager, _testEnvironment, _loggerFactory, _rpcWorkerChannelFactory, _optionsMonitor, testMetricsLogger);
+
+            IRpcWorkerChannel nodeWorkerChannel = CreateTestChannel(RpcWorkerConstants.NodeLanguageWorkerName);
+
+            await _rpcWorkerChannelManager.SpecializeAsync();
+
+            // Verify logs
+            var traces = _testLogger.GetLogMessages();
+            Assert.True(traces.Count() == 0);
+
+            // Verify channel
+            var initializedChannel = await _rpcWorkerChannelManager.GetChannelAsync(RpcWorkerConstants.NodeLanguageWorkerName);
+            Assert.Null(initializedChannel);
+        }
+
         [Fact]
         public async Task ShutdownStandbyChannels_WorkerRuntime_Not_Set()
         {