Fix environment variables casing bug (#604)

* fix env var casing bug

* localize testing of casing to Windows

* update test

* update startApp tests too

Author: hossam-nasr

src/eventHandlers/FunctionEnvironmentReloadHandler.ts

@@ -35,7 +35,10 @@ export class FunctionEnvironmentReloadHandler extends EventHandler<
             logCategory: LogCategory.System,
         });
 
-        process.env = Object.assign({}, msg.environmentVariables);
+        // reset existing env vars
+        Object.keys(process.env).map((key) => delete process.env[key]);
+        // set new env vars
+        Object.assign(process.env, msg.environmentVariables);
 
         // Change current working directory
         if (msg.functionAppDirectory) {

test/eventHandlers/FunctionEnvironmentReloadHandler.test.ts

@@ -74,14 +74,14 @@ describe('FunctionEnvironmentReloadHandler', () => {
     let originalEnv: NodeJS.ProcessEnv;
     let originalCwd: string;
     before(() => {
+        originalEnv = { ...process.env };
         originalCwd = process.cwd();
-        originalEnv = process.env;
         ({ stream, channel } = beforeEventHandlerSuite());
         channel.hostVersion = '2.7.0';
     });
 
     after(() => {
-        process.env = originalEnv;
+        Object.assign(process.env, originalEnv);
     });
 
     afterEach(async () => {
@@ -108,6 +108,32 @@ describe('FunctionEnvironmentReloadHandler', () => {
         expect(process.env.PlaceholderVariable).to.be.undefined;
     });
 
+    it('preserves OS-specific casing behavior of environment variables', async () => {
+        process.env.PlaceholderVariable = 'TRUE';
+        stream.addTestMessage({
+            requestId: 'id',
+            functionEnvironmentReloadRequest: {
+                environmentVariables: {
+                    hello: 'world',
+                    SystemDrive: 'Q:',
+                },
+                functionAppDirectory: null,
+            },
+        });
+        await stream.assertCalledWith(Msg.reloadEnvVarsLog(2), Msg.reloadSuccess);
+        expect(process.env.hello).to.equal('world');
+        expect(process.env.SystemDrive).to.equal('Q:');
+        expect(process.env.PlaceholderVariable).to.be.undefined;
+        expect(process.env.placeholdervariable).to.be.undefined;
+        if (process.platform === 'win32') {
+            expect(process.env.HeLlO).to.equal('world');
+            expect(process.env.systemdrive).to.equal('Q:');
+        } else {
+            expect(process.env.HeLlO).to.be.undefined;
+            expect(process.env.systemdrive).to.be.undefined;
+        }
+    });
+
     it('reloading environment variables removes existing environment variables', async () => {
         process.env.PlaceholderVariable = 'TRUE';
         process.env.NODE_ENV = 'Debug';

test/startApp.test.ts

@@ -48,13 +48,13 @@ describe('startApp', () => {
 
     before(async () => {
         originalCwd = process.cwd();
-        originalEnv = process.env;
+        originalEnv = { ...process.env };
         ({ stream, channel } = beforeEventHandlerSuite());
         coreApi = await import('@azure/functions-core');
     });
 
     after(() => {
-        process.env = originalEnv;
+        Object.assign(process.env, originalEnv);
     });
 
     afterEach(async () => {