Added ValidateAspNetCoreUrls (#2466)

This pull request introduces a validation check for the
`ASPNETCORE_URLS` environment variable to ensure it is in the correct
format before starting the engine in the `Program` class. This change
helps in preventing runtime errors due to misconfigured URLs.

Key changes:

* Added a new method `ValidateAspNetCoreUrls` to check the format of the
`ASPNETCORE_URLS` environment variable. This method splits the
environment variable by commas or semicolons and ensures each part is a
valid absolute URI.
* Integrated the `ValidateAspNetCoreUrls` method into the `Main` method
to validate the URLs before proceeding with the engine start. If the
validation fails, an error message is printed, and the application exits
with an error code.

## Why make this change?

The primary motivation is to return a more clear error message to the
user.

Closes #2465

## What is this change?

Startup validation.

## How was this tested?

- [ ] Integration Tests
- [ ] Unit Tests

## Sample Request(s)

Valid value in END file:
`ASPNETCORE_URLS="http://localhost:5000;https://localhost:5001"`

Invalid value in END file:
`ASPNETCORE_URLS=http://localhost:5000;https://localhost:5001`

---------

Co-authored-by: Jerry Nixon <jerry.nixon@microsoft.com>

src/Service.Tests/Unittests/EnvironmentTests.cs

@@ -0,0 +1,46 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System;
+using System.IO;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Azure.DataApiBuilder.Service.Tests.UnitTests;
+
+/// <summary>
+/// Contains test involving environment variables.
+/// </summary>
+[TestClass]
+public class EnvironmentTests
+{
+    /// <summary>
+    /// Tests the behavior of the <c>Main</c> method when the <c>ASPNETCORE_URLS</c> environment variable is set to an invalid value.
+    /// </summary>
+    /// <remarks>
+    /// This test sets the <c>ASPNETCORE_URLS</c> environment variable to an invalid value, invokes the <c>Main</c> method,
+    /// and verifies that the application exits with an error code of -1. Additionally, it checks if the error message
+    /// contains the name of the invalid environment variable.
+    /// </remarks>
+    [TestMethod]
+    public void Main_WhenAspNetCoreUrlsInvalid_ShouldExitWithError()
+    {
+        const string ASPNETCORE_URLS_NAME = "ASPNETCORE_URLS";
+        const string ASPNETCORE_URLS_INVALID_VALUE = nameof(Main_WhenAspNetCoreUrlsInvalid_ShouldExitWithError);
+        string originalEnvValue = Environment.GetEnvironmentVariable(ASPNETCORE_URLS_NAME);
+
+        // Arrange
+        Environment.SetEnvironmentVariable(ASPNETCORE_URLS_NAME, ASPNETCORE_URLS_INVALID_VALUE);
+        using StringWriter consoleOutput = new();
+        Console.SetError(consoleOutput);
+
+        // Act
+        Program.Main(Array.Empty<string>());
+
+        // Assert
+        Assert.AreEqual(-1, Environment.ExitCode);
+        StringAssert.Contains(consoleOutput.ToString(), ASPNETCORE_URLS_NAME, StringComparison.Ordinal);
+
+        // Cleanup
+        Environment.SetEnvironmentVariable(ASPNETCORE_URLS_NAME, originalEnvValue);
+    }
+}

src/Service/Program.cs

@@ -4,6 +4,7 @@
 using System;
 using System.CommandLine;
 using System.CommandLine.Parsing;
+using System.Linq;
 using System.Threading.Tasks;
 using Azure.DataApiBuilder.Config;
 using Azure.DataApiBuilder.Service.Exceptions;
@@ -26,6 +27,13 @@ public class Program
 
         public static void Main(string[] args)
         {
+            if (!ValidateAspNetCoreUrls())
+            {
+                Console.Error.WriteLine("Invalid ASPNETCORE_URLS format. e.g.: ASPNETCORE_URLS=\"http://localhost:5000;https://localhost:5001\"");
+                Environment.ExitCode = -1;
+                return;
+            }
+
             if (!StartEngine(args))
             {
                 Environment.ExitCode = -1;
@@ -224,5 +232,17 @@ private static void AddConfigurationProviders(
                 .AddEnvironmentVariables(prefix: FileSystemRuntimeConfigLoader.ENVIRONMENT_PREFIX)
                 .AddCommandLine(args);
         }
+
+        private static bool ValidateAspNetCoreUrls()
+        {
+            if (Environment.GetEnvironmentVariable("ASPNETCORE_URLS") is not string value)
+            {
+                return true; // If the environment variable is missing, then it cannot be invalid.
+            }
+
+            return value
+                .Split(new[] { ',', ';' }, StringSplitOptions.RemoveEmptyEntries)
+                .All(x => Uri.TryCreate(x.Trim(), UriKind.Absolute, out _));
+        }
     }
 }