Fix dab validate schema fetch Error from URL (#2099)

## Why make this change?

- Closes #2013
- An error is thrown when NJsonSchema tries to fetch the schema from
url, due to failing to add refrences.

## What is this change?

- since, we only need to fetch the data from the schema file, we can
simply make a get call to the url, instead of using NJsonSchema.

## How was this tested?

- [ ] Integration Tests
- [ ] Unit Tests

## Sample Request(s)

- Example REST and/or GraphQL request to demonstrate modifications
- Example of CLI usage to demonstrate modifications

src/Core/Configurations/JsonConfigSchemaValidator.cs

@@ -16,16 +16,19 @@ public class JsonConfigSchemaValidator
 {
     private ILogger<JsonConfigSchemaValidator> _logger;
     private IFileSystem _fileSystem;
+    private HttpClient _httpClient;
 
     /// <summary> 
-    /// Sets the logger and file system for the JSON config schema validator. 
+    /// Sets the logger, file system and httpClient for the JSON config schema validator. 
     /// </summary> 
     /// <param name="jsonSchemaValidatorLogger">The logger to use for the JSON schema validator.</param> 
     /// <param name="fileSystem">The file system to use for the JSON schema validator.</param>
-    public JsonConfigSchemaValidator(ILogger<JsonConfigSchemaValidator> jsonSchemaValidatorLogger, IFileSystem fileSystem)
+    /// <param name="httpClient">The http client to use for the JSON schema validator. If not provided, a new HttpClient will be used.</param>
+    public JsonConfigSchemaValidator(ILogger<JsonConfigSchemaValidator> jsonSchemaValidatorLogger, IFileSystem fileSystem, HttpClient? httpClient = null)
     {
         _logger = jsonSchemaValidatorLogger;
         _fileSystem = fileSystem;
+        _httpClient = httpClient ?? new();
     }
 
     /// <summary> 
@@ -71,12 +74,21 @@ public async Task<JsonSchemaValidationResult> ValidateJsonConfigWithSchemaAsync(
         {
             try
             {
-                JsonSchema jsonSchema = await JsonSchema.FromUrlAsync(runtimeConfig.Schema);
-                return jsonSchema.ToJson();
+                // Send a GET request to the URL specified in runtimeConfig.Schema to get the JSON schema.
+                HttpResponseMessage response = await _httpClient.GetAsync(runtimeConfig.Schema);
+                if (response.IsSuccessStatusCode)
+                {
+                    string jsonSchema = await response.Content.ReadAsStringAsync();
+                    return jsonSchema;
+                }
+                else
+                {
+                    _logger!.LogWarning($"Received response: ({response.StatusCode}) while fetching schema from url: {runtimeConfig.Schema}");
+                }
             }
             catch (Exception e)
             {
-                _logger!.LogError($"Failed to get schema from url: {runtimeConfig.Schema}\n{e}");
+                _logger!.LogWarning($"Failed to send GET request to fetch schema from url: {runtimeConfig.Schema}\n{e}");
             }
         }
 

src/Service.Tests/Configuration/ConfigurationTests.cs

@@ -42,6 +42,7 @@
 using Microsoft.IdentityModel.Tokens;
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Moq;
+using Moq.Protected;
 using VerifyMSTest;
 using static Azure.DataApiBuilder.Config.FileSystemRuntimeConfigLoader;
 using static Azure.DataApiBuilder.Service.Tests.Configuration.ConfigurationEndpoints;
@@ -1323,6 +1324,101 @@ public async Task TestEngineCanStartConfigWithCustomProperties()
             }
         }
 
+        /// <summary>
+        /// This test checks that the GetJsonSchema method of the JsonConfigSchemaValidator class
+        /// correctly downloads a JSON schema from a given URL, and that the downloaded schema matches the expected schema.
+        /// </summary>
+        [TestMethod]
+        public async Task GetJsonSchema_DownloadsSchemaFromUrl()
+        {
+            // Arrange
+            Mock<HttpMessageHandler> handlerMock = new(MockBehavior.Strict);
+            string jsonSchemaContent = "{\"type\": \"object\", \"properties\": {\"property1\": {\"type\": \"string\"}}}";
+            handlerMock
+            .Protected()
+            .Setup<Task<HttpResponseMessage>>(
+                "SendAsync",
+                ItExpr.IsAny<HttpRequestMessage>(),
+                ItExpr.IsAny<CancellationToken>()
+            )
+            .ReturnsAsync(new HttpResponseMessage()
+            {
+                StatusCode = HttpStatusCode.OK,
+                Content = new StringContent(jsonSchemaContent, Encoding.UTF8, "application/json"),
+            })
+            .Verifiable();
+
+            HttpClient mockHttpClient = new(handlerMock.Object);
+            Mock<ILogger<JsonConfigSchemaValidator>> schemaValidatorLogger = new();
+            JsonConfigSchemaValidator jsonConfigSchemaValidator = new(schemaValidatorLogger.Object, new MockFileSystem(), mockHttpClient);
+
+            string url = "http://example.com/schema.json";
+            RuntimeConfig runtimeConfig = new(
+                Schema: url,
+                DataSource: new(DatabaseType.MSSQL, "connectionString", null),
+                new RuntimeEntities(new Dictionary<string, Entity>())
+            );
+
+            // Act
+            string receivedJsonSchema = await jsonConfigSchemaValidator.GetJsonSchema(runtimeConfig);
+
+            // Assert
+            Assert.AreEqual(jsonSchemaContent, receivedJsonSchema);
+            handlerMock.Protected().Verify(
+            "SendAsync",
+            Times.Exactly(1),
+            ItExpr.Is<HttpRequestMessage>(req =>
+                req.Method == HttpMethod.Get
+                && req.RequestUri == new Uri(url)),
+            ItExpr.IsAny<CancellationToken>());
+        }
+
+        /// <summary>
+        /// This test checks that even when the schema download fails, the GetJsonSchema method
+        /// fetches the schema from the package succesfully.
+        /// </summary>
+        [TestMethod]
+        public async Task GetJsonSchema_DownloadsSchemaFromUrlFailure()
+        {
+            // Arrange
+            Mock<HttpMessageHandler> handlerMock = new(MockBehavior.Strict);
+            handlerMock
+            .Protected()
+            .Setup<Task<HttpResponseMessage>>(
+                "SendAsync",
+                ItExpr.IsAny<HttpRequestMessage>(),
+                ItExpr.IsAny<CancellationToken>()
+            )
+            .ReturnsAsync(new HttpResponseMessage()
+            {
+                StatusCode = HttpStatusCode.InternalServerError,    // Simulate a failure
+                Content = new StringContent("", Encoding.UTF8, "application/json"),
+            })
+            .Verifiable();
+
+            HttpClient mockHttpClient = new(handlerMock.Object);
+            Mock<ILogger<JsonConfigSchemaValidator>> schemaValidatorLogger = new();
+            JsonConfigSchemaValidator jsonConfigSchemaValidator = new(schemaValidatorLogger.Object, new MockFileSystem(), mockHttpClient);
+
+            string url = "http://example.com/schema.json";
+            RuntimeConfig runtimeConfig = new(
+                Schema: url,
+                DataSource: new(DatabaseType.MSSQL, "connectionString", null),
+                new RuntimeEntities(new Dictionary<string, Entity>())
+            );
+
+            // Act
+            string receivedJsonSchema = await jsonConfigSchemaValidator.GetJsonSchema(runtimeConfig);
+
+            // Assert
+            Assert.IsFalse(string.IsNullOrEmpty(receivedJsonSchema));
+
+            // Sanity check to ensure the schema is valid
+            Assert.IsTrue(receivedJsonSchema.Contains("$schema"));
+            Assert.IsTrue(receivedJsonSchema.Contains("data-source"));
+            Assert.IsTrue(receivedJsonSchema.Contains("entities"));
+        }
+
         /// <summary>
         /// Set the connection string to an invalid value and expect the service to be unavailable
         /// since without this env var, it would be available - guaranteeing this env variable