Http request exception handling (#1743)

* add some exception handling and helpful error logging to failed http requests

* add simple test

* addressed pr comments: updated error messages and use environment.newline

doc/hosts/appservice.md

@@ -152,5 +152,5 @@ path, removing `/home/site/wwwroot` from it.
 
 When using App Service with a Virtual Network or an App Service Environment, you will need to allow outbound access 
 from the webapp to `oryx-cdn.microsoft.io` on port `443`. `oryx-cdn.microsoft.io` hosts the Oryx packages corresponding
-to each SDK language and version. If this network dependency is blocked, then App Servicewill not be able to build your 
+to each SDK language and version. If this network dependency is blocked, then App Service will not be able to build your 
 application using Oryx.

src/BuildScriptGenerator/Constants.cs

@@ -33,5 +33,9 @@ namespace Microsoft.Oryx.BuildScriptGenerator
         public const string BenvDynamicInstallRootDirKey = "dynamic_install_root_dir";
 
         public const string BuildConfigurationFileHelp = "https://aka.ms/troubleshoot-buildconfig";
+
+        public const string NetworkConfigurationHelpText = "Please ensure that your " +
+            "network configuration allows traffic to required Oryx dependencies, as documented in " +
+            "'https://github.com/microsoft/Oryx/blob/main/doc/hosts/appservice.md#network-dependencies'";
     }
 }

src/BuildScriptGenerator/Helpers/ListBlobsHelper.cs

@@ -2,7 +2,9 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license.
 // --------------------------------------------------------------------------------------------
+using System;
 using System.Linq;
+using System.Net.Http;
 using System.Xml.Linq;
 using Microsoft.Oryx.BuildScriptGenerator.Common;
 
@@ -10,14 +12,31 @@ namespace Microsoft.Oryx.BuildScriptGenerator
 {
     internal static class ListBlobsHelper
     {
-        public static XDocument GetAllBlobs(string sdkStorageBaseUrl, string platform, System.Net.Http.HttpClient httpClient, string oryxSdkStorageAccountAccessToken)
+        public static XDocument GetAllBlobs(string sdkStorageBaseUrl, string platform, HttpClient httpClient, string oryxSdkStorageAccountAccessToken)
         {
             var oryxSdkStorageAccountAccessArgs = oryxSdkStorageAccountAccessToken?.TrimStart(new char[] { '?' }) ?? string.Empty;
 
             var url = string.Format(SdkStorageConstants.ContainerMetadataUrlFormat, sdkStorageBaseUrl, platform, string.Empty, oryxSdkStorageAccountAccessArgs);
-            var blobList = httpClient
-                .GetStringAsync(url)
-                .Result;
+            string blobList;
+            try
+            {
+                blobList = httpClient
+                    .GetStringAsync(url)
+                    .Result;
+            }
+            catch (AggregateException ae)
+            {
+                throw new AggregateException(
+                    $"Http request to retrieve the SDKs available to download from '{sdkStorageBaseUrl}' " +
+                    $"failed. {Constants.NetworkConfigurationHelpText}{Environment.NewLine}{ae}");
+            }
+
+            if (string.IsNullOrEmpty(blobList))
+            {
+                throw new InvalidOperationException(
+                    $"Http request to retrieve the SDKs available to download from'{sdkStorageBaseUrl}' cannot return an empty result.");
+            }
+
             var xdoc = XDocument.Parse(blobList);
             var marker = xdoc.Root.Element("NextMarker").Value;
 

src/BuildScriptGenerator/SdkStorageVersionProviderBase.cs

@@ -8,6 +8,7 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Net.Http;
+using System.Threading.Tasks;
 using System.Xml.XPath;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
@@ -97,9 +98,25 @@ namespace Microsoft.Oryx.BuildScriptGenerator
             this.logger.LogDebug("Getting the default version from url {defaultVersionUrl}.", defaultVersionUrl);
 
             // get default version
-            var defaultVersionContent = httpClient
-                .GetStringAsync($"{defaultVersionUrl}{this.commonOptions.OryxSdkStorageAccountAccessToken}")
-                .Result;
+            string defaultVersionContent;
+            try
+            {
+                defaultVersionContent = httpClient
+                    .GetStringAsync($"{defaultVersionUrl}{this.commonOptions.OryxSdkStorageAccountAccessToken}")
+                    .Result;
+            }
+            catch (AggregateException ae)
+            {
+                throw new AggregateException(
+                    $"Http request to retrieve the default version from '{defaultVersionUrl}' failed. " +
+                    $"{Constants.NetworkConfigurationHelpText}{Environment.NewLine}{ae}");
+            }
+
+            if (string.IsNullOrEmpty(defaultVersionContent))
+            {
+                throw new InvalidOperationException(
+                    $"Http request to retrieve the default version from '{defaultVersionUrl}' cannot return an empty result.");
+            }
 
             string defaultVersion = null;
             using (var stringReader = new StringReader(defaultVersionContent))

tests/Oryx.Integration.Tests/StorageAccountSanityTestBase.cs

@@ -23,6 +23,8 @@ namespace Oryx.Integration.Tests
     public abstract class StorageAccountSanityTestBase
         : PlatformEndToEndTestsBase, IClassFixture<RepoRootDirTestFixture>
     {
+        private const string _fakeStorageUrl = "https://oryx-cdn-fake.microsoft.io";
+
         private readonly string _storageUrl;
         private readonly string _repoRootDir;
         private readonly string _sdkStorageAccountAccessToken;
@@ -171,6 +173,17 @@ namespace Oryx.Integration.Tests
             AssertExpectedDefaultVersion("maven", "java", "maven");
         }
 
+        [Fact]
+        public void Throws_CorrectHttpErrorMessage()
+        {
+            // Act
+            var error = Assert.Throws<AggregateException>(() => 
+                ListBlobsHelper.GetAllBlobs(_fakeStorageUrl, "dotnet", _httpClient, _sdkStorageAccountAccessToken));
+
+            // Assert
+            Assert.Contains(Microsoft.Oryx.BuildScriptGenerator.Constants.NetworkConfigurationHelpText, error.Message);
+        }
+
         private void AssertExpectedDefaultVersion(string platformName, params string[] expectedPlatformPath)
         {
             foreach (var debianFlavor in _debianFlavors)