C#: Only use the default package source when using nuget.exe if it is reachable.

Author: michaelnebel

csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/NugetExeWrapper.cs

@@ -33,7 +33,7 @@ internal class NugetExeWrapper : IDisposable
         /// <summary>
         /// Create the package manager for a specified source tree.
         /// </summary>
-        public NugetExeWrapper(FileProvider fileProvider, DependencyDirectory packageDirectory, Semmle.Util.Logging.ILogger logger)
+        public NugetExeWrapper(FileProvider fileProvider, DependencyDirectory packageDirectory, Semmle.Util.Logging.ILogger logger, Func<bool> useDefaultFeed)
         {
             this.fileProvider = fileProvider;
             this.packageDirectory = packageDirectory;
@@ -43,7 +43,7 @@ public NugetExeWrapper(FileProvider fileProvider, DependencyDirectory packageDir
             {
                 logger.LogInfo($"Found packages.config files, trying to use nuget.exe for package restore");
                 nugetExe = ResolveNugetExe();
-                if (HasNoPackageSource())
+                if (HasNoPackageSource() && useDefaultFeed())
                 {
                     // We only modify or add a top level nuget.config file
                     nugetConfigPath = Path.Combine(fileProvider.SourceDir.FullName, "nuget.config");

csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/NugetPackageRestorer.cs

@@ -164,7 +164,7 @@ public HashSet<AssemblyLookupLocation> Restore()
                     explicitNugetSources = MakeRestoreSourcesArgument(allFeeds);
                 }
 
-                using (var nuget = new NugetExeWrapper(fileProvider, legacyPackageDirectory, logger))
+                using (var nuget = new NugetExeWrapper(fileProvider, legacyPackageDirectory, logger, IsDefaultFeedReachable))
                 {
                     var count = nuget.InstallPackages();
 
@@ -258,6 +258,17 @@ private List<string> GetReachableNuGetFeeds(HashSet<string> feedsToCheck, bool i
             return reachableFeeds;
         }
 
+        private bool IsDefaultFeedReachable()
+        {
+            if (CheckNugetFeedResponsiveness)
+            {
+                var (initialTimeout, tryCount) = GetFeedRequestSettings(isFallback: false);
+                return IsFeedReachable(PublicNugetOrgFeed, initialTimeout, tryCount, allowNonTimeoutExceptions: false);
+            }
+
+            return true;
+        }
+
         private List<string> GetReachableFallbackNugetFeeds(HashSet<string>? feedsFromNugetConfigs)
         {
             var fallbackFeeds = EnvironmentVariables.GetURLs(EnvironmentVariableNames.FallbackNugetFeeds).ToHashSet();