Clean up error experience when downloading non-tools (#43045)

Author: marcpopMSFT

src/Cli/dotnet/NugetPackageDownloader/INuGetPackageDownloader.cs

@@ -16,7 +16,8 @@ Task<string> DownloadPackageAsync(PackageId packageId,
             bool includePreview = false,
             bool? includeUnlisted = null,
             DirectoryPath? downloadFolder = null,
-            PackageSourceMapping packageSourceMapping = null);
+            PackageSourceMapping packageSourceMapping = null,
+            bool isTool = false);
 
         Task<string> GetPackageUrl(PackageId packageId,
             NuGetVersion packageVersion = null,

src/Cli/dotnet/NugetPackageDownloader/LocalizableStrings.resx

@@ -126,6 +126,9 @@
   <data name="IsNotFoundInNuGetFeeds" xml:space="preserve">
     <value>{0} is not found in NuGet feeds {1}.</value>
   </data>
+  <data name="NotATool" xml:space="preserve">
+    <value>Package {0} is not a .NET tool.</value>
+  </data>
   <data name="DownloadVersionFailed" xml:space="preserve">
     <value>Downloading {0} version {1} failed.</value>
   </data>

src/Cli/dotnet/NugetPackageDownloader/NuGetPackageDownloader.cs

@@ -83,19 +83,45 @@ public async Task<string> DownloadPackageAsync(PackageId packageId,
             bool includePreview = false,
             bool? includeUnlisted = null,
             DirectoryPath? downloadFolder = null,
-            PackageSourceMapping packageSourceMapping = null)
+            PackageSourceMapping packageSourceMapping = null,
+            bool isTool = false)
         {
             CancellationToken cancellationToken = CancellationToken.None;
 
             (var source, var resolvedPackageVersion) = await GetPackageSourceAndVersion(packageId, packageVersion,
                 packageSourceLocation, includePreview, includeUnlisted ?? packageVersion is not null, packageSourceMapping).ConfigureAwait(false);
 
-            FindPackageByIdResource resource = null;
             SourceRepository repository = GetSourceRepository(source);
 
-            resource = await repository.GetResourceAsync<FindPackageByIdResource>(cancellationToken)
-                .ConfigureAwait(false);
+            // TODO: Fix this to use the PackageSearchResourceV3 once https://github.com/NuGet/NuGet.Client/pull/5991 is completed.
+            if (isTool && await repository.GetResourceAsync<ServiceIndexResourceV3>().ConfigureAwait(false) is ServiceIndexResourceV3 serviceIndex)
+            {
+                // See https://learn.microsoft.com/en-us/nuget/api/package-base-address-resource#download-package-manifest-nuspec
+                var uri = serviceIndex.GetServiceEntries("PackageBaseAddress/3.0.0")[0].Uri;
+                var queryUri = uri + $"{packageId}/{packageVersion}/{packageId}.nuspec";
+
+                using HttpClient client = new(new HttpClientHandler() { CheckCertificateRevocationList = true });
+                using HttpResponseMessage response = await client.GetAsync(queryUri).ConfigureAwait(false);
+
+                if (response.IsSuccessStatusCode)
+                {
+                    string nuspec = await response.Content.ReadAsStringAsync().ConfigureAwait(false);
+
+                    XDocument doc = XDocument.Parse(nuspec);
+
+                    if (!ToolPackageInstance.IsToolPackage(doc))
+                    {
+                        throw new GracefulException(string.Format(LocalizableStrings.NotATool, packageId));
+                    }
+                }
+                else
+                {
+                    throw new GracefulException(string.Format(LocalizableStrings.NotATool, packageId));
+                }
+            }
 
+            FindPackageByIdResource resource = await repository.GetResourceAsync<FindPackageByIdResource>(cancellationToken)
+                .ConfigureAwait(false);
             if (resource == null)
             {
                 throw new NuGetPackageNotFoundException(