Improve packaged source updating (#3657) (#3682)

This change refactors the index package updating to enable an optimization; using an HTTP header to determine the available version rather than reading the package contents remotely.  If the header is present, containing a valid package version string, it will be used as the available version.  If not, the existing package content examination will be used.

The refactoring was required to do all package inspection steps after downloading the package, rather than before.  This enables the single version value to be sufficient until we decide to update, and then in the very unlikely event of the package not meeting criteria we will delete it after having downloaded it.

.github/actions/spelling/expect.txt

@@ -429,6 +429,7 @@ SMTO
 sortof
 sourceforge
 SOURCESDIRECTORY
+sourceversion
 spamming
 SPAPI
 Srinivasan

src/AppInstallerCommonCore/Downloader.cpp

@@ -1,6 +1,5 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
-
 #include "pch.h"
 #include "Public/AppInstallerErrors.h"
 #include "Public/AppInstallerRuntime.h"
@@ -17,6 +16,9 @@
 using namespace AppInstaller::Runtime;
 using namespace AppInstaller::Settings;
 using namespace AppInstaller::Filesystem;
+using namespace winrt::Windows::Web::Http;
+using namespace winrt::Windows::Web::Http::Headers;
+using namespace winrt::Windows::Web::Http::Filters;
 
 namespace AppInstaller::Utility
 {
@@ -141,6 +143,37 @@ namespace AppInstaller::Utility
         return result;
     }
 
+    std::map<std::string, std::string> GetHeaders(std::string_view url)
+    {
+        AICLI_LOG(Core, Verbose, << "Retrieving headers from url: " << url);
+
+        HttpBaseProtocolFilter filter;
+        filter.CacheControl().ReadBehavior(HttpCacheReadBehavior::MostRecent);
+
+        HttpClient client(filter);
+        client.DefaultRequestHeaders().Connection().Clear();
+        client.DefaultRequestHeaders().Append(L"Connection", L"close");
+        client.DefaultRequestHeaders().UserAgent().ParseAdd(Utility::ConvertToUTF16(Runtime::GetDefaultUserAgent().get()));
+
+        winrt::Windows::Foundation::Uri uri{ Utility::ConvertToUTF16(url) };
+        HttpRequestMessage request(HttpMethod::Head(), uri);
+
+        HttpResponseMessage response = client.SendRequestAsync(request, HttpCompletionOption::ResponseHeadersRead).get();
+
+        THROW_HR_IF(
+            MAKE_HRESULT(SEVERITY_ERROR, FACILITY_HTTP, response.StatusCode()),
+            response.StatusCode() != HttpStatusCode::Ok);
+
+        std::map<std::string, std::string> result;
+
+        for (const auto& header : response.Headers())
+        {
+            result.emplace(Utility::ConvertToUTF8(header.Key()), Utility::ConvertToUTF8(header.Value()));
+        }
+
+        return result;
+    }
+
     std::optional<std::vector<BYTE>> DownloadToStream(
         const std::string& url,
         std::ostream& dest,

src/AppInstallerCommonCore/Public/AppInstallerDownloader.h

@@ -7,6 +7,7 @@
 #include <wrl/client.h>
 
 #include <filesystem>
+#include <map>
 #include <optional>
 #include <ostream>
 #include <string>
@@ -59,6 +60,9 @@ namespace AppInstaller::Utility
         bool computeHash = false,
         std::optional<DownloadInfo> info = {});
 
+    // Gets the headers for the given URL.
+    std::map<std::string, std::string> GetHeaders(std::string_view url);
+
     // Determines if the given url is a remote location.
     bool IsUrlRemote(std::string_view url);