Gracefully handle mirror failures for offline scenarios (#448)

Addresses #432

src/BaGet.Core/Mirror/MirrorService.cs

@@ -36,8 +36,12 @@ public class MirrorService : IMirrorService
  string id,
  CancellationToken cancellationToken)
  {
- var upstreamVersions = await _upstreamClient.ListPackageVersionsAsync(id, includeUnlisted: true, cancellationToken);
- if (!upstreamVersions.Any())
+ var upstreamVersions = await RunOrNull(
+ id,
+ "versions",
+ () => _upstreamClient.ListPackageVersionsAsync(id, includeUnlisted: true, cancellationToken));
+
+ if (upstreamVersions == null || !upstreamVersions.Any())
  {
  return null;
  }
@@ -51,8 +55,12 @@ public class MirrorService : IMirrorService
 
  public async Task<IReadOnlyList<Package>> FindPackagesOrNullAsync(string id, CancellationToken cancellationToken)
  {
- var items = await _upstreamClient.GetPackageMetadataAsync(id, cancellationToken);
- if (!items.Any())
+ var items = await RunOrNull(
+ id,
+ "metadata",
+ () => _upstreamClient.GetPackageMetadataAsync(id, cancellationToken));
+
+ if (items == null || !items.Any())
  {
  return null;
  }
@@ -168,6 +176,20 @@ private IEnumerable<PackageDependency> FindDependenciesFromDependencyGroup(Depen
  });
  }
 
+ private async Task<T> RunOrNull<T>(string id, string data, Func<Task<T>> x)
+ where T : class
+ {
+ try
+ {
+ return await x();
+ }
+ catch (Exception e)
+ {
+ _logger.LogError(e, "Unable to mirror package {Package}'s upstream {Data}", id, data);
+ return null;
+ }
+ }
+
  private async Task IndexFromSourceAsync(string id, NuGetVersion version, CancellationToken cancellationToken)
  {
  cancellationToken.ThrowIfCancellationRequested();