Iterate in IAsyncenumerable over DB results (#307)

* Iterate in IAsyncenumerable over DB results

---------

Co-authored-by: Boris Ahrens <[email protected]>

Author: borisahrens

src/MalwareSampleExchange.Console/Database/MongoMetadataHandler.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Runtime.CompilerServices;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.Extensions.Hosting;
@@ -19,7 +20,7 @@ public interface ISampleMetadataHandler
     /// <param name="sampleSet"></param>
     /// <param name="token"></param>
     /// <returns></returns>
-    Task<IEnumerable<ExportSample>> GetSamplesAsync(DateTime start, DateTime? end, string? sampleSet, CancellationToken token = default);
+    IAsyncEnumerable<ExportSample> GetSamplesAsync(DateTime start, DateTime? end, string? sampleSet, CancellationToken token = default);
 
     Task InsertSampleAsync(RequestExportSample sample, CancellationToken token = default);
 }
@@ -35,18 +36,25 @@ public MongoMetadataHandler(IOptions<MongoMetadataOptions> options)
         _mongoClient = new MongoClient(options.Value.ConnectionString);
     }
 
-    public async Task<IEnumerable<ExportSample>> GetSamplesAsync(DateTime start, DateTime? end, string? sampleSet, CancellationToken token = default)
+    public async IAsyncEnumerable<ExportSample> GetSamplesAsync(DateTime start, DateTime? end, string? sampleSet, [EnumeratorCancellation] CancellationToken token = default)
     {
         var mongoDatabase = _mongoClient.GetDatabase(_options.DatabaseName);
         var sampleCollection = mongoDatabase.GetCollection<ExportSample>(_options.CollectionName);
         var list = end == null
             ? await sampleCollection
-                .FindAsync(sample => sample.SampleSet == sampleSet && sample.Imported >= start, cancellationToken: token)
+                .FindAsync(sample => sample.SampleSet == sampleSet && sample.Imported >= start && sample.DoNotUseBefore <= DateTime.Now, cancellationToken: token)
             : await sampleCollection
-                .FindAsync(sample => sample.SampleSet == sampleSet && sample.Imported >= start && sample.Imported <= end, cancellationToken: token);
-        return list.ToList(cancellationToken: token);
-    }
+                .FindAsync(sample => sample.SampleSet == sampleSet && sample.Imported >= start && sample.Imported <= end && sample.DoNotUseBefore <= DateTime.Now, cancellationToken: token);
 
+        while (await list.MoveNextAsync(token))
+        {
+            foreach (var current in list.Current)
+            {
+                yield return current;
+            }
+        }
+    }
+    
     public async Task InsertSampleAsync(RequestExportSample sample, CancellationToken token = default)
     {
         var mongoDatabase = _mongoClient.GetDatabase(_options.DatabaseName);

src/MalwareSampleExchange.Console/ListRequester/ListRequester.cs

@@ -43,10 +43,9 @@ public async IAsyncEnumerable<Token> RequestList(string username, DateTime start
     {
         var includeFamilyName = _partnerProvider.Partners.Single(_ => _.Name == username).IncludeFamilyName;
         var sampleSet = _partnerProvider.Partners.SingleOrDefault(_ => _.Name == username)?.Sampleset;
+        var samples = _sampleMetadataHandler.GetSamplesAsync(start, end, sampleSet, token);
 
-        var samples = await _sampleMetadataHandler.GetSamplesAsync(start, end, sampleSet, token);
-
-        foreach (var sample in samples.Where(sample => sample.DoNotUseBefore <= DateTime.Now))
+        await foreach (var sample in samples)
         {
             var fileSize = sample.FileSize == 0
                 ? await _sampleStorageHandler.GetFileSizeAsync(sample.Sha256, token)