Add gRPC server example with file download

TestGrpc/Services/GreeterService.cs

@@ -0,0 +1,49 @@
+using Google.Protobuf;
+using Grpc.Core;
+using TestGrpc;
+
+namespace TestGrpc.Services;
+
+public class GreeterService : Greeter.GreeterBase
+{
+    private readonly ILogger<GreeterService> _logger;
+    public GreeterService(ILogger<GreeterService> logger)
+    {
+        _logger = logger;
+    }
+
+    public override async Task DownloadFile(FileRequest request, IServerStreamWriter<ChunkMsg> responseStream, ServerCallContext context)
+    {
+        string filePath = request.FilePath;
+
+        if (!File.Exists(filePath))
+        {
+            return;
+        }
+
+        var fileInfo = new FileInfo(filePath);
+
+        var chunk = new ChunkMsg
+        {
+            FileName = Path.GetFileName(filePath),
+            FileSize = fileInfo.Length
+        };
+
+        int fileChunkSize = 64 * 1024;
+
+        byte[] fileByteArray = File.ReadAllBytes(filePath);
+        byte[] fileChunk = new byte[fileChunkSize];
+        int fileOffset = 0;
+
+        while (fileOffset < fileByteArray.Length && !context.CancellationToken.IsCancellationRequested)
+        {
+            int length = Math.Min(fileChunkSize, fileByteArray.Length - fileOffset);
+            Buffer.BlockCopy(fileByteArray, fileOffset, fileChunk, 0, length);
+            fileOffset += length;
+            ByteString byteString = ByteString.CopyFrom(fileChunk);
+
+            chunk.Chunk = byteString;
+            await responseStream.WriteAsync(chunk).ConfigureAwait(false);
+        }
+    }
+}