Add support for streaming binary serial read buffers

Bonsai.System/IO/Ports/ObservableSerialPort.cs

@@ -7,6 +7,44 @@ namespace Bonsai.IO.Ports
 {
     static class ObservableSerialPort
     {
+        public static IObservable<byte[]> Read(string portName, int count)
+        {
+            return Observable.Create<byte[]>((observer, cancellationToken) =>
+            {
+                return Task.Factory.StartNew(() =>
+                {
+                    using var connection = SerialPortManager.ReserveConnection(portName);
+                    using var cancellation = cancellationToken.Register(connection.Dispose);
+                    var serialPort = connection.SerialPort;
+                    while (!cancellationToken.IsCancellationRequested)
+                    {
+                        try
+                        {
+                            var bytesRead = 0;
+                            var buffer = new byte[count];
+                            while (bytesRead < count)
+                            {
+                                bytesRead += serialPort.Read(buffer, bytesRead, count - bytesRead);
+                            }
+                            observer.OnNext(buffer);
+                        }
+                        catch (Exception ex)
+                        {
+                            if (!cancellationToken.IsCancellationRequested)
+                            {
+                                observer.OnError(ex);
+                            }
+
+                            break;
+                        }
+                    }
+                },
+                cancellationToken,
+                TaskCreationOptions.LongRunning,
+                TaskScheduler.Default);
+            });
+        }
+
         public static IObservable<string> ReadLine(string portName, string newLine)
         {
             return Observable.Create<string>((observer, cancellationToken) =>

Bonsai.System/IO/Ports/SerialRead.cs

@@ -2,6 +2,7 @@
 using System.ComponentModel;
 using System.Reactive;
 using System.Reactive.Linq;
+using System.Threading.Tasks;
 using System.Xml.Serialization;
 
 namespace Bonsai.IO.Ports
@@ -38,7 +39,7 @@ public class SerialRead : Source<byte[]>
         /// </returns>
         public override IObservable<byte[]> Generate()
         {
-            return Generate(Observable.Return(Unit.Default));
+            return ObservableSerialPort.Read(PortName, Count);
         }
 
         /// <summary>
@@ -60,18 +61,18 @@ public IObservable<byte[]> Generate<TSource>(IObservable<TSource> source)
         {
             var count = Count;
             return Observable.Using(
-                () => SerialPortManager.ReserveConnection(PortName),
-                connection =>
+                cancellationToken => Task.FromResult(SerialPortManager.ReserveConnection(PortName)),
+                (connection, cancellationToken) => Task.FromResult(source.Select(_ =>
                 {
-                    var serialPort = connection.SerialPort;
-                    return source.SelectMany(async (_, cancellationToken) =>
+                    using var cancellation = cancellationToken.Register(connection.Dispose);
+                    var bytesRead = 0;
+                    var buffer = new byte[count];
+                    while (bytesRead < count)
                     {
-                        var buffer = new byte[count];
-                        await serialPort.BaseStream.ReadAsync(
-                            buffer, 0, buffer.Length, cancellationToken);
-                        return buffer;
-                    });
-                });
+                        bytesRead += connection.SerialPort.Read(buffer, bytesRead, count - bytesRead);
+                    }
+                    return buffer;
+                })));
         }
     }
 }