More ready event in xfer logic.

src/NTwain/Data/TWAINH.cs

@@ -2385,7 +2385,7 @@ namespace NTwain.Data
   [StructLayout(LayoutKind.Sequential, Pack = 2)]
   public struct TW_PENDINGXFERS
   {
-    public ushort Count;
+    public short Count;
     public uint EOJ;
   }
 

src/NTwain/TransferReadyEventArgs.cs

@@ -0,0 +1,85 @@
+using NTwain.Data;
+using System;
+
+namespace NTwain
+{
+  /// <summary>
+  /// Contains event data when a data transfer is ready to be processed.
+  /// </summary>
+  public class TransferReadyEventArgs : EventArgs
+  {
+    public TransferReadyEventArgs(TwainAppSession twain, int pendingCount, TWEJ endOfJobFlag)
+    {
+      _twain = twain;
+      PendingCount = pendingCount;
+      EndOfJobFlag = endOfJobFlag;
+    }
+
+
+    /// <summary>
+    /// Gets or sets whether the current transfer should be skipped
+    /// and continue next transfer if there are more data.
+    /// </summary>
+    public bool SkipCurrent { get; set; }
+
+    /// <summary>
+    /// Gets or sets whether to cancel the capture phase.
+    /// </summary>
+    public CancelType Cancel { get; set; }
+
+    /// <summary>
+    /// Gets the end of job flag value for this transfer if job control is enabled.
+    /// </summary>
+    public TWEJ EndOfJobFlag { get; private set; }
+
+    /// <summary>
+    /// Gets the known pending transfer count. This may not be appilicable 
+    /// for certain scanning modes.
+    /// </summary>
+    public int PendingCount { get; private set; }
+
+    TW_IMAGEINFO? _imgInfo;
+    private readonly TwainAppSession _twain;
+
+    /// <summary>
+    /// Gets the tentative image information for the current transfer if applicable.
+    /// This may differ from the final image depending on the transfer mode used (mostly when doing mem xfer).
+    /// </summary>
+    public TW_IMAGEINFO? PendingImageInfo
+    {
+      get
+      {
+        // only get it if requested since it could be slow
+        if (!_imgInfo.HasValue)
+        {
+          if (_twain.GetImageInfo(out TW_IMAGEINFO info).RC == TWRC.SUCCESS)
+          {
+            _imgInfo = info;
+          }
+        }
+        return _imgInfo;
+      }
+    }
+
+  }
+
+  public enum CancelType
+  {
+    /// <summary>
+    /// No cancel.
+    /// </summary>
+    None,
+    /// <summary>
+    /// Skips current transfer.
+    /// </summary>
+    SkipCurrent,
+    /// <summary>
+    /// Stops feeder but continue receiving already scanned images in the app.
+    /// </summary>
+    Graceful,
+    /// <summary>
+    /// Stops feeder and discard any pending images.
+    /// </summary>
+    EndNow
+  }
+}

src/NTwain/TwainAppSession.PropEvents.cs

@@ -140,5 +140,16 @@ namespace NTwain
     /// Fires when there's an error during transfer.
     /// </summary>
     public event EventHandler<TransferErrorEventArgs>? TransferError;
+
+    /// <summary>
+    /// Fires when there's an upcoming transfer. App can inspect the image info
+    /// and cancel if needed.
+    /// </summary>
+    public event EventHandler<TransferReadyEventArgs>? TransferReady;
+
+    /// <summary>
+    /// Fires when transferred data is available for app to use.
+    /// </summary>
+    public event EventHandler<DataTransferredEventArgs>? DataTransferred;
   }
 }

src/NTwain/TwainAppSession.Xfers.cs

@@ -18,6 +18,11 @@ namespace NTwain
     // so the array max is made with 32 MB. Typical usage should be a lot less.
     static readonly ArrayPool<byte> XferMemPool = ArrayPool<byte>.Create(32505856, 4);
 
+    public STS GetImageInfo(out TW_IMAGEINFO info)
+    {
+      return WrapInSTS(DGImage.ImageInfo.Get(ref _appIdentity, ref _currentDS, out info));
+    }
+
 
     /// <summary>
     /// Start the transfer loop.
@@ -49,14 +54,22 @@ namespace NTwain
         }
       }
 
-      //if (xferImage)
+      if (xferImage)
-      //{
+      {
-      //  imgXferMech = session.CurrentSource.Capabilities.ICapXferMech.GetCurrent();
+        if (GetCapCurrent(CAP.ICAP_XFERMECH, out TW_CAPABILITY cap).RC == TWRC.SUCCESS)
-      //}
+        {
-      //if (xferAudio)
+          // todo:
-      //{
+          cap.Free(this);
-      //  audXferMech = session.CurrentSource.Capabilities.ACapXferMech.GetCurrent();
+        }
-      //}
+      }
+      else if (xferAudio)
+      {
+        if (GetCapCurrent(CAP.ACAP_XFERMECH, out TW_CAPABILITY cap).RC == TWRC.SUCCESS)
+        {
+          // todo:
+          cap.Free(this);
+        }
+      }
 
       TW_PENDINGXFERS pending = default;
       var rc = DGControl.PendingXfers.Get(ref _appIdentity, ref _currentDS, ref pending);
@@ -64,20 +77,37 @@ namespace NTwain
       {
         do
         {
-          // cancel for now
+          var readyArgs = new TransferReadyEventArgs(this, pending.Count, (TWEJ)pending.EOJ);
-          //rc = DGControl.PendingXfers.Reset(ref _appIdentity, ref _currentDS, ref pending);
+          _uiThreadMarshaller.Invoke(() =>
+          {
+            TransferReady?.Invoke(this, readyArgs);
+          });
 
+          switch (readyArgs.Cancel)
+          {
+            case CancelType.SkipCurrent:
+              rc = DGControl.PendingXfers.EndXfer(ref _appIdentity, ref _currentDS, ref pending);
+              break;
+            case CancelType.EndNow:
+              rc = DGControl.PendingXfers.Reset(ref _appIdentity, ref _currentDS, ref pending);
+              break;
+            case CancelType.Graceful:
+              //??? oh boy
+              rc = DGControl.PendingXfers.EndXfer(ref _appIdentity, ref _currentDS, ref pending);
+              break;
+            default:
+              // normal capture
+              if (xferImage)
+              {
 
-          rc = DGControl.PendingXfers.EndXfer(ref _appIdentity, ref _currentDS, ref pending);
+              }
+              else if (xferAudio)
+              {
 
-          //if (xferType.HasFlag(DG.AUDIO))
+              }
-          //{
+              rc = DGControl.PendingXfers.EndXfer(ref _appIdentity, ref _currentDS, ref pending);
-          //  DoTransferAudio();
+              break;
-          //}
+          }
-          //else // just defaults to image
-          //{
-          //  DoTransferImage();
-          //}
 
         } while (rc == TWRC.SUCCESS && pending.Count != 0);
       }