vendoring NetVips

vendor/NetVips/SourceCustom.cs

@@ -0,0 +1,117 @@
+using System.Buffers;
+using System.IO;
+using System.Runtime.InteropServices;
+
+namespace NetVips;
+
+/// <summary>
+/// An source you can connect delegates to implement behaviour.
+/// </summary>
+public class SourceCustom : Source
+{
+    /// <summary>
+    /// A read delegate.
+    /// </summary>
+    /// <remarks>
+    /// The interface is exactly as <see cref="Stream.Read(byte[], int, int)"/>.
+    /// The handler is given a number of bytes to fetch, and should return a
+    /// bytes-like object containing up to that number of bytes. If there is
+    /// no more data available, it should return <see langword="0"/>.
+    /// </remarks>
+    /// <param name="buffer">An array of bytes.</param>
+    /// <param name="length">The maximum number of bytes to be read.</param>
+    /// <returns>The total number of bytes read into the buffer.</returns>
+    public delegate int ReadDelegate(byte[] buffer, int length);
+
+    /// <summary>
+    /// A seek delegate.
+    /// </summary>
+    /// <remarks>
+    /// The interface is exactly as <see cref="Stream.Seek"/>. The handler is given
+    /// parameters for offset and whence with the same meanings. It also returns the
+    /// new position within the current source.
+    ///
+    /// Seek handlers are optional. If you do not set one, your source will be
+    /// treated as unseekable and libvips will do extra caching.
+    /// </remarks>
+    /// <param name="offset">A byte offset relative to the <paramref name="origin"/>
+    /// parameter.</param>
+    /// <param name="origin">A value of type <see cref="SeekOrigin"/> indicating the
+    /// reference point used to obtain the new position.</param>
+    /// <returns>The new position within the current source.</returns>
+    public delegate long SeekDelegate(long offset, SeekOrigin origin);
+
+    /// <summary>
+    /// Attach a read delegate.
+    /// </summary>
+    public event ReadDelegate OnRead;
+
+    /// <summary>
+    /// Attach a seek delegate.
+    /// </summary>
+    public event SeekDelegate OnSeek;
+
+    /// <inheritdoc cref="Source"/>
+    public SourceCustom() : base(Internal.VipsSourceCustom.New())
+    {
+        SignalConnect("read", (Internal.VipsSourceCustom.ReadSignal)ReadHandler);
+        SignalConnect("seek", (Internal.VipsSourceCustom.SeekSignal)SeekHandler);
+    }
+
+    /// <summary>
+    /// The internal read handler.
+    /// </summary>
+    /// <param name="sourcePtr">The underlying pointer to the source.</param>
+    /// <param name="buffer">A pointer to an array of bytes.</param>
+    /// <param name="length">The maximum number of bytes to be read.</param>
+    /// <param name="userDataPtr">User data associated with the source.</param>
+    /// <returns>The total number of bytes read into the buffer.</returns>
+    internal long ReadHandler(nint sourcePtr, nint buffer, long length, nint userDataPtr)
+    {
+        if (length <= 0)
+        {
+            return 0;
+        }
+
+        var tempArray = ArrayPool<byte>.Shared.Rent((int)length);
+        try
+        {
+            var readLength = OnRead?.Invoke(tempArray, (int)length);
+            if (!readLength.HasValue)
+            {
+                return -1;
+            }
+
+            if (readLength.Value > 0)
+            {
+                Marshal.Copy(tempArray, 0, buffer, readLength.Value);
+            }
+
+            return readLength.Value;
+        }
+        catch
+        {
+            return -1;
+        }
+        finally
+        {
+            ArrayPool<byte>.Shared.Return(tempArray);
+        }
+    }
+
+    /// <summary>
+    /// The internal seek handler.
+    /// </summary>
+    /// <param name="sourcePtr">The underlying pointer to the source.</param>
+    /// <param name="offset">A byte offset relative to the <paramref name="whence"/>
+    /// parameter.</param>
+    /// <param name="whence">A value of type <see cref="SeekOrigin"/> indicating the
+    /// reference point used to obtain the new position.</param>
+    /// <param name="userDataPtr">User data associated with the source.</param>
+    /// <returns>The new position within the current source.</returns>
+    internal long SeekHandler(nint sourcePtr, long offset, int whence, nint userDataPtr)
+    {
+        var newPosition = OnSeek?.Invoke(offset, (SeekOrigin)whence);
+        return newPosition ?? -1;
+    }
+}