vendoring NetVips

vendor/NetVips/SourceStream.cs

@@ -0,0 +1,88 @@
+using System;
+using System.IO;
+
+namespace NetVips;
+
+/// <summary>
+/// An source connected to a readable <see cref="Stream"/>.
+/// </summary>
+internal class SourceStream : SourceCustom
+{
+    /// <summary>
+    /// Read from this stream.
+    /// </summary>
+    private readonly Stream _stream;
+
+    /// <summary>
+    /// The start position within the stream.
+    /// </summary>
+    private readonly long _startPosition;
+
+    /// <inheritdoc cref="SourceCustom"/>
+    internal SourceStream(Stream stream)
+    {
+        var seekable = stream.CanSeek;
+
+        _stream = stream;
+        _startPosition = seekable ? _stream.Position : 0;
+
+        OnRead += Read;
+        if (seekable)
+        {
+            OnSeek += Seek;
+        }
+    }
+
+    /// <summary>
+    /// Create a <see cref="SourceStream"/> attached to an <see cref="Stream"/>.
+    /// </summary>
+    /// <param name="stream">Read from this stream.</param>
+    /// <returns>A new <see cref="SourceStream"/>.</returns>
+    /// <exception cref="T:System.ArgumentException">If <paramref name="stream"/> is not readable.</exception>
+    internal static SourceStream NewFromStream(Stream stream)
+    {
+        if (!stream.CanRead)
+        {
+            throw new ArgumentException("The stream should be readable.", nameof(stream));
+        }
+
+        return new SourceStream(stream);
+    }
+
+    /// <summary>
+    /// Attach a read handler.
+    /// </summary>
+    /// <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 int Read(byte[] buffer, int length)
+    {
+        return _stream.Read(buffer, 0, length);
+    }
+
+    /// <summary>
+    /// Attach a seek handler.
+    /// </summary>
+    /// <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 stream.</returns>
+    public long Seek(long offset, SeekOrigin origin)
+    {
+        try
+        {
+            return origin switch
+            {
+                SeekOrigin.Begin => _stream.Seek(_startPosition + offset, SeekOrigin.Begin) - _startPosition,
+                SeekOrigin.Current => _stream.Seek(offset, SeekOrigin.Current) - _startPosition,
+                SeekOrigin.End => _stream.Seek(offset, SeekOrigin.End) - _startPosition,
+                _ => -1
+            };
+        }
+        catch
+        {
+            return -1;
+        }
+    }
+}