From d0b5fdc7bf255be95026482296a016a36f162b29 Mon Sep 17 00:00:00 2001
From: Lilith River <lilith@imazen.io>
Date: Fri, 8 Mar 2024 23:08:17 -0700
Subject: [PATCH] Add failing test; fix BufferedStreamSource bug where
 .Position is queried on non-seekable streams, causing a failure.

---
 src/Imageflow/Fluent/BufferedStreamSource.cs  |  2 +-
 tests/Imageflow.Test/NonSeekableReadStream.cs | 62 +++++++++++++++++++
 tests/Imageflow.Test/TestApi.cs               |  6 +-
 3 files changed, 66 insertions(+), 4 deletions(-)
 create mode 100644 tests/Imageflow.Test/NonSeekableReadStream.cs

diff --git a/src/Imageflow/Fluent/BufferedStreamSource.cs b/src/Imageflow/Fluent/BufferedStreamSource.cs
index cd2b69b..6fca985 100644
--- a/src/Imageflow/Fluent/BufferedStreamSource.cs
+++ b/src/Imageflow/Fluent/BufferedStreamSource.cs
@@ -8,7 +8,7 @@ public sealed class BufferedStreamSource : IAsyncMemorySource, IMemorySource
 {
     private BufferedStreamSource(Stream stream, bool disposeUnderlying, bool seekToStart)
     {
-        if (stream.Position != 0 && !stream.CanSeek && seekToStart)
+        if (!stream.CanSeek && seekToStart)
         {
             throw new ArgumentException("Stream must be seekable if seekToStart is true");
         }
diff --git a/tests/Imageflow.Test/NonSeekableReadStream.cs b/tests/Imageflow.Test/NonSeekableReadStream.cs
new file mode 100644
index 0000000..c3fac57
--- /dev/null
+++ b/tests/Imageflow.Test/NonSeekableReadStream.cs
@@ -0,0 +1,62 @@
+namespace Imageflow.Test;
+
+using System;
+using System.IO;
+
+public class NonSeekableReadStream : Stream
+{
+    private byte[] data;
+    private long position = 0; // Current position within the data
+
+    public NonSeekableReadStream(byte[] dataSource)
+    {
+        data = dataSource ?? throw new ArgumentNullException(nameof(dataSource));
+    }
+
+    public override bool CanRead => true;
+    public override bool CanSeek => false;
+    public override bool CanWrite => false;
+
+    public override long Length => data.Length;
+
+    public override long Position
+    {
+        get => throw new NotSupportedException("Seeking not supported.");
+        set => throw new NotSupportedException("Seeking not supported.");
+    }
+
+    public override void Flush()
+    {
+        // No-op for read-only stream
+    }
+
+    public override int Read(byte[] buffer, int offset, int count)
+    {
+        if (buffer == null) throw new ArgumentNullException(nameof(buffer));
+        if (offset < 0 || count < 0) throw new ArgumentOutOfRangeException("offset or count is negative.");
+        if (buffer.Length - offset < count) throw new ArgumentException("The sum of offset and count is greater than the buffer length.");
+
+        int available = data.Length - (int)position;
+        if (available <= 0) return 0; // End of stream
+
+        int toCopy = Math.Min(available, count);
+        Array.Copy(data, position, buffer, offset, toCopy);
+        position += toCopy;
+        return toCopy;
+    }
+
+    public override long Seek(long offset, SeekOrigin origin)
+    {
+        throw new NotSupportedException("Seeking not supported.");
+    }
+
+    public override void SetLength(long value)
+    {
+        throw new NotSupportedException("Setting length not supported.");
+    }
+
+    public override void Write(byte[] buffer, int offset, int count)
+    {
+        throw new NotSupportedException("Writing not supported.");
+    }
+}
diff --git a/tests/Imageflow.Test/TestApi.cs b/tests/Imageflow.Test/TestApi.cs
index cba1968..e3b5464 100644
--- a/tests/Imageflow.Test/TestApi.cs
+++ b/tests/Imageflow.Test/TestApi.cs
@@ -332,7 +332,7 @@ public async Task TestBuildCommandStringWithStreamsAndWatermarksLegacy()
             var stream1 = new BufferedStream(new MemoryStream(imageBytes));
             Assert.Equal(137, stream1.ReadByte());
             stream1.Seek(0, SeekOrigin.Begin);
-            var stream2 = new BufferedStream(new MemoryStream(imageBytes));
+            var stream2 = new NonSeekableReadStream(imageBytes);
             var stream3 = new BufferedStream(new MemoryStream(imageBytes));
             using (var b = new ImageJob())
             {
@@ -361,12 +361,12 @@ public async Task TestBuildCommandStringWithStreamsAndWatermarks()
             var stream1 = new BufferedStream(new MemoryStream(imageBytes));
             Assert.Equal(137, stream1.ReadByte());
             stream1.Seek(0, SeekOrigin.Begin);
-            var stream2 = new BufferedStream(new MemoryStream(imageBytes));
+            var stream2 = new NonSeekableReadStream(imageBytes);
             var stream3 = new BufferedStream(new MemoryStream(imageBytes));
             using var b = new ImageJob();
             var watermarks = new List<InputWatermark>();
             watermarks.Add(new InputWatermark(BufferedStreamSource.UseEntireStreamAndDisposeWithSource(stream1), new WatermarkOptions()));
-            watermarks.Add(new InputWatermark(BufferedStreamSource.UseEntireStreamAndDisposeWithSource(stream2), new WatermarkOptions().SetGravity(new ConstraintGravity(100, 100))));
+            watermarks.Add(new InputWatermark(BufferedStreamSource.UseStreamRemainderAndDisposeWithSource(stream2), new WatermarkOptions().SetGravity(new ConstraintGravity(100, 100))));
 
             var r = await b.BuildCommandString(
                 BufferedStreamSource.UseEntireStreamAndDisposeWithSource(stream3),