From bae16c0471bb67b39efd1dc9ed0d7bfc84e78c27 Mon Sep 17 00:00:00 2001
From: Martin <mautner@vrvis.at>
Date: Tue, 27 Aug 2024 17:03:16 +0200
Subject: [PATCH] Add Stream.ReadBytes extension

---
 .../Extensions/StreamExtensions.cs            | 36 +++++++
 .../Extensions/StreamTests.cs                 | 93 +++++++++++++++++++
 2 files changed, 129 insertions(+)
 create mode 100644 src/Aardvark.Base/Extensions/StreamExtensions.cs
 create mode 100644 src/Tests/Aardvark.Base.Tests/Extensions/StreamTests.cs

diff --git a/src/Aardvark.Base/Extensions/StreamExtensions.cs b/src/Aardvark.Base/Extensions/StreamExtensions.cs
new file mode 100644
index 00000000..ed6e701c
--- /dev/null
+++ b/src/Aardvark.Base/Extensions/StreamExtensions.cs
@@ -0,0 +1,36 @@
+using System.IO;
+
+namespace Aardvark.Base
+{
+    public static class StreamExtensions
+    {
+        /// <summary>
+        /// Reads <paramref name="count"/> number of bytes from the current stream and advances the position within the stream.
+        /// </summary>
+        /// <param name="stream">The stream to read from.</param>
+        /// <param name="buffer">The buffer to read into.</param>
+        /// <param name="offset">The byte offset in <paramref name="buffer"/> at which to begin storing the data read from the current stream.</param>
+        /// <param name="count">The number of bytes to be read from the current stream. Defaults to the buffer length if negative.</param>
+        /// <exception cref="EndOfStreamException"></exception>
+        public static void ReadBytes(this Stream stream, byte[] buffer, int offset = 0, int count = -1)
+        {
+            if (count < 0) count = buffer.Length;
+#if NET8_0_OR_GREATER
+            stream.ReadExactly(buffer, offset, count);
+#else
+            int totalRead = 0;
+
+            while (totalRead < count)
+            {
+                int read = stream.Read(buffer, offset + totalRead, count - totalRead);
+                if (read == 0)
+                {
+                    throw new EndOfStreamException();
+                }
+
+                totalRead += read;
+            }
+#endif
+        }
+    }
+}
diff --git a/src/Tests/Aardvark.Base.Tests/Extensions/StreamTests.cs b/src/Tests/Aardvark.Base.Tests/Extensions/StreamTests.cs
new file mode 100644
index 00000000..7fd70c6c
--- /dev/null
+++ b/src/Tests/Aardvark.Base.Tests/Extensions/StreamTests.cs
@@ -0,0 +1,93 @@
+using NUnit.Framework;
+using System;
+using System.Reflection;
+using System.IO;
+using Aardvark.Base;
+using System.Linq;
+
+namespace Aardvark.Tests.Extensions
+{
+    internal class TestStream(Stream inner) : Stream
+    {
+        private bool isDiposed = false;
+        private readonly RandomSystem rnd = new RandomSystem();
+
+        public TestStream(byte[] data) : this(new MemoryStream(data))
+        { }
+
+        public override bool CanRead => inner.CanRead;
+
+        public override bool CanSeek => inner.CanSeek;
+
+        public override bool CanWrite => inner.CanWrite;
+
+        public override long Length => inner.Length;
+
+        public override long Position
+        {
+            get => inner.Position;
+            set => inner.Position = value;
+        }
+
+        public override void Flush() => inner.Flush();
+
+        public override long Seek(long offset, SeekOrigin origin) => inner.Seek(offset, origin);
+
+        public override void SetLength(long value) => inner.SetLength(value);
+
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            if (count > 1)
+            {
+                count = 1 + rnd.UniformInt(count - 1);
+            }
+
+            return inner.Read(buffer, offset, count);
+        }
+
+        public override void Write(byte[] buffer, int offset, int count)
+        {
+            inner.Write(buffer, offset, count);
+        }
+
+        protected override void Dispose(bool disposing)
+        {
+            if (!isDiposed) inner.Dispose();
+            isDiposed = true;
+        }
+    }
+
+    static class StreamTests
+    {
+        [Test]
+        public static void ReadBytes([Values(false, true)] bool netStandard20)
+        {
+            var rnd = new RandomSystem();
+            var data = new byte[1234];
+            for (int i = 0; i < data.Length; i++) data[i] = (byte)rnd.UniformInt();
+
+            using TestStream s = new TestStream(data);
+            var result = new byte[57];
+            var offset = 3;
+            var count = result.Length - offset;
+
+            if (netStandard20)
+            {
+                // We want to test the netstandard2.0 implementation, is there an easier way?
+                var asm = Assembly.LoadFile(Path.GetFullPath(Path.Combine("..", "netstandard2.0", "Aardvark.Base.dll")));
+                var ext = asm.GetType($"Aardvark.Base.{nameof(StreamExtensions)}");
+                Type[] parameters = [typeof(Stream), typeof(byte[]), typeof(int), typeof(int)];
+                var mi = ext.GetMethod(nameof(StreamExtensions.ReadBytes), parameters);
+
+                mi.Invoke(null, [s, result, offset, count]);
+            }
+            else
+            {
+                s.ReadBytes(result, offset, count);
+            }
+
+            for (int i = 0; i < count; i++)
+                Assert.AreEqual(data[i], result[i + offset]);
+        }
+    }
+}