✨ Implement slice for DataStream

docs/articles/core/binary/datastream.md

@@ -38,6 +38,14 @@ Another use case is reading a binary format with sections. By creating a
 modular and safe. It would prevent reading data outside the range of the
 section.
 
+We can create a _sub-stream_ from the `DataStream` constructor:
+
+[!code-csharp[SubStreamConstructor](./../../../../src/Yarhl.Examples/IO/DataStreamExamples.cs?name=SubStreamConstructor)]
+
+or from the `Slice` API:
+
+[!code-csharp[SubStreamConstructor](./../../../../src/Yarhl.Examples/IO/DataStreamExamples.cs?name=SubStreamSlice)]
+
 ## Factory
 
 The constructors of `DataStream` takes a `Stream` with optional offset and

src/Yarhl.Examples/IO/DataStreamExamples.cs

@@ -0,0 +1,44 @@
+// Copyright (c) 2023 SceneGate
+
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+namespace Yarhl.Examples.IO;
+
+using Yarhl.IO;
+
+public static class DataStreamExamples
+{
+    public static void CreateSubStreamConstructor()
+    {
+        #region SubStreamConstructor
+        var baseStream = new FileStream("container.bin", FileMode.Open);
+        using var file1Stream = new DataStream(baseStream, 0x100, 0x2C0);
+        using var file2Stream = new DataStream(baseStream, 0x3C0, 0x80);
+        #endregion
+    }
+
+    public static void CreateSubStreamSlice()
+    {
+        #region SubStreamSlice
+        DataStream containerStream = DataStreamFactory.FromFile("container.bin", FileOpenMode.Read);
+        using DataStream file1Stream = containerStream.Slice(0x100, 0x2C0);
+        using DataStream file2Stream = containerStream.Slice(0x3C0, 0x80);
+        using DataStream lastFileStream = containerStream.Slice(0x8400);
+        #endregion
+    }
+}

src/Yarhl.UnitTests/IO/DataStreamTests.cs

@@ -979,6 +979,107 @@ public void ReadBufferOutOfRange()
             stream.Dispose();
         }
 
+        [Test]
+        public void SliceUsesSameBaseStream()
+        {
+            baseStream.Write(new byte[] { 0xCA, 0xFE });
+            using var parent = new DataStream(baseStream);
+
+            using DataStream slice = parent.Slice(1);
+
+            Assert.That(parent.BaseStream, Is.SameAs(baseStream));
+            Assert.That(slice.BaseStream, Is.SameAs(baseStream));
+        }
+
+        [Test]
+        public void SliceStream()
+        {
+            using var stream = new DataStream();
+            stream.WriteByte(0xBE);
+            stream.WriteByte(0xBA);
+            stream.WriteByte(0xCA);
+            stream.WriteByte(0xFE);
+
+            using DataStream testSlice = stream.Slice(2);
+            Assert.That(testSlice, Is.Not.Null);
+
+            Assert.Multiple(() => {
+                Assert.That(testSlice.Position, Is.EqualTo(0));
+                Assert.That(testSlice.Offset, Is.EqualTo(2));
+                Assert.That(testSlice.Length, Is.EqualTo(2));
+                Assert.That(testSlice.ReadByte(), Is.EqualTo(0xCA));
+            });
+        }
+
+        [Test]
+        public void SliceWithLength()
+        {
+            baseStream.Write(new byte[] { 0xBE, 0xBA, 0xCA, 0xFE });
+            using var stream = new DataStream(baseStream);
+
+            using DataStream testSlice = stream.Slice(2, 1);
+
+            Assert.That(testSlice, Is.Not.Null);
+            Assert.Multiple(() => {
+                Assert.That(testSlice.Position, Is.EqualTo(0));
+                Assert.That(testSlice.Offset, Is.EqualTo(2));
+                Assert.That(testSlice.Length, Is.EqualTo(1));
+                Assert.That(testSlice.ReadByte(), Is.EqualTo(0xCA));
+            });
+        }
+
+        [Test]
+        public void SliceZeroLengthSucceeds()
+        {
+            baseStream.Write(new byte[] { 0xBE, 0xBA, 0xCA, 0xFE });
+            using var stream = new DataStream(baseStream);
+
+            using DataStream testSlice = stream.Slice(2, 0);
+
+            Assert.That(testSlice, Is.Not.Null);
+            Assert.Multiple(() => {
+                Assert.That(testSlice.Offset, Is.EqualTo(2));
+                Assert.That(testSlice.Length, Is.EqualTo(0));
+            });
+
+            using DataStream endSlice = stream.Slice(4);
+            Assert.That(endSlice, Is.Not.Null);
+            Assert.Multiple(() => {
+                Assert.That(endSlice.Offset, Is.EqualTo(4));
+                Assert.That(endSlice.Length, Is.EqualTo(0));
+            });
+        }
+
+        [Test]
+        public void SliceCannotExpand()
+        {
+            baseStream.Write(new byte[] { 0xBE, 0xBA, 0xCA, 0xFE });
+            using var stream = new DataStream(baseStream);
+
+            using DataStream testSlice = stream.Slice(2, 1);
+
+            testSlice.Position = 1;
+            Assert.That(() => testSlice.WriteByte(0xC0), Throws.InstanceOf<InvalidOperationException>());
+
+            using DataStream endSlice = stream.Slice(4, 0);
+            Assert.That(() => endSlice.WriteByte(0xC0), Throws.InstanceOf<InvalidOperationException>());
+        }
+
+        [Test]
+        public void SliceThrowsWithInvalidArgs()
+        {
+            baseStream.Write(new byte[] { 0xBE, 0xBA, 0xCA, 0xFE });
+            using var stream = new DataStream(baseStream);
+
+            Assert.Multiple(() => {
+                Assert.That(() => stream.Slice(-1), Throws.InstanceOf<ArgumentOutOfRangeException>());
+                Assert.That(() => stream.Slice(5), Throws.InstanceOf<ArgumentOutOfRangeException>());
+                Assert.That(() => stream.Slice(-1, 1), Throws.InstanceOf<ArgumentOutOfRangeException>());
+                Assert.That(() => stream.Slice(5, 1), Throws.InstanceOf<ArgumentOutOfRangeException>());
+                Assert.That(() => stream.Slice(0, 5), Throws.InstanceOf<ArgumentOutOfRangeException>());
+            });
+        }
+
         [Test]
         public void WritesAByteAndIncreasePosition()
         {

src/Yarhl/IO/DataStream.cs

@@ -720,6 +720,39 @@ public bool Compare(Stream otherStream)
             return result;
         }
 
+        /// <summary>
+        /// Creates a substream starting in a defined position.
+        /// </summary>
+        /// <returns>The substream defined by offset and length parameters.</returns>
+        /// <param name="start">Defined starting position.</param>
+        public DataStream Slice(long start)
+        {
+            if (start < 0 || start > Length) {
+                throw new ArgumentOutOfRangeException(nameof(start));
+            }
+
+            return new DataStream(this, start, Length - start);
+        }
+
+        /// <summary>
+        /// Creates a substream starting in a defined position and with a defined length.
+        /// </summary>
+        /// <returns>The substream defined by offset and length parameters.</returns>
+        /// <param name="start">Defined starting position.</param>
+        /// <param name="length">Defined length to be written.</param>
+        public DataStream Slice(long start, long length)
+        {
+            if (start < 0 || start > Length) {
+                throw new ArgumentOutOfRangeException(nameof(start));
+            }
+
+            if (length < 0 || start + length > Length) {
+                throw new ArgumentOutOfRangeException(nameof(length));
+            }
+
+            return new DataStream(this, start, length);
+        }
+
         /// <summary>
         /// Releases all resource used by the <see cref="DataStream"/>
         /// object.