Override all Read methods in NullTextReader and NullStreamReader (#64301)

Author: bgrainger

src/libraries/System.IO/tests/Stream/Stream.NullTests.cs

@@ -123,6 +123,16 @@ public static void TestNullStream_WriteByte()
             Assert.Equal(0, source.Position);
         }
 
+        [Theory]
+        [MemberData(nameof(NullReaders))]
+        public static void TestNullTextReaderDispose(TextReader input)
+        {
+            // dispose should be a no-op
+            input.Dispose();
+            input.Dispose();
+            Assert.Equal("", input.ReadToEnd());
+        }
+
         [Theory]
         [MemberData(nameof(NullReaders))]
         public static void TestNullTextReader(TextReader input)
@@ -131,16 +141,54 @@ public static void TestNullTextReader(TextReader input)
 
             if (sr != null)
                 Assert.True(sr.EndOfStream, "EndOfStream property didn't return true");
-            input.ReadLine();
-            input.Dispose();
-
-            input.ReadLine();
+            Assert.Null(input.ReadLine());
             if (sr != null)
                 Assert.True(sr.EndOfStream, "EndOfStream property didn't return true");
-            input.Read();
-            input.Peek();
-            input.Read(new char[2], 0, 2);
-            input.ReadToEnd();
+
+            Assert.Equal(-1, input.Read());
+            Assert.Equal(-1, input.Peek());
+            var chars = new char[2];
+            Assert.Equal(0, input.Read(chars, 0, chars.Length));
+            Assert.Equal(0, input.Read(chars.AsSpan()));
+            Assert.Equal(0, input.ReadBlock(chars, 0, chars.Length));
+            Assert.Equal(0, input.ReadBlock(chars.AsSpan()));
+            Assert.Equal("", input.ReadToEnd());
+            input.Dispose();
+        }
+
+        [Theory]
+        [MemberData(nameof(NullReaders))]
+        public static async Task TestNullTextReaderAsync(TextReader input)
+        {
+            var chars = new char[2];
+            Assert.Equal(0, await input.ReadAsync(chars, 0, chars.Length));
+            Assert.Equal(0, await input.ReadAsync(chars.AsMemory(), default));
+            Assert.Equal(0, await input.ReadBlockAsync(chars, 0, chars.Length));
+            Assert.Equal(0, await input.ReadBlockAsync(chars.AsMemory(), default));
+            Assert.Null(await input.ReadLineAsync());
+            Assert.Null(await input.ReadLineAsync(default));
+            Assert.Equal("", await input.ReadToEndAsync());
+            Assert.Equal("", await input.ReadToEndAsync(default));
+            input.Dispose();
+        }
+
+        [Theory]
+        [MemberData(nameof(NullReaders))]
+        public static async Task TestCanceledNullTextReaderAsync(TextReader input)
+        {
+            using CancellationTokenSource tokenSource = new CancellationTokenSource();
+            tokenSource.Cancel();
+            var token = tokenSource.Token;
+            var chars = new char[2];
+            OperationCanceledException ex;
+            ex = await Assert.ThrowsAnyAsync<OperationCanceledException>(async () => await input.ReadAsync(chars.AsMemory(), token));
+            Assert.Equal(token, ex.CancellationToken);
+            ex = await Assert.ThrowsAnyAsync<OperationCanceledException>(async () => await input.ReadBlockAsync(chars.AsMemory(), token));
+            Assert.Equal(token, ex.CancellationToken);
+            ex = await Assert.ThrowsAnyAsync<OperationCanceledException>(async () => await input.ReadLineAsync(token));
+            Assert.Equal(token, ex.CancellationToken);
+            ex = await Assert.ThrowsAnyAsync<OperationCanceledException>(async () => await input.ReadToEndAsync(token));
+            Assert.Equal(token, ex.CancellationToken);
             input.Dispose();
         }
 

src/libraries/System.Private.CoreLib/src/System/IO/StreamReader.cs

@@ -1386,7 +1386,7 @@ private void ThrowIfDisposed()
 
         // No data, class doesn't need to be serializable.
         // Note this class is threadsafe.
-        private sealed class NullStreamReader : StreamReader
+        internal sealed class NullStreamReader : StreamReader
         {
             public override Encoding CurrentEncoding => Encoding.Unicode;
 
@@ -1395,35 +1395,46 @@ protected override void Dispose(bool disposing)
                 // Do nothing - this is essentially unclosable.
             }
 
-            public override int Peek()
-            {
-                return -1;
-            }
+            public override int Peek() => -1;
 
-            public override int Read()
-            {
-                return -1;
-            }
+            public override int Read() => -1;
 
-            public override int Read(char[] buffer, int index, int count)
-            {
-                return 0;
-            }
+            public override int Read(char[] buffer, int index, int count) => 0;
 
-            public override string? ReadLine()
-            {
-                return null;
-            }
+            public override int Read(Span<char> buffer) => 0;
 
-            public override string ReadToEnd()
-            {
-                return string.Empty;
-            }
+            public override Task<int> ReadAsync(char[] buffer, int index, int count) => Task.FromResult(0);
 
-            internal override int ReadBuffer()
-            {
-                return 0;
-            }
+            public override ValueTask<int> ReadAsync(Memory<char> buffer, CancellationToken cancellationToken) =>
+                cancellationToken.IsCancellationRequested ? ValueTask.FromCanceled<int>(cancellationToken) : default;
+
+            public override int ReadBlock(char[] buffer, int index, int count) => 0;
+
+            public override int ReadBlock(Span<char> buffer) => 0;
+
+            public override Task<int> ReadBlockAsync(char[] buffer, int index, int count) => Task.FromResult(0);
+
+            public override ValueTask<int> ReadBlockAsync(Memory<char> buffer, CancellationToken cancellationToken) =>
+                cancellationToken.IsCancellationRequested ? ValueTask.FromCanceled<int>(cancellationToken) : default;
+
+            public override string? ReadLine() => null;
+
+            public override Task<string?> ReadLineAsync() => Task.FromResult<string?>(null);
+
+            public override ValueTask<string?> ReadLineAsync(CancellationToken cancellationToken) =>
+                cancellationToken.IsCancellationRequested ? ValueTask.FromCanceled<string?>(cancellationToken) : default;
+
+            public override string ReadToEnd() => "";
+
+            public override Task<string> ReadToEndAsync() => Task.FromResult("");
+
+            public override Task<string> ReadToEndAsync(CancellationToken cancellationToken) =>
+                cancellationToken.IsCancellationRequested ? Task.FromCanceled<string>(cancellationToken) : Task.FromResult("");
+
+            internal override ValueTask<int> ReadAsyncInternal(Memory<char> buffer, CancellationToken cancellationToken) =>
+                cancellationToken.IsCancellationRequested ? ValueTask.FromCanceled<int>(cancellationToken) : default;
+
+            internal override int ReadBuffer() => 0;
         }
     }
 }

src/libraries/System.Private.CoreLib/src/System/IO/TextReader.cs

@@ -19,7 +19,8 @@ namespace System.IO
     // There are methods on the Stream class for reading bytes.
     public abstract partial class TextReader : MarshalByRefObject, IDisposable
     {
-        public static readonly TextReader Null = new NullTextReader();
+        // Create our own instance to avoid static field initialization order problems on Mono.
+        public static readonly TextReader Null = new StreamReader.NullStreamReader();
 
         protected TextReader() { }
 
@@ -338,21 +339,6 @@ internal async ValueTask<int> ReadBlockAsyncInternal(Memory<char> buffer, Cancel
         }
         #endregion
 
-        private sealed class NullTextReader : TextReader
-        {
-            public NullTextReader() { }
-
-            public override int Read(char[] buffer, int index, int count)
-            {
-                return 0;
-            }
-
-            public override string? ReadLine()
-            {
-                return null;
-            }
-        }
-
         public static TextReader Synchronized(TextReader reader)
         {
             if (reader == null)