lateapexearlyspeed-issue-30778 Create method: TryReadExact(). (#57921)

* lateapexearlyspeed-issue-30778 Create method: TryReadExact(). * issue-30778 Add test for SequenceReader.TryReadExact(). * issue-30778 Fix comment: format return xml doc. Co-authored-by: Jeff Handley <[email protected]> Co-authored-by: Jeff Handley <[email protected]>
dotnet · Oct 13, 2021 · 6890b50 · 6890b50
1 parent 9dc925d
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diff --git a/src/libraries/System.Memory/ref/System.Memory.cs b/src/libraries/System.Memory/ref/System.Memory.cs
@@ -314,6 +314,7 @@ public void Rewind(long count) { }
         public bool TryReadTo(out System.ReadOnlySpan<T> span, T delimiter, T delimiterEscape, bool advancePastDelimiter = true) { throw null; }
         public bool TryReadToAny(out System.Buffers.ReadOnlySequence<T> sequence, System.ReadOnlySpan<T> delimiters, bool advancePastDelimiter = true) { throw null; }
         public bool TryReadToAny(out System.ReadOnlySpan<T> span, System.ReadOnlySpan<T> delimiters, bool advancePastDelimiter = true) { throw null; }
+        public bool TryReadExact(int count, out System.Buffers.ReadOnlySequence<T> sequence) { throw null; }
     }
     public readonly partial struct StandardFormat : System.IEquatable<System.Buffers.StandardFormat>
     {

diff --git a/src/libraries/System.Memory/src/System/Buffers/SequenceReader.Search.cs b/src/libraries/System.Memory/src/System/Buffers/SequenceReader.Search.cs
@@ -502,6 +502,32 @@ public bool TryReadTo(out ReadOnlySequence<T> sequence, ReadOnlySpan<T> delimite
             return false;
         }
 
+        /// <summary>
+        /// Try to read data with given <paramref name="count"/>.
+        /// </summary>
+        /// <param name="count">Read count.</param>
+        /// <param name="sequence">The read data, if successfully read requested <paramref name="count"/> data.</param>
+        /// <returns><c>true</c> if remaining items in current <see cref="SequenceReader{T}" /> is enough for <paramref name="count"/>.</returns>
+        public bool TryReadExact(int count, out ReadOnlySequence<T> sequence)
+        {
+            if (count < 0)
+            {
+                ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.count);
+            }
+            if (count > Remaining)
+            {
+                sequence = default;
+                return false;
+            }
+
+            sequence = Sequence.Slice(Position, count);
+            if (count != 0)
+            {
+                Advance(count);
+            }
+            return true;
+        }
+
         /// <summary>
         /// Advance until the given <paramref name="delimiter"/>, if found.
         /// </summary>

diff --git a/src/libraries/System.Memory/tests/SequenceReader/ReadTo.cs b/src/libraries/System.Memory/tests/SequenceReader/ReadTo.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Linq;
 using System.Buffers;
 using Xunit;
 
@@ -107,6 +108,38 @@ public void TryReadTo_Sequence(bool advancePastDelimiter, bool useEscapeOverload
             }
         }
 
+        [Fact]
+        public void TryReadExact_Sequence()
+        {
+            ReadOnlySequence<int> data = SequenceFactory.Create(new int[][] {
+                new int[] { 0 },
+                new int[] { 1, 2 },
+                new int[] { },
+                new int[] { 3, 4 }
+            });
+
+            var sequenceReader = new SequenceReader<int>(data);
+
+            Assert.True(sequenceReader.TryReadExact(0, out ReadOnlySequence<int> sequence));
+            Assert.Equal(0, sequence.Length);
+
+            for (int i = 0; i < 2; i++)
+            {
+                Assert.True(sequenceReader.TryReadExact(2, out sequence));
+                Assert.Equal(Enumerable.Range(i * 2, 2), sequence.ToArray());
+            }
+
+            // There is only 1 item in sequence reader
+            Assert.False(sequenceReader.TryReadExact(2, out _));
+
+            // The last 1 item was not advanced so still can be fetched
+            Assert.True(sequenceReader.TryReadExact(1, out sequence));
+            Assert.Equal(1, sequence.Length);
+            Assert.Equal(4, sequence.FirstSpan[0]);
+
+            Assert.True(sequenceReader.End);
+        }
+
         [Theory,
             InlineData(false),
             InlineData(true),]