Fix LookAheadBuffer trying to read from the stream after reaching its…

… end

+semver:patch

YamlDotNet.Test/Core/ScannerTests.cs

@@ -26,6 +26,7 @@
 using System.IO;
 using System.Reflection;
 using System;
+using System.Linq;
 
 #if !PORTABLE && !NETCOREAPP1_0
 using System.Runtime.Serialization.Formatters.Binary;
@@ -407,6 +408,14 @@ public void Slow_stream_is_parsed_correctly()
             scanner.MoveNext();
         }
 
+        [Fact]
+        public void Issue_553_562()
+        {
+            var yaml = "MainItem4:\n" + string.Join("\n", Enumerable.Range(1, 100).Select(e => $"- {{item: {{foo1: {e}, foo2: 'bar{e}' }}}}"));
+
+            var scanner = new Scanner(new StringReader(yaml));
+            while (scanner.MoveNext()) ;
+        }
 
         private void AssertPartialSequenceOfTokensFrom(Scanner scanner, params Token[] tokens)
         {

YamlDotNet/Core/LookAheadBuffer.cs

@@ -20,6 +20,7 @@
 //  SOFTWARE.
 
 using System;
+using System.Diagnostics;
 using System.IO;
 using YamlDotNet.Helpers;
 
@@ -125,14 +126,19 @@ public void Cache(int length)
 
         private void FillBuffer()
         {
+            if (endOfInput)
+            {
+                return;
+            }
+
             var remainingSize = blockSize;
             do
             {
                 var readCount = input.Read(buffer, writeOffset, remainingSize);
                 if (readCount == 0)
                 {
                     endOfInput = true;
-                    break;
+                    return;
                 }
 
                 remainingSize -= readCount;
@@ -144,6 +150,8 @@ private void FillBuffer()
             {
                 writeOffset = 0;
             }
+
+            Debug.Assert(writeOffset == 0 || writeOffset == blockSize);
         }
 
         /// <summary>