Fix GetMoreBytesFromStream to handle final block correctly

docs/standard/serialization/system-text-json/snippets/how-to/csharp/Utf8ReaderPartialRead.cs

@@ -32,49 +32,61 @@ public static void Run()
             Console.WriteLine($"String in buffer is: {Encoding.UTF8.GetString(buffer)}");
 
             // Search for "Summary" property name
-            while (reader.TokenType != JsonTokenType.PropertyName || !reader.ValueTextEquals("Summary"))
+            var foundSummary = false;
+            while (reader.Read() || GetMoreBytesFromStream(stream, ref buffer, ref reader))
             {
-                if (!reader.Read())
+                if (reader.TokenType == JsonTokenType.PropertyName && 
+                    reader.ValueTextEquals("Summary"))
                 {
-                    // Not enough of the JSON is in the buffer to complete a read.
-                    GetMoreBytesFromStream(stream, ref buffer, ref reader);
+                    foundSummary = true;
+                    break;
                 }
             }
 
-            // Found the "Summary" property name.
-            Console.WriteLine($"String in buffer is: {Encoding.UTF8.GetString(buffer)}");
-            while (!reader.Read())
+            if (foundSummary)
             {
-                // Not enough of the JSON is in the buffer to complete a read.
-                GetMoreBytesFromStream(stream, ref buffer, ref reader);
+                // Found the "Summary" property name.
+                Console.WriteLine($"String in buffer is: {Encoding.UTF8.GetString(buffer)}");
+                if (!reader.Read() && (!GetMoreBytesFromStream(stream, ref buffer, ref reader) || !reader.Read()))
+                    throw new Exception("Invalid JSON");
+
+                // Display value of Summary property, that is, "Hot".
+                Console.WriteLine($"Got property value: {reader.GetString()}");
             }
-            // Display value of Summary property, that is, "Hot".
-            Console.WriteLine($"Got property value: {reader.GetString()}");
         }
 
-        private static void GetMoreBytesFromStream(
+        private static bool GetMoreBytesFromStream(
             MemoryStream stream, ref byte[] buffer, ref Utf8JsonReader reader)
         {
+            // If we've reached the end of the JSON data, return false.
+            if (reader.IsFinalBlock)
+                return false;
             int bytesRead;
             if (reader.BytesConsumed < buffer.Length)
             {
                 ReadOnlySpan<byte> leftover = buffer.AsSpan((int)reader.BytesConsumed);
-
+        
                 if (leftover.Length == buffer.Length)
                 {
                     Array.Resize(ref buffer, buffer.Length * 2);
                     Console.WriteLine($"Increased buffer size to {buffer.Length}");
                 }
-
+
+                // Move any leftover bytes to the beginning of the buffer.
                 leftover.CopyTo(buffer);
+                // Read more data from the stream to fill the rest of the buffer.
                 bytesRead = stream.Read(buffer.AsSpan(leftover.Length));
             }
             else
             {
                 bytesRead = stream.Read(buffer);
             }
+            // If we've reached the end of the stream, set isFinalBlock to true.
+            if (stream.Position == stream.Length)
+                Array.Resize(ref buffer, buffer.Length - (int)reader.BytesConsumed + bytesRead);
             Console.WriteLine($"String in buffer is: {Encoding.UTF8.GetString(buffer)}");
-            reader = new Utf8JsonReader(buffer, isFinalBlock: bytesRead == 0, reader.CurrentState);
+            reader = new Utf8JsonReader(buffer, isFinalBlock: stream.Position == stream.Length, reader.CurrentState);
+            return bytesRead > 0;
         }
     }
 }