Fix Console.Write on iOS

src/libraries/System.Console/src/System/ConsolePal.iOS.cs

@@ -1,22 +1,34 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics;
 using System.IO;
+using System.Runtime.InteropServices;
 using System.Text;
 
 namespace System
 {
     internal sealed class NSLogStream : ConsoleStream
     {
+        private readonly StringBuilder _buffer = new StringBuilder();
+
         public NSLogStream() : base(FileAccess.Write) {}
 
         public override int Read(Span<byte> buffer) => throw Error.GetReadNotSupported();
 
         public override unsafe void Write(ReadOnlySpan<byte> buffer)
         {
-            fixed (byte* ptr = buffer)
+            ReadOnlySpan<char> charSpan = MemoryMarshal.Cast<byte, char>(buffer);
+
+            lock (_buffer)
             {
-                Interop.Sys.Log(ptr, buffer.Length);
+                AccumulateNewLines(_buffer, charSpan, line =>
+                {
+                    fixed (char* ptr = line)
+                    {
+                        Interop.Sys.Log((byte*)ptr, line.Length * 2);
+                    }
+                });
             }
         }
     }

src/libraries/System.Console/src/System/IO/ConsoleStream.cs

@@ -3,6 +3,7 @@
 
 using System.Diagnostics;
 using System.Runtime.InteropServices;
+using System.Text;
 
 namespace System.IO
 {
@@ -90,5 +91,37 @@ protected void ValidateWrite(byte[] buffer, int offset, int count)
                 throw Error.GetWriteNotSupported();
             }
         }
+
+        protected static void AccumulateNewLines(StringBuilder accumulator, ReadOnlySpan<char> buffer, Action<string> printer)
+        {
+            int lineStartIndex = 0;
+            for (int i = 0; i < buffer.Length; i++)
+            {
+                if (buffer[i] == '\n')
+                {
+                    ReadOnlySpan<char> sliceWithNl = buffer.Slice(lineStartIndex, i - lineStartIndex);
+                    if (accumulator.Length > 0)
+                    {
+                        // we found a new line, append content from accumulator if it's not empty
+                        accumulator.Append(sliceWithNl);
+                        printer(accumulator.ToString());
+                        accumulator.Clear();
+                    }
+                    else
+                    {
+                        // accumulator is empty - print the line as it is
+                        printer(sliceWithNl.ToString());
+                    }
+                    lineStartIndex = i + 1;
+                }
+            }
+
+            if (buffer.Length > 0 && buffer[^1] != '\n')
+            {
+                // add a line without '\n' to accumulator
+                ReadOnlySpan<char> appendix = buffer.Slice(lineStartIndex, buffer.Length - lineStartIndex);
+                accumulator.Append(appendix);
+            }
+        }
     }
 }