From cb813e1ffce4498a51fe87487554669dfdcb3903 Mon Sep 17 00:00:00 2001
From: Marc Gravell <marc.gravell@gmail.com>
Date: Sun, 30 Jun 2019 09:59:46 +0100
Subject: [PATCH] check the *actual* length to allow more stack usage *and*
 allow smaller pool rentals

---
 src/csharp/Grpc.Core/Grpc.Core.csproj           |  2 ++
 src/csharp/Grpc.Core/Internal/CallSafeHandle.cs | 10 +++++++++-
 src/csharp/Grpc.Core/Internal/MarshalUtils.cs   | 10 +++++++++-
 3 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/csharp/Grpc.Core/Grpc.Core.csproj b/src/csharp/Grpc.Core/Grpc.Core.csproj
index afd60e73a21..1844ce335bc 100755
--- a/src/csharp/Grpc.Core/Grpc.Core.csproj
+++ b/src/csharp/Grpc.Core/Grpc.Core.csproj
@@ -100,6 +100,8 @@
 
   <ItemGroup>
     <PackageReference Include="System.Interactive.Async" Version="3.2.0" />
+    <!-- System.Buffers *may* come in transitively, but: we can *always* use ArrayPool -->
+    <PackageReference Include="System.Buffers" Version="4.5.0" />
   </ItemGroup>
 
   <ItemGroup Condition=" '$(TargetFramework)' == 'net45' ">
diff --git a/src/csharp/Grpc.Core/Internal/CallSafeHandle.cs b/src/csharp/Grpc.Core/Internal/CallSafeHandle.cs
index 67efb031629..c62297b0972 100644
--- a/src/csharp/Grpc.Core/Internal/CallSafeHandle.cs
+++ b/src/csharp/Grpc.Core/Internal/CallSafeHandle.cs
@@ -135,8 +135,16 @@ namespace Grpc.Core.Internal
             {
                 var ctx = completionQueue.CompletionRegistry.RegisterBatchCompletion(CompletionHandler_ISendStatusFromServerCompletionCallback, callback);
                 var optionalPayloadLength = optionalPayload != null ? new UIntPtr((ulong)optionalPayload.Length) : UIntPtr.Zero;
-                int maxBytes = MarshalUtils.GetMaxBytesUTF8(status.Detail);
+
                 const int MaxStackAllocBytes = 256;
+                int maxBytes = MarshalUtils.GetMaxByteCountUTF8(status.Detail);
+                if (maxBytes > MaxStackAllocBytes)
+                {
+                    // pay the extra to get the *actual* size; this could mean that
+                    // it ends up fitting on the stack after all, but even if not
+                    // it will mean that we ask for a *much* smaller buffer
+                    maxBytes = MarshalUtils.GetByteCountUTF8(status.Detail);
+                }
 
                 if (maxBytes <= MaxStackAllocBytes)
                 {   // for small status, we can encode on the stack without touching arrays
diff --git a/src/csharp/Grpc.Core/Internal/MarshalUtils.cs b/src/csharp/Grpc.Core/Internal/MarshalUtils.cs
index ec3ce9ca72d..54b4370935d 100644
--- a/src/csharp/Grpc.Core/Internal/MarshalUtils.cs
+++ b/src/csharp/Grpc.Core/Internal/MarshalUtils.cs
@@ -66,9 +66,17 @@ namespace Grpc.Core.Internal
         /// <summary>
         /// Returns the maximum number of bytes required to encode a given string.
         /// </summary>
-        public static int GetMaxBytesUTF8(string str)
+        public static int GetMaxByteCountUTF8(string str)
         {
             return EncodingUTF8.GetMaxByteCount(str.Length);
         }
+
+        /// <summary>
+        /// Returns the actual number of bytes required to encode a given string.
+        /// </summary>
+        public static int GetByteCountUTF8(string str)
+        {
+            return EncodingUTF8.GetByteCount(str);
+        }
     }
 }