Handle error on command for FFI client + C# example

csharp/lib/AsyncClient.cs

@@ -62,14 +62,12 @@ private void SuccessCallback(ulong index, IntPtr str)
         });
     }
 
-    private void FailureCallback(ulong index)
+    private void FailureCallback(ulong index, ErrorType error_type, IntPtr error_msg_ptr)
     {
+        var error = error_msg_ptr == IntPtr.Zero ? null : Marshal.PtrToStringAnsi(error_msg_ptr);
         // Work needs to be offloaded from the calling thread, because otherwise we might starve the client's thread pool.
-        Task.Run(() =>
-        {
-            var message = messageContainer.GetMessage((int)index);
-            message.SetException(new Exception("Operation failed"));
-        });
+        _ = Task.Run(() => messageContainer.GetMessage((int)index)
+                .SetException(Errors.MakeException(error_type, error)));
     }
 
     ~AsyncClient() => Dispose();
@@ -95,7 +93,13 @@ private void FailureCallback(ulong index)
     #region FFI function declarations
 
     private delegate void StringAction(ulong index, IntPtr str);
-    private delegate void FailureAction(ulong index);
+    /// <summary>
+    /// Glide request failure callback.
+    /// </summary>
+    /// <param name="index">Request ID</param>
+    /// <param name="error_type">Error type</param>
+    /// <param name="error_msg_ptr">Error message</param>
+    private delegate void FailureAction(ulong index, ErrorType error_type, IntPtr error_msg_ptr);
     [DllImport("libglide_rs", CallingConvention = CallingConvention.Cdecl, EntryPoint = "get")]
     private static extern void GetFfi(IntPtr client, ulong index, IntPtr key);
 
@@ -109,5 +113,25 @@ private void FailureCallback(ulong index)
     [DllImport("libglide_rs", CallingConvention = CallingConvention.Cdecl, EntryPoint = "close_client")]
     private static extern void CloseClientFfi(IntPtr client);
 
+    internal enum ErrorType : uint
+    {
+        /// <summary>
+        /// Represented by <see cref="Errors.UnspecifiedException"/> for user
+        /// </summary>
+        Unspecified = 0,
+        /// <summary>
+        /// Represented by <see cref="Errors.ExecutionAbortedException"/> for user
+        /// </summary>
+        ExecAbort = 1,
+        /// <summary>
+        /// Represented by <see cref="TimeoutException"/> for user
+        /// </summary>
+        Timeout = 2,
+        /// <summary>
+        /// Represented by <see cref="Errors.DisconnectedException"/> for user
+        /// </summary>
+        Disconnect = 3,
+    }
+
     #endregion
 }

csharp/lib/Errors.cs

@@ -0,0 +1,33 @@
+/**
+ * Copyright GLIDE-for-Redis Project Contributors - SPDX Identifier: Apache-2.0
+ */
+
+using static Glide.AsyncClient;
+
+namespace Glide;
+
+public abstract class Errors
+{
+    public sealed class UnspecifiedException : Exception
+    {
+        internal UnspecifiedException(string? message) : base(message) { }
+    }
+
+    public sealed class ExecutionAbortedException : Exception
+    {
+        internal ExecutionAbortedException(string? message) : base(message) { }
+    }
+
+    public sealed class DisconnectedException : Exception
+    {
+        internal DisconnectedException(string? message) : base(message) { }
+    }
+
+    internal static Exception MakeException(ErrorType type, string? message) => type switch
+    {
+        ErrorType.ExecAbort => new ExecutionAbortedException(message),
+        ErrorType.Disconnect => new DisconnectedException(message),
+        ErrorType.Timeout => new TimeoutException(message),
+        _ => new UnspecifiedException(message),
+    };
+}

csharp/lib/src/lib.rs

@@ -2,6 +2,7 @@
  * Copyright GLIDE-for-Redis Project Contributors - SPDX Identifier: Apache-2.0
  */
 use glide_core::connection_request;
+use glide_core::errors::{error_message, error_type, RequestErrorType};
 use glide_core::{client::Client as GlideClient, connection_request::NodeAddress};
 use redis::{Cmd, FromRedisValue, RedisResult};
 use std::{
@@ -22,7 +23,7 @@ pub enum Level {
 pub struct Client {
     client: GlideClient,
     success_callback: unsafe extern "C" fn(usize, *const c_char) -> (),
-    failure_callback: unsafe extern "C" fn(usize) -> (), // TODO - add specific error codes
+    failure_callback: unsafe extern "C" fn(usize, RequestErrorType, *const c_char) -> (),
     runtime: Runtime,
 }