From 096e0e75f82af45242481aadede4e978f619ac4e Mon Sep 17 00:00:00 2001
From: Martin Evans <martindevans@gmail.com>
Date: Mon, 15 Jan 2024 15:19:54 +0000
Subject: [PATCH 1/2] Check that the model file actually exists immediately
 before loading it. Improve #395

---
 LLama/Native/SafeLlamaModelHandle.cs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/LLama/Native/SafeLlamaModelHandle.cs b/LLama/Native/SafeLlamaModelHandle.cs
index 8ffa2be3..761a7c3a 100644
--- a/LLama/Native/SafeLlamaModelHandle.cs
+++ b/LLama/Native/SafeLlamaModelHandle.cs
@@ -2,6 +2,7 @@
 using System.Buffers;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.IO;
 using System.Runtime.InteropServices;
 using System.Text;
 using LLama.Exceptions;
@@ -63,6 +64,9 @@ namespace LLama.Native
         /// <exception cref="RuntimeError"></exception>
         public static SafeLlamaModelHandle LoadFromFile(string modelPath, LLamaModelParams lparams)
         {
+            if (!File.Exists(modelPath))
+                throw new FileNotFoundException("Model file does not exist", modelPath);
+
             var model = llama_load_model_from_file(modelPath, lparams);
             if (model == null)
                 throw new RuntimeError($"Failed to load model {modelPath}.");

From de2b20aae5b9c062768e8f1916f50acd06f015ad Mon Sep 17 00:00:00 2001
From: Martin Evans <martindevans@gmail.com>
Date: Mon, 15 Jan 2024 15:29:31 +0000
Subject: [PATCH 2/2] - Added a specific exception for failing to load model
 weights.  - Checking if model is readable

---
 LLama/Exceptions/RuntimeError.cs     | 19 +++++++++++++++++++
 LLama/Native/SafeLlamaModelHandle.cs | 18 ++++++++++--------
 2 files changed, 29 insertions(+), 8 deletions(-)

diff --git a/LLama/Exceptions/RuntimeError.cs b/LLama/Exceptions/RuntimeError.cs
index a8ea0531..c56d78ff 100644
--- a/LLama/Exceptions/RuntimeError.cs
+++ b/LLama/Exceptions/RuntimeError.cs
@@ -17,4 +17,23 @@ public class RuntimeError
     {
 
     }
+}
+
+/// <summary>
+/// Loading model weights failed
+/// </summary>
+public class LoadWeightsFailedException
+    : RuntimeError
+{
+    /// <summary>
+    /// The model path which failed to load
+    /// </summary>
+    public string ModelPath { get; }
+
+    /// <inheritdoc />
+    public LoadWeightsFailedException(string modelPath)
+        : base($"Failed to load model '{modelPath}'")
+    {
+        ModelPath = modelPath;
+    }
 }
\ No newline at end of file
diff --git a/LLama/Native/SafeLlamaModelHandle.cs b/LLama/Native/SafeLlamaModelHandle.cs
index 761a7c3a..5724ec7e 100644
--- a/LLama/Native/SafeLlamaModelHandle.cs
+++ b/LLama/Native/SafeLlamaModelHandle.cs
@@ -64,14 +64,16 @@ namespace LLama.Native
         /// <exception cref="RuntimeError"></exception>
         public static SafeLlamaModelHandle LoadFromFile(string modelPath, LLamaModelParams lparams)
         {
-            if (!File.Exists(modelPath))
-                throw new FileNotFoundException("Model file does not exist", modelPath);
-
-            var model = llama_load_model_from_file(modelPath, lparams);
-            if (model == null)
-                throw new RuntimeError($"Failed to load model {modelPath}.");
-
-            return model;
+            // Try to open the model file, this will check:
+            // - File exists (automatically throws FileNotFoundException)
+            // - File is readable (explicit check)
+            // This provides better error messages that llama.cpp, which would throw an access violation exception in both cases.
+            using (var fs = new FileStream(modelPath, FileMode.Open))
+                if (!fs.CanRead)
+                    throw new InvalidOperationException($"Model file '{modelPath}' is not readable");
+
+            return llama_load_model_from_file(modelPath, lparams)
+                ?? throw new LoadWeightsFailedException($"Failed to load model {modelPath}.");
         }
 
         #region native API