fix for #325: add descriptive/better error message (include URL) if model download fails

sdk/cs/src/FoundryLocalManager.cs

@@ -258,30 +258,38 @@ public async Task<List<ModelInfo>> ListCachedModelsAsync(CancellationToken ct =
             IgnorePipeReport = true
         };
 
-        var response = await _serviceClient!.PostAsJsonAsync("/openai/download", request, ct);
-        response.EnsureSuccessStatusCode();
-        var responseBody = await response.Content.ReadAsStringAsync(ct);
-
-        // Find the last '{' to get the start of the JSON object
-        var jsonStart = responseBody.LastIndexOf('{');
-        if (jsonStart == -1)
+        try
         {
-            throw new InvalidOperationException("No JSON object found in response.");
-        }
+            var response = await _serviceClient!.PostAsJsonAsync("/openai/download", request, ct);
+            response.EnsureSuccessStatusCode();
+            var responseBody = await response.Content.ReadAsStringAsync(ct);
 
-        var jsonPart = responseBody[jsonStart..];
+            // Find the last '{' to get the start of the JSON object
+            var jsonStart = responseBody.LastIndexOf('{');
+            if (jsonStart == -1)
+            {
+                throw new InvalidOperationException("No JSON object found in response.");
+            }
 
-        // Parse the JSON part
-        using var jsonDoc = JsonDocument.Parse(jsonPart);
-        var success = jsonDoc.RootElement.GetProperty("success").GetBoolean();
-        var errorMessage = jsonDoc.RootElement.GetProperty("errorMessage").GetString();
+            var jsonPart = responseBody[jsonStart..];
 
-        if (!success)
+            // Parse the JSON part
+            using var jsonDoc = JsonDocument.Parse(jsonPart);
+            var success = jsonDoc.RootElement.GetProperty("success").GetBoolean();
+            var errorMessage = jsonDoc.RootElement.GetProperty("errorMessage").GetString();
+
+            if (!success)
+            {
+                throw new InvalidOperationException($"Failed to download model: {errorMessage}");
+            }
+
+            return modelInfo;
+        }
+        catch (Exception)
         {
-            throw new InvalidOperationException($"Failed to download model: {errorMessage}");
+            Console.WriteLine($"Failed to download model from: {modelInfo.Uri}");
+            throw;
         }
-
-        return modelInfo;
     }
 
     public async Task<bool> IsModelUpgradeableAsync(string aliasOrModelId, DeviceType? device = null, CancellationToken ct = default)

sdk/cs/test/FoundryLocal.Tests/DownloadExceptionTest.cs

@@ -0,0 +1,64 @@
+// --------------------------------------------------------------------------------------------------------------------
+// <copyright company="Microsoft">
+//   Copyright (c) Microsoft. All rights reserved.
+// </copyright>
+// --------------------------------------------------------------------------------------------------------------------
+
+namespace Microsoft.AI.Foundry.Local.Tests;
+
+using System;
+using System.Collections.Generic;
+using System.Net.Http;
+using System.Reflection;
+using System.Text.Json;
+using System.Threading.Tasks;
+using Microsoft.AI.Foundry.Local;
+using RichardSzalay.MockHttp;
+using Xunit;
+
+public class DownloadExceptionTest
+{
+    [Fact]
+    public async Task DownloadModelAsync_RethrowsException_AndPrintsUrl()
+    {
+        // Arrange
+        using var mockHttp = new MockHttpMessageHandler();
+        var client = mockHttp.ToHttpClient();
+        client.BaseAddress = new Uri("http://localhost:5272");
+
+        using var manager = new FoundryLocalManager();
+
+        // Inject the mock client
+        typeof(FoundryLocalManager)
+            .GetField("_serviceUri", BindingFlags.NonPublic | BindingFlags.Instance)!
+            .SetValue(manager, client.BaseAddress);
+
+        typeof(FoundryLocalManager)
+            .GetField("_serviceClient", BindingFlags.NonPublic | BindingFlags.Instance)!
+            .SetValue(manager, client);
+
+        // Mock catalog to return a model
+        var modelInfo = new ModelInfo
+        {
+            ModelId = "test-model:1",
+            Uri = "https://example.com/model.onnx",
+            Alias = "test-model",
+            Runtime = new Runtime { DeviceType = DeviceType.CPU }
+        };
+        var catalog = new List<ModelInfo> { modelInfo };
+        var catalogJson = JsonSerializer.Serialize(catalog, ModelGenerationContext.Default.ListModelInfo);
+
+        mockHttp.When(HttpMethod.Get, "/foundry/list").Respond("application/json", catalogJson);
+        mockHttp.When(HttpMethod.Get, "/openai/models").Respond("application/json", "[]");
+
+        // Mock download to throw an exception
+        mockHttp.When(HttpMethod.Post, "/openai/download").Throw(new HttpRequestException("SSL connection failed"));
+
+        // Act & Assert
+        var ex = await Assert.ThrowsAsync<HttpRequestException>(() => manager.DownloadModelAsync("test-model"));
+        Assert.Equal("SSL connection failed", ex.Message);
+
+        // Note: Verifying Console.WriteLine is difficult in this setup without redirecting Console.Out, 
+        // but we verified the exception is rethrown.
+    }
+}