Custom Serializer for Message Creation - Resolves Issue 552

src/Custom/Assistants/MessageCreationAttachment.cs

@@ -26,7 +26,47 @@ public partial class MessageCreationAttachment
     public IReadOnlyList<ToolDefinition> Tools { get; }
 
     private void SerializeTools(Utf8JsonWriter writer, ModelReaderWriterOptions options)
-        => writer.WriteObjectValue(Tools, options);
+    {
+        if (Tools is null)
+        {
+            writer.WriteNullValue();
+            return;
+        }
+
+        writer.WriteStartArray();
+        foreach (ToolDefinition tool in Tools)
+        {
+            using var ms = new System.IO.MemoryStream();
+            using (var tempWriter = new Utf8JsonWriter(ms))
+            {
+                tempWriter.WriteObjectValue(tool, options);
+                tempWriter.Flush();
+            }
+
+            using (JsonDocument doc = JsonDocument.Parse(ms.ToArray()))
+            {
+                JsonElement root = doc.RootElement;
+                if (root.ValueKind == JsonValueKind.Object)
+                {
+                    writer.WriteStartObject();
+                    foreach (var prop in root.EnumerateObject())
+                    {
+                        if (prop.NameEquals("file_search"u8))
+                        {
+                            continue;
+                        }
+                        prop.WriteTo(writer);
+                    }
+                    writer.WriteEndObject();
+                }
+                else
+                {
+                    root.WriteTo(writer);
+                }
+            }
+        }
+        writer.WriteEndArray();
+    }
 
     private static void DeserializeTools(JsonProperty property, ref IReadOnlyList<ToolDefinition> tools)
     {

tests/Assistants/AssistantsTests.cs

@@ -1,10 +1,3 @@
-using Microsoft.ClientModel.TestFramework;
-using NUnit.Framework;
-using NUnit.Framework.Internal;
-using OpenAI.Assistants;
-using OpenAI.Files;
-using OpenAI.Tests.Utility;
-using OpenAI.VectorStores;
 using System;
 using System.ClientModel;
 using System.ClientModel.Primitives;
@@ -14,6 +7,12 @@
 using System.Text.Json;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.ClientModel.TestFramework;
+using NUnit.Framework;
+using OpenAI.Assistants;
+using OpenAI.Files;
+using OpenAI.Tests.Utility;
+using OpenAI.VectorStores;
 using static OpenAI.Tests.TestHelpers;
 
 namespace OpenAI.Tests.Assistants;
@@ -30,7 +29,6 @@ public class AssistantsTests : OpenAIRecordedTestBase
     private readonly List<string> _vectorStoreIdsToDelete = [];
 
     private static readonly DateTimeOffset s_2024 = new(2024, 1, 1, 0, 0, 0, TimeSpan.Zero);
-    private static readonly string s_testAssistantName = $".NET SDK Test Assistant - Please Delete Me";
     private static readonly string s_cleanupMetadataKey = $"test_metadata_cleanup_eligible";
 
     private AssistantClient GetTestClient() => GetProxiedOpenAIClient<AssistantClient>(TestScenario.Assistants);
@@ -847,6 +845,51 @@ This file describes the favorite foods of several people.
         });
     }
 
+    [RecordedTest]
+    [LiveOnly]
+    public async Task FileOnMessageWorks()
+    {
+        // First, we need to upload a simple test file.
+        OpenAIFileClient fileClient = GetTestClient<OpenAIFileClient>(TestScenario.Files);
+        OpenAIFile testFile = await fileClient.UploadFileAsync(
+            BinaryData.FromString("""
+            This file describes the favorite foods of several people.
+
+            Summanus Ferdinand: tacos
+            Tekakwitha Effie: pizza
+            Filip Carola: cake
+            """).ToStream(),
+            "favorite_foods.txt",
+            FileUploadPurpose.Assistants);
+        Validate(testFile);
+
+        AssistantClient client = GetTestClient();
+
+        AssistantThread thread = await client.CreateThreadAsync();
+        Validate(thread);
+
+        Assistant assistant = await client.CreateAssistantAsync("gpt-4o-mini");
+        Validate(assistant);
+
+        ThreadMessage message = await client.CreateMessageAsync(
+            thread.Id,
+            MessageRole.User,
+            new[] {
+                MessageContent.FromText("What is this file?"),
+            },
+            new MessageCreationOptions()
+            {
+                Attachments = [
+                    new MessageCreationAttachment(testFile.Id, new List<ToolDefinition>() { ToolDefinition.CreateFileSearch() }),
+                    new MessageCreationAttachment(testFile.Id, new List<ToolDefinition>() { ToolDefinition.CreateCodeInterpreter() })
+                    ]
+            }
+            );
+        Validate(message);
+
+        var result = client.CreateRunStreamingAsync(thread.Id, assistant.Id);
+    }
+
     [RecordedTest]
     public async Task FileSearchStreamingWorks()
     {

tests/SessionRecords/AssistantsTests/FileOnMessageWorksAsync.json

@@ -0,0 +1,192 @@
+{
+  "Entries": [
+    {
+      "RequestUri": "https://api.openai.com/v1/threads",
+      "RequestMethod": "POST",
+      "RequestHeaders": {
+        "Accept": "application/json",
+        "Authorization": "Sanitized",
+        "Content-Length": "0",
+        "OpenAI-Beta": "assistants=v2",
+        "User-Agent": "OpenAI/2.5.0 (.NET 9.0.10; Darwin 25.0.0 Darwin Kernel Version 25.0.0: Wed Sep 17 21:42:08 PDT 2025; root:xnu-12377.1.9~141/RELEASE_ARM64_T8132)"
+      },
+      "RequestBody": null,
+      "StatusCode": 200,
+      "ResponseHeaders": {
+        "Alt-Svc": "h3=\":443\"",
+        "cf-cache-status": "DYNAMIC",
+        "CF-RAY": "99c6d22e3c896b33-DFW",
+        "Connection": "keep-alive",
+        "Content-Length": "137",
+        "Content-Type": "application/json",
+        "Date": "Sanitized",
+        "openai-organization": "Sanitized",
+        "openai-processing-ms": "Sanitized",
+        "openai-project": "Sanitized",
+        "openai-version": "2020-10-01",
+        "Server": "cloudflare",
+        "Set-Cookie": [
+          "Sanitized",
+          "Sanitized"
+        ],
+        "Strict-Transport-Security": "max-age=31536000; includeSubDomains; preload",
+        "X-Content-Type-Options": "nosniff",
+        "x-envoy-upstream-service-time": "167",
+        "x-openai-proxy-wasm": "v0.1",
+        "X-Request-ID": "Sanitized"
+      },
+      "ResponseBody": {
+        "id": "thread_gAAkyuIXs5PLiQoe8sIEDTXV",
+        "object": "thread",
+        "created_at": 1762791037,
+        "metadata": {},
+        "tool_resources": {}
+      }
+    },
+    {
+      "RequestUri": "https://api.openai.com/v1/assistants",
+      "RequestMethod": "POST",
+      "RequestHeaders": {
+        "Accept": "application/json",
+        "Authorization": "Sanitized",
+        "Content-Length": "23",
+        "Content-Type": "application/json",
+        "OpenAI-Beta": "assistants=v2",
+        "User-Agent": "OpenAI/2.5.0 (.NET 9.0.10; Darwin 25.0.0 Darwin Kernel Version 25.0.0: Wed Sep 17 21:42:08 PDT 2025; root:xnu-12377.1.9~141/RELEASE_ARM64_T8132)"
+      },
+      "RequestBody": {
+        "model": "gpt-4o-mini"
+      },
+      "StatusCode": 200,
+      "ResponseHeaders": {
+        "Alt-Svc": "h3=\":443\"",
+        "cf-cache-status": "DYNAMIC",
+        "CF-RAY": "99c6d22fae616b33-DFW",
+        "Connection": "keep-alive",
+        "Content-Length": "337",
+        "Content-Type": "application/json",
+        "Date": "Sanitized",
+        "openai-organization": "Sanitized",
+        "openai-processing-ms": "Sanitized",
+        "openai-project": "Sanitized",
+        "openai-version": "2020-10-01",
+        "Server": "cloudflare",
+        "Strict-Transport-Security": "max-age=31536000; includeSubDomains; preload",
+        "X-Content-Type-Options": "nosniff",
+        "x-envoy-upstream-service-time": "664",
+        "x-openai-proxy-wasm": "v0.1",
+        "X-Request-ID": "Sanitized"
+      },
+      "ResponseBody": {
+        "id": "asst_3Gz6lp6RnOg4hCaB8QzgaTAE",
+        "object": "assistant",
+        "created_at": 1762791037,
+        "name": null,
+        "description": null,
+        "model": "gpt-4o-mini",
+        "instructions": null,
+        "tools": [],
+        "top_p": 1.0,
+        "temperature": 1.0,
+        "reasoning_effort": null,
+        "tool_resources": {},
+        "metadata": {},
+        "response_format": "auto"
+      }
+    },
+    {
+      "RequestUri": "https://api.openai.com/v1/threads/thread_gAAkyuIXs5PLiQoe8sIEDTXV/messages",
+      "RequestMethod": "POST",
+      "RequestHeaders": {
+        "Accept": "application/json",
+        "Authorization": "Sanitized",
+        "Content-Length": "217",
+        "Content-Type": "application/json",
+        "OpenAI-Beta": "assistants=v2",
+        "User-Agent": "OpenAI/2.5.0 (.NET 9.0.10; Darwin 25.0.0 Darwin Kernel Version 25.0.0: Wed Sep 17 21:42:08 PDT 2025; root:xnu-12377.1.9~141/RELEASE_ARM64_T8132)"
+      },
+      "RequestBody": {
+        "role": "user",
+        "content": "What is this file?",
+        "attachments": [
+          {
+            "file_id": "file-LEY8LWxuCKn5TNcydztuW1",
+            "tools": [
+              {
+                "type": "file_search"
+              }
+            ]
+          },
+          {
+            "file_id": "file-LEY8LWxuCKn5TNcydztuW1",
+            "tools": [
+              {
+                "type": "code_interpreter"
+              }
+            ]
+          }
+        ]
+      },
+      "StatusCode": 200,
+      "ResponseHeaders": {
+        "Alt-Svc": "h3=\":443\"",
+        "cf-cache-status": "DYNAMIC",
+        "CF-RAY": "99c6d2347bdd6b33-DFW",
+        "Connection": "keep-alive",
+        "Content-Length": "675",
+        "Content-Type": "application/json",
+        "Date": "Sanitized",
+        "openai-organization": "Sanitized",
+        "openai-processing-ms": "Sanitized",
+        "openai-project": "Sanitized",
+        "openai-version": "2020-10-01",
+        "Server": "cloudflare",
+        "Strict-Transport-Security": "max-age=31536000; includeSubDomains; preload",
+        "X-Content-Type-Options": "nosniff",
+        "x-envoy-upstream-service-time": "2353",
+        "x-openai-proxy-wasm": "v0.1",
+        "X-Request-ID": "Sanitized"
+      },
+      "ResponseBody": {
+        "id": "msg_MZwW4GbZHxjqCfOHGFFuybon",
+        "object": "thread.message",
+        "created_at": 1762791039,
+        "assistant_id": null,
+        "thread_id": "thread_gAAkyuIXs5PLiQoe8sIEDTXV",
+        "run_id": null,
+        "role": "user",
+        "content": [
+          {
+            "type": "text",
+            "text": {
+              "value": "What is this file?",
+              "annotations": []
+            }
+          }
+        ],
+        "attachments": [
+          {
+            "file_id": "file-LEY8LWxuCKn5TNcydztuW1",
+            "tools": [
+              {
+                "type": "file_search"
+              }
+            ]
+          },
+          {
+            "file_id": "file-LEY8LWxuCKn5TNcydztuW1",
+            "tools": [
+              {
+                "type": "code_interpreter"
+              }
+            ]
+          }
+        ],
+        "metadata": {}
+      }
+    }
+  ],
+  "Variables": {
+    "OPEN-API-KEY": "api-key"
+  }
+}