OpenAI library doesn't work with Gemini's OpenAI compat endpoint

[stephentoub]

Service

OpenAI

Describe the bug

Google blogged about how they now expose an OpenAI-compatible endpoint for gemini:
https://developers.googleblog.com/en/gemini-is-now-accessible-from-the-openai-library/

but the .NET OpenAI library doesn't work with it. Gemini is sending back a role of "model" as part of the response, but the OpenAI library is trying to validate that any role is one of only five hardcoded values, and anything else causes the request to fail:

openai-dotnet/src/Generated/Models/ChatMessageRole.Serialization.cs

Lines 21 to 29 in 539172f

	public static ChatMessageRole ToChatMessageRole(this string value)
	{
	if (StringComparer.OrdinalIgnoreCase.Equals(value, "system")) return ChatMessageRole.System;
	if (StringComparer.OrdinalIgnoreCase.Equals(value, "user")) return ChatMessageRole.User;
	if (StringComparer.OrdinalIgnoreCase.Equals(value, "assistant")) return ChatMessageRole.Assistant;
	if (StringComparer.OrdinalIgnoreCase.Equals(value, "tool")) return ChatMessageRole.Tool;
	if (StringComparer.OrdinalIgnoreCase.Equals(value, "function")) return ChatMessageRole.Function;
	throw new ArgumentOutOfRangeException(nameof(value), value, "Unknown ChatMessageRole value.");
	}

Steps to reproduce

Run the .NET equivalent to the code in that blog post:

using OpenAI;
using OpenAI.Chat;

var client = new OpenAIClient(new("gemini_api_key"), new()
{
    Endpoint = new("https://generativelanguage.googleapis.com/v1beta/"),
}).GetChatClient("gemini-1.5-flash");

var response = await client.CompleteChatAsync(
[
    ChatMessage.CreateSystemMessage("You are a helpful AI assistant."),
    ChatMessage.CreateUserMessage("Explain to me how AI works"),
]);

Console.WriteLine(response.Value.Content[0].Text);

It fails with:

Unhandled exception. System.ArgumentOutOfRangeException: Unknown ChatMessageRole value. (Parameter 'value')
Actual value was model.
   at OpenAI.Chat.ChatMessageRoleExtensions.ToChatMessageRole(String value)
   at OpenAI.Chat.InternalChatCompletionResponseMessage.DeserializeInternalChatCompletionResponseMessage(JsonElement element, ModelReaderWriterOptions options)
   at OpenAI.Chat.InternalCreateChatCompletionResponseChoice.DeserializeInternalCreateChatCompletionResponseChoice(JsonElement element, ModelReaderWriterOptions options)
   at OpenAI.Chat.ChatCompletion.DeserializeChatCompletion(JsonElement element, ModelReaderWriterOptions options)
   at OpenAI.Chat.ChatCompletion.FromResponse(PipelineResponse response)
   at OpenAI.Chat.ChatClient.CompleteChatAsync(IEnumerable`1 messages, ChatCompletionOptions options, CancellationToken cancellationToken)
   at OpenAI.Chat.ChatClient.CompleteChatAsync(ChatMessage[] messages)
   at Program.<Main>$(String[] args)

Code snippets

OS

any

.NET version

.NET 8

Library version

2.1.0-beta.2

[cosmez]

after adding the new role to the Serializer seems to be working fine. i assume this library is generated automatically. but i couldnt find instructions on how to fix the generation code. havent tested anything complex, but this patch seems to work:

--- a/src/Generated/Models/ChatMessageRole.Serialization.cs
+++ b/src/Generated/Models/ChatMessageRole.Serialization.cs
@@ -15,6 +15,7 @@ namespace OpenAI.Chat
             ChatMessageRole.Assistant => "assistant",
             ChatMessageRole.Tool => "tool",
             ChatMessageRole.Function => "function",
+            ChatMessageRole.Model => "model",
             _ => throw new ArgumentOutOfRangeException(nameof(value), value, "Unknown ChatMessageRole value.")
         };

@@ -23,6 +24,7 @@ namespace OpenAI.Chat
             if (StringComparer.OrdinalIgnoreCase.Equals(value, "system")) return ChatMessageRole.System;
             if (StringComparer.OrdinalIgnoreCase.Equals(value, "user")) return ChatMessageRole.User;
             if (StringComparer.OrdinalIgnoreCase.Equals(value, "assistant")) return ChatMessageRole.Assistant;
+            if (StringComparer.OrdinalIgnoreCase.Equals(value, "model")) return ChatMessageRole.Model;
             if (StringComparer.OrdinalIgnoreCase.Equals(value, "tool")) return ChatMessageRole.Tool;
             if (StringComparer.OrdinalIgnoreCase.Equals(value, "function")) return ChatMessageRole.Function;
             throw new ArgumentOutOfRangeException(nameof(value), value, "Unknown ChatMessageRole value.");