Add support for json response format

Author: OkGoDoIt

OpenAI_API/Chat/ChatRequest.cs

@@ -1,6 +1,10 @@
 using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+using OpenAI_API.Models;
 using System;
 using System.Collections.Generic;
+using System.ComponentModel;
+using System.IO;
 using System.Linq;
 using System.Text;
 
@@ -119,6 +123,28 @@ public string StopSequence
 		[JsonProperty("user")]
 		public string user { get; set; }
 
+		/// <summary>
+		/// An object specifying the format that the model must output. Setting to <see cref="ResponseFormats.JsonObject"/> enables JSON mode, which guarantees the message the model generates is valid JSON, assuming that the <see cref="ChatChoice.FinishReason"/> is not "length".
+		/// Important: when using JSON mode, you must also instruct the model to produce JSON yourself via a system or user message. Without this, the model may generate an unending stream of whitespace until the generation reaches the token limit, resulting in a long-running and seemingly "stuck" request.Also note that the message content may be partially cut off if `finish_reason= "length"`, which indicates the generation exceeded `max_tokens` or the conversation exceeded the max context length.
+		/// </summary>
+		[JsonIgnore]
+		public string ResponseFormat { get; set; } = "text";
+
+		/// <summary>
+		/// This is only used for serializing the request into JSON, do not use it directly.
+		/// </summary>
+		[JsonProperty("response_format", DefaultValueHandling=DefaultValueHandling.Ignore)]
+		public Dictionary<string, string> ResponseFormatRaw
+		{
+			get
+			{
+				if (ResponseFormat == null || ResponseFormat == ResponseFormats.Text)
+					return null;
+				else
+					return new Dictionary<string, string>() { { "type", ResponseFormat } };
+			}
+		}
+
 		/// <summary>
 		/// Creates a new, empty <see cref="ChatRequest"/>
 		/// </summary>
@@ -133,7 +159,6 @@ public ChatRequest(ChatRequest basedOn)
 		{
 			if (basedOn == null)
 				return;
-
 			this.Model = basedOn.Model;
 			this.Messages = basedOn.Messages;
 			this.Temperature = basedOn.Temperature;
@@ -145,5 +170,20 @@ public ChatRequest(ChatRequest basedOn)
 			this.PresencePenalty = basedOn.PresencePenalty;
 			this.LogitBias = basedOn.LogitBias;
 		}
+
+		/// <summary>
+		/// Options for the <see cref="ChatRequest.ResponseFormat"/> property
+		/// </summary>
+		public static class ResponseFormats
+		{
+			/// <summary>
+			/// The default response format, which is may be any type of text
+			/// </summary>
+			public const string Text = "text";
+			/// <summary>
+			/// The response format is guaranteed to be valid JSON, assuming that the <see cref="ChatChoice.FinishReason"/> is not "length"
+			/// </summary>
+			public const string JsonObject = "json_object";
+		}
 	}
 }

OpenAI_Tests/ChatEndpointTests.cs

@@ -1,10 +1,12 @@
-using NUnit.Framework;
+using Newtonsoft.Json;
+using NUnit.Framework;
 using OpenAI_API.Chat;
 using OpenAI_API.Completions;
 using OpenAI_API.Models;
 using OpenAI_API.Moderation;
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
@@ -453,5 +455,46 @@ public async Task StreamingConversation(string model)
 			Assert.AreEqual(result, chat.Messages.Last().Content);
 		}
 
+		[TestCase("gpt-4-1106-preview")]
+		[TestCase("gpt-3.5-turbo-1106")]
+		public void ChatJsonFormat(string model)
+		{
+			var api = new OpenAI_API.OpenAIAPI();
+			ChatRequest chatRequest = new ChatRequest()
+			{
+				Model = model,
+				Temperature = 0.0,
+				MaxTokens = 500,
+				ResponseFormat = ChatRequest.ResponseFormats.JsonObject,
+				Messages = new ChatMessage[] {
+					new ChatMessage(ChatMessageRole.System, "You are a helpful assistant designed to output JSON."),
+					new ChatMessage(ChatMessageRole.User, "Who won the world series in 2020?  Return JSON of a 'wins' dictionary with the year as the numeric key and the winning team as the string value.")
+				}
+			};
+
+			var results = api.Chat.CreateChatCompletionAsync(chatRequest).Result;
+			Assert.IsNotNull(results);
+			
+			Assert.NotNull(results.Object);
+			Assert.NotNull(results.Choices);
+			Assert.NotZero(results.Choices.Count);
+			Assert.AreEqual(ChatMessageRole.Assistant, results.Choices[0].Message.Role);
+			Assert.That(results.Choices.All(c => c.Message.Content.Length > 1));
+			Assert.AreEqual("stop", results.Choices[0].FinishReason);
+
+			using (StringReader stringReader = new StringReader(results.Choices[0].Message.Content))
+			{
+				using (JsonTextReader jsonReader= new JsonTextReader(stringReader))
+				{
+					var serializer = new JsonSerializer();
+					var json = serializer.Deserialize<Dictionary<string, Dictionary<int, string>>>(jsonReader);
+					Assert.NotNull(json);
+					Assert.IsTrue(json.ContainsKey("wins"));
+					Assert.IsTrue(json["wins"].ContainsKey(2020));
+					Assert.AreEqual("Los Angeles Dodgers", json["wins"][2020]);
+				}
+			}
+
+		}
 	}
 }