Added response_format capabilities and integration test covering it (TheoKanning#388)

Author: PrimosK

api/src/main/java/com/theokanning/openai/completion/chat/ChatCompletionRequest.java

@@ -34,6 +34,19 @@ public class ChatCompletionRequest {
     @JsonProperty("frequency_penalty")
     Double frequencyPenalty;
 
+    /**
+     * <p>An object specifying the format that the model must output.</p>
+     *
+     * <p>Setting to { "type": "json_object" } enables JSON mode, which guarantees the message the model generates is valid JSON.</p>
+     *
+     * <p><b>Important:</b> 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.</p>
+     */
+    @JsonProperty("response_format")
+    ResponseFormat responseFormat;
+
     /**
      * Accepts a json object that maps tokens (specified by their token ID in the tokenizer) to an associated bias value from -100
      * to 100. Mathematically, the bias is added to the logits generated by the model prior to sampling. The exact effect will
@@ -117,4 +130,18 @@ public static ChatCompletionRequestFunctionCall of(String name) {
         }
 
     }
+
+    @Data
+    @Builder
+    @AllArgsConstructor
+    @NoArgsConstructor
+    public static class ResponseFormat {
+        String type;
+
+        public static ResponseFormat of(String type) {
+            return new ResponseFormat(type);
+        }
+
+    }
+
 }

service/src/test/java/com/theokanning/openai/service/ChatCompletionTest.java

@@ -2,11 +2,14 @@
 
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.annotation.JsonPropertyDescription;
+import com.fasterxml.jackson.core.JsonParser;
 import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.node.ObjectNode;
 import com.theokanning.openai.completion.chat.*;
 import org.junit.jupiter.api.Test;
 
+import java.io.IOException;
 import java.util.*;
 
 import static org.junit.jupiter.api.Assertions.*;
@@ -23,7 +26,7 @@ static class Weather {
     }
 
     enum WeatherUnit {
-        CELSIUS, FAHRENHEIT;
+        CELSIUS, FAHRENHEIT
     }
 
     static class WeatherResponse {
@@ -300,4 +303,46 @@ void streamChatCompletionWithDynamicFunctions() {
         assertNotNull(accumulatedMessage.getFunctionCall().getArguments().get("unit"));
     }
 
+    @Test
+    void streamChatCompletionWithJsonResponseFormat() {
+        final List<ChatMessage> messages = new ArrayList<>();
+
+        // The system message is deliberately vague in order to not give too much of a direction of how response should look like.
+        // The main gist there is that chat competition should always contain JSON content.
+        final ChatMessage systemMessage = new ChatMessage(
+                ChatMessageRole.SYSTEM.value(),
+                "You are a dog and will speak as such - but please do it in JSON."
+        );
+
+        messages.add(systemMessage);
+
+        ChatCompletionRequest chatCompletionRequest = ChatCompletionRequest
+                .builder()
+                .model("gpt-4-1106-preview")
+                .messages(messages)
+                .n(1)
+                .maxTokens(256)
+                .responseFormat(ChatCompletionRequest.ResponseFormat.of("json_object"))
+                .build();
+
+        ChatCompletionResult chatCompletion = service.createChatCompletion(chatCompletionRequest);
+
+        ChatCompletionChoice chatCompletionChoice = chatCompletion.getChoices().get(0);
+        String expectedJsonContent = chatCompletionChoice.getMessage().getContent();
+
+        assertTrue(isValidJSON(expectedJsonContent), "Invalid JSON response:\n\n" + expectedJsonContent);
+    }
+
+    private boolean isValidJSON(String json) {
+        try (final JsonParser parser = new ObjectMapper().createParser(json)) {
+            while (parser.nextToken() != null) {
+                // Just try to read all tokens in order to verify whether this is valid json.
+            }
+            return true;
+        } catch (IOException ioe) {
+            ioe.printStackTrace();
+            return false;
+        }
+    }
+
 }