Refine User-Agent header implementation in OpenAiApi with constants and tests

  - Extract hardcoded User-Agent string to HTTP_USER_AGENT_HEADER constant
  - Extract hardcoded spring-ai value to SPRING_AI_USER_AGENT constant
  - Add integration test to verify User-Agent header is sent in requests
  - Add documentation explaining User-Agent header purpose and usage for API providers

  This refines the User-Agent header feature introduced in commit e3aaf32
  by replacing magic strings with public constants, test coverage for the feature
  and reference docs in openai-chat.adoc.

Signed-off-by: Soby Chacko <soby.chacko@broadcom.com>

Author: sobychacko

models/spring-ai-openai/src/main/java/org/springframework/ai/openai/api/OpenAiApi.java

@@ -70,6 +70,10 @@
  */
 public class OpenAiApi {
 
+	public static final String HTTP_USER_AGENT_HEADER = "User-Agent";
+
+	public static final String SPRING_AI_USER_AGENT = "spring-ai";
+
 	/**
 	 * Returns a builder pre-populated with the current configuration for mutation.
 	 */
@@ -140,7 +144,7 @@ public OpenAiApi(String baseUrl, ApiKey apiKey, MultiValueMap<String, String> he
 		// @formatter:off
 		Consumer<HttpHeaders> finalHeaders = h -> {
 			h.setContentType(MediaType.APPLICATION_JSON);
-			h.set("User-Agent", "spring-ai");
+			h.set(HTTP_USER_AGENT_HEADER, SPRING_AI_USER_AGENT);
 			h.addAll(headers);
 		};
 		this.restClient = restClientBuilder.clone()

models/spring-ai-openai/src/test/java/org/springframework/ai/openai/api/OpenAiApiIT.java

@@ -20,6 +20,9 @@
 import java.util.Base64;
 import java.util.List;
 
+import okhttp3.mockwebserver.MockResponse;
+import okhttp3.mockwebserver.MockWebServer;
+import okhttp3.mockwebserver.RecordedRequest;
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.condition.EnabledIfEnvironmentVariable;
@@ -35,6 +38,8 @@
 import org.springframework.ai.openai.api.OpenAiApi.Embedding;
 import org.springframework.ai.openai.api.OpenAiApi.EmbeddingList;
 import org.springframework.core.io.ClassPathResource;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.MediaType;
 import org.springframework.http.ResponseEntity;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -237,4 +242,58 @@ void chatCompletionEntityWithServiceTier(OpenAiApi.ServiceTier serviceTier) {
 		assertThat(response.getBody().serviceTier()).containsIgnoringCase(serviceTier.getValue());
 	}
 
+	@Test
+	void userAgentHeaderIsSentInChatCompletionRequests() throws Exception {
+		try (MockWebServer mockWebServer = new MockWebServer()) {
+			mockWebServer.start();
+
+			// Mock response from OpenAI
+			mockWebServer.enqueue(new MockResponse().setResponseCode(200)
+				.addHeader(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
+				.setBody("""
+						{
+							"id": "chatcmpl-123",
+							"object": "chat.completion",
+							"created": 1677652288,
+							"model": "gpt-3.5-turbo",
+							"choices": [{
+								"index": 0,
+								"message": {
+									"role": "assistant",
+									"content": "Hello there!"
+								},
+								"finish_reason": "stop"
+							}],
+							"usage": {
+								"prompt_tokens": 9,
+								"completion_tokens": 2,
+								"total_tokens": 11
+							}
+						}
+						"""));
+
+			// Create OpenAiApi instance pointing to mock server
+			OpenAiApi testApi = OpenAiApi.builder()
+				.apiKey(System.getenv("OPENAI_API_KEY"))
+				.baseUrl(mockWebServer.url("/").toString())
+				.build();
+
+			// Make a request
+			ChatCompletionMessage message = new ChatCompletionMessage("Hello world", Role.USER);
+			ResponseEntity<ChatCompletion> response = testApi
+				.chatCompletionEntity(new ChatCompletionRequest(List.of(message), "gpt-3.5-turbo", 0.8, false));
+
+			// Verify the response succeeded
+			assertThat(response).isNotNull();
+			assertThat(response.getBody()).isNotNull();
+
+			// Verify the User-Agent header was sent in the request
+			RecordedRequest recordedRequest = mockWebServer.takeRequest();
+			assertThat(recordedRequest.getHeader(OpenAiApi.HTTP_USER_AGENT_HEADER))
+				.isEqualTo(OpenAiApi.SPRING_AI_USER_AGENT);
+
+			mockWebServer.shutdown();
+		}
+	}
+
 }

spring-ai-docs/src/main/antora/modules/ROOT/pages/api/chat/openai-chat.adoc

@@ -120,6 +120,14 @@ The prefix `spring.ai.openai` is used as the property prefix that lets you conne
 TIP: For users that belong to multiple organizations (or are accessing their projects through their legacy user API key), you can optionally specify which organization and project is used for an API request.
 Usage from these API requests will count as usage for the specified organization and project.
 
+==== User-Agent Header
+
+Spring AI automatically sends a `User-Agent: spring-ai` header with all requests to OpenAI.
+This helps OpenAI identify requests originating from Spring AI for analytics and support purposes.
+This header is sent automatically and requires no configuration from Spring AI users.
+
+If you are an API provider building an OpenAI-compatible service, you can track Spring AI usage by reading the `User-Agent` HTTP header from incoming requests on your server.
+
 ==== Configuration Properties
 
 [NOTE]