Public constant for webtestclient-request-id header

Issue: SPR-15575

spring-test/src/main/java/org/springframework/test/web/reactive/server/DefaultWebTestClient.java

@@ -180,7 +180,7 @@ class DefaultWebTestClient implements WebTestClient {
 		DefaultRequestBodySpec(WebClient.RequestBodySpec spec) {
 			this.bodySpec = spec;
 			this.requestId = String.valueOf(requestIndex.incrementAndGet());
-			this.bodySpec.header(WiretapConnector.REQUEST_ID_HEADER_NAME, this.requestId);
+			this.bodySpec.header(WebTestClient.WEBTESTCLIENT_REQUEST_ID, this.requestId);
 		}
 
 

spring-test/src/main/java/org/springframework/test/web/reactive/server/MockServerExchangeMutator.java

@@ -23,6 +23,7 @@ import java.util.function.UnaryOperator;
 
 import reactor.core.publisher.Mono;
 
+import org.springframework.http.HttpHeaders;
 import org.springframework.util.Assert;
 import org.springframework.web.server.ServerWebExchange;
 import org.springframework.web.server.WebFilter;
@@ -82,9 +83,15 @@ public class MockServerExchangeMutator implements WebFilter {
 	}
 
 	private Function<ServerWebExchange, ServerWebExchange> getMutatorsFor(ServerWebExchange exchange) {
-		String id = WiretapConnector.getRequestIdHeader(exchange.getRequest().getHeaders());
-		Function<ServerWebExchange, ServerWebExchange> m = this.perRequestMutators.remove(id);
-		return (m != null ? this.mutator.andThen(m) : this.mutator);
+		String id = getRequestId(exchange.getRequest().getHeaders());
+		Function<ServerWebExchange, ServerWebExchange> clientMutator = this.perRequestMutators.remove(id);
+		return (clientMutator != null ? this.mutator.andThen(clientMutator) : this.mutator);
+	}
+
+	private String getRequestId(HttpHeaders headers) {
+		String id = headers.getFirst(WebTestClient.WEBTESTCLIENT_REQUEST_ID);
+		Assert.notNull(id, "No \"" + WebTestClient.WEBTESTCLIENT_REQUEST_ID + "\" header");
+		return id;
 	}
 
 
@@ -103,8 +110,7 @@ public class MockServerExchangeMutator implements WebFilter {
 			UnaryOperator<ServerWebExchange> mutator, UnaryOperator<ServerWebExchange>... mutators) {
 
 		return client.filter((request, next) -> {
-			String id = request.headers().getFirst(WiretapConnector.REQUEST_ID_HEADER_NAME);
-			Assert.notNull(id, "No request-id header");
+			String id = getRequestId(request.headers());
 			registerPerRequestMutator(id, mutator);
 			for (UnaryOperator<ServerWebExchange> current : mutators) {
 				registerPerRequestMutator(id, current);

spring-test/src/main/java/org/springframework/test/web/reactive/server/WebTestClient.java

@@ -75,6 +75,16 @@ import org.springframework.web.util.UriBuilderFactory;
  */
 public interface WebTestClient {
 
+	/**
+	 * The name of a request header used to assign a unique id to every request
+	 * performed through the {@code WebTestClient}. This can be useful for
+	 * storing contextual information at all phases of request processing (e.g.
+	 * from a server-side component) under that id and later to look up
+	 * that information once an {@link ExchangeResult} is available.
+	 */
+	String WEBTESTCLIENT_REQUEST_ID = "WebTestClient-Request-Id";
+
+
 	/**
 	 * Prepare an HTTP GET request.
 	 * @return a spec for specifying the target URL

spring-test/src/main/java/org/springframework/test/web/reactive/server/WiretapConnector.java

@@ -24,7 +24,6 @@ import java.util.function.Function;
 
 import reactor.core.publisher.Mono;
 
-import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.client.reactive.ClientHttpConnector;
 import org.springframework.http.client.reactive.ClientHttpRequest;
@@ -42,15 +41,12 @@ import org.springframework.util.Assert;
  */
 class WiretapConnector implements ClientHttpConnector {
 
-	public static final String REQUEST_ID_HEADER_NAME = "webtestclient-request-id";
-
-
 	private final ClientHttpConnector delegate;
 
 	private final Map<String, ExchangeResult> exchanges = new ConcurrentHashMap<>();
 
 
-	public WiretapConnector(ClientHttpConnector delegate) {
+	WiretapConnector(ClientHttpConnector delegate) {
 		this.delegate = delegate;
 	}
 
@@ -69,7 +65,8 @@ class WiretapConnector implements ClientHttpConnector {
 				})
 				.map(response ->  {
 					WiretapClientHttpRequest wrappedRequest = requestRef.get();
-					String requestId = getRequestIdHeader(wrappedRequest.getHeaders());
+					String requestId = wrappedRequest.getHeaders().getFirst(WebTestClient.WEBTESTCLIENT_REQUEST_ID);
+					Assert.notNull(requestId, "No \"" + WebTestClient.WEBTESTCLIENT_REQUEST_ID + "\" header");
 					WiretapClientHttpResponse wrappedResponse = new WiretapClientHttpResponse(response);
 					ExchangeResult result = new ExchangeResult(wrappedRequest, wrappedResponse);
 					this.exchanges.put(requestId, result);
@@ -77,18 +74,12 @@ class WiretapConnector implements ClientHttpConnector {
 				});
 	}
 
-	public static String getRequestIdHeader(HttpHeaders headers) {
-		String requestId = headers.getFirst(REQUEST_ID_HEADER_NAME);
-		Assert.notNull(requestId, "No \"" + REQUEST_ID_HEADER_NAME + "\" header");
-		return requestId;
-	}
-
 	/**
 	 * Retrieve the {@code ExchangeResult} for the given "request-id" header value.
 	 */
 	public ExchangeResult claimRequest(String requestId) {
 		ExchangeResult result = this.exchanges.get(requestId);
-		Assert.notNull(result, "No match for request with header " + REQUEST_ID_HEADER_NAME + "=" + requestId);
+		Assert.notNull(result, "No match for " + WebTestClient.WEBTESTCLIENT_REQUEST_ID + "=" + requestId);
 		return result;
 	}
 

spring-test/src/test/java/org/springframework/test/web/reactive/server/WebTestClientConnectorTests.java

@@ -50,7 +50,7 @@ public class WebTestClientConnectorTests {
 		ClientHttpConnector connector = (method, uri, fn) -> fn.apply(request).then(Mono.just(response));
 
 		ClientRequest clientRequest = ClientRequest.method(HttpMethod.GET, URI.create("/test"))
-				.header(WiretapConnector.REQUEST_ID_HEADER_NAME, "1").build();
+				.header(WebTestClient.WEBTESTCLIENT_REQUEST_ID, "1").build();
 
 		WiretapConnector wiretapConnector = new WiretapConnector(connector);
 		ExchangeFunction function = ExchangeFunctions.create(wiretapConnector);