Reapply "WebClientStreamableHttpTransport: use Spring-5 compatible methods (#649)" (#696)

This reverts commit 06fdc71.

Author: He-Pin

mcp-spring/mcp-spring-webflux/src/main/java/io/modelcontextprotocol/client/transport/WebClientStreamableHttpTransport.java

@@ -313,7 +313,7 @@ public Mono<Void> sendMessage(McpSchema.JSONRPCMessage message) {
 
 					// The spec mentions only ACCEPTED, but the existing SDKs can return
 					// 200 OK for notifications
-					if (response.statusCode().is2xxSuccessful()) {
+					if (is2xx(response)) {
 						Optional<MediaType> contentType = response.headers().contentType();
 						long contentLength = response.headers().contentLength().orElse(-1);
 						// Existing SDKs consume notifications with no response body nor
@@ -397,14 +397,14 @@ private Flux<McpSchema.JSONRPCMessage> extractError(ClientResponse response, Str
 			}
 			catch (IOException ex) {
 				toPropagate = new McpTransportException("Sending request failed, " + e.getMessage(), e);
-				logger.debug("Received content together with {} HTTP code response: {}", response.statusCode(), body);
+				logger.debug("Received content together with {} HTTP code response: {}", getStatusCode(response), body);
 			}
 
 			// Some implementations can return 400 when presented with a
 			// session id that it doesn't know about, so we will
 			// invalidate the session
 			// https://github.com/modelcontextprotocol/typescript-sdk/issues/389
-			if (responseException.getStatusCode().isSameCodeAs(HttpStatus.BAD_REQUEST)) {
+			if (isBadRequest(responseException)) {
 				if (!sessionRepresentation.equals(MISSING_SESSION_ID)) {
 					return Mono.error(new McpTransportSessionNotFoundException(sessionRepresentation, toPropagate));
 				}
@@ -424,16 +424,8 @@ private Flux<McpSchema.JSONRPCMessage> eventStream(McpTransportStream<Disposable
 		return Flux.from(sessionStream.consumeSseStream(idWithMessages));
 	}
 
-	private static boolean isNotFound(ClientResponse response) {
-		return response.statusCode().isSameCodeAs(HttpStatus.NOT_FOUND);
-	}
-
-	private static boolean isNotAllowed(ClientResponse response) {
-		return response.statusCode().isSameCodeAs(HttpStatus.METHOD_NOT_ALLOWED);
-	}
-
 	private static boolean isEventStream(ClientResponse response) {
-		return response.statusCode().is2xxSuccessful() && response.headers().contentType().isPresent()
+		return is2xx(response) && response.headers().contentType().isPresent()
 				&& response.headers().contentType().get().isCompatibleWith(MediaType.TEXT_EVENT_STREAM);
 	}
 
@@ -612,4 +604,39 @@ public WebClientStreamableHttpTransport build() {
 
 	}
 
+	/**
+	 * Needed for Spring 5 compatibility, user can extend and override this method
+	 */
+	protected int getStatusCode(final ClientResponse response) {
+		return response.statusCode().value();
+	}
+
+	/**
+	 * Needed for Spring 5 compatibility, user can extend and override this method
+	 */
+	protected boolean isBadRequest(final WebClientResponseException responseException) {
+		return responseException.getStatusCode().isSameCodeAs(HttpStatus.BAD_REQUEST);
+	}
+
+	/**
+	 * Needed for Spring 5 compatibility, user can extend and override this method
+	 */
+	protected boolean isNotFound(ClientResponse response) {
+		return response.statusCode().isSameCodeAs(HttpStatus.NOT_FOUND);
+	}
+
+	/**
+	 * Needed for Spring 5 compatibility, user can extend and override this method
+	 */
+	protected boolean isNotAllowed(ClientResponse response) {
+		return response.statusCode().isSameCodeAs(HttpStatus.NOT_FOUND);
+	}
+
+	/**
+	 * Needed for Spring 5 compatibility, user can extend and override this method
+	 */
+	private static boolean is2xx(final ClientResponse response) {
+		return response.statusCode().is2xxSuccessful();
+	}
+
 }