Improve RequestAttributesThreadLocalAccessor

Ensure access to request attributes after initial REQUEST dispatch
is done, and the RequestAttributes markedCompleted.

Closes gh-32296

spring-web/src/main/java/org/springframework/web/context/request/RequestAttributesThreadLocalAccessor.java

@@ -16,7 +16,12 @@
 
 package org.springframework.web.context.request;
 
+import java.util.Enumeration;
+import java.util.HashMap;
+import java.util.Map;
+
 import io.micrometer.context.ThreadLocalAccessor;
+import jakarta.servlet.http.HttpServletRequest;
 
 import org.springframework.lang.Nullable;
 
@@ -26,6 +31,7 @@ import org.springframework.lang.Nullable;
  * {@link RequestAttributes} propagation.
  *
  * @author Tadaya Tsuyukubo
+ * @author Rossen Stoyanchev
  * @since 6.2
  */
 public class RequestAttributesThreadLocalAccessor implements ThreadLocalAccessor<RequestAttributes> {
@@ -44,7 +50,11 @@ public class RequestAttributesThreadLocalAccessor implements ThreadLocalAccessor
 	@Override
 	@Nullable
 	public RequestAttributes getValue() {
-		return RequestContextHolder.getRequestAttributes();
+		RequestAttributes request = RequestContextHolder.getRequestAttributes();
+		if (request instanceof ServletRequestAttributes sra && !(sra instanceof SnapshotServletRequestAttributes)) {
+			request = new SnapshotServletRequestAttributes(sra);
+		}
+		return request;
 	}
 
 	@Override
@@ -57,4 +67,82 @@ public class RequestAttributesThreadLocalAccessor implements ThreadLocalAccessor
 		RequestContextHolder.resetRequestAttributes();
 	}
 
+
+	/**
+	 * ServletRequestAttributes that takes another instance, and makes a copy of the
+	 * request attributes at present to provides extended read access during async
+	 * handling when the DispatcherServlet has exited from the initial REQUEST dispatch
+	 * and marked the request {@link ServletRequestAttributes#requestCompleted()}.
+	 * <p>Note that beyond access to request attributes, here is no attempt to support
+	 * setting or removing request attributes, nor to access session attributes after
+	 * the initial REQUEST dispatch has exited.
+	 */
+	private static final class SnapshotServletRequestAttributes extends ServletRequestAttributes {
+
+		private final ServletRequestAttributes delegate;
+
+		private final Map<String, Object> attributeMap;
+
+		public SnapshotServletRequestAttributes(ServletRequestAttributes requestAttributes) {
+			super(requestAttributes.getRequest(), requestAttributes.getResponse());
+			this.delegate = requestAttributes;
+			this.attributeMap = getAttributes(requestAttributes.getRequest());
+		}
+
+		private static Map<String, Object> getAttributes(HttpServletRequest request) {
+			Map<String, Object> map = new HashMap<>();
+			Enumeration<String> names = request.getAttributeNames();
+			while (names.hasMoreElements()) {
+				String name = names.nextElement();
+				map.put(name, request.getAttribute(name));
+			}
+			return map;
+		}
+
+		// Delegate methods that check isRequestActive()
+
+		@Nullable
+		@Override
+		public Object getAttribute(String name, int scope) {
+			if (scope == RequestAttributes.SCOPE_REQUEST && !this.delegate.isRequestActive()) {
+				return this.attributeMap.get(name);
+			}
+			try {
+				return this.delegate.getAttribute(name, scope);
+			}
+			catch (IllegalStateException ex) {
+				if (scope == RequestAttributes.SCOPE_REQUEST) {
+					return this.attributeMap.get(name);
+				}
+				throw ex;
+			}
+		}
+
+		@Override
+		public String[] getAttributeNames(int scope) {
+			if (scope == RequestAttributes.SCOPE_REQUEST && !this.delegate.isRequestActive()) {
+				return this.attributeMap.keySet().toArray(new String[0]);
+			}
+			try {
+				return this.delegate.getAttributeNames(scope);
+			}
+			catch (IllegalStateException ex) {
+				if (scope == RequestAttributes.SCOPE_REQUEST) {
+					return this.attributeMap.keySet().toArray(new String[0]);
+				}
+				throw ex;
+			}
+		}
+
+		@Override
+		public void setAttribute(String name, Object value, int scope) {
+			this.delegate.setAttribute(name, value, scope);
+		}
+
+		@Override
+		public void removeAttribute(String name, int scope) {
+			this.delegate.removeAttribute(name, scope);
+		}
+	}
+
 }