Merge branch '5.3.x'

Author: poutsma

spring-web/src/main/java/org/springframework/http/codec/multipart/PartGenerator.java

@@ -209,6 +209,7 @@ void emitError(Throwable t) {
 
 	void requestToken() {
 		if (upstream() != null &&
+				this.state.get().canRequest() &&
 				this.requestOutstanding.compareAndSet(false, true)) {
 			request(1);
 		}
@@ -252,6 +253,13 @@ private interface State {
 		default void error(Throwable throwable) {
 		}
 
+		/**
+		 * Indicates whether the current state is ready to accept a new token.
+		 */
+		default boolean canRequest() {
+			return true;
+		}
+
 		/**
 		 * Cleans up any state.
 		 */
@@ -755,6 +763,11 @@ private Mono<Void> writeInternal(DataBuffer dataBuffer) {
 			}
 		}
 
+		@Override
+		public boolean canRequest() {
+			return false;
+		}
+
 		@Override
 		public void dispose() {
 			this.disposed = true;