Automatically clean up multipart temp files

This commit ensures that any resources created for multipart handling,
obtained via ServerWebExchange.getMultipartData(), are automatically
deleted after handling the completing the response.

Resource for parts obtained via BodyExtractors::toMultipartData and
BodyExtractors::toParts are not cleaned automatically, and
should be cleaned via Part::delete.

Closes gh-27633

spring-web/src/main/java/org/springframework/web/server/adapter/HttpWebHandlerAdapter.java

@@ -18,7 +18,9 @@
 
 import java.util.Arrays;
 import java.util.HashSet;
+import java.util.Map;
 import java.util.Set;
+import java.util.function.Function;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -32,6 +34,7 @@
 import org.springframework.http.HttpStatusCode;
 import org.springframework.http.codec.LoggingCodecSupport;
 import org.springframework.http.codec.ServerCodecConfigurer;
+import org.springframework.http.codec.multipart.Part;
 import org.springframework.http.server.reactive.HttpHandler;
 import org.springframework.http.server.reactive.ServerHttpRequest;
 import org.springframework.http.server.reactive.ServerHttpResponse;
@@ -249,6 +252,7 @@ public Mono<Void> handle(ServerHttpRequest request, ServerHttpResponse response)
 		return getDelegate().handle(exchange)
 				.doOnSuccess(aVoid -> logResponse(exchange))
 				.onErrorResume(ex -> handleUnresolvedError(exchange, ex))
+				.then(cleanupMultipart(exchange))
 				.then(Mono.defer(response::setComplete));
 	}
 
@@ -323,4 +327,23 @@ private boolean isDisconnectedClientError(Throwable ex) {
 		return DISCONNECTED_CLIENT_EXCEPTIONS.contains(ex.getClass().getSimpleName());
 	}
 
+	private Mono<Void> cleanupMultipart(ServerWebExchange exchange) {
+		return exchange.getMultipartData()
+				.onErrorResume(t -> Mono.empty()) // ignore errors reading multipart data
+				.flatMapIterable(Map::values)
+				.flatMapIterable(Function.identity())
+				.flatMap(this::deletePart)
+				.then();
+	}
+
+	private Mono<Void> deletePart(Part part) {
+		return part.delete().onErrorResume(ex -> {
+					if (logger.isWarnEnabled()) {
+						logger.warn("Failed to perform cleanup of multipart items", ex);
+					}
+					return Mono.empty();
+				});
+	}
+
+
 }

spring-webflux/src/main/java/org/springframework/web/reactive/function/BodyExtractors.java

@@ -137,6 +137,9 @@ public static BodyExtractor<Mono<MultiValueMap<String, String>>, ReactiveHttpInp
 
 	/**
 	 * Extractor to read multipart data into a {@code MultiValueMap<String, Part>}.
+	 * <p><strong>Note:</strong> that resources used for part handling,
+	 * like storage for the uploaded files, is not deleted automatically, but
+	 * should be done via {@link Part#delete()}.
 	 * @return {@code BodyExtractor} for multipart data
 	 */
 	// Parameterized for server-side use
@@ -151,6 +154,9 @@ public static BodyExtractor<Mono<MultiValueMap<String, Part>>, ServerHttpRequest
 
 	/**
 	 * Extractor to read multipart data into {@code Flux<Part>}.
+	 * <p><strong>Note:</strong> that resources used for part handling,
+	 * like storage for the uploaded files, is not deleted automatically, but
+	 * should be done via {@link Part#delete()}.
 	 * @return {@code BodyExtractor} for multipart request parts
 	 */
 	// Parameterized for server-side use

spring-webflux/src/test/java/org/springframework/web/reactive/function/MultipartIntegrationTests.java

@@ -25,6 +25,7 @@
 
 import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
+import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.core.scheduler.Schedulers;
 import reactor.test.StepVerifier;
@@ -168,7 +169,9 @@ public Mono<ServerResponse> multipartData(ServerRequest request) {
 							assertThat(parts.size()).isEqualTo(2);
 							assertThat(((FilePart) parts.get("fooPart")).filename()).isEqualTo("foo.txt");
 							assertThat(((FormFieldPart) parts.get("barPart")).value()).isEqualTo("bar");
-							return ServerResponse.ok().build();
+							return Flux.fromIterable(parts.values())
+									.concatMap(Part::delete)
+									.then(ServerResponse.ok().build());
 						}
 						catch(Exception e) {
 							return Mono.error(e);
@@ -183,7 +186,9 @@ public Mono<ServerResponse> parts(ServerRequest request) {
 							assertThat(parts.size()).isEqualTo(2);
 							assertThat(((FilePart) parts.get(0)).filename()).isEqualTo("foo.txt");
 							assertThat(((FormFieldPart) parts.get(1)).value()).isEqualTo("bar");
-							return ServerResponse.ok().build();
+							return Flux.fromIterable(parts)
+									.concatMap(Part::delete)
+									.then(ServerResponse.ok().build());
 						}
 						catch(Exception e) {
 							return Mono.error(e);