Synchronoss should create temp directory lazily

The SynchronossPartHttpMessageReader should only create temp directory
when needed, not at startup.

Closes gh-27092

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

@@ -17,7 +17,6 @@
 package org.springframework.http.codec.multipart;
 
 import java.io.IOException;
-import java.io.UncheckedIOException;
 import java.nio.channels.Channels;
 import java.nio.channels.FileChannel;
 import java.nio.channels.ReadableByteChannel;
@@ -31,6 +30,7 @@
 import java.util.Map;
 import java.util.Optional;
 import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 
 import org.synchronoss.cloud.nio.multipart.DefaultPartBodyStreamStorageFactory;
@@ -46,6 +46,7 @@
 import reactor.core.publisher.FluxSink;
 import reactor.core.publisher.Mono;
 import reactor.core.publisher.SignalType;
+import reactor.core.scheduler.Schedulers;
 
 import org.springframework.core.ResolvableType;
 import org.springframework.core.codec.DecodingException;
@@ -93,7 +94,7 @@ public class SynchronossPartHttpMessageReader extends LoggingCodecSupport implem
 
 	private int maxParts = -1;
 
-	private Path fileStorageDirectory = createTempDirectory();
+	private final AtomicReference<Path> fileStorageDirectory = new AtomicReference<>();
 
 
 	/**
@@ -178,29 +179,46 @@ public boolean canRead(ResolvableType elementType, @Nullable MediaType mediaType
 
 	@Override
 	public Flux<Part> read(ResolvableType elementType, ReactiveHttpInputMessage message, Map<String, Object> hints) {
-		return Flux.create(new SynchronossPartGenerator(message, this.fileStorageDirectory))
-				.doOnNext(part -> {
-					if (!Hints.isLoggingSuppressed(hints)) {
-						LogFormatUtils.traceDebug(logger, traceOn -> Hints.getLogPrefix(hints) + "Parsed " +
-								(isEnableLoggingRequestDetails() ?
-										LogFormatUtils.formatValue(part, !traceOn) :
-										"parts '" + part.name() + "' (content masked)"));
-					}
-				});
+		return getFileStorageDirectory().flatMapMany(directory ->
+				Flux.create(new SynchronossPartGenerator(message, directory))
+						.doOnNext(part -> {
+							if (!Hints.isLoggingSuppressed(hints)) {
+								LogFormatUtils.traceDebug(logger, traceOn -> Hints.getLogPrefix(hints) + "Parsed " +
+										(isEnableLoggingRequestDetails() ?
+												LogFormatUtils.formatValue(part, !traceOn) :
+												"parts '" + part.name() + "' (content masked)"));
+							}
+						}));
 	}
 
 	@Override
 	public Mono<Part> readMono(ResolvableType elementType, ReactiveHttpInputMessage message, Map<String, Object> hints) {
 		return Mono.error(new UnsupportedOperationException("Cannot read multipart request body into single Part"));
 	}
 
-	private static Path createTempDirectory() {
-		try {
-			return Files.createTempDirectory(FILE_STORAGE_DIRECTORY_PREFIX);
-		}
-		catch (IOException ex) {
-			throw new UncheckedIOException(ex);
-		}
+	private Mono<Path> getFileStorageDirectory() {
+		return Mono.defer(() -> {
+			Path directory = this.fileStorageDirectory.get();
+			if (directory != null) {
+				return Mono.just(directory);
+			}
+			else {
+				return Mono.fromCallable(() -> {
+					Path tempDirectory = Files.createTempDirectory(FILE_STORAGE_DIRECTORY_PREFIX);
+					if (this.fileStorageDirectory.compareAndSet(null, tempDirectory)) {
+						return tempDirectory;
+					}
+					else {
+						try {
+							Files.delete(tempDirectory);
+						}
+						catch (IOException ignored) {
+						}
+						return this.fileStorageDirectory.get();
+					}
+				}).subscribeOn(Schedulers.boundedElastic());
+			}
+		});
 	}