Automatically remove multipart temporary files

[ikhoon]

When files are uploaded to an Armeria server with multipart/form, it is stored to multipartUploadsLocation() when @Param of annotated services or GraphQL multipart request is used.
https://armeria.dev/docs/server-multipart#using-typeparam-annotation

armeria/graphql-protocol/src/main/java/com/linecorp/armeria/server/graphql/protocol/AbstractGraphqlService.java

Lines 101 to 103 in 0a5a3d7

	// See https://github.com/jaydenseric/graphql-multipart-request-spec/blob/master/readme.md
	if (contentType.is(MediaType.MULTIPART_FORM_DATA)) {
	return HttpResponse.of(FileAggregatedMultipart.aggregateMultipart(ctx, request)

As Armeria does not automatically delete the uploaded files, users should manually remove the temporary files themselves.

armeria/graphql-protocol/src/main/java/com/linecorp/armeria/server/graphql/protocol/AbstractGraphqlService.java

Lines 101 to 103 in 0a5a3d7

	// See https://github.com/jaydenseric/graphql-multipart-request-spec/blob/master/readme.md
	if (contentType.is(MediaType.MULTIPART_FORM_DATA)) {
	return HttpResponse.of(FileAggregatedMultipart.aggregateMultipart(ctx, request)

It would be useful if we provided some options for how to handle multipart files.

enum MultipartRemovalStrategy {
    /**
     * This option would be preferred if a file is transferred using an asynchronous job.
     * Users may want to delete the file when the job is done.
     */
    NEVER,
    /**
     * Remove after a response for the multipart request is fully sent.
     */
    ON_RESPONSE_COMPLETE,
    /**
     * Clean up all temporary files when JVM shuts down.
     * File.deleteOnExit() could be used for this option
     */
    ON_JVM_SHUTDOWN
}

The option can be set via ServerBuilder, VirtualHostBuilder, or ServiceBindingBuilder.

Server
  .builder()
  .multipartRemovalStrategy(MultipartRemovalStrategy.ON_RESPONSE_COMPLETE)
  ...