Spring Slow webflux multipart upload

Hello,

We are developing a document submission application using WebFlux. However, we have noticed that handling multipart requests is slower with WebFlux compared to MVC. For example, when using MultipartFile in MVC, sending a 200MB file takes about 700ms, whereas it takes 4.2s with WebFlux (FilePart) and 4.5s with PartEvent.

Did we miss something?

Here is a repository reproducing the issue: Repo

Spring boot version : 3.4.4 Java 21

Comment From: sdeleuze

I suspected that when working in this area recently in #34178 and #34388 but was not 100% sure, but your report seems to confirm there is something to improve there, so I will try to have a deeper look.

What I saw was slow upload locally with big files, so I know how to reproduce even if for now, I am not sure about the reason.

Comment From: xyraclius

Hello @sdeleuze

I’d like to contribute to this, may I ?

I've reduced the elapsed time from 4.2s to 700ms locally

Before:

~/IdeaProjects/WebfluxSlowMultipart git:[main]
curl -w "\nElapsed: %{time_total}s\n" \
     -F file="@200mb.pdf" \
     http://localhost:8080/part-event \
     -o /dev/null -s
Elapsed: 4.260208s


~/IdeaProjects/WebfluxSlowMultipart git:[main]
curl -w "\nElapsed: %{time_total}s\n" \
  -F file="@200mb.pdf" \
  http://localhost:8080/file-part \
  -o /dev/null -s
  Elapsed: 4.346252s

After:

~/IdeaProjects/WebfluxSlowMultipart git:[main]
curl -w "\nElapsed: %{time_total}s\n" \
     -F file="@200mb.pdf" \
     http://localhost:8080/part-event \
     -o /dev/null -s
Elapsed: 0.391556s


~/IdeaProjects/WebfluxSlowMultipart git:[main]
curl -w "\nElapsed: %{time_total}s\n" \
  -F file="@200mb.pdf" \
  http://localhost:8080/file-part \
  -o /dev/null -s
Elapsed: 0.407896s