axum::extract::multipart::Field should implement Clone

[haiderlikesrust]

Bug Report

Version

0.5.5

├── axum v0.5.5
│ ├── axum-core v0.2.4
│ ├── axum-core v0.2.4 (*)

Platform

Linux asus 5.18.12-arch1-1 #1 SMP PREEMPT_DYNAMIC Fri, 15 Jul 2022 15:33:02 +0000 x86_64 GNU/Linux

Description

axum::extract::multipart::Field should implement Clone its really hard to if a field.name() equals to what we are looking for because it can't be cloned, all getter methods are self not &self. Implementing Clone will make it easy or else its really hard.

fn create_post(mut form: Multipart) -> Result<Json<String>, ApiError> {
  while let Some(field) = form.next_field().await.unwrap() {
      // &self - no problem
      match field.name() {
         // Did call field.text() which is &self
         "foo" => {..}
         ...
         _ => ()
      }
      // Checking if the content_type is image or video and then processes it.
      // Error here because field was deleted by text() method
      match field.content_type() { ... }
   }
}

[haiderlikesrust]

Just made a pull request to fix it

[davidpdrsn]

Field cannot be Clone because it contains a &mut Multipart. That is required to uphold an invariant.

Think of Field as a "pointer into a the request body stream" meaning it doesn't make sense to clone since you cannot consume a stream twice. That is why the Field::text takes self and is async.

Seems to me that putting a continue in your loop should fix your problem.