bugfix/dart-dio/multipart-file-handling

[vasilich6107]

in case if we have

      responses:
        '200':
          description: File downloaded successfully
          content:
            application/octet-stream:
              schema:
                type: string
                format: binary

The code fails with Exception

 final rawData = _response.data;
      _responseData = rawData == null
          ? null
          : deserialize<MultipartFile, MultipartFile>(rawData, 'MultipartFile',
              growable: true);

cause deserialize does not have a case for MultipartFile

This PR added handling the case 'MultipartFile':

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[vasilich6107]

@jaumard (2018/09) @josh-burton (2019/12) @amondnet (2019/12) @sbu-WBT (2020/12) @kuhnroyal (2020/12) @agilob (2020/12) @ahmednfwela (2021/08)

[ahmednfwela]

Question is, should a MultipartFile be returned when response type is application/octet-stream ?
I think it's better to change the return type entirely to Uint8List but I am not sure how

[vasilich6107]

Hey @ahmednfwela
For now it is just a bugfix with deserializtion

[ahmednfwela]

well, this fix will still not fix the bug, since rawData will never be a MultipartFile

[kaal-dam]

Hello, I stumbled upon this pull request while encountering this issue.

In my case it was with application/pdf not application/octet-stream.

From all my test before coming here looking it seems that the following schema :

schema:
                type: string
                format: binary

always result in a Uint8List being returned as rawData

In addition MultipartFile in itself isn't really a usefull object when trying to download file as most of the time you will need to finalize it before exploiting it which result in a Stream<Uint8List> so we go back to Uint8List

[vasilich6107]

Hey @kaal-dam probably we have to eliminate multiplart file from type mapping

[kaal-dam]

@vasilich6107 file download should most likely be handled as Uint8List but upload via multipart request should still be handled by MultipartFile in my opinion https://swagger.io/docs/specification/v3_0/describing-request-body/file-upload/
especially since dio support MultipartFile for file upload natively via FormData.

by definition MultipartFile are for upload purposes not really for download purposes.

but that's just my opinion, hope you find a solution soon

have a nice day

[vasilich6107]

Hey @kaal-dam
This package does not seem to be actively supported so i fixed the issue somehow locally with Multipart and have no plans to improve this PR

[vasilich6107]

There is an attempt to create new generator
#18970