List<int> is not sent as string in multipart request.

[Simouche]

I have this multipart request:

  @multipart
  Future<Response<Homework>> create_(
    @Part("teacher") int teacher,
    @Part("title") String title,
    @Part("description") String description,
    @Part("subject") int subject,
    @Part("classes") List<int> classes,
    @Part("dueDate") String dueDate,
    // @PartFile("homeworkFiles") List<PartValueFile<String>> homeworkFiles,
  );

the classes part, is being sent as a string, and causing the backend to respond with http 400 with this error:

{"classes":["Incorrect type. Expected pk value, received str."],"homeworkFiles":["This field is required."]}

anyway to fix this issue?

Also, how to send multiple files under the same field name? uncommenting the last line makes it fail (without throwing any errors).

[techouse]

Hey 👋

You might want to look at this method for clues.

Would be great if you can come up with a test case here.

Also, this and this StackOverflow answer might be of some help.

I'll take a deeper look into it once I find some free time.

[techouse]

@Simouche can you check if this fixes it for you? #439

[Simouche]

@techouse how do i test it? i tried referencing it like this:

  chopper:
    git:
      url: https://github.com/techouse/chopper.git
      ref: fix/issue-438-multipart-list

and i had this error:

Could not find a file named "pubspec.yaml" in https://github.com/techouse/chopper.git e70429782820caa346cc299909eec0a5dc1f28fb.
pub get failed
command: "C:\flutter\bin\cache\dart-sdk\bin\dart __deprecated_pub --directory . get --example"
pub env: {
  "FLUTTER_ROOT": "C:\flutter",
  "PUB_ENVIRONMENT": "flutter_cli:get",
  "PUB_CACHE": "C:\Users\pc\AppData\Local\Pub\Cache",
}
exit code: 1

[techouse]

chopper:
git:
url: https://github.com/techouse/chopper.git
ref: fix/issue-438-multipart-list

You need to also specify the path.

chopper:
  git:
    url: https://github.com/techouse/chopper.git
    ref: fix/issue-438-multipart-list
    path: chopper

[Simouche]

yeah right, i did that and i got this now:

Because chopper_generator 6.0.1 depends on chopper ^6.0.0 and no versions of chopper_generator match >6.0.1 <7.0.0, chopper_generator ^6.0.1 requires chopper from hosted.
So, because go_class_teacher depends on both chopper from git and chopper_generator ^6.0.1, version solving failed.
pub get failed
command: "C:\flutter\bin\cache\dart-sdk\bin\dart __deprecated_pub --directory . get --example"
pub env: {
  "FLUTTER_ROOT": "C:\flutter",
  "PUB_ENVIRONMENT": "flutter_cli:get",
  "PUB_CACHE": "C:\Users\pc\AppData\Local\Pub\Cache",
}
exit code: 1

even if i change the dependency of the generator to any, i still get another error for null sound safety.

[techouse]

You might need to put that into dependency_overrides, so

dependency_overrides:
  chopper:
    git:
      url: https://github.com/techouse/chopper.git
      ref: fix/issue-438-multipart-list
      path: chopper

[Simouche]

This doesn't fix it, it seems your solution is changing the field name to contain an index, causing the backend to not detect the field.
i had this error 400:
"classes":["This list may not be empty."]

when I printed the request body on the backend i received this:

QueryDict: {'classes[0]': ['15'], 'classes[1]': ['12'], 'due_date': ['29/05/2023 18:05'], ...}>

but when i try with postman i receive this:

<QueryDict: {'classes': ['6', '7', '8'], ...}>

for reference that's how i send it from postman:

[techouse]

That is the only solution.

fields[0]=123
fields[1]=456

It's pretty standard HTTP practice. If all of them have the same name they would overwrite each other.

As the values need to be essentially stringified, a List<int> like

final List<int> ints = [1, 2, 3];

would become ints=[1, 2, 3] which is maybe workable but if it's strings

final List<String> ints = [
  'lorem',
  'ipsum',
  'dolor, something after an in string comma',
];

it would become strings=[lorem, ipsum, dolor, something after an in string comma] which is kinda terrible.

[Simouche]

Why is the case of postman working properly? The backend receives it as a list of strings as you can see, in my previous answer, and it works just fine... :/

[techouse]

What's the actual HTTP request that postman makes?

And FYI I did try using something like fields[] as the name and it would still overwrite itself, so I had to go for fields[$i]

This is how they do it in retrofit.

[Simouche]

this is the dart code that postman proposes:

var headers = {
  'Authorization': 'Token ********'
};
var request = http.MultipartRequest('POST', Uri.parse('http://127.0.0.1:8002/api/homeworks/'));
request.fields.addAll({
  'title': 'first home work',
  'description': 'random description',
  'dueDate': '20/04/2023 00:00',
  'subject': '1',
  'teacher': '9',
  'classes': '6',
  'classes': '7',
  'classes': '8'
});
request.files.add(await http.MultipartFile.fromPath('homework_files', '/C:/Users/pc/Pictures/wallpapers/wallpaper1.png'));
request.files.add(await http.MultipartFile.fromPath('homework_files', '/C:/Users/pc/Pictures/wallpapers/wallpaper3.png'));
request.files.add(await http.MultipartFile.fromPath('homework_files', '/C:/Users/pc/Pictures/wallpapers/wallpaper5.png'));
request.headers.addAll(headers);

http.StreamedResponse response = await request.send();

if (response.statusCode == 200) {
  print(await response.stream.bytesToString());
}
else {
  print(response.reasonPhrase);
}

[techouse]

Hmm, ok. I've updated the code. Pull the repo and try again.

[Simouche]

I still get the same output as the previous one...

[techouse]

Yeah, I've only fixed it for the files. The dictionary with the integers, as in your example, can't have repeated keys.

What's the cURL code it generates?

[Simouche]

cURL:

curl --location 'http://127.0.0.1:8002/api/homeworks/' \
--header 'Authorization: Token 21017a48e6e9156ae84299c59754f88b7ac5c803' \
--form 'title="first home work"' \
--form 'description="random description"' \
--form 'dueDate="20/04/2023 00:00"' \
--form 'subject="1"' \
--form 'teacher="9"' \
--form 'classes="6"' \
--form 'classes="7"' \
--form 'classes="8"' \
--form 'homework_files=@"/C:/Users/pc/Pictures/wallpapers/wallpaper1.png"' \
--form 'homework_files=@"/C:/Users/pc/Pictures/wallpapers/wallpaper3.png"' \
--form 'homework_files=@"/C:/Users/pc/Pictures/wallpapers/wallpaper5.png"'

[techouse]

While that will work with cURL it won't work with MultipartRequest fields because they are a dictionary and keys can't be repeated.

[Simouche]

Then why does this snippet, which uses dio, works just fine?

  Future createDio(Map<String, dynamic> data, List<String> files) async {
    final fs = [];
    for (var file in files) {
      fs.add(await dio.MultipartFile.fromFile(file));
    }
    final formData = dio.FormData.fromMap({
      ...data,
      'homeworkFiles': fs,
    });
    final response =
        await dioClient.post('${baseURL}homeworks/', data: formData);
    return response;
  }

on the backend i receive this (just like postman):

<QueryDict: {'..., 'classes': ['6', '13'], 'teacher': ['9'], 'homework_files': [...]}>

[techouse]

Because Dio doesn't use http like chopper does.

MultipartRequest.fields is a Map<String, String> and as such can not have duplicate keys.

This has been mentioned previously in #77 where @humazed provided a solution

@Post(path: "store/orders")
@multipart
Future<Response<Order>> createTripOrder(
  @Part("trip") int trip,
  @PartFile("images[]") List<MultipartFile> images,
);

What you want is not possible with http and has been discussed here dart-lang/http#277 and here dart-lang/http#24.

The solution I implemented is exactly the same as suggested here dart-lang/http#277 (comment)

As I said above, using this kind of annotation field[0], field[1], field[2] is pretty common and I'm not sure why your backend doesn't accept it.

Effectively you have 2 options:

1. use Dio
2. wait for 🐛 fix Multipart for List<int> and List<String> #439 to land and update your backend to accept field[0], field[1], field[2]

[techouse]

@Simouche please continue any further discussion in #439