How to upload images and file to a server in Flutter?

I use a web service for image processing , it works well in Postman:

Now I want to make http request in flutter with Dart:

import 'package:http/http.dart' as http;

static ocr(File image) async {
    var url = '${API_URL}ocr';
    var bytes = image.readAsBytesSync();
    
    var response = await http.post(
        url,
        headers:{ "Content-Type":"multipart/form-data" } ,
        body: { "lang":"fas" , "image":bytes},
        encoding: Encoding.getByName("utf-8")
    );

    return response.body;

  }

but I don't know how to upload the image file, in above code I get exception: Bad state: Cannot set the body fields of a Request with content-type "multipart/form-data".
How should I write the body of request?

Your workaround should work; many servers will accept application/x-www-form-urlencoded as an alternative (although data is encoded moderately inefficiently).

However, it is possible to use dart:http to do this. Instead of using http.post, you'll want to use a http.MultipartFile object.

From the dart documentation:

var request = new http.MultipartRequest("POST", url);
request.fields['user'] = '[email protected]';
request.files.add(http.MultipartFile.fromPath(
    'package',
    'build/package.tar.gz',
    contentType: new MediaType('application', 'x-tar'),
));
request.send().then((response) {
  if (response.statusCode == 200) print("Uploaded!");
});

I'd like to recommend dio package to you , dio is a powerful Http client for Dart/Flutter, which supports Interceptors, FormData, Request Cancellation, File Downloading, Timeout etc.

dio is very easy to use, in this case you can:

Sending FormData:

FormData formData = new FormData.from({
   "name": "wendux",
   "file1": new UploadFileInfo(new File("./upload.jpg"), "upload1.jpg")
});
response = await dio.post("/info", data: formData)

More details please refer to dio。

This can be achieved using the MultipartRequest class (https://pub.dev/documentation/http/latest/http/MultipartRequest-class.html)

Change the media type and uri as needed.

uploadFile() async {
    var postUri = Uri.parse("<APIUrl>");
    var request = new http.MultipartRequest("POST", postUri);
    request.fields['user'] = 'blah';
    request.files.add(new http.MultipartFile.fromBytes('file', await File.fromUri("<path/to/file>").readAsBytes(), contentType: new MediaType('image', 'jpeg')))

    request.send().then((response) {
      if (response.statusCode == 200) print("Uploaded!");
    });
  }

I found a working example without using any external plugin , this only uses

import 'package:http/http.dart' as http;
import 'dart:io';
import 'package:path/path.dart';
import 'package:async/async.dart';
import 'dart:convert';

Code

var stream =
        new http.ByteStream(DelegatingStream.typed(imageFile.openRead()));
    // get file length
    var length = await imageFile.length(); //imageFile is your image file
    Map<String, String> headers = {
      "Accept": "application/json",
      "Authorization": "Bearer " + token
    }; // ignore this headers if there is no authentication

    // string to uri
    var uri = Uri.parse(Constants.BASE_URL + "api endpoint here");

    // create multipart request
    var request = new http.MultipartRequest("POST", uri);

  // multipart that takes file
    var multipartFileSign = new http.MultipartFile('profile_pic', stream, length,
        filename: basename(imageFile.path));

    // add file to multipart
    request.files.add(multipartFileSign);

    //add headers
    request.headers.addAll(headers);

    //adding params
    request.fields['loginId'] = '12';
    request.fields['firstName'] = 'abc';
   // request.fields['lastName'] = 'efg';
 
    // send
    var response = await request.send();

    print(response.statusCode);

    // listen for response
    response.stream.transform(utf8.decoder).listen((value) {
      print(value);
    
    });

How to upload image file using restAPI in flutter/dart.

This work for me.

var postUri = Uri.parse("apiUrl");

http.MultipartRequest request = new http.MultipartRequest("POST", postUri);

http.MultipartFile multipartFile = await http.MultipartFile.fromPath(
    'file', filePath); 

request.files.add(multipartFile);

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


print(response.statusCode);

Use MultipartRequest class. How to upload image file using restAPI in flutter/dart

  void uploadImage1(File _image) async {

    // open a byteStream
    var stream = new http.ByteStream(DelegatingStream.typed(_image.openRead()));
    // get file length
    var length = await _image.length();

    // string to uri
    var uri = Uri.parse("enter here upload URL");

    // create multipart request
    var request = new http.MultipartRequest("POST", uri);

    // if you need more parameters to parse, add those like this. i added "user_id". here this "user_id" is a key of the API request
    request.fields["user_id"] = "text";

    // multipart that takes file.. here this "image_file" is a key of the API request
    var multipartFile = new http.MultipartFile('image_file', stream, length, filename: basename(_image.path));

    // add file to multipart
    request.files.add(multipartFile);

    // send request to upload image
    await request.send().then((response) async {
      // listen for response
      response.stream.transform(utf8.decoder).listen((value) {
        print(value);
      });

    }).catchError((e) {
      print(e);
    });
  }

name spaces:

import 'package:path/path.dart';
import 'package:async/async.dart';
import 'dart:io';
import 'package:http/http.dart' as http;

UPLOAD IMAGE TO SERVER WITH FORM DATA

To upload image to server you need a dio library.

Features:

1. Authorization (adding token)
2. Adding extra field like: username, etc
3. Adding Image to upload

Code example:

import 'package:dio/dio.dart' as dio;
import 'dart:convert';

    try {
      ///[1] CREATING INSTANCE
      var dioRequest = dio.Dio();
      dioRequest.options.baseUrl = '<YOUR-URL>';
       
      //[2] ADDING TOKEN
      dioRequest.options.headers = {
        'Authorization': '<IF-YOU-NEED-ADD-TOKEN-HERE>',
        'Content-Type': 'application/x-www-form-urlencoded'
      };

      //[3] ADDING EXTRA INFO
      var formData =
          new dio.FormData.fromMap({'<SOME-EXTRA-FIELD>': 'username-forexample'});

      //[4] ADD IMAGE TO UPLOAD
      var file = await dio.MultipartFile.fromFile(image.path,
            filename: basename(image.path),
            contentType: MediaType("image", basename(image.path)));

      formData.files.add(MapEntry('photo', file));

      //[5] SEND TO SERVER
      var response = await dioRequest.post(
        url,
        data: formData,
      );
      final result = json.decode(response.toString())['result'];
    } catch (err) {
      print('ERROR  $err');
    }

Updated 2021 way:

using flutter http and mime

import 'package:mime/mime.dart';
import 'package:http/http.dart' as http;
import 'package:http_parser/http_parser.dart';
import 'dart:io';


  Future<dynamic> multipartImageUpload(String baseUrl, String api, File image) async {
    var uri = Uri.parse(baseUrl + api);
    final mimeTypeData =
        lookupMimeType(image.path, headerBytes: [0xFF, 0xD8]).split('/');

    // Intilize the multipart request
    final imageUploadRequest = http.MultipartRequest('PUT', uri);

    // Attach the file in the request
    final file = await http.MultipartFile.fromPath('image', image.path,
        contentType: MediaType(mimeTypeData[0], mimeTypeData[1]));
    imageUploadRequest.files.add(file);

	// add headers if needed
    //imageUploadRequest.headers.addAll(<some-headers>);

    try {
      final streamedResponse = await imageUploadRequest.send();
      final response = await http.Response.fromStream(streamedResponse);
      return response;
    } catch (e) {
      print(e);
      return null;
    }
  }

To add a header and use http multipart with https://pub.dev/packages/multi_image_picker Plugin,

This is the code.

var request =  http.MultipartRequest(
        'POST', Uri.parse(myurl)

      );
      //Header....
      request.headers['Authorization'] ='bearer $authorizationToken';
      
       request.fields['PropertyName'] = propertyName;
    request.fields['Country'] = country.toString();
    request.fields['Description'] = des;
    request.fields['State'] = state.toString();
       request.files.add(http.MultipartFile.fromBytes(
      'ImagePaths',
      learnImage,
      filename: 'some-file-name.jpg',
  contentType: MediaType("image", "jpg"),
    )
        );
var response = await request.send();
print(response.stream);
print(response.statusCode);
final res = await http.Response.fromStream(response);
  print(res.body);

To use HTTP and https://pub.dev/packages/image_picker PLUGIN

This is the code

var request =  http.MultipartRequest(
        'POST', Uri.parse(myurl)

      );
      request.headers['Authorization'] ='bearer $authorizationToken';
       request.fields['PropertyName'] = propertyName;
    request.fields['Country'] = country.toString();
    request.fields['Description'] = des;
    request.fields['State'] = state.toString();
       request.files.add(await http.MultipartFile.fromPath(
      'ImagePaths',
      file.path
    )
        );
var response = await request.send();
    print(response.stream);
    print(response.statusCode);
    final res = await http.Response.fromStream(response);
      print(res.body);

Just leaving this here, if anyone is trying to upload a pdf or any other document using MultipartRequest method.

Just add the content type as - contentType: new MediaType('application', 'pdf')

Working Code

String path = userSelectedImagePath;
    Map<String, String> data = {
      "name": firstName!,
      "email": userEmail!
    };
   

    String token = await LocaldbHelper().getToken();
    Map<String, String> headers = {
      'X-Requested-With': 'XMLHttpRequest',
      'authorization': 'Bearer $token',
    };


   var request = http.MultipartRequest(
        'POST',
        Uri.parse(ApiUrl.updateProfile),
      );
      request.fields.addAll(data);
      request.headers.addAll(headers);
      var multipartFile = await http.MultipartFile.fromPath(
          'avatar', path); //returns a Future<MultipartFile>
      request.files.add(multipartFile);
      http.StreamedResponse response = await request.send();
      final respStr = await response.stream.bytesToString();
      var jsonData = jsonDecode(respStr);
      if (response.statusCode == 200) {
        // success
      } else {
        // error
      }

With Hearder upload image

Future uploadImageMedia(File fileImage, String token) async {


  final mimeTypeData =
        lookupMimeType(fileImage.path, headerBytes: [0xFF, 0xD8]).split('/');
         final imageUploadRequest =
        http.MultipartRequest('POST', Uri.parse(mainUrlSite + "wp-json/wp/v2/media"));

    final file = await http.MultipartFile.fromPath('file', fileImage.path,
        contentType: MediaType(mimeTypeData[0], mimeTypeData[1]));
    
    imageUploadRequest.files.add(file);
    imageUploadRequest.headers.addAll({
      "Authorization": "Bearer " + token
    });
    try {
      final streamedResponse = await imageUploadRequest.send();

      streamedResponse.stream.transform(utf8.decoder).listen((value) {
        print(value);
        return Future.value(value);
      });
    } catch (e) {
      print(e);
    }
}

I use Dio library with put method:

    var formData = FormData.fromMap({
      'simpleParam': 'example',
      'file': await MultipartFile.fromFile(filePath, filename: 'file.jpg')
    });

    var dio = Dio();
    dio.options.headers[HttpHeaders.authorizationHeader] = myToken;

    var response = new Response(); //Response from Dio
    response = await dio.put(myUrl + "/myApi", data: formData);

The result is in response.data

Good code with Dio and FilePicker for post file on your server. I use flutter for the web.

FilePicker Dio

1. First you need writing Dio post method.

    Future postImportClient(PlatformFile file) async {
        try {
          var urlBase = 'your url';
          var mfile = MultipartFile.fromBytes(file.bytes!, filename: file.name);
          var formData = FormData();
          formData.files.add(MapEntry('file', mfile));
          await _dio.post(urlBase, data: formData);
        } on DioError catch (error) {
          throw Exception(error);
        }
      }

2. Initial FilePicker and get file.

FilePickerResult? result = await FilePickerWeb.platform.pickFiles();
if (result != null) {
var file = result.files.single;
await client.postImportClient(file);
}

Good luck!

try {
  result[HttpKeys.status] = false;
  var request = http.MultipartRequest('POST', url);
  request.fields.addAll(body);

  if (avatar.path.isNotEmpty) {
    request.files.add(await http.MultipartFile.fromPath('uploadedImg', avatar.path));
  }

  request.headers.addAll(headers);

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

  final response = await http.Response.fromStream(streamResponse);

  if (response.statusCode == 200) {
    var resMap = jsonDecode(response.body);
    debugPrint('<== 𝕊𝕚𝕘𝕟 𝕦𝕡 𝕤𝕦𝕔𝕔𝕖𝕤𝕤𝕗𝕦𝕝𝕝𝕪 ==>');
    // debugPrint(response.body);
    result[HttpKeys.status] = true;
    result[HttpKeys.message] = resMap[HttpKeys.message];
    result[HttpKeys.data] = resMap['data'];

    return result;
  } else {
    var resMap = jsonDecode(response.body);
    result[HttpKeys.message] = resMap[HttpKeys.message];
    return result;
  }
} catch (error) {
  result[HttpKeys.message] = error.toString();
  return result;
}

With dio I do like this:

Future<void> _uploadFileAsFormData(String path) async {
  try {
    final dio = Dio();

    dio.options.headers = {
      'Content-Type': 'application/x-www-form-urlencoded'
    };

    final file =
      await MultipartFile.fromFile(path, filename: 'test_file');

    final formData = FormData.fromMap({'file': file}); // 'file' - this is an api key, can be different

    final response = await dio.put( // or dio.post
      uploadFileUrlAsString,
      data: formData,
    );
  } catch (err) {
    print('uploading error: $err');
  }
}