如何解决 400 statusCode 和 Unexpected character (at character 1) 错误？

Question

我有一个机器学习模型可以拍摄照片并 returns 进行预测，我将其上传到烧瓶服务器并在我使用 HTML 创建的网站上对其进行了测试并且它有效，但是当我尝试将它与 flutter 应用程序一起使用时，出现此错误：Unhandled Exception: FormatException: Unexpected character (at character 1) 当我尝试从我的应用程序上传图片时。另外，我得到的 statusCode 是 400 .. 这些是我的代码。任何帮助将不胜感激。

This is my python code that I created the flask instance in ( I run it on my cmd when I try to establish a connection using the flutter app)

from flask import Flask, render_template, request, jsonify
import cv2
import numpy as np
import pandas as pd
import tensorflow
from tensorflow import keras
from tensorflow.python.keras import backend as k

app = Flask(__name__)

model = tensorflow.keras.models.load_model('model.h5')


@app.route('/')
def index():
    return render_template("index.html", data="hey")


@app.route("/prediction", methods=["POST"])
def prediction():

    
    img = request.files['img']  
    img.save("img.jpg")
    image = cv2.imread("img.jpg")
    image = cv2.resize(image, (224,224))
    image = np.reshape(image, (1,224,224,3))
    pred = model.predict(image)

    pred = pred > 0.5
    if(pred):
        predd="Malignant"
    else:
        predd="Benign"

    return jsonify({"prediction": predd,})
    
#this ip is my network's IPv4
#(I connected both my laptop and mobile to this WiFi while establishing the connection)
if __name__ == "__main__":
    app.run(debug=False,host='192.168.1.103',port=5000)

And this is the code I used in flutter to establish the connection

  sendImageToServer(File imageFile) async {
    var stream = new http.ByteStream(imageFile.openRead());
    stream.cast();
    var length = await imageFile.length();
    print(length);
    
    //this ip is my network's IPv4 
    //(I connected both my laptop and mobile 
    //to this WiFi while establishing the connection) 

    var uri = Uri.parse('http://192.168.1.103:5000/prediction');
    var request = new http.MultipartRequest("POST", uri);
    var multipartFile = new http.MultipartFile('file', stream, length,
        filename:
            basename(imageFile.path));

    request.files.add(multipartFile);
    request.headers["Content-Type"] = 'multipart/form-data';
    var streamedResponse = await request.send();
    var response = await http.Response.fromStream(streamedResponse);
    
    print(response);

    final Map<String, dynamic> responseJson =
        json.decode(response.toString()) as Map<String, dynamic>;
    print(responseJson.toString());

    pre = responseJson["prediction"];
    print(pre);

    setState(() {
      prediction = pre;
    });
  }

  Future getImage() async {
    final image = await picker.getImage(source: ImageSource.gallery);
    sendImageToServer(File(image.path));

    setState(() {
      fileImage = File(image.path);
      sendImageToServer(fileImage);
    });
  }

Also this is what I get on the cmd when I send the request

192.168.1.108 - - [20/Mar/2021 19:14:39] "←[1m←[31mPOST /prediction HTTP/1.1←[0m" 400 -

Answer 1

更新答案

所以你得到的异常是告诉你服务器无法理解你发送的请求，我认为现在的问题是你在这里发送请求的密钥

var multipartFile = new http.MultipartFile('file', stream, length,
        filename:
            basename(imageFile.path));

在您的后端，您使用的是密钥“img”

img = request.files['img']

所以这些应该是一样的，试试下面的

var multipartFile = new http.MultipartFile('img', stream, length,
        filename:
            basename(imageFile.path));

我真的希望这会奏效，同时检查以下链接可能会帮助您更多地了解问题，

https://dev.to/carminezacc/advanced-flutter-networking-part-1-uploading-a-file-to-a-rest-api-from-flutter-using-a-multi-part-form-data-post-request-2ekm

和计算器问题

旧答案

错误消息没有说明错误的确切位置，所以这样做，将您的代码添加到 try catch 块中，这样您就可以捕获抛出的任何异常并知道错误是什么。

try {
sendImageToServer(File imageFile) async {
    var stream = new http.ByteStream(imageFile.openRead());
    stream.cast();
    var length = await imageFile.length();
    print(length);
    
    //this ip is my network's IPv4 
    //(I connected both my laptop and mobile 
    //to this WiFi while establishing the connection) 

    var uri = Uri.parse('http://192.168.1.103:5000/prediction');
    var request = new http.MultipartRequest("POST", uri);
    var multipartFile = new http.MultipartFile('file', stream, length,
        filename:
            basename(imageFile.path));

    request.files.add(multipartFile);
    request.headers["Content-Type"] = 'multipart/form-data';
    var streamedResponse = await request.send();
    var response = await http.Response.fromStream(streamedResponse);
    
     //print(response);//this will print instance of response not the response itself
     // i cleared this a bit so we can trace where the error started from
     print(response.statusCode); // the status code of your response
     print(response.reasonPhrase); // the reason it failed "in case it did"
     print(response.body); // the body of the response -> this what you really interested in

  }
} catch (e,s) {
  // this is your life saver, it will tell you everything 
  // you need to know to trace the error (well mostly :D)
  // note : this will catch any exceptions that is thrown in the code, this not related to the response
  // the (e) is error it self so your should print that to know what is the error
  print(e.toString());
  // the (s) is the stackTrace, it will tell you when and where the error 
  // happened, so you should also print it
  print(e.toString());
}

如何解决 400 statusCode 和 Unexpected character (at character 1) 错误？

How to solve 400 statusCode and Unexpected character (at character 1) error?

python

multipart

request

flask

flutter

更新答案

旧答案