来自swift前端的POST请求问题

Question

我正在尝试实现 Swift 前端，以便它可以将数据上传到数据库，该数据库是通过 Flask 用 Python 编写并利用 PostgreSQL。我用于发送 POST 请求的前端 Swift 代码目前如下，如果重要的话，它是在 View Controller 中编写的：

func PostData(){

        let parameters:[String: Any]=["latitude":  35.0094040,
                        "longitude": -85.3275640,
                        "tag": "this is my fancy tag",
                        "image":"icecream.jpg"]
        let jsonURLString="http://localhost/api/tags"
        guard let url=URL(string: jsonURLString) else{
            return
        }
        var request=URLRequest(url: url)
        request.httpMethod="POST"
        request.addValue("application/json", forHTTPHeaderField: "Content-Type")
        guard let httpBody=try? JSONSerialization.data(withJSONObject: parameters, options: [])  else{
            return
        }
        request.httpBody=httpBody
        let session=URLSession.shared
        session.dataTask(with: request) { (data, _, error) in


            if let data=data{
                do{
                    try JSONSerialization.jsonObject(with: data, options: [])  
                }catch{
                    print(error)
                }
            }
            }.resume()
    }

我接受post请求的后端代码如下：

@app.route('/api/tags',  methods=  ["GET",  "POST"])
def get_tags_api():
    if request.method == "POST":
        latitude  =  request.form.get("latitude")
        longitude  =  request.form.get("longitude")
        text  =  request.form.get("tag")
        image_  =  request.form.get("image", None)
        print (latitude)
        print (longitude)
        print (text) 
        print (image_)
        create_tags(latitude=latitude, longitude=longitude, text=text, image=image_)

当我尝试运行以下代码时，我最终收到了来自 Xcode 的以下错误消息：

Error Domain=NSCocoaErrorDomain Code=3840 "JSON text did not start with array or object and option to allow fragments not set." UserInfo={NSDebugDescription=JSON text did not start with array or object and option to allow fragments not set.}

在后端，所有变量都打印为 None，并带有以下错误消息：

[SQL: INSERT INTO tags (text, longitude, latitude, image) VALUES (%(text)s, %(longitude)s, %(latitude)s, %(image)s) RETURNING tags.id]
[parameters: {'text': None, 'longitude': None, 'latitude': None, 'image': None}]
(Background on this error at: http://sqlalche.me/e/gkpj)

鉴于前端PostData函数运行时后端显示错误消息，请求肯定已经发送，但后端没有从请求中检测到任何数据，我不知道这是为什么。我不确定我在这里做错了什么。我对 Swift 比较陌生，而且我对 Flask 没有太多经验。请帮忙。

Answer 1

我认为你的代码是错误的。

guard let httpBody=try? JSONSerialization.data(withJSONObject: parameters, options: [])  else {
     return
}

可以参考Alamofire - ParameterEncoding.swift

Answer 2

我认为您需要在向服务器发出请求之前对数据进行编码。你可以试试这段代码：

guard let jsonData=try? JSONSerialization.data(withJSONObject: parameters, options: [])  else {return}
let jsonString = String(data: jsonData, encoding: .utf8)!;

Answer 3

例子：

let parameters:[String: Any] = ["latitude":  35.0094040,
                                "longitude": -85.3275640,
                                "tag": "this is my fancy tag",
                                "image":"icecream.jpg"]

private func query(_ parameters: [String: Any]) -> String {
    var components: [(String, String)] = []
    for key in parameters.keys.sorted(by: <) {
        let value = parameters[key]!
        components.append((escape(key), escape("\(value)")))
    }
    return components.map { "\($0)=\($1)" }.joined(separator: "&")
}

public func escape(_ string: String) -> String {
      let generalDelimitersToEncode = ":#[]@"
      let subDelimitersToEncode = "!$&'()*+,;="
      var allowedCharacterSet = CharacterSet.urlQueryAllowed
      allowedCharacterSet.remove(charactersIn: "\(generalDelimitersToEncode)\(subDelimitersToEncode)")
      var escaped = ""
      if #available(iOS 8.3, *) {
         escaped = string.addingPercentEncoding(withAllowedCharacters: allowedCharacterSet) ?? string
      } else {
         let batchSize = 50
         var index = string.startIndex
         while index != string.endIndex {
               let startIndex = index
               let endIndex = string.index(index, offsetBy: batchSize, limitedBy: string.endIndex) ?? string.endIndex
               let range = startIndex..<endIndex
               let substring = string[range]
               escaped += substring.addingPercentEncoding(withAllowedCharacters: allowedCharacterSet) ?? String(substring)
               index = endIndex
         }
      }      
    return escaped
}
request.httpBody = query(parameters).data(using: .utf8, allowLossyConversion: false)