如何在 Swift 中使用 Codable 和 URLSession.shared.uploadTask (multipart/form-data) 上传图像文件？

Question

我想使用某个 URL 端点将图像文件上传到后端服务器。 我可以使用 Alamofire 的上传请求作为 multipartFormData 轻松做到这一点。 但是我想摆脱 Alamofire 以尽量减少对第三方框架的依赖。 这是有效的 Alamofire 代码：

func uploadRequestAlamofire(parameters: [String: Any], imageData: Data?, completion: @escaping(CustomError?) -> Void ) {

let url = imageUploadEndpoint!

let headers: HTTPHeaders = ["X-User-Agent": "ios",
                            "Accept-Language": "en",
                            "Accept": "application/json",
                            "Content-type": "multipart/form-data",
                            "ApiKey": KeychainService.getString(by: KeychainKey.apiKey) ?? ""]

Alamofire.upload(multipartFormData: { (multipartFormData) in
    for (key, value) in parameters {
        multipartFormData.append("\(value)".data(using: String.Encoding.utf8)!, withName: key as String)
    }

    if let data = imageData {
        multipartFormData.append(data, withName: "file", fileName: "image.png", mimeType: "image/jpg")
    }

}, usingThreshold: UInt64.init(), to: url, method: .post, headers: headers) { (result) in
    switch result {
    case .success(let upload, _, _):
        upload.responseJSON { response in

            completion(CustomError(errorCode: response.response!.statusCode))

            print("Succesfully uploaded")
        }
    case .failure(let error):
        print("Error in upload: \(error.localizedDescription)")

    }
}
}

这是 URLSession 上传任务，它不起作用：

func requestNativeImageUpload(imageData: Data, orderExtId: String) {

var request = URLRequest(url: imageUploadEndpoint!)
request.httpMethod = "POST"
request.timeoutInterval = 10

    request.allHTTPHeaderFields = [
        "X-User-Agent": "ios",
        "Accept-Language": "en",
        "Accept": "application/json",
        "Content-type": "multipart/form-data",
        "ApiKey": KeychainService.getString(by: KeychainKey.apiKey) ?? ""
    ]

let body = OrderUpload(order_ext_id: orderExtId, file: imageData)

do {
    request.httpBody = try encoder.encode(body)
} catch let error {
    print(error.localizedDescription)
}

let session = URLSession.shared



session.uploadTask(with: request, from: imageData)  { data, response, error in
    guard let response = response as? HTTPURLResponse else { return }

    print(response)
    if error != nil {
        print(error!.localizedDescription)
    }


    }.resume()
}

这是我为 Alamofire 和 URLSession 调用方法的方式：

uploadRequestAlamofire(parameters: ["order_ext_id": order_ext_id, "file": "image.jpg"], imageData: uploadImage) { [weak self] response in } 

requestNativeImageUpload(imageData: uploadImage!, orderExtId: order_ext_id)

以下是后端服务器希望在请求正文中收到的内容：

let order_ext_id: String
let description: String
let file: string($binary)

这是为请求的 httpBody 编码的 Codable 结构。

struct OrderUpload: Codable {
    let order_ext_id: String
    let description: String 
    let file: String
}

虽然在这个演示中我的方法可能并不完全合适并且我不处理响应状态代码，但 Alamofire 方法效果很好。

为什么 URLSession 不能工作？

Answer 1

1. header 中的 Content-Type 错误。 它应该看起来像：

var request = URLRequest(url: imageUploadEndpoint!)

let boundary = "Boundary-\(UUID().uuidString)"
request.setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")

2. 您需要根据 object 中的每个字段形成正文，就像您在 Alamofire 示例中向 multipartFormData 添加值一样（您在那里使用了字典）

let body = NSMutableData()

let boundaryPrefix = "--\(boundary)\r\n"

for (key, value) in parameters {
    body.appendString(boundaryPrefix)
    body.appendString("Content-Disposition: form-data; name=\"\(key)\"\r\n\r\n")
    body.appendString("\(value)\r\n")
}

body.appendString(boundaryPrefix)
body.appendString("Content-Disposition: form-data; name=\"file\"; filename=\"\(filename)\"\r\n")
body.appendString("Content-Type: \(mimeType)\r\n\r\n")
body.append(imageData)
body.appendString("\r\n")
body.appendString("--".appending(boundary.appending("--")))

帮助将字符串添加到您的数据：

extension NSMutableData {
    func appendString(_ string: String) {
        let data = string.data(using: .utf8)
        append(data!)
    }
}

Answer 2

最后我能够找到解决方案。 来源是： URLSession: Multipart Form-Data Requests | Swift 3，Xcode 8 。 在我的具体情况下，我需要提供 orderExtId 作为后端服务器接受我的图像的参数。 您的情况可能会有所不同，具体取决于后端的要求。

func requestNativeImageUpload(image: UIImage, orderExtId: String) {

    guard let url = imageUploadEndpoint else { return }
    let boundary = generateBoundary()
    var request = URLRequest(url: url)

    let parameters = ["order_ext_id": orderExtId]

    guard let mediaImage = Media(withImage: image, forKey: "file") else { return }

    request.httpMethod = "POST"

    request.allHTTPHeaderFields = [
                "X-User-Agent": "ios",
                "Accept-Language": "en",
                "Accept": "application/json",
                "Content-Type": "multipart/form-data; boundary=\(boundary)",
                "ApiKey": KeychainService.getString(by: KeychainKey.apiKey) ?? ""
            ]

    let dataBody = createDataBody(withParameters: parameters, media: [mediaImage], boundary: boundary)
    request.httpBody = dataBody

    let session = URLSession.shared
    session.dataTask(with: request) { (data, response, error) in
        if let response = response {
            print(response)
        }

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


func generateBoundary() -> String {
    return "Boundary-\(NSUUID().uuidString)"
}

func createDataBody(withParameters params: [String: String]?, media: [Media]?, boundary: String) -> Data {

    let lineBreak = "\r\n"
    var body = Data()

    if let parameters = params {
        for (key, value) in parameters {
            body.append("--\(boundary + lineBreak)")
            body.append("Content-Disposition: form-data; name=\"\(key)\"\(lineBreak + lineBreak)")
            body.append("\(value + lineBreak)")
        }
    }

    if let media = media {
        for photo in media {
            body.append("--\(boundary + lineBreak)")
            body.append("Content-Disposition: form-data; name=\"\(photo.key)\"; filename=\"\(photo.fileName)\"\(lineBreak)")
            body.append("Content-Type: \(photo.mimeType + lineBreak + lineBreak)")
            body.append(photo.data)
            body.append(lineBreak)
        }
    }

    body.append("--\(boundary)--\(lineBreak)")

    return body
}


extension Data {
    mutating func append(_ string: String) {
        if let data = string.data(using: .utf8) {
            append(data)
        }
    }
}


struct Media {
    let key: String
    let fileName: String
    let data: Data
    let mimeType: String

    init?(withImage image: UIImage, forKey key: String) {
        self.key = key
        self.mimeType = "image/jpg"
        self.fileName = "\(arc4random()).jpeg"

        guard let data = image.jpegData(compressionQuality: 0.5) else { return nil }
        self.data = data
    }
}

Answer 3

这是我根据这个答案制作的多部分编码器， Custom Swift 字符串资源格式的编码器/解码器，您可以直接将其转换为多部分表单数据。 Append 编码数据到你的正文数据。

import Foundation

/// An object that encodes instances of a data type
/// as strings following the simple strings file format.
public class MultipartEncoder {
    
    var boundary: String = ""
    /// Returns a strings file-encoded representation of the specified value.
    public func encode<T: Encodable>(_ value: T) throws -> Data {
        let multipartencoding = MultipartEncoding()
        try value.encode(to: multipartencoding)
        return dataFromFormat(from: multipartencoding.data.strings)
    }
    
    private func dataFromFormat(from strings: [String: String]) -> Data {
        let lineBreak = "\r\n"
        //return dotStrings.joined(separator: "\n")
        var fieldData = Data()
        for (key, value) in strings{
            fieldData.append("--\(boundary + lineBreak)")
            fieldData.append("Content-Disposition: form-data; name=\"\(key)\"\(lineBreak + lineBreak)")
            fieldData.append(value)
            fieldData.append(lineBreak)
        }
        
        
        print("multipartdata \(String(data: fieldData, encoding: .ascii) )")
        
        return fieldData as Data
    }
}


fileprivate struct MultipartEncoding: Encoder {
    
    /// Stores the actual strings file data during encoding.
    fileprivate final class dictData {
        private(set) var strings: [String: String] = [:]
        
        func encode(key codingKey: [CodingKey], value: String) {
            let key = codingKey.map { $0.stringValue }.joined(separator: ".")
            strings[key] = value
        }
    }
    
    fileprivate var data: dictData
    
    init(to encodedData: dictData = dictData()) {
        self.data = encodedData
    }

    var codingPath: [CodingKey] = []
    
    let userInfo: [CodingUserInfoKey : Any] = [:]
    
    func container<Key: CodingKey>(keyedBy type: Key.Type) -> KeyedEncodingContainer<Key> {
        var container = StringsKeyedEncoding<Key>(to: data)
        print("in container keyed")
        container.codingPath = codingPath
        return KeyedEncodingContainer(container)
    }
    
    func unkeyedContainer() -> UnkeyedEncodingContainer {
        var container = StringsUnkeyedEncoding(to: data)
        container.codingPath = codingPath
        return container
   }
    
    func singleValueContainer() -> SingleValueEncodingContainer {
        var container = StringsSingleValueEncoding(to: data)
        container.codingPath = codingPath
        return container
    }
}

fileprivate struct StringsKeyedEncoding<Key: CodingKey>: KeyedEncodingContainerProtocol {

    private let data: MultipartEncoding.dictData
    
    init(to data: MultipartEncoding.dictData) {
        self.data = data
    }
    
    var codingPath: [CodingKey] = []
    
    mutating func encodeNil(forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: "nil")
    }
    
    mutating func encode(_ value: Bool, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }
    
    mutating func encode(_ value: String, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value)
    }
    mutating func encode(_ value: Date, forKey key: Key) throws {
        var formatter = getDayFormatter()
        print("value is \(formatter.string(from: value))")
        data.encode(key: codingPath + [key], value:  formatter.string(from: value))
    }
    mutating func encode(_ value: Double, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }
    
    mutating func encode(_ value: Float, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }
    
    mutating func encode(_ value: Int, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }
    
    mutating func encode(_ value: Int8, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }
    
    mutating func encode(_ value: Int16, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }
    
    mutating func encode(_ value: Int32, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }
    
    mutating func encode(_ value: Int64, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }
    
    mutating func encode(_ value: UInt, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }
    
    mutating func encode(_ value: UInt8, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }
    
    mutating func encode(_ value: UInt16, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }
    
    mutating func encode(_ value: UInt32, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }
    
    mutating func encode(_ value: UInt64, forKey key: Key) throws {
        data.encode(key: codingPath + [key], value: value.description)
    }
    
    mutating func encode<T: Encodable>(_ value: T, forKey key: Key) throws {
        if T.self == Date.self{
            var formatter = getDayFormatter()
            print("value is \(formatter.string(from: value as! Date))")
            data.encode(key: codingPath + [key], value:  formatter.string(from: value as! Date))
        }else{
            var stringsEncoding = MultipartEncoding(to: data)
            stringsEncoding.codingPath.append(key)
            try value.encode(to: stringsEncoding)
        }
    }
    
    mutating func nestedContainer<NestedKey: CodingKey>(
        keyedBy keyType: NestedKey.Type,
        forKey key: Key) -> KeyedEncodingContainer<NestedKey> {
        var container = StringsKeyedEncoding<NestedKey>(to: data)
        container.codingPath = codingPath + [key]
        return KeyedEncodingContainer(container)
    }
    
    mutating func nestedUnkeyedContainer(forKey key: Key) -> UnkeyedEncodingContainer {
        var container = StringsUnkeyedEncoding(to: data)
        container.codingPath = codingPath + [key]
        return container
    }
    
    mutating func superEncoder() -> Encoder {
        let superKey = Key(stringValue: "super")!
        return superEncoder(forKey: superKey)
    }
    
    mutating func superEncoder(forKey key: Key) -> Encoder {
        var stringsEncoding = MultipartEncoding(to: data)
        stringsEncoding.codingPath = codingPath + [key]
        return stringsEncoding
    }
}

fileprivate struct StringsUnkeyedEncoding: UnkeyedEncodingContainer {

    private let data: MultipartEncoding.dictData
    
    init(to data: MultipartEncoding.dictData) {
        self.data = data
    }
    
    var codingPath: [CodingKey] = []

    private(set) var count: Int = 0
    
    private mutating func nextIndexedKey() -> CodingKey {
        let nextCodingKey = IndexedCodingKey(intValue: count)!
        count += 1
        return nextCodingKey
    }
    
    private struct IndexedCodingKey: CodingKey {
        let intValue: Int?
        let stringValue: String

        init?(intValue: Int) {
            self.intValue = intValue
            self.stringValue = intValue.description
        }

        init?(stringValue: String) {
            return nil
        }
    }

    mutating func encodeNil() throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: "nil")
    }
    
    mutating func encode(_ value: Bool) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }
    mutating func encode(_ value: Date) throws {
        let formatter = getDayFormatter()
        print("value2 is \(formatter.string(from: value))")
        data.encode(key: codingPath + [nextIndexedKey()], value: formatter.string(from: value))
    }
    mutating func encode(_ value: String) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value)
    }
    
    mutating func encode(_ value: Double) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }
    
    mutating func encode(_ value: Float) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }
    
    mutating func encode(_ value: Int) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }
    
    mutating func encode(_ value: Int8) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }
    
    mutating func encode(_ value: Int16) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }
    
    mutating func encode(_ value: Int32) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }
    
    mutating func encode(_ value: Int64) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }
    
    mutating func encode(_ value: UInt) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }
    
    mutating func encode(_ value: UInt8) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }
    
    mutating func encode(_ value: UInt16) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }
    
    mutating func encode(_ value: UInt32) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }
    
    mutating func encode(_ value: UInt64) throws {
        data.encode(key: codingPath + [nextIndexedKey()], value: value.description)
    }
    
    mutating func encode<T: Encodable>(_ value: T) throws {
        var stringsEncoding = MultipartEncoding(to: data)
        stringsEncoding.codingPath = codingPath + [nextIndexedKey()]
        try value.encode(to: stringsEncoding)
    }
    
    mutating func nestedContainer<NestedKey: CodingKey>(
        keyedBy keyType: NestedKey.Type) -> KeyedEncodingContainer<NestedKey> {
        var container = StringsKeyedEncoding<NestedKey>(to: data)
        container.codingPath = codingPath + [nextIndexedKey()]
        return KeyedEncodingContainer(container)
    }
    
    mutating func nestedUnkeyedContainer() -> UnkeyedEncodingContainer {
        var container = StringsUnkeyedEncoding(to: data)
        container.codingPath = codingPath + [nextIndexedKey()]
        return container
    }
    
    mutating func superEncoder() -> Encoder {
        var stringsEncoding = MultipartEncoding(to: data)
        stringsEncoding.codingPath.append(nextIndexedKey())
        return stringsEncoding
    }
}
fileprivate struct StringsSingleValueEncoding: SingleValueEncodingContainer {
    
    private let data: MultipartEncoding.dictData
    
    init(to data: MultipartEncoding.dictData) {
        self.data = data
    }

    var codingPath: [CodingKey] = []
    
    mutating func encodeNil() throws {
        data.encode(key: codingPath, value: "nil")
    }
    
    mutating func encode(_ value: Bool) throws {
        data.encode(key: codingPath, value: value.description)
    }
    
    mutating func encode(_ value: String) throws {
        data.encode(key: codingPath, value: value)
    }
    
    mutating func encode(_ value: Double) throws {
        data.encode(key: codingPath, value: value.description)
    }
    mutating func encode(_ value: Date) throws {
        let formatter = getDayFormatter()
        print("value3 is \(formatter.string(from: value))")
        data.encode(key: codingPath, value: formatter.string(from: value))
    }
    mutating func encode(_ value: Float) throws {
        data.encode(key: codingPath, value: value.description)
    }
    
    mutating func encode(_ value: Int) throws {
        data.encode(key: codingPath, value: value.description)
    }
    
    mutating func encode(_ value: Int8) throws {
        data.encode(key: codingPath, value: value.description)
    }
    
    mutating func encode(_ value: Int16) throws {
        data.encode(key: codingPath, value: value.description)
    }
    
    mutating func encode(_ value: Int32) throws {
        data.encode(key: codingPath, value: value.description)
    }
    
    mutating func encode(_ value: Int64) throws {
        data.encode(key: codingPath, value: value.description)
    }
    
    mutating func encode(_ value: UInt) throws {
        data.encode(key: codingPath, value: value.description)
    }
    
    mutating func encode(_ value: UInt8) throws {
        data.encode(key: codingPath, value: value.description)
    }
    
    mutating func encode(_ value: UInt16) throws {
        data.encode(key: codingPath, value: value.description)
    }
    
    mutating func encode(_ value: UInt32) throws {
        data.encode(key: codingPath, value: value.description)
    }
    
    mutating func encode(_ value: UInt64) throws {
        data.encode(key: codingPath, value: value.description)
    }
    
    mutating func encode<T: Encodable>(_ value: T) throws {
        var stringsEncoding = MultipartEncoding(to: data)
        stringsEncoding.codingPath = codingPath
        try value.encode(to: stringsEncoding)
    }
}

用法：

func imageFormField(named name: String,
                               data: Data,
                               mimeType: String) -> Data {
        var fieldData = Data()

        fieldData.append("--\(boundary)\r\n")
        fieldData.append("Content-Disposition: form-data; name=\"\(name)\";filename=\"photo.jpg\"\r\n")
        fieldData.append("Content-Type: \(mimeType)\r\n")
        fieldData.append("\r\n")
        fieldData.append(data)
        fieldData.append("\r\n")

        return fieldData as Data
    }
let encoder = MultipartEncoder()
            encoder.boundary = self.boundary
            //encoder.dateEncodingStrategy = .formatted(getDayFormatter())
            let jsondata = try encoder.encode(user)
            
            
            bodydata.append(imageFormField(named: "profileUrl", data: image, mimeType: "image/jpeg"))
            bodydata.append(jsondata)
            bodydata.append("--\(boundary)\r\n")