iOS Development

Simple multipart file add for Swift

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I consider that you have already heard concerning the well-known multipart-data add method that everybody likes to add recordsdata and submit kind information, but when not, hopefully this text will enable you slightly bit to grasp this stuff higher.

Let’s begin with some concept. Don’t fret, it is only one hyperlink, concerning the multipart/form-data content material kind specification. To rapidly summarize it first I might prefer to inform you just a few phrases about how the HTTP layer works. In a nutshell, you ship some information with some headers (give it some thought as a key-value consumer data object) to a given URL utilizing a technique and as a response you will get again a standing code, some headers and possibly some kind of response information too. 🥜

  • HTTP request = Technique + URL + Headers + Physique (request information)
  • HTTP response = Standing code + Headers + Physique (response information)

The request methodology & URL is fairly easy, the attention-grabbing half is once you specify the Content material-Kind HTTP header, in our case the multipart/form-data;boundary="xxx" worth means, that we’ll ship a request physique utilizing a number of elements and we’ll use the “xxx” boundary string as a separator between the elements. Oh, by the way in which every half can have it is personal kind and title, we’ll use the Content material-Disposition: form-data; title="field1" line to let the server learn about these fields, earlier than we really ship the precise content material worth.

That is greater than sufficient concept for now, let me snow you the way we will implement all of this utilizing Swift 5. Initially, we want to have the ability to append string values to a Information object, so we’ll lengthen Information kind with an ‘append string utilizing encoding’ methodology:

import Basis

public extension Information {

    mutating func append(
        _ string: String,
        encoding: String.Encoding = .utf8
    ) {
        guard let information = string.information(utilizing: encoding) else {

Subsequent, we’d like one thing that may assemble the HTTP multipart physique information, for this objective we’ll construct a MultipartRequest object. We are able to set the boundary once we init this object and we’ll append the elements wanted to assemble the HTTP physique information.

The non-public strategies will assist to assemble every little thing, we merely append string values to the non-public information object that holds our information construction. The general public API solely consists of two add capabilities that you should utilize to append a key-value primarily based kind area or a whole file utilizing its information. 👍

public struct MultipartRequest {
    public let boundary: String
    non-public let separator: String = "rn"
    non-public var information: Information

    public init(boundary: String = UUID().uuidString) {
        self.boundary = boundary
        self.information = .init()
    non-public mutating func appendBoundarySeparator() {
    non-public mutating func appendSeparator() {

    non-public func disposition(_ key: String) -> String {
        "Content material-Disposition: form-data; title="(key)""

    public mutating func add(
        key: String,
        worth: String
    ) {
        information.append(disposition(key) + separator)
        information.append(worth + separator)

    public mutating func add(
        key: String,
        fileName: String,
        fileMimeType: String,
        fileData: Information
    ) {
        information.append(disposition(key) + "; filename="(fileName)"" + separator)
        information.append("Content material-Kind: (fileMimeType)" + separator + separator)

    public var httpContentTypeHeadeValue: String {
        "multipart/form-data; boundary=(boundary)"

    public var httpBody: Information {
        var bodyData = information
        return bodyData

The final remaining two public variables are helpers to simply get again the HTTP associated content material kind header worth utilizing the right boundary and the entire information object that you need to to ship to the server. Here is how one can assemble the HTTP URLRequest utilizing the multipart struct.

var multipart = MultipartRequest()
for area in [
    "firstName": "John",
    "lastName": "Doe"
] {
    multipart.add(key: area.key, worth: area.worth)

    key: "file",
    fileName: "pic.jpg",
    fileMimeType: "picture/png",
    fileData: "fake-image-data".information(utilizing: .utf8)!

let url = URL(string: "")!
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.setValue(multipart.httpContentTypeHeadeValue, forHTTPHeaderField: "Content material-Kind")
request.httpBody = multipart.httpBody

let (information, response) = strive await URLSession.shared.information(for: request)

print((response as! HTTPURLResponse).statusCode)
print(String(information: information, encoding: .utf8)!)

As you possibly can see it is comparatively easy, you simply add the shape fields and the recordsdata that you simply wish to add, and get again the HTTP associated values utilizing the helper API. I hope this text will enable you to simulate kind submissions utilizing multipart requests with out problem. 😊

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