Simple multipart file add for Swift

I imagine that you’ve got already heard in regards to the well-known multipart-data add method that everybody likes to add information and submit kind information, but when not, hopefully this text will assist you a bit of bit to know this stuff higher.

Let’s begin with some principle. Don’t fret, it is only one hyperlink, in regards to the multipart/form-data content material sort specification. To rapidly summarize it first I might wish to let you know a number of 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 way and as a response you may get again a standing code, some headers and perhaps some type of response information too. 🥜

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

The request methodology & URL is fairly easy, the fascinating half is if you specify the Content material-Sort 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 best way every half can have it is personal sort 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 principle for now, let me snow you ways we are able to implement all of this utilizing Swift 5. To start with, we wish to have the ability to append string values to a Information object, so we’ll lengthen Information sort 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 {
            return
        }
        append(information)
    }
}

Subsequent, we want one thing that may assemble the HTTP multipart physique information, for this function 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 personal strategies will assist to assemble all the pieces, we merely append string values to the personal information object that holds our information construction. The general public API solely consists of two add capabilities that you should use to append a key-value based mostly kind area or a whole file utilizing its information. 👍

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

    public init(boundary: String = UUID().uuidString) {
        self.boundary = boundary
        self.information = .init()
    }
    
    personal mutating func appendBoundarySeparator() {
        information.append("--(boundary)(separator)")
    }
    
    personal mutating func appendSeparator() {
        information.append(separator)
    }

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

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

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

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

    public var httpBody: Information {
        var bodyData = information
        bodyData.append("--(boundary)--")
        return bodyData
    }
}

The final remaining two public variables are helpers to simply get again the HTTP associated content material sort header worth utilizing the right boundary and the entire information object that you must 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)
}

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


let url = URL(string: "https://httpbin.org/put up")!
var request = URLRequest(url: url)
request.httpMethod = "POST"
request.setValue(multipart.httpContentTypeHeadeValue, forHTTPHeaderField: "Content material-Sort")
request.httpBody = multipart.httpBody


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

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

As you’ll be able to see it is comparatively easy, you simply add the shape fields and the information that you simply need to add, and get again the HTTP associated values utilizing the helper API. I hope this text will assist you to simulate kind submissions utilizing multipart requests with out problem. 😊