How to Send Post Parameters in Swift

HTTP Request in Swift with POST method

The key is that you want to:

set the httpMethod to POST;
optionally, set the Content-Type header, to specify how the request body was encoded, in case server might accept different types of requests;
optionally, set the Accept header, to request how the response body should be encoded, in case the server might generate different types of responses; and
set the httpBody to be properly encoded for the specific Content-Type; e.g. if application/x-www-form-urlencoded request, we need to percent-encode the body of the request.

E.g., in Swift 3 and later you can:

let url = URL(string: "https://httpbin.org/post")!
var request = URLRequest(url: url)
request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField: "Content-Type")
request.setValue("application/json", forHTTPHeaderField: "Accept")
request.httpMethod = "POST"
let parameters: [String: Any] = [
    "id": 13,
    "name": "Jack & Jill"
]
request.httpBody = parameters.percentEncoded()

let task = URLSession.shared.dataTask(with: request) { data, response, error in
    guard 
        let data = data, 
        let response = response as? HTTPURLResponse, 
        error == nil 
    else {                                                               // check for fundamental networking error
        print("error", error ?? URLError(.badServerResponse))
        return
    }
    
    guard (200 ... 299) ~= response.statusCode else {                    // check for http errors
        print("statusCode should be 2xx, but is \(response.statusCode)")
        print("response = \(response)")
        return
    }
    
    // do whatever you want with the `data`, e.g.:
    
    do {
        let responseObject = try JSONDecoder().decode(ResponseObject<Foo>.self, from: data)
        print(responseObject)
    } catch {
        print(error) // parsing error
        
        if let responseString = String(data: data, encoding: .utf8) {
            print("responseString = \(responseString)")
        } else {
            print("unable to parse response as string")
        }
    }
}

task.resume()

Where the following extensions facilitate the percent-encoding request body, converting a Swift Dictionary to a application/x-www-form-urlencoded formatted Data:

extension Dictionary {
    func percentEncoded() -> Data? {
        map { key, value in
            let escapedKey = "\(key)".addingPercentEncoding(withAllowedCharacters: .urlQueryValueAllowed) ?? ""
            let escapedValue = "\(value)".addingPercentEncoding(withAllowedCharacters: .urlQueryValueAllowed) ?? ""
            return escapedKey + "=" + escapedValue
        }
        .joined(separator: "&")
        .data(using: .utf8)
    }
}

extension CharacterSet { 
    static let urlQueryValueAllowed: CharacterSet = {
        let generalDelimitersToEncode = ":#[]@" // does not include "?" or "/" due to RFC 3986 - Section 3.4
        let subDelimitersToEncode = "!$&'()*+,;="
        
        var allowed: CharacterSet = .urlQueryAllowed
        allowed.remove(charactersIn: "\(generalDelimitersToEncode)\(subDelimitersToEncode)")
        return allowed
    }()
}

And the following Decodable model objects facilitate the parsing of the application/json response using JSONDecoder:

// sample Decodable objects for https://httpbin.org

struct ResponseObject<T: Decodable>: Decodable {
    let form: T    // often the top level key is `data`, but in the case of https://httpbin.org, it echos the submission under the key `form`
}

struct Foo: Decodable {
    let id: String
    let name: String
}

This checks for both fundamental networking errors as well as high-level HTTP errors. This also properly percent escapes the parameters of the query.

Note, I used a name of Jack & Jill, to illustrate the proper x-www-form-urlencoded result of name=Jack%20%26%20Jill, which is “percent encoded” (i.e. the space is replaced with %20 and the & in the value is replaced with %26).

See previous revision of this answer for Swift 2 rendition.

Swift 5, make http post request

Below is the code for Post Method,using URLSession

let Url = String(format: "http://10.10.10.53:8080/sahambl/rest/sahamblsrv/userlogin")
    guard let serviceUrl = URL(string: Url) else { return }
    let parameters: [String: Any] = [
        "request": [
                "xusercode" : "YOUR USERCODE HERE",
                "xpassword": "YOUR PASSWORD HERE"
        ]
    ]
    var request = URLRequest(url: serviceUrl)
    request.httpMethod = "POST"
    request.setValue("Application/json", forHTTPHeaderField: "Content-Type")
    guard let httpBody = try? JSONSerialization.data(withJSONObject: parameters, options: []) else {
        return
    }
    request.httpBody = httpBody
    request.timeoutInterval = 20
    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()
}