(iOS / Swift) Simple Post Request with Key-Value Failed, But Succeeded using Postman

Question

I created a simple POST Request using Postman and it succeeded. This is the screenshot of the body and response

This is the screenshot of the header in Postman

Now I am creating a POST request in iOS app using Swift. This is the code:

public func getResultItem(url: URL, _ completion:@escaping (ResultItem?, Error?) -> Void){
    let parameter = ["uname":"21120113120038", "pass":"123456"]

    var request = URLRequest(url: url)
    request.httpMethod = "POST"
    request.setValue("application/x-www-form-urlencoded", forHTTPHeaderField:"Content-Type")
    guard let httpBody = try? JSONSerialization.data(withJSONObject: parameter, options: []) else {return}
    request.httpBody = httpBody

    URLSession.shared.dataTask(with: request) { (data, response, error) in
        var resultItem: ResultItem?

        guard let data = data else {
            completion(resultItem, error)
            return
        }

        do {
            resultItem = try JSONDecoder().decode(ResultItem.self, from: data)
            completion(resultItem, error)
        } catch let error as NSError{
            completion(resultItem, error)
        }
    }.resume()
}

The problem is, the "data" from dataTask completion handler is always 0 byte. Looks like my request is not valid so it is not returning the JSON. Since the data is 0 byte, the "do" block always fail when decoding the JSON, and turn to "catch" block. The error.description in this "catch" block here is -> 'The given data was not valid JSON'.

Which part of my code is wrong? My first assumption is there was a problem with the request. Maybe the parameter or the httpbody request is wrong, but I don't know how to fix it.

Thanks

https://stackoverflow.com/questions/31937686/how-to-make-http-post-request-with-json-body-in-swift — Paulw11, Oct 28 '19 at 08:11
@Paulw11 the code in the link you provided is almost identical with mine — Aji Saputra Raka Siwi, Oct 28 '19 at 08:47
Yes, almost. You will notice that you should be specifying application/json as the content type — Paulw11, Oct 28 '19 at 08:49

score 1 · Accepted Answer · answered Oct 28 '19 at 08:35

Your content type is application/x-www-form-urlencoded, but you're setting the body as JSON instead of URL-encoded parameters. The way your HTTP body looks with the way you have it now is something like:

{"uname":"21120113120038","pass":"123456"}

...but you want it to look like this:

uname=21120113120038&pass=123456

So, replace this line:

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

...with something like this:

guard let httpBody = parameter.map({
    [$0.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? "",
     $1.addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? ""].joined(separator: "=")
}).joined(separator: "&").data(using: .utf8) else { return }

(However, I think that's a bit messy, so here are some extensions to clean it up somewhat:)

extension String {
    var urlEncodedQueryKeyOrValue: String {
        return addingPercentEncoding(withAllowedCharacters: .alphanumerics) ?? ""
    }
}

extension Dictionary where Key == String, Value == String {
    var wwwFormURLEncodedString: String {
        return map { "\($0.urlEncodedQueryKeyOrValue)=\($1.urlEncodedQueryKeyOrValue)" }.joined(separator: "&")
    }
}

And then you'd use it like this:

[...]
guard let httpBody = parameter.wwwFormURLEncodedString.data(using: .utf8) else { return }
request.httpBody = httpBody
[...]

(iOS / Swift) Simple Post Request with Key-Value Failed, But Succeeded using Postman

1 Answers1