Can't make post request using params as dictionary with Swift 4 & Alamofire - swift

Question

I'm trying to learn to call API with/without library. But the problem here confuses me.
I have params like this:
let parameters: [String:String] =
["key":"MY_KEY" ,
"q":sourceText,
"source": sourceLanguage),
"target": target)]
let headers: HTTPHeaders = [ "Content-type": "application/json"]
I make a post call like this:
Alamofire.request(urlString, method: HTTPMethod.post, parameters: parameters, headers: headers)
.responseJSON{ response in
guard response.result.error == nil else {
print("error calling POST on /todos/1")
print(response.result.error!)
return
}
// make sure we got some JSON since that's what we expect
guard let json = response.result.value as? [String: Any] else {
print("didn't get todo object as JSON from API")
print("Error: \(response.result.error)")
return
}
By this I get an error 403, saying that I do not have a valid API key (I tested the key with postman, and it is okay).
After many efforts, I have to change the code like this
let stringparams = "key=MY_KEY&q=\(sourceText)&source=\(sourceLanguage)&target=\(target)"
request.httpBody = stringparams.data(using: String.Encoding.utf8)
and using this: Alamofire.request(request)
it works!
I'm using Google Cloud Translation api. And the web use a REST api as said here: https://cloud.google.com/translate/docs/reference/translate
So why can't I use params as dictionary, but using the string (like formdata) will work here?
My guess is Alamofire didn't make the right BODY for the request from the parameters because other arguments is okay. But I don't know why.
And I think Google should accept a json params as they mentioned, in stead of using form data? I did try the original method, but it didn't work with JSON.

Answer 1

From what actually works for you it looks like you need to encode the parameters in the same style as a query. Try this:
struct ParameterQueryEncoding: ParameterEncoding {
func encode(_ urlRequest: URLRequestConvertible, with parameters: Parameters?) throws -> URLRequest {
var request = try urlRequest.asURLRequest()
request.httpBody = parameters?
.map { "\($0)=\($1)" }
.joined(separator: "&")
.data(using: .utf8)
return request
}
}
You should then be able to perform the original call that you had before:
Alamofire.request(urlString,
method: HTTPMethod.post,
parameters: parameters,
encoding: ParameterQueryEncoding(),
headers: headers)
.responseJSON { response in
...
}

Answer 2

Try by using JSON encoding. Make sure you have removed ) from dictionary.
Alamofire.request(URL, method: method, parameters: parameters, encoding: JSONEncoding.default, headers: headers)