Getting bad request error with alamofire JSON request - json

Question

I have been converting this curl syntax
curl -L -X POST 'https://driver-vehicle-licensing.api.gov.uk/vehicleenquiry/v1/vehicles' \-H 'x-api-key: REPLACE WITH YOUR API KEY' \-H 'Content-Type: application/json' \-d '{"registrationNumber": "TE57VRN"}'
into Swift with Alamofire and have got this syntax
guard let url = URL(string: "https://driver-vehicle-licensing.api.gov.uk/vehicle-enquiry/v1/vehicles") else { return }
let headers : HTTPHeaders = [
"x-api-key": "mykey",
"Content-Type": "application/json"
]
let params: Parameters = [
"registrationNumber" : "myreg"
]
AF.request(url, method: .post, parameters: params, encoding: URLEncoding(destination: .httpBody), headers: headers).responseJSON(completionHandler: { response in
print(response)
})
However, I have got the output
success({
errors = (
{
code = ENQ103;
detail = "Invalid format for field - vehicle registration number";
status = 400;
title = "Bad Request";
}
);
Please could someone explain what I have done wrong. Thanks

Answer 1

The API expects the parameters to be sent as JSON, but you are sending as URL encoded.
Try using JSONParameterEncoder.default as the encoder instead of URL encoding.
Check Usage from the docs: POST request with JSON Parameters
let parameters: Parameters = [
"registrationNumber" : "myreg"
]
AF.request(url, method: .post, parameters: parameters, encoder: JSONParameterEncoder.default)

Answer 2

You have a working curl command, small (or big) tip: AlamoFire can print the request as a curl command!
In "one step":
AF.request(url, method: .post,
parameters: params,
encoding: URLEncoding(destination: .httpBody),
headers: headers)
.cURLDescription(calling: { curlCommand in
print("curlCommand1: \(curlCommand)")
}).responseJSON(completionHandler: { response in
print(response)
})
In "two steps", if you prefer to separate your calls and not chain them all:
let request = AF.request(url, method: .post,
parameters: params,
encoding: URLEncoding(destination: .httpBody),
headers: headers)
request.cURLDescription { curlCommand in
print("curlCommand2: \(curlCommand)")
}
request.responseJSON(completionHandler: { response in
print(response)
})
And you should have output:
curl -v \
-X POST \
-H "Accept-Encoding: br;q=1.0, gzip;q=0.9, deflate;q=0.8" \
-H "User-Agent: Alamofired/1.0 (...; build:1; iOS 14.5.0) Alamofire/5.4.0" \
-H "Accept-Language: en;q=1.0, fr-US;q=0.9" \
-H "Content-Type: application/json" \
-H "x-api-key: mykey" \
-d "registrationNumber=myreg" \
"https://driver-vehicle-licensing.api.gov.uk/vehicle-enquiry/v1/vehicles"
Now, if we compare with yours:
curl \
-L \
-X POST \
'https://driver-vehicle-licensing.api.gov.uk/vehicleenquiry/v1/vehicles' \
-H 'x-api-key: REPLACE WITH YOUR API KEY' \
-H 'Content-Type: application/json' \
-d '{"registrationNumber": "TE57VRN"}'
I added some \ to make it sill valid...
We shouldn't care about the order, the "Accept-Language", "User-Agent", "Accept-Encoding" headers that are added with Alamofire shouldn't be an issue.
Try your command with no -L parameter maybe to check if it's "important" (if it's --location).
And then, the difference is with the data paramater (-d). Once is JSON, the other is URL encoded.
Then, let's see your code, and URLEncoding(destination: .httpBody)
might be the culprit. Using JSONEncoding.default instead will work.
Now, if you didn't have had the curl command, just by seeing your code, I spotted it. If you think about it:
You are saying there that you will provide the parameter in body following the JSON protocol.
let headers : HTTPHeaders = ["Content-Type": "application/json"]
And later, you used URL Encoding protocol.
URLEncoding(destination: .httpBody)
Doesn't make sense, right? You're contradicting yourself.