Date decoding in URL query parameters

[letatas]

Hello, I am trying to retrieve a date from a query parameter encoded in IS8601:

/resources?since=2020-08-18T12:00:00

Unfortunately it seems that the Date in this format is not recognized.

Steps to reproduce

Create a new project vapor new date-issue
In the routes.swift add these lines :

app.get("resources") { req -> String in
    let date = req.query[Date.self, at: "since"]
    return date.debugDescription
}

Run the project, and in your terminal, call:

curl "127.0.0.1:8080/resources?since=2020-08-18T12:00:00"

Expected behavior

I would expect date to be nil only when the parameter since is absent or badly formatted. I expect date to contain the IS8601 decoded value of the since parameter.

Actual behavior

Whatever the parameter since is populated or not, date is always nil, even when a correctly encoded date is set.

Environment

• Vapor Framework version: 4.29.0
• Vapor Toolbox version: 12.2.2
• OS version: macOS Catalina 10.15.6 (19G2021)

[avario]

I think for URL encoded parameters the default date decoding strategy is secondsSince1970 not iso8601. You can change this by modifying the ContentConfiguration.

let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601

ContentConfiguration.global.use(decoder: decoder, for: .urlEncodedForm)

See: https://docs.vapor.codes/4.0/content/#override-defaults

[letatas]

Thanks @avario for your answer. Unfortunately, I didn't manage to make it work. I set the content configuration in the configure method, but the route still returns nil 🤷‍♂️

[avario]

@letatas Sorry, it should look like this for what you want:

let decoder = URLEncodedFormDecoder(configuration: .init(dateDecodingStrategy: .iso8601))
ContentConfiguration.global.use(urlDecoder: decoder)

[Craz1k0ek]

According to Swift, the date you're passing is invalid. As an example using an example struct.

struct Example: Codable {
    let date: Date
}

First we'll try to decode the time string you provide.

let input = "{\"date\": \"2020-08-18T12:00:00\"}".data(using: .utf8)!
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .iso8601

do {
    let e = try decoder.decode(Example.self, from: input)
    print(e)
} catch {
    print(error)
}

You can see how the JSON object is created. This will always print an error.

dataCorrupted(Swift.DecodingError.Context(codingPath: [CodingKeys(stringValue: "date", intValue: nil)], debugDescription: "Expected date string to be ISO8601-formatted.", underlyingError: nil))

So clearly, Swift doesn't understand what you're providing. So, what is it Swift does expect. Well, let's try the other way around.

let formatter = DateFormatter()
formatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss"
let date = formatter.date(from: "2020-08-18T12:00:00")!

let encoder = JSONEncoder()
encoder.dateEncodingStrategy = .iso8601

do {
    let e = Example(date: date)
    let output = try encoder.encode(e)
} catch {
    print(error)
}

If we were to print output as String, we would get

{"date":"2020-08-18T10:00:00Z"}

This might seem a bit odd, but I'm in a different time zone, which is automatically adjusted. This does however show your problem, you're missing the Z at the end.

So fixing your issue, replace the time you're providing with 2020-08-18T10:00:00Z and it should work!
Note: ISO 8601 also specifies a standard using the fractional seconds, which isn't supported by default either. You can use below extension if you were to need it.

extension JSONDecoder.DateDecodingStrategy {
    
    /// The strategy that formats dates according to the ISO 8601 standard.
    /// - Note: This includes the fractional seconds, unlike the standard `.iso8601`, which fails to decode those.
    static var iso8601withFractionalSeconds: JSONDecoder.DateDecodingStrategy {
        JSONDecoder.DateDecodingStrategy.custom { (decoder) in
            let singleValue = try decoder.singleValueContainer()
            let dateString  = try singleValue.decode(String.self)
            let formatter = ISO8601DateFormatter()
            formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
            
            guard let date = formatter.date(from: dateString) else {
                throw DecodingError.dataCorruptedError(in: singleValue, debugDescription: "Failed to decode string to ISO 8601 date.")
            }
            return date
        }
    }
    
}

[seriyvolk83]

avario's answer is correct, but in case you need a custom decoder, then you can use the following:

        let f = DateFormatter()
        f.dateFormat = "yyyy-MM-dd" 

        // Date encoder for GET parameters
        ContentConfiguration.global.use(urlDecoder: URLEncodedFormDecoder.createDateDecoder(formatter: f))

...

extension URLEncodedFormDecoder {
    
    /** Creates decoder with custom date formatter
     - Parameter formatter: the formatter
     
     Example:
     ```
     let f = DateFormatter()
     f.dateFormat = "yyyy-MM-dd"
     
     // Date encoder for GET parameters
     ContentConfiguration.global.use(urlDecoder: URLEncodedFormDecoder.createDateDecoder(formatter: f))
     ```
     */
    static func createDateDecoder(formatter: DateFormatter) -> URLQueryDecoder {
        let urlDecoder: URLQueryDecoder = URLEncodedFormDecoder(configuration: .init(dateDecodingStrategy: .custom({ (d: Decoder) -> Date in
            let string = try d.singleValueContainer().decode(String.self)
            if let date = formatter.date(from: string) {
                return date
            }
            throw Abort(HTTPResponseStatus.badRequest)
        })))
        return urlDecoder
    }
}

[0xTim]

Closing as the answer is #2481 (comment)