[SWIFT4] JSON Decoding fails to parse all valid date-time values

Created by: grEvenX

Description

The OpenAPI 3.0 specification specifies that string with format: date-time should match the definition of date-time specified in https://xml2rfc.ietf.org/public/rfc/html/rfc3339.html#anchor14.

The current implementation only handles date-time values that contains micro-seconds, which is per the RFC optional. The Swift 4 version of the library should support all valid date-time values.

openapi-generator version

3.1.2

OpenAPI declaration file content or url

https://gist.github.com/grEvenX/089a8c9ecf029560299523ff048cfd5b

Command line used for generation

docker run --rm -v $(pwd)/generated:/out openapitools/openapi-generator-cli:latest generate -I https://gist.githubusercontent.com/grEvenX/089a8c9ecf029560299523ff048cfd5b/raw/375e5a1759d3a92edab2060d08ecf0650ba8d177/example-openapi-datetime.yaml -g swift4 -o /out/swift4

Steps to reproduce

1. Generate Swift4 client
2. Use the generated client with a GET request containing model with date-time format
3. Have the server/stub return a time in date-time format without microseconds (e.g. 2018-04-30T00:00:00+00:00)
4. Run the code, the client will crash due to not being able to decode the time properly

Suggest a fix/enhancement

Currently there is a CodableHelper.swift class generated that is used in decoding JSON. This class opens up for providing your own DateFormatter used for parsing the dates and also provides a default code if the date formatter is not set. The default one provided by openapi-generator should support date-time with and without microseconds, and I think we could by default set the dataformatter to an instance of a class that we can provide, e.g. a new class OpenAPIDateFormatter which can handle this case.

I've worked around this issue by specifying my own implementation of the DateFormatter with the following code:

import Foundation

class OpenAPIDateFormatter: DateFormatter {
    override init() {
        super.init()
        
        self.calendar = Calendar(identifier: .iso8601)
        self.locale = Locale(identifier: "en_US_POSIX")
        self.timeZone = TimeZone(secondsFromGMT: 0)
        self.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZZZZZ"
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func date(from string: String) -> Date? {
        if let validDate = super.date(from: string) {
            return validDate
        }
        
        // first parse-attempt failed, try parsing date without micro-seconds
        let newFormatter = self.copy() as! DateFormatter
        newFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ssZZZZZ"
        return newFormatter.date(from: string)
    }
}