Formatting JSON in swift: Invalid type in JSON write (OS_dispatch_data)

Question

I am trying to send a post request to and api that contains a list of "items" that can be either an image or text.

However, I keep getting an error (listed in Title)

Here is the code turning my objects into JSON

    var json = [String: Any]()
    var jsonItems = [Any]()

    for i in 0...(items.count - 1){

        var it = [String: Any]()
        if let imageData = items[i].image?.jpgData(){
            it["image"] = imageData
        }

        if let text = items[i].text{
            it["text"] = text
        }

        if i == 0 {
            it["is_profile"] = true
            it["face_detected"] = faceDetected
        }

        jsonItems.append(it)
    }
    json["items"] = jsonItems

Is there any reason why this would not be formatted correctly?

EDIT:

The jpgData function

func jpgData() -> Data? {
    return UIImageJPEGRepresentation(self, 0.8)
}

Example code that causes crash:

extension Dictionary {
    var json: String {
        let invalidJson = "Not a valid JSON"
        do {
            let jsonData = try JSONSerialization.data(withJSONObject: self, options: .prettyPrinted)
            return String(bytes: jsonData, encoding: String.Encoding.utf8) ?? invalidJson
        } catch {
            return invalidJson
        }
    }
}

In addition to my sample code, passing the created dict as the param for Alamofire requests, URLSession requests, etc all cause a crash with the error from the title

EDIT: Solution Image data did need to be encoded. Feels so obvious in hindsight. Base64 encoding worked for printing out the structure like in my extension, but for network requests I ended up using Alamofire's MultipartFormData class (a custom wrapper around it) and appended as an application/octet-stream for the mimetype. Wish I could use a facepalm emoji here. I accepted one of the two answers that talked about encoding that actually had sample code.

JSON doesn't support raw data. You will need to convert your image data to base64encodedString to be able to send it in your json — Leo Dabus, Sep 07 '18 at 02:31
@daredevil1234 The code you posted does not give an error. And the code you posted doesn't do any JSON processing, it just builds a dictionary. Update your question with the code that actually gives the error. — rmaddy, Sep 07 '18 at 02:58

score 1 · Accepted Answer · answered Sep 07 '18 at 12:18

1

After converting to JPEG Data try encoding to base64

let strBase64 = imageData.base64EncodedString(options: .lineLength64Characters)

Check this answer for more info Convert between UIImage and Base64 string

answered Sep 07 '18 at 12:18

DionizB

1,487
2
10
20

score 0 · Answer 2 · answered Sep 07 '18 at 11:05

0

A Data cannot be put into JSON. The Data object will have to be encoded. Probably using base64 encoding.

answered Sep 07 '18 at 11:05

Daniel T.

32,821
6
50
72

Formatting JSON in swift: Invalid type in JSON write (OS_dispatch_data)

2 Answers2