Convert Base64 to PNG-File and save on Ktor Backende

Question

I need to save an image from the Client App as PNG on the Backend. Im sending the Image as Base64 with Post to the Backend. I cant find a way to convert the Base64 String to an PNG File and dont know, how I could save them as File on the Server.

Thats the function I use to get the Data from the client. In val picture I get the Image as Base64.

fun savepicture(data: getpicture) =
        transaction {
            val userid= data.userid
            val date = data.date 
            val time = data.time 
            val picture= data.picture
            println("$picture")

            try {
                decodeImage(aufnahme)
            }
            catch(e: Exception) {
                println("Fehler: $e")
            }

            if (picture.isNotEmpty()) {
                return@transaction true
            }
            return@transaction  false
        }

fun decodeImage(image: String) {

        val pictureBytes = Base64.getDecoder().decode(image)
        val path = Path("Path/to/destination")
        path.writeBytes(pictureBytes)
    }

With this function i create the Base64 String. The Bitmap is created of a picture taken form the Device.

fun encodeImage(bm: Bitmap): String? {
        val baos = ByteArrayOutputStream()
        bm.compress(Bitmap.CompressFormat.PNG, 90, baos)
        val b = baos.toByteArray()
        return java.util.Base64.getEncoder().encodeToString(b)
    }

I hope someone could help me to convert and save my image.

Answer 1

You can use java.util.Base64 to decode your base64 string into bytes. Then you'll need to write the bytes into a file.

For instance:

val picture: String = "the base64 data here as a string"

// decode the base64 text into bytes
val pictureBytes = Base64.getDecoder().decode(picture)

// write the bytes to a file
val path = Path("the/path/to/the/file.png")
path.writeBytes(pictureBytes)