Swift base64 decoding returns nil - ios

Question

I am trying to decode a base64 string to an image in Swift using the following code:
let decodedData=NSData(base64EncodedString: encodedImageData, options: NSDataBase64DecodingOptions.IgnoreUnknownCharacters)
Unfortunately, the variable decodedData turns out to have a value of nil
Debugging through the code, I verified that the variable encodedImageData is not nil and is the correct encoded image data(verified by using an online base64 to image converter). What could possibly be the reason behind my issue?

Answer 1

This method requires padding with “=“, the length of the string must be multiple of 4.
In some implementations of base64 the padding character is not needed for decoding, since the number of missing bytes can be calculated. But in Fundation's implementation it is mandatory.
Updated:
As noted on the comments, it's a good idea to check first if the string lenght is already a multiple of 4. if encoded64 has your base64 string and it's not a constant, you can do something like this:
Swift 2
let remainder = encoded64.characters.count % 4
if remainder > 0 {
encoded64 = encoded64.stringByPaddingToLength(encoded64.characters.count + 4 - remainder,
withPad: "=",
startingAt: 0)
}
Swift 3
let remainder = encoded64.characters.count % 4
if remainder > 0 {
encoded64 = encoded64.padding(toLength: encoded64.characters.count + 4 - remainder,
withPad: "=",
startingAt: 0)
}
Swift 4
let remainder = encoded64.count % 4
if remainder > 0 {
encoded64 = encoded64.padding(toLength: encoded64.count + 4 - remainder,
withPad: "=",
startingAt: 0)
}
Updated one line version:
Or you can use this one line version that returns the same string when its length is already a multiple of 4:
encoded64.padding(toLength: ((encoded64.count+3)/4)*4,
withPad: "=",
startingAt: 0)

Answer 2

When the number of characters is divisible by 4, you need to avoid padding.
private func base64PaddingWithEqual(encoded64: String) -> String {
let remainder = encoded64.characters.count % 4
if remainder == 0 {
return encoded64
} else {
// padding with equal
let newLength = encoded64.characters.count + (4 - remainder)
return encoded64.stringByPaddingToLength(newLength, withString: "=", startingAtIndex: 0)
}
}

Answer 3

(Swift 3)
I been in this situation, Trying to get the data using base64 encoded string returns nil with me when I used this line
let imageData = Data(base64Encoded: strBase64, options: .ignoreUnknownCharacters)
Tried padding the string and didn't work out too
This is what worked with me
func imageForBase64String(_ strBase64: String) -> UIImage? {
do{
let imageData = try Data(contentsOf: URL(string: strBase64)!)
let image = UIImage(data: imageData)
return image!
}
catch{
return nil
}
}

Answer 4

Check the content of your decodedData variable and look for this prefix "data:image/png;base64", I had this issue and noticed that my String base64 had a prefix like this, so I used this approached and it worked
extension String {
func getImageFromBase64() -> UIImage? {
guard let url = URL(string: self) else {
return nil
}
do {
let data = try Data(contentsOf: url)
return UIImage(data: data)
} catch {
return nil
}
}
}

Answer 5

This helped me:
extension String {
func fromBase64() -> String? {
guard let data = Data(base64Encoded: self.replacingOccurrences(of: "_", with: "="), options: Data.Base64DecodingOptions(rawValue: 0)) else {
return nil
}
return String(data: data, encoding: .utf8)
}
}
Usage:
print(base64EncodedString.fromBase64())

Answer 6

Another one-line version:
let length = encoded64.characters.count
encoded64 = encoded64.padding(toLength: length + (4 - length % 4) % 4, withPad: "=", startingAt: 0)

Answer 7

It's make problem with special character, but an interesting point is if we use NSData and NSString then it's working fine.
static func decodeBase64(input: String)->String{
let base64Decoded = NSData(base64Encoded: input, options: NSData.Base64DecodingOptions(rawValue: 0))
.map({ NSString(data: $0 as Data, encoding: String.Encoding.utf8.rawValue) })
return base64Decoded!! as String
}

Answer 8

You can use this extension to make sure that the string has the correct length fro decoding with Foundation (divisible by 4):
extension String {
var paddedForBase64Decoding: String {
appending(String(repeating: "=", count: (4 - count % 4) % 4))
}
}
Usage:
Data(base64Encoded: base64String.paddedForBase64Decoding)