How to crop file content string on string slices swift? - ios

Question

I'm trying to crop string on slices and send them to the server. Let’s take an example: I have file with such size of its string - 813753. I have to crop it on slices with max size 10000.All below code will be in file picker function:
func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]) {
let file = urls[0]
do{
let fileData = try Data.init(contentsOf: file.absoluteURL)
let encodedString = String.init(data: fileData, encoding: .isoLatin1)!
let fileName = file.lastPathComponent
let time = Int64(NSDate().timeIntervalSince1970)
}
}
At the beginning after selection I figure out whether file has result of division >0:
let sliceCounts = encodedString.count%10000 > 0 ? encodedString.count/10000 + 1 : encodedString.count/10000
then in loop I'm trying to get file content slices:
for slice in 0...sliceCounts{
let partSize = slice*10000
let content = encodedString.count%10000 > 0 && partSize >= encodedString.count
? substring(from: partSize - 10000, to: encodedString.count, s:
encodedString) : substring(from: partSize, to: partSize+10000, s: encodedString)
}
I use such method for getting file part:
func substring(from : Int, to : Int, s : String) -> String {
let start = s.index(s.startIndex, offsetBy: from)
let end = s.index(s.startIndex, offsetBy: to)
return String(s[start..<end])
}
And the problem is that I receive such error:
Fatal error: String index is out of bounds: file Swift/StringCharacterView.swift, line 60
It happens when I'm trying to get the last slice. I think the problem is connected with this condition :
encodedString.count%10000 > 0 && partSize >= encodedString.count
and also I think that maybe I have some problems with sending indexes to my method, due to the error. Maybe someone will see where I make a mistake and will help :)

Answer 1

I see a few issues in your for loop, first you loop one iteration to much and secondly for the end of the string you need to consider that the last chunk might be smaller.
for slice in 0..<sliceCounts {
let partSize = slice * maxSize
let content: String
if partSize + maxSize > encodedString.count {
content = String(encodedString.suffix(encodedString.count - partSize))
} else {
content = encodedString.count%maxSize > 0 && partSize >= encodedString.count
? substring(from: partSize - maxSize, to: encodedString.count, s:
encodedString) : substring(from: partSize, to: partSize+maxSize, s: encodedString)
}
}
Note that I used a constant maxSize instead of a hardcoded value in my code