Crashalot Crashalot - 6 months ago 60
iOS Question

Encoding UIImage to Base64 string not working when transferred to server

Encoding an UIImage as a Base64 string works on the device, but transferring the string to the server somehow corrupts the string and prevents the server from successfully decoding the image.

Any suggestions on the problem?

// Define params
params["thumbnail_base64"] = imageToBase64(blockSet.thumbnailURL)
...

// Convert params -> query string
let postString = buildQueryString(params)

// Define upload URL
let uploadURL = NSURL(string: RootURL + UploadFilePath)!

// Hit server
let request = NSMutableURLRequest(URL: uploadURL)
request.HTTPMethod = "POST"
request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
...

private func buildQueryString(parameters: [String:String], omitQuestionMark: Bool = false) -> String {
var urlVars = [String]()
for (k, var v) in parameters {
v = v.stringByAddingPercentEncodingWithAllowedCharacters(NSCharacterSet.URLQueryAllowedCharacterSet())!
urlVars += [k + "=" + "\(v)"]
}
return ((urlVars.isEmpty || omitQuestionMark) ? "" : "?") + urlVars.joinWithSeparator("&")
}


private func imageToBase64(filename: String) -> String {
// Get image path
let imagePath = getFilePath(filename)

// Convert image to base64 or return empty string
if let imageData = NSData(contentsOfFile: imagePath) {
let base64String = imageData.base64EncodedStringWithOptions(.EncodingEndLineWithLineFeed)
return base64String
} else {
printError("Error converting image to Base64: missing image. Filename: \(filename)")
return ""
}
}

Answer

The problem is with the queryString, base64 is long text with many characters, let JSON do the work for you

Use the next (with some example of NodeJS)

  let params = NSMutableDictionary();
  //you can only set `serializable` values
  params.setValue(imageToBase64(),forKey:"base64")
  params.setValue(username,forKey:"username")
  params.setValue(["array","of","string"],forKey:"arr")

  let uploadURL = NSURL(string: theURL)!

  // Hit server
  let request = NSMutableURLRequest(URL: uploadURL)
  request.HTTPMethod = "POST"

  request.setValue("application/json", forHTTPHeaderField: "Content-Type")

  do {
      let jsonData = try NSJSONSerialization.dataWithJSONObject(params, options: NSJSONWritingOptions(rawValue: 0))
      request.HTTPBody = jsonData
      let session = NSURLSession.sharedSession()

      session.dataTaskWithRequest(request, completionHandler: {data, response, error -> Void in
          print("Response: \(response)")
      }).resume()


  } catch let error as NSError {
      print(error)
  }

nodejs:

var buffer = new Buffer(request.body["base64"], 'base64')
fs.writeFile('test.jpeg',buffer,"base64"); //Works
var username = request.body["username"];
var someStringsArr  = request.body["arr"]

by the way...

you wrote the function buildQueryString, which is already exists in Foundation

let urlComponents = NSURLComponents(string: "http://myUrl.com/getApi/")!
urlComponents.queryItems = [NSURLQueryItem]()
urlComponents.queryItems!.append(NSURLQueryItem(name:"myKeyA",value:"myValueA"))
urlComponents.queryItems!.append(NSURLQueryItem(name:"myKeyB",value:"myValueB"))

print(urlComponents.URL!) //http://myUrl.com/getApi/?myKeyA=myValueA&myKeyB=myValueB

Use url query if want to send GET parameters via the URL