Retrieve the content-type from the data signature

Data+Extension.swift

// recognized content-type
private let data_sign = [
    "7z¼¯'": "application/x-7z-compressed",
    "AIFF": "audio/x-aiff",
    "AVI": "video/x-msvideo",
    "BM": "image/bmp",
    "BZh": "application/x-bzip2",
    "MSCF": "application/vnd.ms-cab-compressed",
    "ITSF": "application/vnd.ms-htmlhelp",
    "!<arch>": "application/x-debian-package",
    "Received:": "message/rfc822",
    "MZ": "application/x-msdownload",
    "GIF87a": "image/gif",
    "GIF89a": "image/gif",
    "Êþº¾": "application/java-vm",
    "ÿØÿÛ": "image/jpeg",
    "ÿØÿà+JFIF": "image/jpeg",
    "ÿØÿà+Exif": "image/jpeg",
    "MThd": "audio/midi",
    "%PDF-": "application/pdf",
    "PNG": "image/png",
    "8BPS": "image/vnd.adobe.photoshop",
    "Rar!": "application/x-rar-compressed",
    "{\rtf1": "application/rtf",
    "CWS": "application/x-shockwave-flash",
    "FWS": "application/x-shockwave-flash",
    "ustar": "application/x-tar",
    "II*.": "image/tiff",
    "MM.*": "image/tiff",
    "WAVE": "audio/x-wav",
    "RIFF+WEBP": "image/webp",
    "wOFF": "application/x-font-woff",
    "wOF2": "application/x-font-woff",
    "PK": "application/zip",
    "<?xml": "application/xml"
]

extension Data
{
      var contentType: String {
        if let prefix = String(data: self.prefix(30), encoding: .isoLatin1)
        {
            for key in data_sign.keys {
                let keys = key.components(separatedBy: "+")
                if prefix.contains(keys) {
                    return data_sign[key]!
                }
            }
        }
        
        return "application/octet-stream"
    }
}

extension String
{
    func contains(_ strings: [String]) -> Bool
    {
        guard strings.count > 0 else {
            return false
        }
        
        var allContained = true
        for string in strings {
            allContained = allContained && contains(string)
        }
        
        return allContained
    }
}