Swift 5.3 判断图片类型

在实际开发中，有时候会碰到图片类型不确定，需要判断图片类型进行其他操作，因此直接给Data做一个扩展，支持检测图片的类型。
扩展支持jpeg tiff bmp ico icns gif png webp等多种格式的图片类型判断。
从图片数据中截取第一个16进制数据，然后比对判断。

extension Data {
    enum ImageType {
        case unknown
        case jpeg
        case tiff
        case bmp
        case ico
        case icns
        case gif
        case png
        case webp
    }
    
    func detectImageType() -> Data.ImageType {
        if self.count < 16 { return .unknown }
        
        var value = [UInt8](repeating:0, count:1)
        
        self.copyBytes(to: &value, count: 1)
        
        switch value[0] {
        case 0x4D, 0x49:
            return .tiff
        case 0x00:
            return .ico
        case 0x69:
            return .icns
        case 0x47:
            return .gif
        case 0x89:
            return .png
        case 0xFF:
            return .jpeg
        case 0x42:
            return .bmp
        case 0x52:
            let subData = self.subdata(in: Range(NSMakeRange(0, 12))!)
            if let infoString = String(data: subData, encoding: .ascii) {
                if infoString.hasPrefix("RIFF") && infoString.hasSuffix("WEBP") {
                    return .webp
                }
            }
            break
        default:
            break
        }
        
        return .unknown
    }
    
    static func detectImageType(with data: Data) -> Data.ImageType {
        return data.detectImageType()
    }
    
    static func detectImageType(with url: URL) -> Data.ImageType {
        if let data = try? Data(contentsOf: url) {
            return data.detectImageType()
        } else {
            return .unknown
        }
    }
    
    static func detectImageType(with filePath: String) -> Data.ImageType {
        let pathUrl = URL(fileURLWithPath: filePath)
        if let data = try? Data(contentsOf: pathUrl) {
            return data.detectImageType()
        } else {
            return .unknown
        }
    }
    
    static func detectImageType(with imageName: String, bundle: Bundle = Bundle.main) -> Data.ImageType? {
        
        guard let path = bundle.path(forResource: imageName, ofType: "") else { return nil }
        let pathUrl = URL(fileURLWithPath: path)
        if let data = try? Data(contentsOf: pathUrl) {
            return data.detectImageType()
        } else {
            return nil
        }
    }
}

源码地址 https://github.com/SunZhiC/DetectImageType
参考资料：
文件头标识大全 https://www.garykessler.net/library/file_sigs.html