从mime字节验证base64编码的图像

Question

我试图从mime类型字节验证一些Base64编码的图像，除了。png文件之外，它们都验证正确

png字节签名是89 50 4E 47 0D 0A 1A 0A

我有一个允许的字节签名数组

    'imageBytes'    => [
        "jpeg"  => "FFD8",
        "png"   => "89504E470D0A1A0A",
        "gif"   => "474946",
        "bmp"   => "424D"
    ],

    public function checkImageMimeBytes(string $imageData, array $imgByteArray) : string
        {
            if (!is_array($imgByteArray) || is_null($imgByteArray) || empty($imgByteArray)) {
                throw new \LogicException('undefined image security config');
            }

            foreach ($imgByteArray as $mime => $hexBytes) {
                $bytes = $this->getBytesFromHexString($hexBytes);
                if (substr($imageData, 0, strlen($bytes)) == $bytes) {
                    return $mime;
                } else {
                    throw new SecurityException;
                }
            }
            throw new \LogicException('Invalid Mime Byte');
        }

        public function getBytesFromHexString(string $hexData) : string
        {

            for ($count = 0; $count < strlen($hexData); $count += 2) {
                $bytes[] = chr(hexdec(substr($hexData, $count, 2)));
            }

            if (!isset($bytes) || !is_array($bytes) || empty($bytes) || is_null($bytes)) {
                throw new \LogicException;
            }

            return implode($bytes);
        }

编辑：用FileReader（）从javascript编码前端

     let reader = new FileReader()
     reader.readAsDataURL(file)
        reader.onloadend = (readEvent) => {
          this.$emit('imageUploadReady', readEvent.currentTarget.result)
        }

Answer 1

和您一样，我也有一个base64图像($imagebase64str)。

我需要得到这个图像的mime类型必须是有效的。

输入:$imagebase64str

function imgMime($imgBytes){
    if(is_null($imgBytes)){
        return(false);
    }
    if(strlen($imgBytes)<12){
        return(false);
    }
    $finfo = new finfo(FILEINFO_MIME_TYPE);
    $mime=$finfo->buffer($imgBytes);
    if(strncmp($mime, "image/", 6) != 0){
        return(false);
    }
    return($mime);
}

$imageBytes=base64_decode($imageBase64Str,true);
if(!$imageBytes){
    throw new Exception("cannot decode image base64");
}
$imageMime=imgMime($imageBytes);
if(!$imageMime){
    throw new Exception("cannot recognize image mime");
}

$allowedMimes=["image/jpeg","image/png","image/gif","image/bmp"];
if(!in_array($imageMime,$allowedMimes,true)){
    throw new Exception("image mime not allowed: ".$imageMime);
}