PHP:来自图像字节的图像mime类型 [英] PHP: image mime type from image bytes

问题描述

我有一个从数据库检索到的base64图像字符串:$imageBase64Str

I have a base64 image string retrieved from a database: $imageBase64Str

我需要从此内容中检索哑剧并显示图像.这是以下代码的作用:

I need to retrieve the mime from this content and display the image. This is what the following code does:

function imgMime($imgBytes){
    if(is_null($imgBytes)){
        return(false);
    }
    if(strlen($imgBytes)<12){
        return(false);
    }
    $file = tmpfile();
    if(!fwrite($file,$imgBytes,12)){
        fclose($file);
        return(false);
    }
    $path = stream_get_meta_data($file)['uri'];
    $mimeCode=exif_imagetype($path);
    fclose($file);
    if(!$mimeCode){
        return(false);
    }
    return(image_type_to_mime_type($mimeCode));
}

$imageBytes=base64_decode($imageBase64Str,true);
if(!$imageBytes){
    throw new Exception("cannot decode image base64");
}
$imageMime=imgMime($imageBytes);
if(!$imageMime){
    throw new Exception("cannot recognize image mime");
}
header('Content-type: '.$imageMime);
echo($imageBytes);

问题

此解决方案的问题在于，它要求我将内容的前12个字节写入一个临时文件.我想知道是否有一种简单的方法可以避免这种情况，而不必手动维护一组哑剧.另外，我想避免调用外部程序(例如，通过exec)，以使我的代码保持可移植性.

Question

The issue I have with this solution is that it requires me to write the 12 first bytes of the content to a temporary file. I am wondering whether there could be a simple way to avoid this without having to maintain a set of mimes manually. Also, I would like to avoid calling an external program (through exec for example) so that my code remains portable.

我希望有一个像exif_imagetype_from_bytes这样的php函数.我的imgMime函数会更简单:

I wish there was a php function like exif_imagetype_from_bytes. My imgMime function would be simpler:

function imgMime($imgBytes){
    if(is_null($imgBytes)){
        return(false);
    }
    if(strlen($imgBytes)<12){
        return(false);
    }
    $mimeCode=exif_imagetype($imgBytes);
    if(!$mimeCode){
        return(false);
    }
    return(image_type_to_mime_type($mimeCode));
}

$imageBytes=base64_decode($imageBase64Str,true);
if(!$imageBytes){
    throw new Exception("cannot decode image base64");
}
$imageMime=imgMime($imageBytes);
if(!$imageMime){
    throw new Exception("cannot recognize image mime");
}
header('Content-type: '.$imageMime);
echo($imageBytes);

基于所选答案的解决方案

非常感谢@Kunal Raut提供的答案，我可以提出以下解决方案:

Solution based on selected answer

Thanks a lot to @Kunal Raut for the answer that allowed me to come up with the following solution:

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(!$imageMime){
    throw new Exception("cannot recognize image mime");
}
header('Content-type: '.$imageMime);
echo($imageBytes);

此解决方案非常优雅，恕我直言.

This solution is a lot more elegant IMHO.

推荐答案

此解决方案的问题在于，它要求我将内容的前12个字节写入一个临时文件.我想知道是否有一种简单的方法可以避免这种情况，而不必手动维护一组哑剧.

The issue I have with this solution is that it requires me to write the 12 first bytes of the content to a temporary file. I am wondering whether there could be a simple way to avoid this without having to maintain a set of mimes manually.

这是因为您的代码的这一部分

This is because of this part of your code

if(!fwrite($file,$imgBytes,12)){
        fclose($file);
        return(false);
    }

它使您可以在文件中写入至少12个字节的数据，然后继续执行.您可以跳过此if()并解决第一个问题.

It makes you write minimum 12 bytes of data in the file and then lets the execution move forward.You can skip this if() and solve your first problem.

我希望有一个像exif_imagetype_from_bytes这样的php函数.我的imgMime函数会更简单

I wish there was a php function like exif_imagetype_from_bytes. My imgMime function would be simpler

是的，该函数可以为您返回 base64_decoded 字符串的类型.

Yes there is such function which returns you the type of the base64_decoded string.

有关此功能的更多详细信息，请单击此处.

For more details regarding this function Click Here.

功能使用

查看此内容

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