正则表达式，解析img src内容并用其他链接替换它

Question

I need to make next feature on my site: user writing an article and attach image in it, images are often stored not on localhost. I need to download this images to localhost and replace links to localhost images.

For example:

<img ... src="http://bob.com/img/image1.png" ... >
<img ... src="http://bob.com/img/image2.png" .... >

Script will find src content, download images and replace it like this:

<img ... src="/images/image1.png" ... >
<img ... src="/images/image2.png" .... >

I understand how to parse all src from code:

$subject = # i will put there article content (with img tags etc)
$result = array();
preg_match("/<img.*?src="(.*?)".*?>/", $subject, $result);

Now $result array will contain all link to images. Nice. Now I have some questions.

1) If I use preg_replace, will it help me to solve this task? In my opinion not, because preg_replace will replace content instantly (so I can't download image, create new link for stored on localhost image and somehow set this as argument for preg_replace, because it is run yet). Am I right with this assumption?

2) Okay. I can form an array, like I said. After that I download all images from this array. After that, somehow, I will replace all old images, for new images. I think it is more realistic. Am I right?

Something like that:

$subject = # i will put there article content (with img tags etc)
$result = array();
preg_match("/<img.*?src="(.*?)".*?>/", $subject, $result);

foreach($result as $src)
{
 $new_src = downloadImage($src);
 # somehow replace old image with new image there. How?
}

3) How exactly I can replace links if I will use 2nd method?

Answer 1

A Php DOMDocument Example how to manipulate HTML image tags.

$dom=new DOMDocument();
$dom->loadHTML($html_src);
$imgs = $dom->getElementsByTagName('img');
foreach($imgs as $img){

    $img_src = $img->getAttribute('src'); // will give you the src String

    //do something here

    $img->setAttribute('src',$new_src); // change your src= value

}

You can manipulate everything with setAttribute when the Attribute exist.

If you want be sure, that src is set, then you can use hasAttribute