使用图像URL和PHP将图像从远程服务器上传/下载/保存到本地服务器？

Question

I am building a Discussion Forum as part of a bigger application I am building, the forum is just 1 section of the Application.

For my TextArea fields when posting a new Topic or a Post Reply, I have decided that nothing is as good as the PageDown Markdown Library . It is the same one that StackOverflow uses on all their sites and it works better than many of it's competitors.

The way the library ships though, I am not happy with the default Insert Image functionality. You hit the button to insert an image and it allows you to enter a URL for an Image and then it inserts the proper MarkDown syntax to show the linked image.

This just won't cut it. I need the functionality that you see on StackOverflow! Very similar anyways.

I need it to show a Dialog when you click the Insert Image button, like it does now, but instead of just an input field for a Image URL, it will have 2 filed options...

• Upload image from your computer
• Insert an Image URL and it will then DOWNLOAD the image from that URL and insert it into the post just as if you had uploaded it from your computer. This is important to not confuse this step. IT should not simply insert the Image linking it to the original Image URL. Instead it will take that URL and download/upload the Image to the same server that the upload from computer option does and then it will insert the NEW Image URL pointing to the newly uploaded image!

Based on some simple HTML like below for a Dialog window with a filed for my Upload from Computer functionality, which I already have working. I need to come up with some JavaScript and PHP that will download/save a remote image to my upload folder on my server when a button is clicked using only the URL that will be inside the URL text input field.

So it will need to do a few things...

• Fetch and save an image file to my uploads folder using PHP when the only thing that the PHP function will receive is a URL of the image which could be on the same server or most likely a remote server.
• After successfully saving/uploading an image from the URL, the PHP function will return a JSON string with the status/error and if successful then it will also return the actual URL and filename of where the new image is saved on the local server. The JavaScript/AJAX script will receive this JSON response and insert the Markdown syntax for the image into the PageDown editor.
• The PHP function will need to ensure that the URL that it is trying to save/download is a valid image file and not some malicious file! Also not simply just some file of the wrong filetype like a non-image file unless we are allowing the file type.

• It will be part of a module installed on many dinosaur servers so it needs to work on as many servers as possible too!

  From the web
  From your computer

I would be greatful of any help, tips, code snippets or anything to help with this. At this stage I really just need to build a nie PHP function that will upload images from a remote URL and also ensure that the URL passed in is a real image file or even better that it is in the allowed file types array!

A couple years ago I had started this but have now lost it and I am starting over and don't remeber much about how I went about doing it then.

Answer 1

The easiest way to download a file from a remote server would be to use copy ( http://php.net/manual/en/function.copy.php ):

copy('http://someurl.com/image.png', '/var/www/uploads/image.png');

As this function returns a bool, it is easy to determine whether the operation was successful and create a JSON response.

To verify that the file is an actual image, there is unfortunately no way that is 100% sure. It is probably enough to check the mimetype though. You can use finfo for that ( http://php.net/manual/en/function.finfo-file.php ):

$finfo = finfo_open(FILEINFO_MIME_TYPE);
echo finfo_file($finfo, $filename);
finfo_close($finfo);

For a gif, this would return image/gif for example. You will have to hardcode a list of all mimetypes you want to allow.