图片跨域上传示例

Image cross-domain upload example.

####跨域上传原理

利用iframe来实现，A站POST到B站，B站处理上传后再跳转回到A站的callback页面，callback页面此时在iframe内（即同域下），再通过window.parent就可以操作父页面的任意元素了。

####跨域上传示例PHP版

当前域名：blog.xxx.com/post.php

```html
<form method="post" target="upload-iframe" enctype="multipart/form-data" action="http://static.xxx.com/uploader.php?callback=http://blog.xxx.com/upload-callback.html">
    <input type="file" name="file" accept="image/*" />
    <input type="submit" id="submit" value="开始上传" />
</form>
<iframe name="upload-iframe" style="display:none;" frameborder="0"></iframe>  
```

图片服务器：static.xxx.com/uploader.php

```php
<?php
$file = 'uploads/' . $_FILES['file']['name'];
// 详细过程略
move_uploaded_file($_FILES['file']['tmp_name'], $file);

$location = $_GET['callback'].'?success=1&message=xxxxxxx&url=http://static.xxx.com/2015/02/15'.$file.'&temp='.date('ymdhis');

header('location:' . $location);
exit;
?>
```

当前域名：blog.xxx.com/upload-callback.html

```html
<script type="text/javascript"> 
    var query = {};
    var urlParams = window.location.search.split('?')[1];
    urlParams = urlParams.split("&");

for (var i = 0; i< urlParams.length; i++) {
        var param = urlParams[i].split("="); 
        query[param[0]] = param[1]; 
    }

var imageDialog = window.parent.document.getElementById(query['dialog_id']);
    //console.log(imageDialog, window.parent.document, window.parent, query);
</script>
```