微信小程序如何直接上传图片到阿里云oss？

首先从后端获取oss的地址及签名策略信息

<?php
function gmt_iso8601($time) {
    date_default_timezone_set("Asia/Shanghai");
    $dtStr = date("c", $time);
    $mydatetime = new \DateTime($dtStr);
    $expiration = $mydatetime->format(\DateTime::ISO8601);
    $pos = strpos($expiration, '+');
    $expiration = substr($expiration, 0, $pos);
    return $expiration."Z";
}
$appid = '';
$appsecret = '';
$host = 'https://test.oss-cn-beijing.aliyuncs.com'; //你的oss地址
$callbackUrl = "http://oss-demo.aliyuncs.com:23450";

$callback_param = array('callbackUrl' => $callbackUrl,
    'callbackBody' => 'filename=${object}&size=${size}&mimeType=${mimeType}&height=${imageInfo.height}&width=${imageInfo.width}',
    'callbackBodyType' => "application/x-www-form-urlencoded");
$callback_string = json_encode($callback_param);

$base64_callback_body = base64_encode($callback_string);
$now = time();
$expire = 30; //设置该policy超时时间是10s. 即这个policy过了这个有效时间，将不能访问
$end = $now + $expire;
$expiration = gmt_iso8601($end);

$dir = 'tempimg/';//oss的上传目录

//最大文件大小.用户可以自己设置
$condition = array(0 => 'content-length-range', 1 => 0, 2 => 1048576000);
$conditions[] = $condition;

//表示用户上传的数据,必须是以$dir开始, 不然上传会失败,这一步不是必须项,只是为了安全起见,防...

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