微信公众号获取OpenId（未授权）（需要关注公众号）

https://open.weixin.qq.com/connect/oauth2/authorize?appid=*******&redirect_uri=你回调的地址&response_type=code&scope=snsapi_base&state=1#wechat_redirect

https://api.weixin.qq.com/sns/oauth2/access_token?appid=***&secret=***&code=***&grant_type=authorization_code

<?php
class Wxmsg extends CI_Controller {
	function __construct()
	{
		parent::__construct();
		$this->load->model('Follow_model');
		$this->load->helper('url');
		$this->load->helper('xml');
	}

	function index($check = 1)
	{
		$echostr = $this->input->get('echostr');
		if (!empty($echostr)) {
			echo $echostr;
			return;
		}

		$token = "hello";

		# step 1: get args
		$slug = array('signature', 'timestamp', 'nonce', 'openid');
		foreach ($slug as $key) {
			$args[$key] = $this->input->get($key);
			if ($check && empty($args[$key]))
				die($key.' 不能为空');
		}

		# step 2: signature check
		$lists = array($args['timestamp'], $args['nonce'], $token);
		sort($lists, SORT_STRING);
		$hashcode = sha1(implode('', $lists));
		if ($check && $hashcode != $args['signature'])
			die('signature 校验错误');

		# step 3: webdata decode
		$webdata = $this->input->raw_input_stream;
		$xml = simplexml_load_string($webdata);
		foreach ($xml->children() as $child) {
			$arr[$child->getName()] = trim((string)$child);
		}

		if (empty($arr['FromUserName']) || empty($arr['ToUserName']))
			die('FromUserName、ToUserName 不能为空');

		if (empty($arr['MsgType']))
			die('MsgType 不能为空');

		if ($arr['MsgType'] == 'text') {
			if (empty($arr['CreateTime']) || empty($arr['Content']) || empty($arr['MsgId']))
				die('CreateTime、Content、MsgId 不能为空');

			# step 4.1 text msg
			$Content = self::msg_text($arr);

		} elseif ($arr['MsgType'] == 'event') {
			if (empty($arr['Event']))
				die('Event 不能为空');

			# step 4.2 event msg
			$Content = self::msg_event($arr);

		} else {
			die('不处理事件:'.$arr['MsgType']);
		}

		self::reply_msg($arr, $Content);
	}

	function reply_msg($arr, $Content)
	{
		$FromUserName = $arr['FromUserName'];
		$ToUserName = $arr['ToUserName'];
		$CreateTime = time();
		$reply =
<<<XML
	<xml>
		<ToUserName><![CDATA[$FromUserName]]></ToUserName>
		<FromUserName><![CDATA[$ToUserName]]></FromUserName>
		<CreateTime>$CreateTime</CreateTime>
		<MsgType><![CDATA[text]]></MsgType>
		<Content><![CDATA[$Content]]></Content>
	</xml>
XML;
		$reply_xml = new SimpleXMLElement($reply);
		echo $reply_xml->asXML();
	}

	function msg_text($arr)
	{
		$FromUserName = $arr['FromUserName'];
		$key = $arr['Content'];

		$Content = '萌萌嗒';
		return $Content;
	}

	function msg_event($arr)
	{
		$event = $arr['Event'];
		if ($event == 'subscribe') {
			$this->Follow_model->change($arr['FromUserName'], $arr['ToUserName'], 1);
			return "功能添加中\n敬请等待\n";
			#return '输入姓名或电话查询单号，输入单号查询物流信息';
		} elseif ($event == 'unsubscribe') {
			$this->Follow_model->change($arr['FromUserName'], $arr['ToUserName'], 0);
		}
		return '';
	}

	function test()
	{
		$openid = $this->input->ip_address();

		$openid = $this->input->cookie("openid");
		if (empty($openid)) {
			$appid = appId;
			$redirect_uri = "http://".HOST.ROOT."/wxmsg/openid";
			$URL = "https://open.weixin.qq.com/connect/oauth2/authorize?appid=$appid&redirect_uri=$redirect_uri&response_type=code&scope=snsapi_base&state=1#wechat_redirect";
			redirect($URL);
		}

		echo "test";
	}

	function openid()
	{
		$code = $this->input->get('code');
		if (empty($code)) {
			die('无法获取code');
		}
		//echo $code;
		#$fp = fopen('/tmp/a.txt', 'w');
		#fwrite($fp, $code);

		$appid = appId;
		$secret = appSecret;
		$URL = "https://api.weixin.qq.com/sns/oauth2/access_token?appid=$appid&secret=$secret&code=$code&grant_type=authorization_code";

		$furl = fopen($URL, 'r') or exit('Open url faild!');
		$res = fgets($furl);
		fclose($furl);

		$res = json_decode($res, True);

//        var_dump($res);
//        echo $res['openid'];

		if (empty($res['openid'])) {
			die('无法获取openid');
		}
		$this->input->set_cookie('openid', $res['openid'], 86400 * 7);

		$URL = ROOT."/wxmsg/test";
		redirect($URL);
	}
}