如何使用PHP开发微信小程序的在线讨论功能？

<!-- discusson.wxml -->
<view>
   <textarea bindinput="onInput"></textarea>
   <button bindtap="onSubmit">提交讨论</button>
</view>

// discussion.js
Page({
  data: {
    content: '', // 讨论内容
  },
  onInput: function(event) {
    this.setData({
      content: event.detail.value,
    });
  },
  onSubmit: function() {
    wx.request({
      url: 'https://your-server-url/discussion-api.php',
      method: 'POST',
      data: {
        content: this.data.content,
      },
      success: function() {
        wx.showToast({
          title: '提交成功',
        });
      },
    });
  },
});

// discussion-api.php
<?php
header('Content-Type: application/json');

// 连接数据库
$conn = new mysqli('localhost', 'username', 'password', 'database');
if ($conn->connect_error) {
    die('数据库连接失败：' . $conn->connect_error);
}

// 获取小程序发送的讨论内容
$content = $_POST['content'];

// 获取小程序发送的用户OpenID
$openid = isset($_SERVER['HTTP_OPENID']) ? $_SERVER['HTTP_OPENID'] : '';

// 插入讨论数据到数据库中
$sql = "INSERT INTO discussions (openid, content) VALUES ('$openid', '$content')";
if ($conn->query($sql) === TRUE) {
    $response = array('status' => 'success');
} else {
    $response = array('status' => 'error', 'message' => '插入数据失败：' . $conn->error);
}

$conn->close();

echo json_encode($response);
?>

wx.request({
  url: 'https://your-server-url/discussion-api.php',
  header: {
    'openid': '用户的OpenID',
  },
  // ...
});