我正在学习如何使用httpclient.post更新mysql数据库。我要插入的表是：
|id-日志|
php文件如下：，

<?php 
   header('Access-Control-Allow-Origin: *');    
    header('Access-Control-Allow-Headers: X-Requested-With');
    header('Access-Control-Allow-Methods: POST, GET, OPTIONS');
include 'db.php';

$postdata=file_get_contents("php://input");
$request = json_decode($postdata);
$message = $request->message;

// Create connection
$conn = new mysqli($server_name, $mysql_username, $mysql_password, $db_name);

 $sql = "INSERT INTO shootingchatlog (id, log) VALUES (NULL, '$message')";

 if($conn -> query($sql) === TRUE ){
 echo "message Uploaded Successfully";
 }else{
 echo "Error Uploading Image";
 }
 mysqli_close($conn);

我在电话线上不断收到错误

$message = $request->message;

这让我想到这个问题与我的代码有关。

httpOptions = {
    headers: new HttpHeaders({
      'Content-Type': 'application/json'
    })
  };

  constructor(private http: HttpClient) { }

  public uploadService(mess: string): void {
    console.log(mess);
     this.http.post(this.url, JSON.stringify({"messasge": mess}), this.httpOptions)
           .subscribe((res: Response) => {
        console.log(res);
      },
      err => {
        console.log("Error occured", err);
      });
    }

最常见的错误是：

SyntaxError: Unexpected token < in JSON at position 0 at JSON.parse

我真的不知道我做错了什么。这方面似乎没有任何文件。或者如果是的话，通常都太抽象了。任何帮助都将不胜感激！