Incorrect response when sending http request in telnet mode

[zhengshuxin]

I telnet the server port listened by asmhttpd and after sending the first line of http request, and the error response got:
Trying 0.0.0.0...
Connected to 0.
Escape character is '^]'.
GET / HTTP/1.1
HTTP/1.1 400 Bad Request
Server: asmttpd/0.4.5

But when I send http request by curl, the response is ok.
$ curl "http://127.0.0.1:8081/" -v

• Trying 127.0.0.1:8081...
• TCP_NODELAY set
• Connected to 127.0.0.1 (127.0.0.1) port 8081 (#0)

GET / HTTP/1.1
Host: 127.0.0.1:8081
User-Agent: curl/7.65.3
Accept: /

• Mark bundle as not supporting multiuse
  < HTTP/1.1 200 OK
  < Server: asmttpd/0.4.5
  < Accept-Ranges: bytes
  < Content-Length: 78
  < Content-Type: text/html
  <

<title>hi</title>

hello world