How to send a JSON message via Python Requests/URL Module to a Pi Django server from a Pizero W on the same router/LAN? - json

Question

I have a Raspberry Pi 3+ and a Raspberry Pizero W connected to the same home wireless network.
The Pi 3+ is hosting a Django server, and the IP address of the Pi 3+ is static on the home network at 192.384.5.767.
The Pizero W has a static IP address on the home network of 192.384.5.343.
When I ping the Pi 3+ Server from the Pizero W, I can see that it is up:
pi#PIZEROW:~$ ping 192.384.5.767
64 bytes from 192.384.5.767: icmp_seq=1 ttl=64 time=10.5 ms
64 bytes from 192.384.5.767: icmp_seq=2 ttl=64 time=30.0 ms
64 bytes from 192.384.5.767: icmp_seq=3 ttl=64 time=32.1 ms
Additionally, when I access the website hosted by the Django server on a tablet, there are no issues.
However, I need two-way communication between the Pizero W and the Django server so would like to test sending a super simple JSON message from the Pizero W to the Pi 3+ server and receive an acknowledgement from the server that it received the message. I don't need the server to do anything with the message other than to receive it, discard it, and send a confirm that the message was received.
I tried doing this from the Pizero W using:
pi#PIZEROW:~$ python3
>>> import requests
>>> import JSON
>>> url = "http://192.384.5.767:8000"
>>> data = {'msg':'test'}
>>> r = requests.post(url, data)
And received the following error:
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/urllib3/connection.py", line 159, in _new_conn
(self._dns_host, self.port), self.timeout, **extra_kw)
File "/usr/lib/python3/dist-packages/urllib3/util/connection.py", line 80, in create_connection
raise err
File "/usr/lib/python3/dist-packages/urllib3/util/connection.py", line 70, in create_connection
sock.connect(sa)
ConnectionRefusedError: [Errno 111] Connection refused
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/urllib3/connectionpool.py", line 600, in urlopen
chunked=chunked)
File "/usr/lib/python3/dist-packages/urllib3/connectionpool.py", line 354, in _make_request
conn.request(method, url, **httplib_request_kw)
File "/usr/lib/python3.7/http/client.py", line 1229, in request
self._send_request(method, url, body, headers, encode_chunked)
File "/usr/lib/python3.7/http/client.py", line 1275, in _send_request
self.endheaders(body, encode_chunked=encode_chunked)
File "/usr/lib/python3.7/http/client.py", line 1224, in endheaders
self._send_output(message_body, encode_chunked=encode_chunked)
File "/usr/lib/python3.7/http/client.py", line 1016, in _send_output
self.send(msg)
File "/usr/lib/python3.7/http/client.py", line 956, in send
self.connect()
File "/usr/lib/python3/dist-packages/urllib3/connection.py", line 181, in connect
conn = self._new_conn()
File "/usr/lib/python3/dist-packages/urllib3/connection.py", line 168, in _new_conn
self, "Failed to establish a new connection: %s" % e)
urllib3.exceptions.NewConnectionError: <urllib3.connection.HTTPConnection object at 0xb5a2b610>: Failed to establish a new connection: [Errno 111] Connection refused
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/requests/adapters.py", line 449, in send
timeout=timeout
File "/usr/lib/python3/dist-packages/urllib3/connectionpool.py", line 638, in urlopen
_stacktrace=sys.exc_info()[2])
File "/usr/lib/python3/dist-packages/urllib3/util/retry.py", line 398, in increment
raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPConnectionPool(host='192.384.5.767', port=8000): Max retries exceeded with url: / (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0xb5a2b610>: Failed to establish a new connection: [Errno 111] Connection refused'))
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3/dist-packages/requests/api.py", line 116, in post
return request('post', url, data=data, json=json, **kwargs)
File "/usr/lib/python3/dist-packages/requests/api.py", line 60, in request
return session.request(method=method, url=url, **kwargs)
File "/usr/lib/python3/dist-packages/requests/sessions.py", line 533, in request
resp = self.send(prep, **send_kwargs)
File "/usr/lib/python3/dist-packages/requests/sessions.py", line 646, in send
r = adapter.send(request, **kwargs)
File "/usr/lib/python3/dist-packages/requests/adapters.py", line 516, in send
raise ConnectionError(e, request=request)
requests.exceptions.ConnectionError: HTTPConnectionPool(host='192.384.5.767', port=8000): Max retries exceeded with url: / (Caused by NewConnectionError('<urllib3.connection.HTTPConnection object at 0xb5a2b610>: Failed to establish a new connection: [Errno 111] Connection refused'))
Not exactly sure what's going on, but it seems like despite the fact that the Django server is up and running as evidence by my tablet and the ping success, I still send and receive messages from the Pizero.
Any help / advice would be appreciated! Thank you!

Answer 1

This could be one of three things:
(1) your django server is not bound to the ip address or to 0.0.0.0. Normally, the runserver command starts django listening on 127.0.0.1 or localhost. To get it to bind to the correct ip address / port use
python manage.py 192.384.5.767:8000
In production environments, django applications are usually served with gunicorn or uwsgi and listening on port 80. If you are running with gunicorn / uwsgi, update the appropriate configuration setting.
(2) a firewall on the pi is blocking access. Depending on the operating system you may need to allow remote access to tcp port 80. Depending on the version of linux you may also have to add rules for apparmor and/or selinux. For example:
iptables -A INPUT -p tcp --port 80 -j ACCEPT
(3) finally, the call using requests is slightly off. It should be
requests.post(url, json=data)