python-restx
Internal Server when sending GET request from Android
I currently ran into a strange issue where the I can send GET requests from a browser or curl and receive a totally fine 200 OK,
<ip> - - [26/Jul/2022 19:37:34] "GET /places/18526165 HTTP/1.1" 200 -
but when I send the very same request from my Android app, the server responds with
[2022-07-26 19:36:25,442] ERROR in app: Exception on /places/18526165 [GET]
Traceback (most recent call last):
File "<path>/venv/lib/python3.10/site-packages/flask/app.py", line 1523, in full_dispatch_request
rv = self.dispatch_request()
File "<path>/venv/lib/python3.10/site-packages/flask/app.py", line 1509, in dispatch_request
return self.ensure_sync(self.view_functions[rule.endpoint])(**req.view_args)
File "<path>/venv/lib/python3.10/site-packages/flask_restx/api.py", line 407, in wrapper
return self.make_response(data, code, headers=headers)
File "<path>/venv/lib/python3.10/site-packages/flask_restx/api.py", line 438, in make_response
raise InternalServerError()
werkzeug.exceptions.InternalServerError: 500 Internal Server Error: The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.
<ip> - - [26/Jul/2022 19:36:25] "GET /places/18526165 HTTP/1.1" 500 -
Before adding flask-restx, the server responded correctly with 200 OK. I do not understand, what causes the 500 Internal Server Error.
The Java code used to issue the GET request:
public String retrieveFromURL(URL url){
StringBuilder stringBuilder = new StringBuilder();
try (BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream(), StandardCharsets.UTF_8))) {
for (String line; (line = reader.readLine()) != null; ) {
stringBuilder.append(line);
}
} catch (IOException e) {
e.printStackTrace();
}
return stringBuilder.toString();
}
I really can't think of why. So I decided to capture HTTP GET on the host running the server:
From Firefox / Swagger UI
root@wow:~# tcpdump -i eth0 -s 0 -A 'tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x47455420'
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
19:51:01.899886 IP <ip> > <ip>: Flags [P.], seq 3108888141:3108888457, ack 3825282718, win 502, options [nop,nop,TS val 1019256520 ecr 2267856041], length 316
E..p`\@.6.~2........{....M.M.........=.....
<....,..GET /places/18526165 HTTP/1.1
Host: <ip:port>
User-Agent: Mozilla/5.0 (redacted)
Accept: application/json
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: <ip:port>
DNT: 1
Connection: keep-alive
Android (500 Internal Server Error):
19:51:40.463262 IP <ip> > <ip>: Flags [P.], seq 2411747994:2411748182, ack 3002101130, win 685, options [nop,nop,TS val 17801935 ecr 2267894550], length 188
[email protected].....
.....-S.GET /places/18526165 HTTP/1.1
User-Agent: Dalvik/2.1.0 (Linux; U; Android 9; SM-J330F Build/PPR1.180610.011)
Host: <ip:port>
Connection: Keep-Alive
Accept-Encoding: gzip
Curl (200 OK)
19:52:10.512679 IP <ip> > <ip>: Flags [P.], seq 1265862891:1265863012, ack 352242510, win 502, options [nop,nop,TS val 1019325130 ecr 2267924651], length 121
[email protected]...........
<....-..GET /places/18526165 HTTP/1.1
Host: <ip:port>
User-Agent: curl/7.84.0
accept: application/json
Environment
Python 3.10.5 Flask 2.1.2 Werkzeug 2.1.2 Flask_restx 0.5.1
Even more baffling is, that when I sent the dysfunctional Android request manually using CURL, the server responds just fine to it with 200.
$ curl -X 'GET' '<ip:port>/places/18526165' -H 'Accept-Encoding: gzip' -H 'Connection: Keep-Alive' -H 'User-Agent: Dalvik/2.1.0 (Linux; U; Android 9; SM-J330F Build/PPR1.180610.011'
Resulting dump:
Host: <ip:port>
Accept: */*
Accept-Encoding: gzip
Connection: Keep-Alive
User-Agent: Dalvik/2.1.0 (Linux; U; Android 9; SM-J330F Build/PPR1.180610.011
It looks like the android request is maybe setting an accept header that the flask-restx app doesn't support.
The bit of code in question in api.py is:
mediatype = request.accept_mimetypes.best_match(
self.representations, default=default_mediatype,
)
Can you manually set the accept: http header in your android request to application/json?
Hello Peter, thanks for the answer. I first thought that I created the very same GET-request using curl, but now I tcpdumped it and saw thaw that curl sends default headers I was not aware of.
Indead, you found the problem, I can reproduce it using curl now:
$ curl -X 'GET' '<url>' -H 'Accept-Encoding: gzip' -H 'Connection: Keep-Alive' -H 'User-Agent: Dalvik/2.1.0 (Linux; U; Android 9; SM-J330F Build/PPR1.180610.011' -H 'Accept:'
<!doctype html>
<html lang=en>
<title>500 Internal Server Error</title>
<h1>Internal Server Error</h1>
<p>The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.</p>
Thanks, so all I got to do is add an Accept header. :) You just saved my day.
I would recommend adjusting flask_restx to either throwing a more explicit error message or allowing to remove the header when sending a request as this is no behavior someone with rudimentary understanding of HTTP would expect ;)