ensure resp.Body is discarded to avoid broken tcp sockets

[tmsmr]

Hi guys,

currently the Blackbox exporter produces server-side (Confirmed with Zuul, NGINX, Python 3 http.server, TCP-Resets in Wireshark) broken pipes when probing with a 'big' HTTP request.

Example:

• Download and start the Blackbox exporter with default configuration

cd /tmp
wget https://github.com/prometheus/blackbox_exporter/releases/download/v0.12.0/blackbox_exporter-0.12.0.linux-amd64.tar.gz
tar xf blackbox_exporter-0.12.0.linux-amd64.tar.gz
(cd blackbox_exporter-0.12.0.linux-amd64 && ./blackbox_exporter &)

• Create some random payload

dd if=/dev/urandom of=small-garbage bs=1k count=10
dd if=/dev/urandom of=big-garbage bs=1k count=1000

• Serve the content

python3 -m http.server &

• Request small-garbage

curl http://localhost:9115/probe\?target\=127.0.0.1:8000/small-garbage\&module\=http_2xx > /dev/null

...
127.0.0.1 - - [14/Aug/2018 15:17:06] "GET /small-garbage HTTP/1.1" 200 -
...

• Request big-garbage

curl http://localhost:9115/probe\?target\=127.0.0.1:8000/big-garbage\&module\=http_2xx > /dev/null

...
Traceback (most recent call last):
  File "/usr/lib/python3.7/socketserver.py", line 647, in process_request_thread                                                                   
    self.finish_request(request, client_address)
  File "/usr/lib/python3.7/socketserver.py", line 357, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/usr/lib/python3.7/http/server.py", line 646, in __init__
    super().__init__(*args, **kwargs)
  File "/usr/lib/python3.7/socketserver.py", line 717, in __init__
    self.handle()
  File "/usr/lib/python3.7/http/server.py", line 426, in handle
    self.handle_one_request()
  File "/usr/lib/python3.7/http/server.py", line 414, in handle_one_request
    method()
  File "/usr/lib/python3.7/http/server.py", line 653, in do_GET
    self.copyfile(f, self.wfile)
  File "/usr/lib/python3.7/http/server.py", line 844, in copyfile
    shutil.copyfileobj(source, outputfile)
  File "/usr/lib/python3.7/shutil.py", line 82, in copyfileobj
    fdst.write(buf)
  File "/usr/lib/python3.7/socketserver.py", line 796, in write
    self._sock.sendall(b)
ConnectionResetError: [Errno 104] Connection reset by peer
----------------------------------------
....

In ProbeHTTP (https://github.com/prometheus/blackbox_exporter/blob/master/prober/http.go#L135) resp.Body is read/discarded only if the payload gets checked for certain contents in https://github.com/prometheus/blackbox_exporter/blob/master/prober/http.go#L42.

The resp.Body should always be read/discarded, no matter whether the body is needed or not.

[brian-brazil]

Can you add the DCO please?

[tmsmr]

Done. I was confused - thought this DCO thingy is for maintainers only...

[brian-brazil]

Thanks!

It's for everyone, it's a legal copyright thingy.