Why running python script causes an error in Apache

Question

Running the following python script through web site works fine and (as expected) stops the playback of MPD:

#!/usr/bin/env python
import subprocess
subprocess.call(["mpc", "stop"])
print ("Content-type: text/plain;charset=utf-8\n\n")
print("Hello")

This script however causes an error (playback starts as expected):

#!/usr/bin/env python
print("Content-type: text/plain;charset=utf-8\n\n")
print ("Hello")

import subprocess
subprocess.call(["mpc", "play"])

The error is:

malformed header from script. Bad header=Scorpions - Eye of the tiger -: play.py, referer: http://...

Apparently whatever is returned by the playback command is taken as the header. When run in terminal, the output looks fine. Why could it be?

Blender · Accepted Answer · 2014-01-11 22:08:48Z

2

You're running your script in some sort of CGI-like environment. I would strongly suggest using a light web framework like Flask or Bottle.

mpc play is writing to stdout. You need to silence it:

import os

with open(os.devnull, 'w') as dev_null:
    subprocess.call(["mpc", "stop"], stdout=dev_null)

For your HTTP headers to be valid, you need to separate them with \r\n, not \n\n.

answered Jan 11, 2014 at 22:08

Blender

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5 Comments

Lukas Over a year ago

1. I will likely use some framework, this are early tries only. 2. Redirecting stdout did help, but that does not explain, why stop works fine and play needs special measures like that (both write to stdout) 3. that does not change the behaviour, but I will

Blender Over a year ago

@Lukas: Terminate your last header with \r\n\r\n instead of just \r\n.

Lukas Over a year ago

I use \r\n\r\n now, still it does not work without redirecting stdout

Blender Over a year ago

@Lukas: The first or the second?

Lukas Over a year ago

first (stop) works from the beginning as is written in the question. The second one (play) works only with stdout redirected. What is used to terminate seems not to be important.

user823738 · Accepted Answer · 2014-01-11 22:06:08Z

0

You need to use \r\n line endings.

answered Jan 11, 2014 at 22:06

user823738

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