Hello group!
I want to mimic the behavior of console application through web
interface: I invoke a process in web2py controller function and try to
pipe its stdout to user's browser (no keyboard input is needed). These
are time-consuming processes that print out their progress with simple
python print command. I wanted the user to see these printed messages
in browser window, gradually as they are printed by a process.
Here is a controller function:
*************************************************************************
import subprocess
def score():
cmd=['ls', '-la']
proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, \
stderr=subprocess.STDOUT)
response.headers['Content-Type'] = 'text/plain'
response.headers['Content-Length'] = 10**6
return response.stream(proc.stdout, 16)
**************************************************************************
Imagine that instead of 'ls -la' we run a process that does something
like:
**************************************************************************
for i in range (10000):
sleep(1000)
print i
*************************************************************************
With this setup I achieved the following: when process ends, the whole
stdout contents is passed to the browser and displayed. But there is
no effect of gradual streaming of printouts to the browser.
If you notice the value 16 in stream command in controller, it's
buffer size. From other experiments with streaming in web2py I managed
to stream very large CSV files output to browser (download) during the
time of their generating; if I make buffering chunks less than initial
portion of data, it streams. Otherwise it waits until the whole file
is ready and then sends it to browser.
subprocess.PIPE is file-like object provided by subprocess module.
But here in subprocess STROUT streaming, this playing with buffer size
does not help. Any ideas?
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