xml - How to use PHP to take raw POST data and save to file? -

i'm working interface standard exchanging information planned, current or projected performance of real-time public transport operations between different computer systems. this standard called siri.

to cut long story short, i've made subscription service sends me xml data through interface every 30 seconds. i've highlighted in red box below, states http used send data have preferred.

i need create php file can listen http data , save file (overwriting previous file every 30 seconds).

i've done preliminary research how can go doing , i've done little reading on:

$http_raw_post_data 

and

php://input 

if can me come php solution doing 1 of these methods or better 1 i'd appreciate it.

all needs done is:

file_put_contents("outputfile.txt", file_get_contents("php://input")); 

apache deal managing incoming requests.