sockets - How do online port checkers work? -

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for example http://www.utorrent.com/testport?port=12345

how work? can server side script attempt open socket?

there many ways of accomplishing through server-side scripting. @oded mentioned, server-side handlers capable of initiating socket connections on arbitrary ports, , of have dedicated port-scanning packages/libraries (php has one in pear repository, python's 'socket' module makes type of tasks breeze, etc...)

keep in mind on shared host platforms, socket connections typically disabled security purposes.

another way easy accomplish use command-line port-scanner such nmap server-side script. i.e in php, echo ``nmap -p $port $ip\


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