Active services (ports) using sockets

Question

I´m going to program an application that shows if there is an active/inactive service in a range of UDP ports, of a given IP.

My first intention it's trying to bind a socket with an address (the port is included in the address). Bind will return -1 if fails, with an errno EADDRINUSE, that means that the specified address is already in use. If the bind is done, I will close the socket, and go to the next port.

I'm a bit lost with sockets and networks things, so I would like to know if my approach is correct, or a clue about the best way to do that.

Thanks

Answer 1

在Windows上，您可以使用GetUdpTable()和GetUdp6Table()向操作系统询问活动的IPv4 / IPv6 UDP套接字列表（TCP套接字有相应的功能）。

Answer 2

In Linux, the /proc/net/udp file lists all open UDP sockets. The 2nd column in the file shows the interface address and port number (in hex):

[root@localhost ~]# head -n 2 /proc/net/udp
  sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode
  33: 00000000:00A1 00000000:0000 07 00000000:00000000 00:00000000 00000000     0        0 9236 2 ffff8102205a8980

Alternatively you can run netstat -au (on POSIX systems you can use the popen() system call to run a program and capture its output as a FILE * ):

[root@localhost ~]# netstat -au
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address               Foreign Address             State
udp        0      0 *:snmp                      *:*

Your bind() technique is not reliable because UDP allows multple bound sockets to the same addresses (depending on socket settings).