The netsailor is a simple implementation of the netcat utility in go that allows to listen and send data over TLS(SSL),TCP and UDP protocols.

The conventional netcat that is used doesn't support TLS connection or any kind of authentication as such.So I thought it will be of use to add TLS protocol and thereby it intrigued me to design netcat command utility purely in golang and adding extra functionality of supporting TLS protocols and few more cool customization.The name net 'sailor' itself comes from the fact that this command line utility is sails across tcp,udp and tls(ssl) protocols.

• Clone the project and build it

  $ git clone https://github.com/gophergala2016/netsailor.git
  $ go build
  

netsailor [-u] [-s] [-a] [-b] [-z] [-v] [hostname] [port]

netsailor [-l] [-u] [-s] [-c] [-n] [-v] [port]

The utility allows to listen UDP\TCP\TLS ports and send data to remote ports over TCP\UDP\TLS. Main usage scenario is testing network protocols and accessibility of the open ports.

The options are as follows:

-l Used to specify that netsailor should listen for an incoming connection rather than initiate a connection to a remote host.

-u Use UDP instead of the default option of TCP.

-s Use TLS instead of the default option of TCP.

-v Have netsailor give more verbose output.

-a Allow authentication mode for client side(allowing client to verify the server by the servername).

-b servername Have client mention the servername(has to be only used when -a mode is on) to verify the server.

-z portrange Have client mention the range of ports to be scanned to check whether they are open or not(should be used with tcp and ssl mode only).

-c path/to/cert/files Have listener mention the path to the certificate files(.key and .pem file) in TLS connection(to be used only when -s flag is set)(default is present working directory).

-n certificatename Have listener mention the name of the certificate file(.key and .pem file) in TLS connection(to be used only when -s flag is set)(default name is server.key and server.pem).

• Generate a private key

openssl genrsa -out server.key 2048

• To generate a certificate

openssl req -new -x509 -key server.key -out server.pem -days 3650

$ netsailor hostname 42

Open a TCP connection to port 42 of hostname.

$ netsailor -u hostname 53

Open a UDP connection to port 53 of hostname.

$ netsailor -v hostname 53

Open a TCP connection to port 53 of hostname in verbose with connection logs.

$ netsailor -s hostname 53

Open a TLS connection to port 53 of hostname.

$ netsailor -s -a -b servername hostname 8000

Open a TLS connection to port 8000 of hostname and verify servername before sending stdin to remote host, and send data from remote host to stdout.

$ netsailor -z hostname 8000-8003

It will scan all the open ports from 8000 to 8003 If -s is mentioned it will scan for all open TLS ports within the specified range else it will scan for open tcp ports.

$ netsailor -l 3000

Listen on TCP port 3000, and once there is a connection, send stdin to the remote host, and send data from the remote host to stdout.

$ netsailor -u -l 3000

Listen on UDP port 3000, and once there is a connection, send stdin to the remote host, and send data from the remote host to stdout.

$ netsailor -s -l 3000

Listen on TLS port 3000, and once there is a connection, send stdin to the remote host, and send data from the remote host to stdout.

$ netsailor -l -v 3000

Listen on TCP port 3000, and once there is a connection, send stdin to the remote host, and send data from the remote host to stdout in verbose mode with connection logs.

$ netsailor -l -s -c path/to/cert/files -n certname 8000

Listen on TLS port 8000, and thereby providing the Certificates from specified path(default present working directory) and specifying the name(default "server")

Start by using nc to listen on a specific port, with output captured into a file:

netsailor -l 1234 > filename.out

Using a second machine, connect to the listening nc process, feeding it the file which is to be tranetsailorferred:

netsailor host.example.com 1234 < filename.in

After the file has been transferred, the connection will close automatically.

• Allowing port scanning for UDP ports as well
• Give an option to disable DNS lookup
• Add more interesting customization like idle timeout etc.