gosher -- A simple Gopher server in a POSIX shell script

gosher is a Gopher server in a POSIX shell script. It requires only a standard netcat(1).

You start the server using:

$ ./gosher [<GOPHERDIR> [<HOSTNAME> [<PORT>]]]

If HOSTNAME is not provided, it will be set to "localhost". If PORT is not specified, it will bind on port 70. If GOPHERDIR is not provided, it defaults to "./". Before starting gosher you might need to modify the values of the variables NETCAT and STYLE in gosher (see "Which netcat?" below).

If the selector is a directory, gosher will look for a file named gophermap to render the submenu. If a gophermap does not exist, gosher looks for the index.gph gopherfile in the folder and, if it exists, renders it as a gophermap. If the required selector has a '.gph' extension, gosher will treat it as a gopherfile, and render it as a gophermap.

Which netcat?

There are currently several different implementations of netcat(1), and each of them works in a slightly different way and/or offers a different set of options. For the sake of using gosher, the main issue is whether your netcat(1) implementation does exit or not when its standard input gets closed. Notably, the original netcat(1) implementation by hobbit@avian.org does not exit, while other common implementations (OpenBSD netcat(1), ncat(1) from the nmap project, and GNU netcat(1)) normally do. The current version of gosher can work with different implementations of netcat(1), provided that the variable NETCAT points to the netcat(1) version you want to use, and that the variable STYLE in gosher is set correctly. In particular, STYLE can pe set equal to either 'pipe' or 'fork'. Please check below what is the recommended combination for your version of netcat(1):

+----------------+--------------+--------------+
| netcat version | STYLE='fork' | STYLE='pipe' |
+----------------+--------------+--------------+
|  traditional   |      YES     |      NO      |
+----------------+--------------+--------------+
|  OpenBSD       |      NO      |      YES     |
+----------------+--------------+--------------+
|  ncat          |      YES     |      YES     |
+----------------+--------------+--------------+

N.B.: Using STYLE='pipe' is preferable, since the '-c' option used by the 'fork' mode is a potential security risk

Running gosher under chroot(8)

In general, it makes sense to run a server in a chroot(8) environment, to reduce the risks connected with remote exploits. If you would like to run gosher under chroot(8) be sure to have the following binaries (and the corresponding libs) available in the chroot-ed environment:

	basename(1) cat(1) cut(1) date(1) dirname(1) mkfifo(1) netcat(1) 
	realpath(1) rm(1) sed(1) sh(1) which(1)

Obviously, netcat(1) will be your preferred netcat(1) implementation.

Why gosher?

Just for fun. There are only a few TCP/IP application protocols left that can be implemented in a few dozen lines of POSIX shell script, and Gopher (RFC 1436) is one of those.

Why calling it gosher?

Well, gosher is just gopher where the p is replaced with an s, and sh(1) is all that you need to run gosher (if we leave netcat(1) out...).

Also, gopher is probably one of the few kosher protocols out there.

According to the Urban Dictionary, gosher is "an insult that can mean anything", so choose your own.