Client Server Software: How Gopher Works

Gopher is an example of client-server software. This means it comes in two parts. The client part is a program that gets information from a server and shows it to you. The client runs locally (on the machine that you are using); that could mean a personal computer or the UICVM mainframe system. In turn, the server half of this partnership is a program that sends information to a client upon request. There are thousands of gopher servers are running throughout the world. The nice trick about gopher is that you can get information from a server without having to know where it is, what machine it is running on, or even that it exists! And the information that you get will be presented to you in the same way, regardless of the gopher server you got it from, because you will always be working with your own gopher client.

Every gopher server holds and distributes information, and may provide other services too. The information and services are organized in a series of menus. These menus are based on the tree-like file structure of directories and subdirectories which is found on computer systems such as DOS or UNIX. Each item in a gopher menu has two parts: its name, which in gopher is actually a fairly long descriptive title, and instructions on where to get the item.

When you first connect to a server, it sends you its "root menu." Because it can contain references to documents (files) or to lower level menus (subdirectories), the gopher server's root menu is very analogous to the root directory in a tree file system. When your gopher client receives a menu, it displays just the titles of the menu's entries for you. When you select an entry from the menu, your client reads the instructions on where to go for the item and sends for it. Depending on what you selected, "it" may be the text a document which you can read or a submenu listing additional documents and submenus.

The key to gopher is that each item in a gopher menu may be on the server where you originally got the menu from, or it may not be. It could be on any machine on the Internet; your client learns the address of the new server from the old menu, and you don't have to pay attention.

In fact, gopher is a bit more versatile than this. Files and directories are not the only type of menu items. Perhaps the most important of the remaining types is the search item. When you select a search item, the client will first ask you to enter search terms. Then when your client connects to the remote server, it will send your search terms to give the remote server a better idea of what information to send back. Usually the remote server uses your search terms to find a set of files that match some criteria, but the actual behavior can be idiosyncratic. At UIC, we use search servers to do database lookups of all sorts.

A gopher server can run on almost anything, from a personal computer to a mainframe. As more people discover this way of making information publicly available, gopher servers are spreading as gophers are wont to. And since a new gopher can include the root menu (or any other item or service) of any other gopher on one of its menus, simply by knowing the Internet address of one other gopher server, essentially all gopher servers in the world are connected.

Gophering software is included in the Network Services Kit, and gopher clients are available for most other types of machines. Also, we can help you if you, your department or group has information you'd like to make available via gopher. Contact the Client Service Office (Room 2267 SEL, 413-0003 or at consult@uic.edu) for more information.