#!/usr/bin/env retro

Atua: A Gopher Server

Atua is a gopher server written in Retro.

This will get run as an inetd service, which keeps things simple as it prevents needing to handle socket I/O directly.


Atua is a minimal server targetting the the basic Gopher0 protocol. It supports a minimal gophermap format for indexes and transfer of static content.

Script Prelude

Atua uses Retro's rre interface layer. Designed to run a single program then exit, this makes using Retro as a scripting language possible.


Atua needs to know:

• the path to the files to serve
• the name of the index file
• The maximum length of a selector
• The maximum file size

~~~'/home/crc/atua 'PATH           s:const '/gophermap     'DEFAULT-INDEX  s:const 'forthworks.com 'SERVER         s:const '70             'PORT           s:const ~~~

I/O Words

Retro only supports basic output by default. The RRE interface that Atua uses adds support for files and stdin, so we use these and provide some other helpers.

Console Output

The Gopher protocol uses tabs and cr/lf for signficant things. To aid in this, I define output words for tabs and end of line.

~~~:eol  (-)  ASCII:CR c:put ASCII:LF c:put ; ~~~

Console Input

Input lines end with a cr, lf, or tab. The eol? checks for this. The gets word could easily be made more generic in terms of what it checks for. This suffices for a Gopher server though.

~~~:eol? (c-f)   [ ASCII:CR eq? ] [ ASCII:LF eq? ] [ ASCII:HT eq? ] tri or or ; :s:get (a-)   buffer:set   #0 [ n:inc c:get dup buffer:add eol? not over #255 lt? and ] while drop ; ~~~

Gopher Namespace

Atua uses a gopher: namespace to group the server related words.

~~~{{ ~~~

First up are buffers for the selector string and the file buffer. The variables and buffers are kept private.

~~~'Selector d:create   #255 n:inc allot   :buffer here ; ~~~

Next up, variables to track information related to the requested selector. Atua will construct filenames based on these.

~~~'Requested-File var 'Requested-Index var ~~~

FID, the file id, tracks the open file handle that Atua uses when reading in a file. The Size variable will hold the size of the file (in bytes).

~~~'FID var 'Size var 'Mode var ~~~

I use a Server-Info variable to decide whether or not to display the index footer. This will become a configurable option in the future.

~~~'Server-Info var ~~~

~~~:with-path (-s)   PATH &Selector s:chop s:append ;   :construct-filenames (-)   with-path s:keep !Requested-File   with-path '/gophermap s:append s:keep !Requested-Index ; ~~~

A gophermap is a file that makes it easier to handle Gopher menus. Atua's gophermap support covers:

• comment lines

Comment lines are static text without any tabs. They will be reformatted according to protocol and sent.

• selector lines

Any line with a tab is treated as a selector line and is transferred without changing.

~~~'Tab var :eol? [ ASCII:LF eq? ] [ ASCII:CR eq? ] bi or ; :tab? @Tab ; :check-tab   dup ASCII:HT eq? [ &Tab v:on ] if ; :gopher:gets (a-)   &Tab v:off   buffer:set   [ @FID file:read dup buffer:add check-tab eol? not ] while   buffer:get drop ; ~~~

The internal helpers are now defined, so switch to the part of the namespace that'll be left exposed to the world.

~~~---reveal--- ~~~

An information line s:get a format like:


The gopher:i displays a string in this format. It's used later for the index footer.

~~~:gopher:i (s-)   'i%s\t\tnull.host\t1 s:format s:put eol ; ~~~

~~~:gopher:get-selector (-)   &Selector s:get ;   :gopher:file-requested? (-f)   &Selector s:chop s:length n:-zero? ;   :gopher:valid-file? (-f)   [ @Requested-File file:R file:open       file:size n:strictly-positive? ]   [ FALSE ] choose ;   :gopher:get-index (-s)   @Requested-Index file:exists?   [ @Requested-Index &Server-Info v:on  ]   [ PATH '/empty.index s:append         ] choose ;   :gopher:file-for-request (-s)   &Mode v:off   construct-filenames   gopher:file-requested?   [ @Requested-File file:exists? gopher:valid-file?     [ @Requested-File  ]     [ gopher:get-index ] choose   ]   [ PATH DEFAULT-INDEX s:append &Server-Info v:on ] choose ;   :gopher:read-file (f-s)   file:R file:open !FID   @FID file:size !Size   @Size [ @FID file:read c:put ] times   @FID file:close ;   :gopher:line (s-)   dup [ ASCII:HT eq? ] s:filter s:length #1 gt?   [ s:put ]   [ s:put tab SERVER s:put tab PORT s:put ] choose   eol ;   :gopher:generate-index (f-)   file:R file:open !FID   @FID file:size !Size   [ buffer gopher:gets     buffer tab? [ gopher:line ] [ gopher:i ] choose     @FID file:tell @Size lt? ] while   @FID file:close ; ~~~

The only thing left is the top level server.

~~~:gopher:server   gopher:get-selector   gopher:file-for-request   @Server-Info   [ gopher:generate-index     '------------------------------------------- gopher:i     'forthworks.com:70_/_atua_/_running_on_retro gopher:i       '. s:put eol ]   [ gopher:read-file ] choose ; ~~~

Close off the helper portion of the namespace.

~~~}} ~~~

And run the gopher:server.

~~~gopher:server reset ~~~