Gopher Server

A few days ago, I noticed a post about building a Gopher Server in Perl 6. I had already implemented a Gopher Client in Factor, and thought it might be fun to show a simple Gopher Server in Factor in around 50 lines of code.

Using the io.servers vocabulary, we will define a new multi-threaded server that has a directory to serve content from and hostname that it can be accessed at:

TUPLE: gopher-server < threaded-server
    { serving-hostname string }
    { serving-directory string } ;

When a file is requested, it can be streamed back to clients:

: send-file ( path -- )
    binary [ [ write ] each-block ] with-file-reader ;

The Gopher protocol is defined in RFC 1436 and lists a few differentiated file types. We use the mime.types vocabulary to return the correct one.

: gopher-type ( entry -- type )
    dup directory? [
        drop "1"
    ] [
        name>> mime-type {
            { [ dup "text/" head? ] [ drop "0" ] }
            { [ dup "image/gif" = ] [ drop "g" ] }
            { [ dup "image/" head? ] [ drop "I" ] }
            [ drop "9" ]
        } cond
    ] if ;

When a directory is requested, we can send a listing of all the sub-directories and files it contains, sending their relative path to the root directory being served so they can be requested properly by the client:

:: send-directory ( server path -- )
    path [
        [
            [ gopher-type ] [ name>> ] bi
            dup path prepend-path
            server serving-directory>> ?head drop
            server serving-hostname>>
            server insecure>>
            "%s%s\t%s\t%s\t%d\r\n" sprintf utf8 encode write
        ] each
    ] with-directory-entries ;

To know which path was requested, we read the line, split on the first tab, carriage return, or newline character we see:

: read-gopher-path ( -- path )
    readln [ "\t\r\n" member? ] split1-when drop ;

With all of that built, we can now implement a word to handle a client request:

M: gopher-server handle-client*
    dup serving-directory>> read-gopher-path append-path
    dup file-info directory? [
        send-directory
    ] [
        send-file drop
    ] if flush ;

Initializing a gopher-server instance and providing a convenience word to start one:

: <gopher-server> ( directory port -- server )
    utf8 gopher-server new-threaded-server
        "gopher.server" >>name
        swap >>insecure
        binary >>encoding
        "localhost" >>serving-hostname
        swap resolve-symlinks >>serving-directory ;

: start-gopher-server ( directory port -- server )
    <gopher-server> start-server ;

This is available in the gopher.server vocabulary with a few improvements such as:

• Support for .gophermap files for alternate results when content is requested.
• Support for .gopherhead files to print headers above directory listings.
• Navigation to parent directories using .. links.
• Display file modified timestamp and file sizes.
• Improved error handling.