Gophor

A Gopher server written in GoLang as a means of learning about the Gopher protocol, and more GoLang.

Linux only for now. Cross-compiled to way too many architectures. Build-script now much improved, but still not pretty...

I'm unemployed and work on open-source projects like this and many others for free. If you would like to help support my work that would be hugely appreciated 💕 https://liberapay.com/grufwub/

WARNING: the development branch is filled with lava, fear and capitalism.

Features

• Built with security, concurrency and efficiency in mind.

• ZERO external dependencies.

• LRU file caching with user-controlled cache size, max cached file size and cache refresh frequency.

• CGI/1.1 support (see below for CGI environment variables set).

• HTTP style URL query and encoding support.

• Executable gophermap support.

• Insert files with automated line reflowing, and inline shell script output within gophermaps.

• Support for all commonly accepted item type characters (beyond just RFC1436 support).

• Automatic replacement of $hostname or $port in gophermap lines with current host information.

• User supplied footer text appended to gophermaps and directory listings.

• Separate system and access logging with output and formatting options.

Please note

Gophermap parsing

Due to the way that gophermap parsing is handled, if a gophermap is larger than the max cache'd file size or file caching is disabled, which is the same as same as setting max size to 0, these gophermaps WILL NOT be parsed by the server. The features you will miss out on for these files is are all those listed as [SERVER ONLY] in the gophermap item types section below.

Chroots and privilege dropping

Previously, chrooting to server directory and dropping privileges was supported by using Go C bindings. Unexpected circumstances have not yet been witnessed... But as this is not officially supported due to unexpected behaviour with .Set{U,G}id() under Linux, and there is a near 10 year ongoing tracked issue (https://github.com/golang/go/issues/1435), I decided to drop this feature for now. As soon as this patch gets merged I'll add support: https://go-review.googlesource.com/c/go/+/210639

In place of removing this, request sanitization has been majorly improved and checks are in place to prevent running Gophor as root.

If you run into issues binding to a lower port number due to insufficient permissions then there are a few alternatives:

• set process capabilities using utility like capsh: https://linux.die.net/man/1/capsh

• use Docker (or some other solution) and configure port forwarding on the host

• start gopher in it's own namespace in a chroot

Usage

gophor [args]
       -root                Change server root directory.
       -bind-addr           Change server bind-address (used in creating
                            socket).
       -port                Change server bind port.

       -fwd-port            Change port used in $port replacement strings
                            (e.g. when port forwarding).
       -hostname            Change server hostname (FQDN).

       -system-log          Path to gophor system log file.
       -access-log          Path to gophor access log file.
       -log-output          Change log output type (disable|stderr|file)
       -log-opts            Comma-separated list of lop opts (timestamp|ip)

       -file-monitor-freq   Change file-cache freshness check frequency.
       -cache-size          Change max no. files in file-cache.
       -cache-file-max      Change maximum allowed size of a cached file.
       -disable-cache       Disable file caching.

       -page-width          Change page width used when formatting output.
       -disable-cgi         Disable CGI and all executable support.

       -footer              Change gophermap footer text (Unix new-line
                            separated lines).
       -no-footer-separator Disable footer text line separator.

       -restrict-files      New-line separated list of regex statements
                            (checked against absolute paths) restricting
                            file access.
       -restricted-commands New-line separated list of regex statements
                            restricting command access in gophermaps.

       -description         Change server description in generated caps.txt.
       -admin-email         Change admin email in generated caps.txt.
       -geoloc              Change geolocation in generated caps.txt.

       -version             Print version string.

Supported gophermap item types

All of the following item types are supported by Gophor, separated into grouped standards. Most handling of item types is performed by the clients connecting to Gophor, but when performing directory listings Gophor will attempt to automatically classify files according to the below types.

Item types listed as [SERVER ONLY] means that these are item types recognised ONLY by Gophor and to be used when crafting a gophermap. They provide additional methods of formatting / functionality within a gophermap, and the output of these item types is usually converted to informational text lines before sending to connecting clients.

RFC 1436 Standard:
Type | Treat as | Meaning
--------------------------
 0   |   TEXT   | Regular file (text)
 1   |   MENU   | Directory (menu)
 2   | EXTERNAL | CCSO flat db; other db
 3   |  ERROR   | Error message
 4   |   TEXT   | Macintosh BinHex file
 5   |  BINARY  | Binary archive (zip, rar, 7zip, tar, gzip, etc)
 6   |   TEXT   | UUEncoded archive
 7   |   INDEX  | Query search engine or CGI script
 8   | EXTERNAL | Telnet to: VT100 series server
 9   |  BINARY  | Binary file (see also, 5)
 T   | EXTERNAL | Telnet to: tn3270 series server
 g   |  BINARY  | GIF format image file (just use I)
 I   |  BINARY  | Any format image file
 +   |     -    | Redundant (indicates mirror of previous item)

GopherII Standard:
Type | Treat as | Meaning
--------------------------
 c   |  BINARY  | Calendar file
 d   |  BINARY  | Word-processing document; PDF document
 h   |   TEXT   | HTML document
 i   |     -    | Informational text (not selectable)
 p   |   TEXT   | Page layout or markup document (plain text w/ ASCII tags)
 m   |  BINARY  | Email repository (MBOX)
 s   |  BINARY  | Audio recordings
 x   |   TEXT   | eXtensible Markup Language document
 ;   |  BINARY  | Video files

Commonly used:
Type | Treat as | Meaning
--------------------------
 .   |     -    | Last line -- stop processing gophermap default
 !   |     -    | [SERVER ONLY] Menu title (set title ONCE per gophermap)
 #   |     -    | [SERVER ONLY] Comment, rest of line is ignored
 -   |     -    | [SERVER ONLY] Hide file/directory from directory listing
 *   |     -    | [SERVER ONLY] Last line + directory listing -- stop processing
     |          |               gophermap and end on a directory listing
 =   |     -    | [SERVER ONLY] Include or execute subgophermap, cgi-bin, regular
     |          |               file or shell command stdout here

Compliance

We aim to comply more with GopherII, given how much newer than Gopher+ this standard is and that the extension, GopherIIbis is seemingly the work of Gopher+ continued.

Item types

Supported item types are listed above.

Informational lines are sent as i<text here>\t/\tnull.host\t0.

Titles are sent as i<title text>\tTITLE\tnull.host\t0.

Web address links are sent as h<text here>\tURL:<address>\thostname\tport. An HTML redirect is sent in response to any requests beginning with URL:.

CGI/1.1

The list of environment variables that gophor sets are as follows.

RFC 3875 standard:

# Set
GATEWAY INTERFACE
SERVER_SOFTWARE
SERVER_PROTOCOL
CONTENT_LENGTH
REQUEST_METHOD
SERVER_NAME
SERVER_PORT
REMOTE_ADDR
QUERY_STRING
SCRIPT_NAME
SCRIPT_FILENAME

# NOT set
    Env Var     |                  Reasoning
----------------------------------------------
PATH_INFO       | This variable can fuck off, having to find the shortest
                | valid part of path heirarchy in a URI every single
                | CGI request so you can split and set this variable is SO
                | inefficient. However, if someone more knowledgeable has
                | other opinions or would like to point out where I'm wrong I
                | will happily change my tune on this.
PATH_TRANSLATED | See above.
AUTH_TYPE       | Until we implement authentication of some kind, ignoring.
CONTENT_TYPE    | Very HTTP-centric relying on 'content-type' header.
REMOTE_IDENT    | Remote client identity information.
REMOTE_HOST     | Basically if the client has a resolving name (not just
                | IP), not really necessary.
REMOTE_USER     | Remote user id, not used as again no user auth yet.

Non-standard:

# Set
SELECTOR
DOCUMENT_ROOT
REQUEST_URI
PATH
COLUMNS
GOPHER_CHARSET

Policy files

Upon request, caps.txt can be provided from the server root directory containing server capabiities. This can either be user or server generated.

Upon request, robots.txt can be provided from the server root directory containing robot access restriction policies. This can either be user or server generated.

Errors

Errors are sent according to GopherII standards, terminating with a last line: 3<error text>CR-LF

Possible Gophor errors:

     Text                 |      Meaning
400 Bad Request           | Request not understood by server due to malformed
                          | syntax
401 Unauthorised          | Request requires authentication
403 Forbidden             | Request received but not fulfilled
404 Not Found             | Server could not find anything matching requested
                          | URL
408 Request Time-out      | Client did not produce request within server wait
                          | time
410 Gone                  | Requested resource no longer available with no
                          | forwarding address
500 Internal Server Error | Server encountered an unexpected condition which
                          | prevented request being fulfilled
501 Not Implemented       | Server does not support the functionality
                          | required to fulfil the request
503 Service Unavailable   | Server currently unable to handle the request
                          | due to temporary overload / maintenance

Terminating full stop

Gophor will send a terminating full-stop for menus, but not for served or executed files.

Placeholder (null) text

All of the following are used as placeholder text in responses...

Null selector: -

Null host: null.host

Null port: 0

Todos

• Character encoding support

• Fix file cache only updating if main gophermap changes (but not sub files)

• Personal user gopherspaces

• Remapping of file paths

• Rotating logs

• Add last-mod-time to directory listings

• TLS support

• Connection throttling + timeouts

Resources used

Gopher-II (The Next Generation Gopher WWIS): https://tools.ietf.org/html/draft-matavka-gopher-ii-00

Gophernicus source (a great gopher daemon in C): https://github.com/gophernicus/gophernicus

All of the below can be viewed from your standard web browser using floodgap's Gopher proxy: https://gopher.floodgap.com/gopher/gw

RFC 1436 (The Internet Gopher Protocol: gopher://gopher.floodgap.com:70/0/gopher/tech/rfc1436.txt

Gopher+ (upward compatible enhancements): gopher://gopher.floodgap.com:70/0/gopher/tech/gopherplus.txt