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).

• URL encoding with query support.

• Serve DIR/gophermap by default, else falls back to directory listing.

• Parsing of any files named gophermap or ending in .gophermap as gophermaps.

• Executable gophermap support.

• Insert files with automated line reflowing, output of any CGI scripts or executable gophermaps 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.

• File remapping support via regex, of format:

  /virtual/file -> /actual/file

  e.g. scripts within cgi-bin to the root directory: /(?P<script>[^/]+) -> /cgi-bin/$script

  Entries are parsed, compiled, and so matched-against in order.

• 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 (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 are features listed [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. This is not officially supported due to weird behaviour with .Set{U,G}id() under Linux. As such, the feature has been dropped for now.

There is a near 10 year ongoing tracked issue (https://github.com/golang/go/issues/1435), and 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 gophor process capabilities: e.g. setcap 'cap_net_bind_service=+ep' /usr/local/bin/gophor

• 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.
       -file-remap           New-line separated list of file remappings of format:
                             /virtual/relative/path -> /actual/relative/path

       -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.
       -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.

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

       -disable-cgi          Disable CGI and all executable support.
       -http-compat-cgi      Enable HTTP CGI script compatibility (will strip
                             HTTP headers).
       -http-header-buf      Change max CGI read count to look for and strip
                             HTTP headers before sending raw (bytes).
       -safe-path            Set safe PATH variable to be used when executing
                             CGI scripts, gophermaps and inline shell
                             commands.
       -max-exec-time        Change max executable CGI, gophermap and inline
                             shell command runtime.

       -socket-write-buf     Change socket write buffer size (bytes).
       -socket-read-buf      Change socket read buffer size (bytes).
       -socket-read-max      Change socket read count max (integer multiplier
                             to socket-read-buf-max).
       -file-read-buf        Change file read buffer size (bytes).

       -socket-read-timeout  Change socket read deadline (timeout).
       -socket-write-timeout Change socket write deadline (timeout).

       -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 or regular
     |          |               file here.

Encoding

By default, URLs are parsed as having standard (HTTP) URL encoding. All other parsed text content (gophermaps) are treated as UTF-8, as this is the default encoding scheme for Go strings. Support for more encoding schemes is planned for the future.

Compliance

We aim to comply more with GopherII (see in references below).

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

• Support setting character encoding

• improve organization of what logs go where (e.g. to sys or acc)

• Move filesystem_read functions to FileSystem struct function

• FastCGI support

• Personal user gopherspaces

• Rotating logs

• 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