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Molly Brown

The Unsinkable Molly Brown is a full-featured Gemini server implemented in Go.

For more information on the Gemini protocol see:

Overview

Molly Brown is intended to be a full-featured Gemini server which is suitable for use in pubnix or similar shared-hosting environments, where users can upload their content but do not have access to the main configuration file (of course, it is also perfectly suitable for single user environments, but its multi-user supports sets it apart from many other Gemini servers).

Molly Brown features:

  • Support for traditional ~username URLs.
  • Automatic directory listings, with support for customised headers and footers, control over file sorting order and the ability to use headings from text/gemini content in place of filenames.
  • Determination of MIME type via filename extension, which can be manually overridden to allow, e.g., serving Atom feeds as application/atom+xml instead of application/xml or text/xml. The file extension for text/gemini defaults to gmi, but this can be overrideen too.
  • Support for temporary and permanent redirects, specified via regular expressions.
  • Dynamic content via CGI and SCGI.
  • Support for "certificate zones", where access to certain paths is restricted to clients providing TLS certificates whose SHA256 fingerprints have been added to a list of approved fingerprints, analogous to SSH's authorized_keys file.
  • The ability for users to override some configuration settings on a per-directory basis using .molly files, analogous to Apache's .htaccess files.

The follow features are planned for the future:

  • Name-based virtual hosting

System requirements

Molly Brown is known to run on:

  • FreeBSD
  • GNU/Linux
  • OpenBSD
  • 9Front

Please let us know if you get it to work on some other platform!

Molly Brown only has a single dependency beyond the Go standard library, which is this TOML parsing library.

The OpenBSD implementation also uses the golang.org/x/sys/unix package to provide the pledge(2) and unveil(2) system calls to provide additional security features.

Installation

The easiest way for now to install Molly Brown is to use the standard Golang tool go (note I said "easiest", not "easy" - this is still a pretty clunky manual process, sorry). Unfortunately, you have to do a little bit of preparation for this to work (unless you're a Go developer yourself in which case you surely already have this done)...

Prepare your $GOPATH

  1. Create an empty directory ~/go.
  2. Set the $GOPATH environment variable to ~/go.

(you can in fact put your $GOPATH anywhere you like, but ~/go is the convention)

Fetch and build Molly Brown

Run go get tildegit.org/solderpunk/molly-brown. If everything goes well, the end result of this will be that you'll have the Molly Brown source code sitting in ~/go/src/tildegit.org/solderpunk/molly-brown and an executable binary sitting at ~/go/bin/molly-brown. If it makes you happier or your life easier, you can copy that binary to /usr/sbin/ or anywhere else.

Configuration

Molly Brown can run without a configuration file, in which case it will use compiled-in default settings. However, these settings are oriented toward quick test runs with all files in the current working directory. For regular use, you will want to override these defaults with more suitable settings from a config file. An example config file showing the syntax for all settings can be found in the ~/go/src/tildegit.org/solderpunk/molly-brown/ directory with the filename example.conf. You can copy this file to /etc/molly.conf and edit it to suit your environment. All the options are explained further below. If you put your configuration file somewhere other than /etc/molly.conf, you will need to use Molly Brown's -c command line option to tell Molly Brown where to find it.

Running

The molly-brown executable recognises the following command line switches:

  • -c: Used to specify a config file.
  • -C: Used to specify a directory to chroot to (unix only).
  • -u: Used to specify the name of an unprivileged user which Molly Brown should switch to running as if started as root or run as a setuid executable (unix only).
  • -v: Print version number and exit.

Molly Brown does not handle details like daemonising itself, changing the user it runs as, etc. You will need to take care of these tasks by, e.g. integrating Molly Brown with your operating system's init system. Some limited instructions on how to do this for common systems follows.

Manual management

You can always use a tool like daemon to take care of daemonising the Molly Brown process, changing the user it runs as, chrooting it to a particular location, etc. You can call daemon from /etc/rc.local (if your OS still supports it) to start it on system boot.

Systemd

An example systemd unit file for Molly Brown, named molly-brown.service.example, can be found in the contrib/init directory of the Molly Brown source directory. After copying this file to /etc/systemd/system/molly-brown.service or /usr/lib/systemd/system/molly-brown.service (consult your system's documentation for the appropriate choice) and making any necessary changes for your environment, you can run the follow commands as root to start Molly Brown and make sure it starts automatically on system boot.

# systemctl daemon-reload
# systemctl enable molly-brown.service
# systemctl start molly-brown.service

OpenRC

An example OpenRC initscript for Molly Brown, named molly-brown.openrc.example, can be found in the contrib/init directory of the Molly Brown source directory.

More detailed instructions on OpenRC setup are welcome!

OpenBSD

An example OpenBSD initscript for Molly Brown, named molly-brown.openbsd.example, can be found in the contrib/init directory of the Molly Brown source directory. After copying this file to /etc/rc.d/mollybrownd, you can add the mollybrownd daemon to your system startup with rcctl or by manually adding mollybrownd to your /etc/rc.conf.local configuration. The following lines in rc.conf.local will autostart your mollybrownd daemon as the user username:

mollybrownd_user=username
pkg_scripts=mollybrownd

Be sure that the user running your mollybrownd daemon has read access to /etc/molly.conf and all of the files and directories listed in /etc/molly.conf. That user will also need write access to the configured log file locations.

You can start your mollybrownd daemon with rcctl:

rcctl start mollybrownd

FreeBSD

An example FreeBSD rc script is in contrib/init/molly-brown.freebsd.example.

Copy rc script to /etc/rc.d/molly, and add molly_enable="YES" to /etc/rc.conf to enable the service.

Make sure the daemon user has access to config locations in molly.conf like CertPath, KeyPath, DocBase, etc.

Start molly with,

service molly start

Configuration Options

The following sections detail all the options which can be set in /etc/molly.conf or any other configuration file specified with the -c option.

The format of the configuration file is TOML, which bares some similarity to the "INI" format. Remember that you can check example.conf for examples of the appropriate syntax.

Basic options

  • Port: The TCP port to listen for connections on (default value 1965).
  • Hostname: The hostname to respond to requests for (default value localhost). Requests for URLs with other hosts will result in a status 53 (PROXY REQUEST REFUSED) response.
  • CertPath: Path to TLS certificate in PEM format (default value cert.pem).
  • KeyPath: Path to TLS private key in PEM format (default value key.pem).
  • DocBase: Base directory for Gemini content (default value /var/gemini/). Only world-readable files stored in or below this directory will be served by Molly Brown.
  • HomeDocBase: Requests for paths beginning with ~/username/ will be looked up relative to DocBase/HomeDocBase/username/ (default value users). Note that Molly Brown does not look inside user's actual home directories like you may expect based on experience with other server software. Of course, you can symlink /var/gemini/users/gus/ to /home/gus/public_gemini/ if you want.
  • AccessLog: Path to access log file (default value access.log, i.e. in the current wrorking directory). Note that all intermediate directories must exist, Molly Brown won't create them for you. Set to - for logging to stdout, or to an empty string to disable access logging.
  • ErrorLog: Path to error log file. If set to an empty string (the default), Molly Brown will log errors to stderr (where they are easily captured by systemd or similar init systems). If set to a file, note that all intermediate directories must exist, Molly Brown won't create them for you.
  • GeminiExt: Files with this extension will be served with a MIME type of text/gemini (default value gmi).
  • MimeOverrides: In this section of the config file, keys are path regexs and values are MIME types. If the path of a file which is about to be served matches one the regexs, the corresponding MIME type will be used instead of one inferred from the filename extension.
  • DefaultLang: If this option is set, it will be served as the lang parameter of the MIME type for all text/gemini content.
  • DefaultEncoding: If this option is set, it will be served as the charset parameter of the MIME type for all text/gemini content.

Directory listings

Molly Brown will automatically generate directory listings for world-readable directories under DocBase which do not contain an index.gmi file. Only world-readable files and directories will be listed. If a world-readable file named .mollyhead is found in a directory, it's contents will be inserted above the directory listing instead of the default "Directory listing" title.

The following options allow users to configure various aspects of the directory listing:

  • DirectorySort: A string specifying how to sort files in automatically generated directory listings. Must be one of "Name", "Size" or "Time" (default value "Name").
  • DirectorySubdirsFirst (boolean): if true, list subdirectories of the directory being listed before files. Subdirs and files will be sorted within their respective categories according to DirectorySort (default value false).
  • DirectoryReverse (boolean): if true, automatically generated directory listings will list files in descending order of whatever DirectorySort is set to (default value false).
  • DirectoryTitles (boolean): if true, automatically generated directory listings will use the first top-level heading (i.e. line beginning with "# ") in files with an extension of GeminiExt instead of the filename (default value false).

Redirects

  • TempRedirects: In this section of the config file, keys are regular expressions which the server will attempt to match against the path component if incoming request URLs. If a match is found, Molly Brown will serve a redirect to a new URL derived by replacing the path component with the value corresponding to the matched key. Within the replacement values, $1, $2, etc. will be replaced by the first, second, etc. submatch in the regular expression. Named captures can also be used for more sophisticated redirect logic - see the documentation for the Go standard library's regexp package for full details.
  • PermRedirects: As per TempRedirects above, but Molly Brown will use the 31 status code instead of 30.

Dynamic content

Molly Brown supports dynamically generated content using an adaptation of the CGI standard, and also the SCGI standard.

The stdout of CGI processes will be sent verbatim as the response to the client, and CGI applications are responsible for generating their own response headers. CGI processes must terminate naturally within 10 seconds of being spawned to avoid being killed. Details about the request are available to CGI applications through environment variables, generally following RFC 3875. In particular, note that if a request URL includes components after the path to an executable (e.g. cgi-bin/script.py/foo/bar/baz) then the environment variable SCRIPT_PATH will contain the part of the URL path mapping to the executable (e.g. /var/gemini/cgi-bin/scripty.py) while the variable PATH_INFO will contain the remainder (e.g. foo/bar/baz).

Molly Brown itself tries very hard to avoid being tricked into serving content that isn't supposed to be served, but it is completely unable to impose any control over what CGI processes can or can't go after they are started! Where possible, Molly Brown will use the operating system's security features to reduce risk, but it is your responsibility to understand what it can and cannot do and weigh the risks accordingly:

When compiled on GNU/Linux with Go version 1.16 or later, or on any other unix operating system with any version of Go, Molly Brown will use the setuid() system call as follows. When the compiled molly-brown executable has its SETUID bit set, so that it starts with the privileges of the user who owns the binary, it will change the effective UID back to the real UID before it begins accepting network connections. This way, config files, log files and TLS keys can be set readable by the user who owns the binary, but not readable by the user who runs the binary. CGI processes will then be unable to read any of those sensitive files. If the binary is not SETUID but is run by the superuser/root, then Molly will change its UID to that of the nobody user (or any other user specified with the -u option) before accepting network connections, so CGI processes will again not be able to read sensitive files. Note that while these measures can protect Molly's own sensitive files from CGI processes, CGI processes may still be able to read other sensitive files anywhere else on the system. Consider chroot()-ing Molly Brown into a small corner of the filesystem (see discussion of the -C option at the start of the Running section) to reduce this risk.

When compiled on GNU/Linux with Go versions 1.15 or earlier, Molly Brown is completley unable to reliably change its UID due to the way early implementations of goroutines interacted with the setuid() system call. In this situation, Molly Brown will refuse to run as superuser/root. It will run as any other user, but CGI processes will necessary run as the same user as the server and so unavoidably will have access to sensitive files. You should proceed with extreme caution and only use carefully vetted CGI programs. Consider using systemd's ability to chroot a non-privileged process at the moment of startup to at least confine the risk to Molly Brown's sensitive files and not the entire system's.

Molly Brown will compile on non-unix operating systems and is known to run on Plan9, for example, but no special security measures are taken on these non-unix platforms. It is your responsibility to understand the risks. If you are aware of security measures for these systems which can be implemented in Go, patches are extremely welcome.

SCGI applications must be started separately (i.e. Molly Brown expects them to already be running and will not attempt to start them itself), and as such they can run e.g. as their own user and/or chrooted into their own filesystem, meaning that they are less of a security threat than CGI applications (in addition to avoiding the overhead of process startup, database connection etc. on each request).

  • CGIPaths: A list of filesystem paths, within which world-executable files will be run as CGI processes. The paths act as prefixes, i.e. if /var/gemini/cgi-bin is listed then /var/gemini/cgi-bin/script.py and /var/gemini/cgi-bin/subdir/subsubdir/script.py will both be run. The paths may include basic wildcard characters, where ? matches a single non-separator character and * matches a sequence of them - if wildcards are used, the path should not end in a trailing slash
    • this appears to be a peculiarity of the Go standard library's filepath.Glob function. Any non-absolute paths will be resolved relative to DocBase.
  • SCGIPaths: In this section of the config file, keys are URL path prefixes and values are filesystem paths to unix domain sockets. Any request for a URL whose path begins with one of the specified prefixes will cause an SCGI request to be sent to the corresponding domain socket. Anything sent back from a program listening on the other end of the socket will be sent as the response to the client. SCGI applications are responsible for generating their own response headers.

TLS options

  • AllowTLS12 (boolean): if true, Molly Brown will accept connections from clients using TLS version 1.2 or later (1.2 is the bare minimum allowed by the Gemini spec). If set to false, Molly Brown will instead require TLS version 1.3 or later - 1.2 to 1.3 was a big change and drastic simplification of the TLS spec which discarded a wide range of old and insecure configurations. (default value true)

Certificate zones

Molly Brown allows you to use client certificates to restrict access to certain resources (which may be static or dynamic). The overall workflow is highly reminiscent of OpenSSH's authorized_keys facility.

  • CertificateZones: In this section of the config file, keys are path regexs and values are lists of hex-encoded SHA256 fingerprints of client certificates. Any requests whose path matches one of the regexs will only be served as normal if the request is made with a client certificate whose fingerprint is in the corresponding list. Requests made without a certificate will cause a response with a status code of 60. Requests made with a certificate not in the list will cause a response with a status code of 60.

.molly files

In order to allow users of shared-hosting who do not have access to the main Molly Brown configuration file to customise some aspects of their Gemini site, Molly Brown features functionality much like Apache's .htaccess files. If the main configuration file contains the line ReadMollyFiles = true, then each directory in the path to a resource will be checked for a file named .molly. These files should be in exactly the same format as the main configuration file, an their contents will override (some) settings from the main file. Each .molly file will override settings specified in .molly files from higher directories.

E.g. when handling a request which maps to /var/gemini/foo/bar/baz/file.gmi, then:

  • The settings in the file /var/gemini/.molly, if it exists, will override those in /etc/molly.conf.
  • The settings in the file /var/gemini/foo/.molly, if it exists, will override those in /var/gemini/.molly.
  • The settings in the file /var/gemini/foo/bar/.molly, if it exists, will override those in /var/gemini/foo/.molly.
  • The settings in the file /var/gemini/foo/bar/baz/.molly, if it exists, will override those in /var/gemini/foo/bar/.molly.

Only the following settings can be overriden by .molly files. Any other settings in .molly files will be ignored:

  • CertificateZones
  • DefaultLang
  • DefaultEncoding
  • DirectorySort
  • DirectorySubdirsFirst
  • DirectoryReverse
  • DirectoryTitles
  • GeminiExt
  • MimeOverrides
  • PermRedirects
  • TempRedirects

Trivia

Margaret Brown was an American philanthropist and socialite who survived the sinking of the RMS Titanic, leading to a Broadway musical and later a film about her life being titled "The Unsinkable Molly Brown". The "unsinkable" moniker inspired NASA astronaut Gus Grissom to name the Gemini 3 capsule he commanded "Molly Brown" - Grissom had almost drowned a few years earlier when his Mercury 4 capsule "Liberty Bell" sank after splashdown.