.\" Copyright (c) 2021, 2022 Omar Polo <op@omarpolo.com>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.Dd $Mdocdate: February 26 2022$
.Dt GMID 1
.Os
.Sh NAME
.Nm gmid
.Nd simple and secure Gemini server
.Sh SYNOPSIS
.Nm
.Bk -words
.Op Fl fnv
.Op Fl c Ar config
.Op Fl D Ar macro Ns = Ns Ar value
.Op Fl P Ar pidfile
.Ek
.Nm
.Bk -words
.Op Fl 6hVv
.Op Fl d Ar certs-dir
.Op Fl H Ar hostname
.Op Fl p Ar port
.Op Fl x Ar cgi
.Op Ar dir
.Ek
.Sh DESCRIPTION
.Nm
is a simple and minimal gemini server that can serve static files,
execute CGI scripts and talk to FastCGI applications.
It can run without a configuration file with a limited set of features
available.
.Pp
.Nm
rereads the configuration file when it receives
.Dv SIGHUP .
.Pp
The options are as follows:
.Bl -tag -width 14m
.It Fl c Ar config
Specify the configuration file.
.It Fl D Ar macro Ns = Ns Ar value
Define
.Ar macro
to be set to
.Ar value
on the command line.
Overrides the definition of
.Ar macro
in the config file if present.
.It Fl f
Stays and logs on the foreground.
.It Fl n
Check that the configuration is valid, but don't start the server.
If specified two or more time, dump the configuration in addition to
verify it.
.It Fl P Ar pidfile
Write daemon's pid to the given location.
.Ar pidfile
will also act as lock: if another process is holding a lock on that
file,
.Nm
will refuse to start.
.El
.Pp
If no configuration file is given,
.Nm
runs in
.Dq config-less mode
.Pq i.e. runs in the foreground to serve a directory from the shell
and looks for the following options
.Bl -tag -width 14m
.It Fl 6
Enable IPv6.
.It Fl d Ar certs-path
Directory where certificates for the config-less mode are stored.
By default it is
.Pa $XDG_DATA_HOME/gmid ,
i.e.
.Pa ~/.local/share/gmid .
.It Fl H Ar hostname
The hostname
.Po
.Ar localhost
by default
.Pc .
Certificates for the given
.Ar hostname
are searched inside the
.Ar certs-dir
directory given with the
.Fl d
option.
They have the form
.Pa hostname.cert.pem
and
.Pa hostname.key.pem .
If a certificate or a key doesn't exist for a given hostname, they
will be generated automatically.
.It Fl h , Fl -help
Print the usage and exit.
.It Fl p Ar port
The port to listen on, by default 1965.
.It Fl V , Fl -version
Print the version and exit.
.It Fl v
Verbose mode.
Multiple
.Fl v
options increase the verbosity.
.It Fl x Ar path
Enable execution of
.Sx CGI
scripts.
See the description of the
.Ic cgi
option in the
.Sq Servers
section below to learn how
.Ar path
is processed.
Cannot be provided more than once.
.It Ar dir
The root directory to serve.
By default the current working directory is assumed.
.El
.Sh CONFIGURATION FILE
The configuration file is divided into three sections:
.Bl -tag -width xxxx
.It Sy Macros
User-defined variables may be defined and used later, simplifying the
configuration file.
.It Sy Global Options
Global settings for
.Nm .
.It Sy Servers
Virtual hosts definition.
.It Sy Types
Media types and extensions.
.El
.Pp
Within the sections, empty lines are ignored and comments can be put
anywhere in the file using a hash mark
.Pq Sq # ,
and extend to the end of the current line.
A boolean is either the symbol
.Sq on
or
.Sq off .
A string is a sequence of characters wrapped in double quotes,
.Dq like this .
Multiple strings one next to the other are joined into a single
string:
.Bd -literal -offset indent
# equivalent to "temporary-failure"
block return 40 "temporary" "-" "failure"
.Ed
.Pp
Furthermore, quoting is necessary only when a string needs to contain
special characters
.Pq like spaces or punctuation ,
something that looks like a number or a reserved keyword.
The last example could have been written also as:
.Bd -literal -offset indent
block return 40 temporary "-" failure
.Ed
.Pp
Strict ordering of the sections is not enforced, so that is possible
to mix macros, options and
.Ic server
blocks.
However, defining all the
.Ic server
blocks after the macros and the global options is recommended.
.Pp
Newlines are often optional, except around top-level instructions, and
semicolons
.Dq \&;
can also be optionally used to separate options.
.Pp
Additional configuration files can be included with the
.Ic include
keyword, for example:
.Bd -literal -offset indent
include "/etc/gmid.conf.local"
.Ed
.Ss Macros
Macros can be defined that will later be expanded in context.
Macro names must start with a letter, digit or underscore and may
contain any of those characters.
Macros names may not be reserved words.
Macros are not expanded inside quotes.
.Pp
Two kinds of macros are supported: variable-like and proper macros.
When a macro is invoked with a
.Dq $
before its name its expanded as a string, whereas when it's invoked
with a
.Dq @
its expanded in-place.
.Pp
For example:
.Bd -literal -offset indent
dir = "/var/gemini"
certdir = "/etc/keys"
common = "lang it; auto index on"

server "foo" {
	root $dir "/foo"         # -> /var/gemini/foo
	cert $certdir "/foo.crt" # -> /etc/keys/foo.crt
	key  $certdir "/foo.pem" # -> /etc/keys/foo.pem
	@common
}
.Ed
.Ss Global Options
.Bl -tag -width 12m
.It Ic chroot Ar path
.Xr chroot 2
the process to the given
.Ar path .
The daemon has to be run with root privileges and thus the option
.Ic user
needs to be provided, so privileges can be dropped.
Note that
.Nm
will enter the chroot after loading the TLS keys, but before opening
the virtual host root directories.
It's recommended to keep the TLS keys outside the chroot.
Future version of
.Nm
may enforce this.
.It Ic ipv6 Ar bool
Enable or disable IPv6 support, off by default.
.It Ic map Ar mime-type Cm to-ext Ar file-extension
Map
.Ar mime-type
to the given
.Ar file-extension .
Both argument are strings.
.It Ic port Ar portno
The port to listen on.
1965 by default.
.It Ic prefork Ar number
Run the specified number of server processes.
This increases the performance and prevents delays when connecting to
a server.
When not in config-less mode,
.Nm
runs 3 server processes by default.
The maximum number allowed is 16.
.It Ic protocols Ar string
Specify the TLS protocols to enable.
Refer to
.Xr tls_config_parse_protocols 3
for the valid protocol string values.
By default, both TLSv1.3 and TLSv1.2 are enabled.
Use
.Dq tlsv1.3
to enable only TLSv1.3.
.It Ic user Ar string
Run the daemon as the given user.
.El
.Ss Servers
Every virtual host is defined by a
.Ic server
block:
.Bl -tag -width Ds
.It Ic server Ar hostname Brq ...
Match the server name using shell globbing rules.
It can be an explicit name,
.Ar www.example.com ,
or a name including a wildcards,
.Ar *.example.com .
.El
.Pp
Followed by a block of options that is enclosed in curly brackets:
.Bl -tag -width Ds
.It Ic alias Ar name
Specify an additional alias
.Ar name
for this server.
.It Ic auto Ic index Ar bool
If no index file is found, automatically generate a directory listing.
Disabled by default.
.It Ic block Op Ic return Ar code Op Ar meta
Send a reply and close the connection;
by default
.Ar code
is 40
and
.Ar meta
is
.Dq temporary failure .
If
.Ar code
is in the 3x range, then
.Ar meta
is mandatory.
Inside
.Ar meta ,
the following special sequences are supported:
.Bl -tag -width Ds -compact
.It \&%\&%
is replaced with a single
.Sq \&% .
.It \&%p
is replaced with the request path.
.It \&%q
is replaced with the query string of the request.
.It \&%P
is replaced with the server port.
.It \&%N
is replaced with the server name.
.El
.It Ic cert Ar file
Path to the certificate to use for this server.
.Ar file
should contain a PEM encoded certificate.
This option is mandatory.
.It Ic cgi Ar path
Execute
.Sx CGI
scripts that matches
.Ar path
using shell globbing rules.
.It Ic default type Ar string
Set the default media type that is used if the media type for a
specified extension is not found.
If not specified, the
.Ic default type
is set to
.Dq application/octet-stream .
.It Ic entrypoint Ar path
Handle all the requests for the current virtual host using the
.Sx CGI
script at
.Ar path ,
relative to the current document root.
.It Ic env Ar name Cm = Ar value
Set the environment variable
.Ar name
to
.Ar value
when executing CGI scripts.
Can be provided more than once.
.\" don't document the "spawn <prog>" form because it probably won't
.\" be kept.
.It Ic fastcgi Oo Ic tcp Oc Ar socket Oo Cm port Ar port Oc
Enable
.Sx FastCGI
instead of serving files.
The
.Ar socket
can either be a UNIX-domain socket or a TCP socket.
If the FastCGI application is listening on a UNIX domain socket,
.Ar socket
is a local path name within the
.Xr chroot 2
root directory of
.Nm .
Otherwise, the
.Ic tcp
keyword must be provided and
.Ar socket
is interpreted as a hostname or an IP address.
.Ar port
can be either a port number or the name of a service enclosed in
double quotes.
If not specified defaults to 9000.
.It Ic index Ar string
Set the directory index file.
If not specified, it defaults to
.Pa index.gmi .
.It Ic key Ar file
Specify the private key to use for this server.
.Ar file
should contain a PEM encoded private key.
This option is mandatory.
.It Ic lang Ar string
Specify the language tag for the text/gemini content served.
If not specified, no
.Dq lang
parameter will be added in the response.
.It Ic location Ar path Brq ...
Specify server configuration rules for a specific location.
.Ar path
argument will be matched against the request path with shell globbing
rules.
In case of multiple location statements in the same context, the first
matching location will be put into effect and the later ones ignored.
Therefore is advisable to match for more specific paths first and for
generic ones later on.
A
.Ic location
section may include most of the server configuration rules
except
.Ic alias , Ic cert , Ic cgi , Ic entrypoint , Ic env , Ic key ,
.Ic location , Ic param No and Ic proxy .
.It Ic log Ar bool
Enable or disable the logging for the current server or location block.
.It Ic param Ar name Cm = Ar value
Set the param
.Ar name
to
.Ar value
for FastCGI.
.It Ic ocsp Ar file
Specify an OCSP response to be stapled during TLS handshakes
with this server.
The
.Ar file
should contain a DER-format OCSP response retrieved from an
OCSP server for the
.Ic cert
in use.
If the OCSP response in
.Ar file
is empty, OCSP stapling will not be used.
The default is to not use OCSP stapling.
.It Ic proxy Oo Cm proto Ar name Oc Oo Cm for-host Ar host : Ns Oo Ar port Oc Oc Brq ...
Set up a reverse proxy.
The optional matching rules
.Cm proto
and
.Cm for-host
can be used to enable proxying only for protocols matching
.Ar name
.Po Dq gemini
by default
.Pc
and/or whose request IRI matches
.Ar host
and
.Ar port
.Pq 1965 by default .
Matching happens using shell globbing rules.
.Pp
In case of multiple matching proxy blocks in the same context, the
first matching proxy will be put into effect and the later ones
ignored.
.Pp
Valid options are:
.Bl -tag -width Ds
.It Ic cert Ar file
Specify the client certificate to use when making requests.
.It Ic key Ar file
Specify the client certificate key to use when making requests.
.It Ic protocols Ar string
Specify the TLS protocols allowed when making remote requests.
Refer to the
.Xr tls_config_parse_protocols 3
function for the valid protocol string values.
By default, both TLSv1.2 and TLSv1.3 are enabled.
.It Ic relay-to Ar host : Ns Op Ar port
Relay the request to the given
.Ar host
at the given
.Ar port ,
1965 by default.
This is the only mandatory option in a
.Ic proxy
block.
.It Ic require Ic client Ic ca Ar file
Allow the proxying only from clients that provide a certificate
signed by the CA certificate in
.Ar file .
.It Ic sni Ar hostname
Use the given
.Ar hostname
instead of the one extracted from the
.Ic relay-to
rule for the TLS handshake with the proxied gemini server.
.It Ic use-tls Ar bool
Specify whether to use TLS when connecting to the proxied host.
Enabled by default.
.It Ic verifyname Ar bool
Enable or disable the TLS server name verification.
Enabled by default.
.El
.It Ic root Ar directory
Specify the root directory for this server
.Pq alas the current Dq document root .
It's relative to the chroot if enabled.
.It Ic require Ic client Ic ca Ar path
Allow requests only from clients that provide a certificate signed by
the CA certificate in
.Ar path .
It needs to be a PEM-encoded certificate and it's not relative to the
chroot.
.It Ic strip Ar number
Strip
.Ar number
components from the beginning of the path before doing a lookup in the
root directory.
It's also considered for the
.Ar meta
parameter in the scope of a
.Ic block return .
.El
.Ss Types
The
.Ic types
section must include one or more lines of the following syntax, enclosed
in curly brances:
.Bl -tag -width Ds
.It Ar type/subtype Ar name Op Ar name ...
Set the media
.Ar type
and
.Ar subtype
to the specified extension
.Ar name .
One or more names can be specified per line.
Earch line may end with an optional semicolon.
.It Ic include Ar file
Include types definition from an external file, for example
.Pa /usr/share/misc/mime.types .
.El
.Sh CGI
When a request for an executable file matches the
.Ic cgi
rule, that file will be executed and its output fed to the client.
.Pp
The CGI scripts are executed in the directory they reside and inherit
the environment from
.Nm
with these additional variables set:
.Bl -tag -width 24m
.It Ev GATEWAY_INTERFACE
.Dq CGI/1.1
.It Ev GEMINI_DOCUMENT_ROOT
The root directory of the virtual host.
.It Ev GEMINI_SCRIPT_FILENAME
Full path to the CGI script being executed.
.It Ev GEMINI_URL
The full IRI of the request.
.It Ev GEMINI_URL_PATH
The path of the request.
.It Ev PATH_INFO
The portion of the requested path that is derived from the the IRI
path hierarchy following the part that identifies the script itself.
Can be unset.
.It Ev PATH_TRANSLATED
Present if and only if
.Ev PATH_INFO
is set.
It represent the translation of the
.Ev PATH_INFO .
.Nm
builds this by appending the
.Ev PATH_INFO
to the virtual host directory root.
.It Ev QUERY_STRING
The decoded query string.
.It Ev REMOTE_ADDR , Ev REMOTE_HOST
Textual representation of the client IP.
.It Ev REQUEST_METHOD
This is present only for RFC3875 (CGI) compliance.
It's always set to the empty string.
.It Ev SCRIPT_NAME
The part of the
.Ev GEMINI_URL_PATH
that identifies the current CGI script.
.It Ev SERVER_NAME
The name of the server
.It Ev SERVER_PORT
The port the server is listening on.
.It Ev SERVER_PROTOCOL
.Dq GEMINI
.It Ev SERVER_SOFTWARE
The name and version of the server, i.e.
.Dq gmid/1.8
.It Ev AUTH_TYPE
The string "Certificate" if the client used a certificate, otherwise
unset.
.It Ev REMOTE_USER
The subject of the client certificate if provided, otherwise unset.
.It Ev TLS_CLIENT_ISSUER
The is the issuer of the client certificate if provided, otherwise
unset.
.It Ev TLS_CLIENT_HASH
The hash of the client certificate if provided, otherwise unset.
The format is
.Dq ALGO:HASH .
.It Ev TLS_VERSION
The TLS version negotiated with the peer.
.It Ev TLS_CIPHER
The cipher suite negotiated with the peer.
.It Ev TLS_CIPHER_STRENGTH
The strength in bits for the symmetric cipher that is being used with
the peer.
.It Ev TLS_CLIENT_NOT_AFTER
The time corresponding to the end of the validity period of the peer
certificate in the ISO 8601 format
.Pq e.g. Dq 2021-02-07T20:17:41Z .
.It Ev TLS_CLIENT_NOT_BEFORE
The time corresponding to the start of the validity period of the peer
certificate in the ISO 8601 format.
.El
.Sh FastCGI
.Nm
optionally supports FastCGI.
A
.Ic fastcgi
rule must be present in a server or location block.
Then, all requests matching that server or location will be handled
via the specified FastCGI backend.
.Pp
By default the following variables
.Pq parameters
are sent, and carry the same semantics as with CGI.
More parameters can be added with the
.Ic param
option.
.Pp
.Bl -bullet -compact
.It
GATEWAY_INTERFACE
.It
GEMINI_URL_PATH
.It
QUERY_STRING
.It
REMOTE_ADDR
.It
REMOTE_HOST
.It
REQUEST_METHOD
.It
SERVER_NAME
.It
SERVER_PROTOCOL
.It
SERVER_SOFTWARE
.It
AUTH_TYPE
.It
REMOTE_USER
.It
TLS_CLIENT_ISSUER
.It
TLS_CLIENT_HASH
.It
TLS_VERSION
.It
TLS_CIPHER
.It
TLS_CIPHER_STRENGTH
.It
TLS_CLIENT_NOT_BEFORE
.It
TLS_CLIENT_NOT_AFTER
.El
.Sh MEDIA TYPES
To auto-detect the MIME type of the response
.Nm
looks at the file extension and consults an internal table.
If no MIME is found, the value of
.Ic default type
matching the file
.Ic location
will be used, or
.Dq application/octet-stream .
.Pp
By default the following mappings are loaded, but they can be
overridden or extended using the
.Ic map
option or the
.Ic type Brq ...
block.
.Pp
.Bl -tag -offset indent -width 14m -compact
.It diff
text/x-patch
.It gemini, gmi
text/gemini
.It gif
image/gif
.It jpeg
image/jpeg
.It jpg
image/jpeg
.It markdown, md
text/markdown
.It patch
text/x-patch
.It pdf
application/pdf
.It png
image/png
.It svg
image/svg+xml
.It txt
text/plain
.It xml
text/xml
.El
.Sh LOGGING
Messages and requests are logged by
.Xr syslog 3
using the
.Dv DAEMON
facility or printed on
.Em stderr .
.Pp
Requests are logged with the
.Dv NOTICE
severity.
Each request log entry has the following fields, separated by
whitespace:
.Pp
.Bl -bullet -compact
.It
Client IP address and the source port number, separated by a colon
.It
.Sy GET
keyword
.It
Request URL
.It
Response status
.It
Response meta
.El
.Sh EXAMPLES
Serve the current directory
.Bd -literal -offset indent
$ gmid .
.Ed
.Pp
To serve the directory
.Pa docs
and enable CGI scripts inside
.Pa docs/cgi
.Bd -literal -offset indent
$ mkdir docs/cgi
$ cat <<EOF > docs/cgi/hello
#!/bin/sh
printf "20 text/plain\er\en"
echo "hello world"
EOF
$ chmod +x docs/cgi/hello
$ gmid -x '/cgi/*' docs
.Ed
.Pp
An X.509 certificate must be provided to run
.Nm
using a configuration file.
First, the RSA certificate is created using a wildcard common name:
.Bd -literal -offset indent
# openssl genrsa \-out /etc/ssl/private/example.com.key 4096
# openssl req \-new \-x509 \e
	\-key /etc/ssl/private/example.com.key \e
	\-out /etc/ssl/example.com.crt \e
	\-days 36500 \-nodes \e
	\-subj "/CN=example.com"
# chmod 600 /etc/ssl/example.com.crt
# chmod 600 /etc/ssl/private/example.com.key
.Ed
.Pp
In the example above, a certificate is valid for one hundred years from
the date it was created, which is normal for TOFU.
.Pp
The following is an example of a possible configuration for a site
that enables only TLSv1.3, adds a mime type for the file extension
.Qq rtf
and defines two virtual host:
.Bd -literal -offset indent
ipv6 on		# enable ipv6

protocols "tlsv1.3"

map "application/rtf" to-ext "rtf"

server "example.com" {
	cert "/etc/ssl/example.com.crt"
	key  "/etc/ssl/private/example.com.key"
	root "/var/gemini/example.com"
}

server "it.example.com" {
	cert "/etc/ssl/example.com.crt"
	key  "/etc/ssl/private/example.com.key"
	root "/var/gemini/it.example.com"

	# enable cgi scripts inside "cgi-bin"
	cgi  "/cgi-bin/*"

	# set the language for text/gemini files
	lang "it"
}
.Ed
.Pp
Yet another example, showing how to enable a
.Ic chroot
and use
.Ic location
rule
.Bd -literal -offset indent
chroot "/var/gemini"
user "_gmid"

server "example.com" {
	cert "/path/to/cert.pem" # absolute path
	key  "/path/to/key.pem"  # also absolute
	root "/example.com"      # relative to the chroot

	location "/static/*" {
		# load the following rules only for
		# requests that matches "/static/*"

		auto index on
		index "index.gemini"
	}
}
.Ed
.Sh ACKNOWLEDGEMENTS
.Nm
uses the
.Dq Flexible and Economical
UTF-8 decoder written by
.An Bjoern Hoehrmann .
.Sh AUTHORS
.An -nosplit
The
.Nm
program was written by
.An Omar Polo Aq Mt op@omarpolo.com .
.Sh CAVEATS
.Bl -bullet
.It
All the root directories are opened during the daemon startup; if a
root directory is deleted and then re-created,
.Nm
won't be able to serve files inside that directory until a restart.
This restriction only applies to the root directories and not their
content.
.It
a %2F sequence is indistinguishable from a literal slash: this is not
RFC3986-compliant.
.It
a %00 sequence is treated as invalid character and thus rejected.
.El