path: root/usr.sbin/smtpd/smtpd-tables.7

.\"	$OpenBSD: smtpd-tables.7,v 1.4 2024/06/09 10:13:05 gilles Exp $
.\"
.\" Copyright (c) 2008 Janne Johansson <jj@openbsd.org>
.\" Copyright (c) 2009 Jacek Masiulaniec <jacekm@dobremiasto.net>
.\" Copyright (c) 2012 Gilles Chehade <gilles@poolp.org>
.\" Copyright (c) 2024 Omar Polo <op@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
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.Dd $Mdocdate: June 9 2024 $
.Dt SMTPD-TABLES 7
.Os
.Sh NAME
.Nm smtpd-tables
.Nd table API for the smtpd daemon
.Sh DESCRIPTION
The
.Xr smtpd 8
daemon provides a Simple Mail Transfer Protocol (SMTPD) implementation,
which allows ordinary machines to become Mail eXchangers (MX).
Some features that are commonly used by MX,
such as querying databases for user credentials,
are outside of the scope of SMTP and too complex to fit in
.Xr smtpd 8 .
.Pp
Because an MX may need to provide these features,
.Xr smtpd 8
provides an API to implement
.Xr table 5
backends with a simple text-based protocol.
.Sh DESIGN
.Nm
are programs that run as unique standalone processes,
they do not share
.Xr smtpd 8
address space.
They are executed by
.Xr smtpd 8
at startup and expected to run in an infinite loop,
reading events and queries from standard input and
writing responses to standard output.
They are not allowed to terminate.
.Pp
Because
.Nm
are standalone programs that communicate with
.Xr smtpd 8 ,
they may run as different users than
.Xr smtpd 8
and may be written in any language.
.Nm
must not use blocking I/O,
they must support answering asynchronously to
.Xr smtpd 8 .
.Sh PROTOCOL
The protocol consist of human-readable lines exchanged between
.Nm
and
.Xr smtpd 8 .
.Pp
The protocol begins with a handshake.
First,
.Xr smtpd 8
provides
.Nm
with general configuration information in the form of
key-value lines, terminated by
.Ql config|ready .
For example:
.Bd -literal -offset indent
config|smtpd-version|7.5.0
config|protocol|0.1
config|tablename|devs
config|ready
.Ed
.Pp
Then,
.Nm
register the supported services, terminating with
.Ql register|ready .
For example:
.Bd -literal -offset indent
register|alias
register|credentials
register|ready
.Ed
.Pp
Finally,
.Xr smtpd 8
can start querying the table.
For example:
.Bd -literal -offset indent
table|0.1|1713795082.354255|devs|lookup|alias|b72508d|op
.Ed
.Pp
The
.Dq |
character is used to separate the fields and may only appear
verbatim in the last field of the payload, in which case it
should be considered a regular character and not a separator.
No other field may contain a
.Dq | .
.Pp
Each request has a common set of fields, followed by some
other fields that are operation-specific.
The common format consists of a protocol prefix
.Sq table ,
the protocol version, the timestamp and the table name.
For example:
.Bd -literal -offset indent
table|0.1|1713795091.202157|devs
.Ed
.Pp
The protocol is inherently asynchronous, so multiple request
may be sent without waiting for the table to reply.
All the replies have a common prefix, followed by the
operation-specific response.
The common format consist of a prefix with the operation name
in followed by
.Sq -result ,
and the unique ID of the request.
For example:
.Bd -literal -offset indent
lookup-result|b72508d
.Ed
.Pp
The list of operations, operation-specific parameters and
responses are as follows:
.Bl -tag -width Ds
.It Cm update Ar id
Ask the table to reload its configuration.
The result is either
.Sq ok
on success or
.Sq error
and a message upon a failure to do so.
.It Cm check Ar service id query
Check whether
.Ar query
is present in the table.
The result is
.Sq found
if found,
.Sq not-found
if not, or
.Sq error
and a message upon an error.
.It Cm lookup Ar service id query
Look up a value in the table for given the
.Ar query .
The result is
.Sq found
and the value if found,
.Sq not-found
if not found, or
.Sq error
and a message upon an error.
.It Cm fetch Ar service id
Fetch the next item from the table, eventually wrapping around.
It is only supported for the
.Ic source
and
.Ic relayhost
services.
The result is
.Sq found
and the value if found,
.Sq not-found
if the table is empty, or
.Sq error
and a message upon an error.
.El
.Pp
Each service has a specific format for the result.
The exact syntax for the values and eventually the keys are
described in
.Xr table 5 .
The services and their result format are as follows:
.Pp
.Bl -tag -width mailaddrmap -compact
.It Ic alias
One or more aliases separated by a comma.
.It Ic auth
Only usable for check.
Lookup key is username and cleartext password separated by
.Sq \&: .
.It Ic domain
A domain name.
.\" XXX are wildcards allowed?
.It Ic credentials
The user name, followed by
.Sq \&:
and the encrypted password as per
.Xr smtpctl 8
.Cm encrypt
subcommand.
.It Ic netaddr
IPv4 and IPv6 address or netmask.
.It Ic userinfo
The user id, followed by
.Sq \&:
then the group id, then
.Sq \&:
and finally the home directory.
.It Ic source
IPv4 and IPv6 address.
.It Ic mailaddr
An username, a domain or a full email address.
.It Ic addrname
Used to map IP addresses to hostnames.
.\" .It Ic mailaddrmap
.\" XXX missing K_RELAYHOST, K_STRING and K_REGEX
.El
.Sh EXAMPLES
Assuming the table is called
.Dq devs ,
here's an example of a failed
.Cm update
transaction:
.Bd -literal -offset indent
table|0.1|1713795097.394049|devs|update|478ff0d2
update-result|478ff0d2|error|failed to connect to the database
.Ed
.Pp
A
.Cm check
request for the
.Ic netaddr
service for the 192.168.0.7 IPv4 address which is
not in the table:
.Bd -literal -offset indent
table|0.1|1713795103.314423|devs|check|netaddr|e5862859|192.168.0.7
check-result|e5862859|not-found
.Ed
.Pp
A successful
.Cm lookup
request for the
.Ic userinfo
service for the user
.Sq op :
.Bd -literal -offset indent
table|0.1|1713795110.354921|devs|lookup|userinfo|f993c74|op
lookup-result|f993c74|found|1000:1000:/home/op
.Ed
.Pp
A series of
.Cm fetch
requests for the
.Cm source
service that wraps around:
.Bd -literal -offset indent
table|0.1|1713795116.227321|devs|fetch|source|189bd3ee
lookup-result|189bd3ee|found|192.168.1.7
table|0.1|1713795120.162438|devs|fetch|source|9e4c56d4
lookup-result|9e4c56d4|found|10.0.0.8
table|0.1|1713795122.930928|devs|fetch|source|f2c8b906
lookup-result|f2c8b906|found|192.168.1.7
.Ed
.Sh SEE ALSO
.Xr smtpd 8
.Sh HISTORY
.Nm
first appeared in
.Ox 7.6 .