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Milter(3)
NAME
Sendmail::Milter - Interface to sendmail's Mail Filter API
SYNOPSIS
use Sendmail::Milter;
my %my_milter_callbacks =
(
'connect' => <!>my_connect_callback,
'helo' => <!>my_helo_callback,
'envfrom' => <!>my_envfrom_callback,
'envrcpt' => <!>my_envrcpt_callback,
'header' => <!>my_header_callback,
'eoh' => <!>my_eoh_callback,
'body' => <!>my_body_callback,
'eom' => <!>my_eom_callback,
'abort' => <!>my_abort_callback,
'close' => <!>my_close_callback,
);
sub my_connect_callback;
sub my_helo_callback;
sub my_envfrom_callback;
sub my_envrcpt_callback;
sub my_header_callback;
sub my_eoh_callback;
sub my_body_callback;
sub my_eom_callback;
sub my_abort_callback;
sub my_close_callback;
BEGIN:
{
# Get myfilter's connection information
# from /etc/mail/sendmail.cf
Sendmail::Milter::auto_setconn("myfilter");
Sendmail::Milter::register("myfilter",
\%my_milter_callbacks, SMFI_CURR_ACTS);
Sendmail::Milter::main();
# Never reaches here, callbacks are called from Milter.
}
DESCRIPTION
Sendmail::Milter is a Perl extension to sendmail's Mail Filter API
(Milter).
Note: You need to have a Perl 5.6 or later interpreter built with
-Dusethreads.
FUNCTIONS
Portions of this document come from comments in the libmilter/mfapi.h
header file.
Main Functions
Note: No functions are exported. You must call these functions explicitly
from the Sendmail::Milter package.
register NAME, CALLBACKS [, FLAGS]
Registers a mail filter NAME with hash reference CALLBACKS callbacks,
and optional capability flags FLAGS. NAME is the same filter name that
you would pass to auto_setconn. CALLBACKS is a hash reference that can
contain any of the following keys:
connect
helo
envfrom
envrcpt
header
eoh
body
eom
abort
close
The values for these keys indicate the callback routine that is
associated with each Milter callback. The values must be either
function names, code references or closures.
This function returns nonzero upon success, the undefined value
otherwise.
%Sendmail::Milter::DEFAULT_CALLBACKS is a hash with default function
names for all of the Milter callbacks. The default callback function
names are:
connect_callback, helo_callback, envfrom_callback, envrcpt_callback,
header_callback, eoh_callback, body_callback, eom_callback,
abort_callback, close_callback.
See the section Writing Milter Callbacks for more information on
writing the callbacks themselves.
For more information on capability flags, see the section Capability
Flags in the @EXPORT section.
main [MAX_INTERPRETERS] [, MAX_REQUESTS]
Starts the mail filter. If successful, this function never returns.
Instead, it launches the Milter engine which will call each of the
callback routines as appropriate.
MAX_INTERPRETERS sets the limit on the maximum number of interpreters
that Sendmail::Milter is allowed to create. These interpreters will
only be created as the need arises and are not all created at startup.
The default value is 0. (No maximum limit)
MAX_REQUESTS sets the limit on the maximum number of requests an
interpreter will process before being recycled. The default value is 0.
(Don't recycle interpreters)
This function returns nonzero on success (if a kill was signaled or
something), the undefined value otherwise.
Note: You should have at least registered a callback and set the
connection information string before calling this function.
setconn CONNECTION_INFO
Sets the connection information string for the filter. The format of
this string is identical to that found in the Milter documentation.
Some examples are "local:/var/run/f1.sock", "inet6:999@localhost",
"inet:3333@localhost".
This function returns nonzero upon success, the undefined value
otherwise.
auto_setconn NAME [, SENDMAIL_CF_FILENAME]
This function automatically sets the connection information by parsing
the sendmail .cf file for the appropriate X line containing the
connection information for the NAME mail filter and calling setconn if
it was successful. It is provided as a helper function and does not
exist in the current Milter library.
Note: This connection information isn't useful for implementing a
Milter that resides on a machine that is remote to the machine running
sendmail. In those cases, you will want to set the connection
information manually with setconn.
This function returns nonzero upon success, the undefined value
otherwise.
SENDMAIL_CF_FILENAME defaults to "/etc/mail/sendmail.cf" if not
specified.
auto_getconn NAME [, SENDMAIL_CF_FILENAME]
Similar to auto_setconn, this function parses the sendmail .cf file for
the appropriate X line containing the connection information for NAME.
It does not, however, call setconn. It only retrieves the connection
information.
This function returns the connection information string for NAME, or
undef on failure.
SENDMAIL_CF_FILENAME defaults to "/etc/mail/sendmail.cf" if not
specified.
settimeout TIMEOUT
Sets the timeout for reads/writes in the Milter engine.
This function returns nonzero upon success, the undefined value
otherwise.
setdbg LEVEL
Sets the debug level for the Milter engine.
This function returns nonzero upon success, the undefined value
otherwise.
Writing Milter Callbacks
Writing Milter callbacks is pretty easy when you're doing simple text
processing.
But remember one thing: Each Milter callback could quite possibly run in a
different instance of the Perl interpreter.
Sendmail::Milter launches multiple persistent Perl interpreters to increase
performance (so it doesn't have to startup and shutdown the interpreters
constantly). Thus, you can't rely on setting external package variables,
global variables, or even running other modules which rely on such things.
This will continue to be true while interpreter thread support in Perl is
experimental. For more information, see perlfork. Most of that information
applies here.
Remember to return one of the SMFIS_* result codes from the callback
routine. Remember there can be multiple message body chunks. And remember
that only eom_callback is allowed to manipulate the headers, recipients,
message body, etc.
See the @EXPORT section for information on the SMFIS_* result codes.
Here is an example of a connect_callback routine:
# External modules are OK, but note the caveats above.
use Socket;
sub connect_callback
{
my $ctx = shift; # The Milter context object.
my $hostname = shift; # The connection's host name.
my $sockaddr_in = shift;
my ($port, $iaddr) = sockaddr_in($sockaddr_in);
print "Hostname is: " . $hostname . "\n";
# Cool, a printable IP address.
print "IP Address is: " . inet_ntoa($iaddr) . "\n";
return SMFIS_CONTINUE; # Returning a value is important!
}
Note: The $ctx Milter context object is not a true Perl object. It's really
a blessed reference to an opaque C structure. Only use the Milter context
functions (described in a later section) with this object. (Don't touch
it, it's evil.)
Milter Callback Interfaces
These interfaces closely mirror their Milter callback counterparts, however
there are some differences that take advantage of Perl's syntactic sugar.
Note: Each callback receives a Milter context object as the first argument.
This context object is used in making Milter Context function calls. See
Milter Context Functions for more details.
connect_callback CTX, HOSTNAME, SOCKADDR_IN
Invoked on each connection. HOSTNAME is the host domain name, as
determined by a reverse lookup on the host address. SOCKADDR_IN is the
AF_INET portion of the host address, as determined by a getpeername(2)
syscall on the SMTP socket. You can use Socket::unpack_sockaddr_in() to
unpack it into a port and IP address.
This callback should return one of the SMFIS_* result codes.
helo_callback CTX, HELOHOST
Invoked on SMTP HELO/EHLO command. HELOHOST is the value passed to
HELO/EHLO command, which should be the domain name of the sending host
(but is, in practice, anything the sending host wants to send).
This callback should return one of the SMFIS_* result codes.
envfrom_callback CTX, ARG1, ARG2, ..., ARGn
Invoked on envelope from. ARG1, ARG2, ... ARGn are SMTP command
arguments. ARG1 is guaranteed to be the sender address. Later arguments
are the ESMTP arguments.
This callback should return one of the SMFIS_* result codes.
envrcpt_callback CTX, ARG1, ARG2, ..., ARGn
Invoked on each envelope recipient. ARG1, ARG2, ... ARGn are SMTP
command arguments. ARG1 is guaranteed to be the recipient address.
Later arguments are the ESMTP arguments.
This callback should return one of the SMFIS_* result codes.
header_callback CTX, FIELD, VALUE
Invoked on each message header. The content of the header may have
folded white space (that is, multiple lines with following white space)
included. FIELD is the header field name, VALUE is the header field
value.
This callback should return one of the SMFIS_* result codes.
eoh_callback CTX
Invoked at end of header.
This callback should return one of the SMFIS_* result codes.
body_callback CTX, BODY, LEN
Invoked for each body chunk. There may be multiple body chunks passed
to the filter. End-of-lines are represented as received from SMTP
(normally Carriage-Return/Line-Feed). BODY contains the body data, LEN
contains the length of the body data.
This callback should return one of the SMFIS_* result codes.
eom_callback CTX
Invoked at end of message. This routine can perform special operations
such as modifying the message header, body, or envelope. See the
section on eom_callback in Milter Context Functions.
This callback should return one of the SMFIS_* result codes.
abort_callback CTX
Invoked if message is aborted outside of the control of the filter, for
example, if the SMTP sender issues an RSET command. If abort_callback
is called, eom_callback will not be called and vice versa.
This callback should return one of the SMFIS_* result codes.
close_callback CTX
Invoked at end of the connection. This is called on close even if the
previous mail transaction was aborted.
This callback should return one of the SMFIS_* result codes.
Milter Context Functions
These routines are object methods that are part of the
Sendmail::Milter::Context pseudo-package for use by Sendmail::Milter
callback functions. Any attempts to use them without a properly blessed
Milter context object will fail miserably. Please see restrictions on when
these routines may be called.
Context routines available to all Milter callback functions:
These functions are available to all types of Milter callback functions. It
is worth noting that passing connection-private data by reference is
probably more efficient than passing by value.
$ctx->setpriv DATA
Each $ctx can contain connection-private data (specific to an SMTP
connection). This routine can be used to allocate this private data.
Calling this function with DATA set to the undefined value will clear
Milter's pointer to this private data. You should always do this to
decrement the private data's reference count.
This function returns nonzero upon success, the undefined value
otherwise.
$ctx->getpriv
Each $ctx can contain connection-private data (specific to an SMTP
connection). This routine can be used to retrieve this private data.
This function returns a scalar containing $ctx's private data.
$ctx->getsymval SYMNAME
Additional information is passed in to the vendor filter routines using
symbols. Symbols correspond closely to sendmail macros. The symbols
defined depend on the context. SYMNAME is the name of the symbol to
access.
This function returns the value of the symbol name SYMNAME.
$ctx->setreply RCODE, XCODE, MESSAGE
Set the specific reply code to be used in response to the active
command. If not specified, a generic reply code is used. RCODE is the
three-digit (RFC 821) SMTP reply code to be returned, e.g. 551. XCODE
is the extended (RFC 2034) reply code, e.g., 5.7.6. MESSAGE is the
text part of the SMTP reply.
This function returns nonzero upon success, the undefined value
otherwise.
Context routines available only to the eom_callback function:
The eom_callback Milter callback is called at the end of a message
(essentially, after the final DATA dot). This routine can call some special
routines to modify the envelope, header, or body of the message before the
message is enqueued. These routines must not be called from any vendor
routine other than eom_callback.
$ctx->addheader FIELD, VALUE
Add a header to the message. FIELD is the header field name. VALUE is
the header field value. This header is not passed to other filters. It
is not checked for standards compliance; the mail filter must ensure
that no protocols are violated as a result of adding this header.
This function returns nonzero upon success, the undefined value
otherwise.
$ctx->chgheader FIELD, INDEX, VALUE
Change/delete a header in the message. FIELD is the header field name.
INDEX is the Nth occurence of the header field name. VALUE is the new
header field value (empty for delete header). It is not checked for
standards compliance; the mail filter must ensure that no protocols are
violated as a result of adding this header.
This function returns nonzero upon success, the undefined value
otherwise.
$ctx->addrcpt RCPT
Add a recipient to the envelope. RCPT is the recipient to be added.
This function returns nonzero upon success, the undefined value
otherwise.
$ctx->delrcpt RCPT
Delete a recipient from the envelope. RCPT is the envelope recipient to
be deleted. This should be in exactly the same form passed to
envrcpt_callback or the address may not be deleted.
This function returns nonzero upon success, the undefined value
otherwise.
$ctx->replacebody DATA
Replace the body of the message. DATA is the scalar containing the
block of message body information to insert. This routine may be called
multiple times if the body is longer than convenient to send in one
call. End of line should be represented as Carriage-Return/Line Feed.
This function returns nonzero upon success, the undefined value
otherwise.
@EXPORT
Sendmail::Milter exports the following constants:
Callback Result Codes
These are the possible result codes that may be returned by the Milter
callback functions. If you do not specify a return value, Sendmail::Milter
will send a default result code of SMFIS_CONTINUE back to Milter.
SMFIS_CONTINUE
Continue processing message/connection
SMFIS_REJECT
Reject the message/connection. No further routines will be called for
this message (or connection, if returned from a connection-oriented
routine).
SMFIS_DISCARD
Accept the message, but silently discard the message. No further
routines will be called for this message. This is only meaningful from
message-oriented routines.
SMFIS_ACCEPT
Accept the message/connection. No further routines will be called for
this message (or connection, if returned from a connection-oriented
routine; in this case, it causes all messages on this connection to be
accepted without filtering).
SMFIS_TEMPFAIL
Return a temporary failure, i.e., the corresponding SMTP command will
return a 4xx status code. In some cases this may prevent further
routines from being called on this message or connection, although in
other cases (e.g., when processing an envelope recipient) processing of
the message will continue.
Capability Flags
These are possible capability flags for what a mail filter can do.
Normally, you should specify each capability explicitly as needed.
SMFIF_ADDHDRS
Allows a mail filter to add headers.
SMFIF_CHGBODY
Allows a mail filter to change the message body.
SMFIF_ADDRCPT
Allows a mail filter to add recipients.
SMFIF_DELRCPT
Allows a mail filter to delete recipients.
SMFIF_CHGHDRS
Allows a mail filter to change headers.
SMFIF_MODBODY
Allows a mail filter to change the message body. (Provided only for
backwards compatibility)
Capability Flag Sets
These provide sets of capability flags that indicate all of the
capabilities in a particular version of Milter. SMFI_CURR_ACTS is set to
the capabilities in the current version of Milter.
SMFI_CURR_ACTS
Enables the set of capabilities available to mail filters in the
current version of Milter.
SMFI_V1_ACTS
Enables the set of capabilities available to mail filters in V1 of
Milter.
SMFI_V2_ACTS
Enables the set of capabilities available to mail filters in V2 of
Milter.
EXAMPLES
Appending a line to the message body
use Sendmail::Milter;
my %my_milter_callbacks =
(
'eoh' => <!>my_eoh_callback,
'body' => <!>my_body_callback,
'eom' => <!>my_eom_callback,
'abort' => <!>my_abort_callback,
);
sub my_eoh_callback
{
my $ctx = shift;
my $body = "";
$ctx->setpriv(\$body);
return SMFIS_CONTINUE;
}
sub my_body_callback
{
my $ctx = shift;
my $body_chunk = shift;
my $body_ref = $ctx->getpriv();
${$body_ref} .= $body_chunk;
# This is crucial, the reference to the body may have
# changed.
$ctx->setpriv($body_ref);
return SMFIS_CONTINUE;
}
sub my_eom_callback
{
my $ctx = shift;
my $body_ref = $ctx->getpriv();
# Note: This doesn't support messages with MIME data.
${$body_ref} .= "---> Append me to this message body!\n";
$ctx->replacebody(${$body_ref});
$ctx->setpriv(undef);
return SMFIS_ACCEPT;
}
sub my_abort_callback
{
my $ctx = shift;
$ctx->setpriv(undef);
return SMFIS_CONTINUE;
}
# The following code does not necessarily need to be in a
# BEGIN block. It just looks funny without it. :)
BEGIN:
{
Sendmail::Milter::auto_setconn("myfilter");
Sendmail::Milter::register("myfilter",
\%my_milter_callbacks, SMFI_CURR_ACTS);
Sendmail::Milter::main();
# Never reaches here, callbacks are called from Milter.
}
See the test.pl sample test case for more callback examples.
AUTHOR
Charles Ying, cying@cpan.org.
COPYRIGHT
Copyright (c) 2000-2001 Charles Ying. All rights reserved. This program is
free software; you can redistribute it and/or modify it under the same
terms as sendmail itself.
The interpreter pools portion (found in the intpools.c, intpools.h, and
test.pl files) of this code is also available under the same terms as perl
itself.
SEE ALSO
perl(1), sendmail(8).
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