FBB::Milter - Interface to the sendmail mail filter facilities
#include <bobcat/milter>
Linking option: -lmilter -lbobcat
Milter defines an abtract base class interfacing to the
sendmail mail filter (milter) facilities. It defines a C++ interface,
based on the assumption that a single mail filter program does not implement
multiple mail filters. The traditional sendmail C-based Milter API
uses a (SMFICTX) pointer representing a mail connection, and a
pointer to connection-specific `private’ data, requiring the Milter
constructor to perform quite a few administrative tasks. While acceptable in
a C environment these administratve tasks distract from the main
task: the Milter’s mail filtering functionality. The
FBB::Milter class hides these administrative tasks from the
programmer, who is then able to concentrate on filtering mail. The main
benefits of Milter are therefore
- o
- Basic administration is performed by the Milter class
- o
- The class’ interface is more C++ like than the raw C
interface offered by the milter API.
- o
- Administration, allocation and communicating of connection specific data
is no longer required
- o
- It is not normally necessary to use connection-specific data, like a
pointer identifying the connection, anymore when implementing the
Milter.
- o
- Milter uses current-day design patterns enforcing principles of
reuable software, thus simplifying the construction of the actual Milter.
To activate a milter from the sendmail.mc configuration file, use,
e.g., INPUT_MAIL_FILTER(`name’, `S=socket’), where
name is the milter’s name, and socket is the name of
the socket. See also the setConnection member below.
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace FBB.
The class defines four enumerations. One enumeration is used to
indicate the callback-functions that need to be called, the second one
renames the flags that can be passed to sendmail to indicate which actions
the milter is allowed to perform. The third one defines status values that
may be used to inform sendmail how to further process a message. The fourth
one defines return values. The enumerations are:
enum CallBack
This enumeration holds the following values:
- o
- CONNECT:
Indicates that the milter defines (overrides) the connection-functionality.
This is the first callback function that can be called by sendmail.
- o
- HELO:
Indicates that the milter defines (overrides) the helo-functionality. This
indicates that the helo function should be called by sendmail,
providing the milter with information about the connecting client.
- o
- SENDER:
Indicates that the milter defines (overrides) the sender-functionality. This
indicates that the sender function should be called by sendmail,
providing the milter with the sender’s envelope information.
- o
- RECIPIENT:
Indicates that the milter defines (overrides) the recipient-functionality.
This indicates that the recipient function should be called by
sendmail, providing the milter with the recipient’s envelope
information.
- o
- HEADER:
Indicates that the milter defines (overrides) the header-functionality. This
indicates that the header function should be called by sendmail for
each mail header that is used in the current mail message.
- o
- EOH:
Indicates that the milter defines (overrides) the
end-of-header-functionality. This indicates that the eoh function
should be called by sendmail once all header lines have been
processed.
- o
- BODY:
Indicates that the milter defines (overrides) the body-functionality. This
indicates that the body function should be called by sendmail,
offering the mail-body to the milter.
- o
- EOM:
Indicates that the milter defines (overrides) the
end-of-message-functionality. This indicates that the eom function
should be called by sendmail, once all elements of the e-mail message have
been processed.
- o
- ABORT:
Indicates that the milter defines (overrides) the abort-functionality. The
abort function may be called by sendmail before eom is
called. It should reclaim all resources used by the message, but not
delete any memory allocated by the milter, as this is
close’s job.
- o
- CLOSE:
Indicates that the milter defines (overrides) the close-functionality. The
close function should delete all (connection specific) memory
allocated by the milter. It may be called `out-of-order’, i.e. even
before connect is called and developers should anticipate this
possibility when crafting their close code. In particular, it is
incorrect to assume the private context pointer will be something other
than 0 in this callback.
- o
- UNKNOWN:
Currently not used. Reserved for versions exceeding version 2 of the
sendmail milter API
- o
- DATA:
Currently not used. Reserved for versions exceeding version 3 of the
sendmail milter API
- o
- ALL_CALLBACKS:
Shortcut to indicate all callback facilities. The CallBack values are
bit-flags. The bit_or operator may be used to combine them, and the
bit_not operator may be used to remove a flag from
ALL_CALLBACKS (e.g., ALL_CALLBACKS && ~ABORT).
enum Flags
This enumeration holds the following values:
- o
- NO_FLAGS:
No flags are defined.
- o
- ADD_HEADERS:
This flag indicates that the milter is allowed to add headers to the current
e-mail message.
- o
- ADD_RECIPIENTS:
This flag indicates that the milter is allowed to add recipients to the
current e-mail message.
- o
- CHANGE_BODY:
This flag indicates that the milter is allowed to modify the
message’s body contents.
- o
- CHANGE_HEADERS:
This flag indicates that the milter is allowed to change headers of the
current e-mail message.
- o
- DELETE_RECIPIENTS:
This flag indicates that the milter is allowed to remove recipients from the
current e-mail message.
- o
- QUARANTINE:
This flag indicates that the milter is allowed to request sendmail to
quarantine the current e-mail message.
- o
- ALL_FLAGS:
Shortcut to indicate all callback facilities. The Flags values are
bit-flags. The bit_or operator may be used to combine them, and the
bit_not operator may be used to remove a flag from ALL_FLAGS
(e.g., ALL_FLAGS && ~QUARANTINE).
Status
This enumeration simplifies the extended SMFIS_ values used by the
C API. These values may be used to return sfsistat values:
- o
- ACCEPT:
This value is equal to SMFIS_ACCEPT, indicating that Sendmail should
accept the message. For a connection-oriented callback (see below at
PROTECTED VIRTUAL MEMBER FUNCTIONS), accept this connection without
further filter processing, call close (see below). For other
callbacks: accept this message without further filtering.
- o
- CONTINUE:
This value is equal to SMFIS_CONTINUE, indicating that Sendmail
should continue processing. This is the default for all callback functions
which are not overridden by the class derived from Milter.
- o
- DISCARD:
This value is equal to SMFIS_DISCARD, indicating that Sendmail should
discard the mail message. It should not be returned by a
connection-oriented callback. For other callbacks: the message is
accepted, but silently discarded.
- o
- REJECT:
This value is equal to SMFIS_REJECT, indicating that Sendmail should
reject the mail message. For a connection-oriented callback, reject this
connection; call close. For a message-oriented callback (except for
eom or abort, see below), reject this message. For a
recipient-oriented callback, reject the current recipient (but continue
processing the current message).
- o
- TEMPFAIL:
This value is equal to SMFIS_TEMPFAIL, indicating that Sendmail
should return a `temporary unavailable’ message to the sender of
the mail message. For a message-oriented callback (except sender,
see below), fail for this message. For a connection-oriented callback,
fail for this connection and call close. For a recipient-oriented
callback, only fail for the current recipient and continue message
processing.
Return
This enumeration simplifies the extended MI_ values used by the
C API. Most return values used by the Milter class, however,
are bool values. The Return values are:
- o
- FAILURE:
This value is equal to MI_FAILURE, indicating that a C-api
function failed to perform its task.
- o
- SUCCESS:
This value is equal to MI_SUCCESS, indicating that a C-api
function succeeded in performing its task.
The default- and copy constructors are available for derived
classes. They perform no actions.
These functions form the heart of the Milter base-class.
They can be called to initialize, start and stop the Milter.
- o
- void initialize(std::string const &name, Milter
&milter, callback_set callbacks = CONNECT, flag_set
flags = NO_FLAGS):
This function initializes the Milter’s administration. It expects the
name of the mailfilter as its first argument. Its second argument is a
reference to a Milter object. Since Milter is an abstract
base class the actual object is always an object of a class derived from
Milter. Its third argument specifies the callbacks to call for this
milter. By default the connect callback will be called. Note that
the close callback is not called by default. This is ok, since the
Milter object doesn’t have to cleanup `private’ data,
as is normal with the C API. The last argument defines flags,
specifying the Milter’s capabilities.
- o
- std::string const &name():
This function returns the milter’s name.
- o
- bool start():
This member function calls smfi_main, controlling the milter’s
event loop. It returns true if the event-loop is successfully
terminated.
- o
- void stop():
This member function terminates the milter’s event loop, after
finishing all threads. Following this call start may be called
again to continue the milter.
The remaining functionality of the class Milter is useful
only for Milter-implementations in classes derived from Milter. The
following members can be overridden by derived classes. Note that
clone must be overridden. Except for clone, all the
members in this sections are callback functions. I.e., the MTA will
call them to process parts of the mail message. Recipient-, message-, and
connection-oriented callbacks are distinguished.
The recipient-oriented callback (recipient, see below) may
affect the processing of a single message to a single recipient.
Connection-oriented callbacks (connect, helo and close) affect
the processing of the entire connection (during which multiple messages may
be delivered to multiple sets of recipients). The remaining callbacks are
message-oriented, affecting the processing of a single message to all its
recipients.
- o
- virtual sfsistat abort():
This message-oriented member may be called at any time during message
processing (i.e. between some message-oriented routine and eom).
abort reclaim any resources allocated on a per-message basis (which
are not the connection specific data, which should be handled by
the derived class’ destructor), and must be tolerant of being
called between any two message-oriented callbacks. abort is only
called if the message is aborted outside the filter’s control and
the filter has not completed its message-oriented processing. For example,
if a filter has already returned ACCEPT, REJECT, or DISCARD
from a message-oriented routine, abort will not be called even if
the message is later aborted outside its control.
- o
- virtual sfsistat body(unsigned char *text, size_t length):
This message-oriented member is called zero or more times between eoh
and eom. text points to a sequence of bytes. It is not
necessarily a 0-terminated. Moreover, the sequence may contain
0-characters. Since message bodies can be very large, defining body
can significantly impact filter performance. End-of-lines are represented
as received from SMTP (normally CR/LF). Later filters will see body
changes made by earlier ones, and message bodies may be sent in multiple
chunks, with one call to body per chunk.
- o
- virtual Milter *clone() const = 0:
This pure virtual function must be implemented by derived classes to return
a newly allocated copy of the derived object passed to the
initialize static member. It is used by the standard `virtual
constructor’ design pattern. The destruction of the allocated
object is the responsibility of clone’s caller.
- o
- virtual sfsistat close():
This connection-oriented member is always called once at the end of each
connection. It may be called "out-of-order", i.e. before even
the connect is called. After a connection is established by the MTA
to the filter, if the MTA decides this connection’s traffic will be
discarded (e.g. via an access_db result), no data will be passed to the
filter from the MTA until the client closes down. At that time,
close is called. It can therefore be the only callback ever used
for a given connection, and developers should anticipate this possibility
when crafting their close code. The member close is called
on close even if the previous mail transaction was aborted.
- o
- virtual sfsistat connect(char *hostname, _SOCK_ADDR *hostaddr):
This connection-oriented member may be called once, at the start of each
SMTP connection. The parameter hostname is he host name of the
message sender, as determined by a reverse lookup on the host address. If
the reverse lookup fails, hostname will contain the message
sender’s IP address enclosed in square brackets (e.g.
[a.b.c.d]). The parameter hostaddr is the host address, as
determined by a getpeername(2) call on the SMTP socket. It is 0 if
the type is not supported in the current version or if the SMTP connection
is made via stdin.
- o
- virtual sfsistat data():
Not yet supported. Will be available with libmilter versions beyond 3.
- o
- virtual sfsistat eoh():
This message-oriented member is called once after all headers have been
processed.
- o
- virtual sfsistat eom():
This message-oriented member is called once after all calls to body
for a given message have been completed. Note that only in this function
modifications to the message headers, body, and envelope can be made (see
the add-, change- and delete- members listed below).
- o
- virtual sfsistat header(char *headerf, char *headerv):
This message-oriented member is called zero or more times between
recipient and eoh, once per message header. The
headerf parameter contains the text of the header, the
headerv parameter contains its value. E.g., if an e-mail message
contains the following headers:
From: sender <f@example.com>
Subject:no
then header will be called twice with the following values for,
respectively headerf and headerv:
First header: "From", " sender <f@example.com>"
Second header: "Subject", "no"
Further details about header information is given in RFC 882.
- o
- virtual sfsistat helo(char *helohost):
This connection-oriented member is called whenever the client sends a
HELO/EHLO command. It may therefore be called between zero and three
times. The helohost parameter should be the domain name of the
sending host (but is, in practice, anything the sending host wants to
send).
- o
- virtual sfsistat recipient(char **argv):
This recipient-oriented member is called once per recipient, hence one or
more times per message, immediately after sender. The parameter
argv is a 0-terminated array of pointers to SMTP command arguments;
argv[0] is guaranteed to be the recipient address. Later arguments are the
ESMTP arguments. TEMPFAIL may be returned indicate that sendmail should
return a temporary failure for this particular recipient; further
recipients may still be sent, abort is not called. REJECT will
reject this particular recipient; further recipients may still be sent,
abort is not called. DISCARD will accept (but discard) the message,
abort will be called. ACCEPT will accept recipient, abort
will not be called. More details on ESTMP responses, are described in RFC
1869.
- o
- virtual sfsistat sender(char **argv):
This message-oriented member is called once at the beginning of each
message, before recipient. argv[0] is guaranteed to be the
sender’s envelope address. Later arguments are the ESMTP arguments.
TEMPFAIL may be returned, indicating that sendmail should return a
temporary failure for this particular message, abort is not called.
REJECT will reject this message, abort is not called. DISCARD will
accept (but discard) the message, abort will be called. ACCEPT will
accept recipient, abort will not be called. More details on ESTMP
responses, are described in RFC 1869.
- o
- virtual sfsistat unknown(char *ptr):
Not yet supported. Will be available with libmilter versions beyond 2.
The following members are non-virtual. They can be called by
members of classes derived from Milter:
- o
- bool addHeader(std::string const &hdrName, std::string const
&hdrValue):
This member may only be called from eom, and the flag
ADD_HEADERS must have been specified or it will fail. The
hdrName and hdrValue must be non-empty strings. Each line of
the header must be under 2048 characters and should be under 998
characters. If longer headers are needed, make them multi-line. To make a
multi-line header, insert a line feed (\n) followed by at least one
whitespace character such as a space or tab (\t). The line feed
should not be preceded by a carriage return. It is the filter
writer’s responsibility to ensure that no standards are
violated.
- o
- bool addRecipient(std::string const &rcptName):
This member may only be called from eom, and the flag
ADD_RECIPIENTS must have been specified or it will fail.
- o
- bool changeHeader(std::string const &hdrName, size_t
headerNr, std::string const &hdrValue):
This member may only be called from eom, and the flag
CHANGE_HEADERS must have been specified or it will fail. See
addHeader for the header-requirements. The headerNr
parameter is a 1-based header index value. A headerNr value of 1
will modify the first occurrence of a header named hdrValue. If
headerNr is greater than the number of times hdrName
appears, a new hdrName-header will be added. If hdrValue is
empty, the header is deleted.
- o
- bool deleteRecipient(std::string const &rcptName):
This member may only be called from eom, and the flag
DELETE_RECIPIENTS must have been specified or it will fail. This
member removes the named recipient from the current message’s
envelope.
- o
- SMFICTX *id() const:
This member may be called by the Milter object to obtain a pointer
identifying its sendmail-connection. Normally it should not be necessary
to call this member.
- o
- bool insertHeader(size_t hdrIdx, std::string const &hdrName,
std::string const &hdrValue):
This member may only be called from eom, and the flag
ADD_HEADERS must have been specified or it will fail. See
addHeader for the header-requirements. The headerNr
parameter is a header index value. A headerNr value of 0 will
insert this header as the first of the hdrName headers. If
headerNr is greater than the number of times hdrName
appears, a new hdrName-header will be added.
- o
- bool openSocket(bool removeIfTrue = true):
This member should be called before start is called. This member
attempts to create the socket specified by setConnection (see
below). This allows the calling application to ensure that the socket can
be created, possibly changing its protection (access rights) before the
milter starts its work. If this member is not called, it will be called
implicitly when run is started. It returns true if the
socket could be created.
- o
- bool quarantine(std::string const &reason):
This member may only be called from eom and causes the MTA to
quarantines the message using the given reason.
- o
- bool replaceBody(std::string const &body):
This member may only be called from eom, and the flag
CHANGE_BODY must have been specified or it will fail. It may be
called multiple times in which case the various body contents are
concatenated in the final message. Newlines should be coded as CRLF.
- o
- bool setBacklog(size_t backlog = 5):
This member should be called before start is called. Sets the
incoming socket backlog used by listen(2). If setBacklog is
not called, the operating system default is used. The function returns
false if the backlog could not be set as requested. It is the
responsibility of the programmer not to call this function with a 0
argument.
- o
- bool setConnection(std::string const &name):
This member should be called before start is called. Sets the socket
through which the filter communicates with sendmail. The socket may be
specified using one of the following variants:
{unix|local}:/path/to/file - A named pipe;
net:port@{hostname|ip-address} - An IPV4 socket;
inet6:port@{hostname|ip-address} - An IPV6 socket.
- If possible, filters should not run as root when communicating over
unix/local domain sockets.
- Unix/local sockets should have their permissions set to 0600 (read/write
permission only for the socket’s owner) or 0660 (read/write
permission for the socket’s owner and group) which is useful if the
sendmail RunAsUser option is used. The permissions for a unix/local domain
socket are determined as usual by umask, which should be set to 007 or
077.
- Possible failure of this function cannot be determined from its return
value. Rather, run will fail.
- o
- setReply(std::string const &rcode, std::string const &xcode =
"", std::string const &msg = ""):
This member sets the default SMTP error reply code. It may be called from
any callback member, except connect. The parameter rcode
should be a he three-digit (RFC 821/2821) SMTP reply code and it must be a
valid 4XX or 5XX reply code. The parameter xcode, when specified,
must be a extended (RFC 1893/2034) reply code. The parameter msg
may be an additional textual message. The Milter class has no
member comparable to the libmilter API function smfi_setmlreply.
the Milter class.
- o
- void setTimeout(size_t seconds = 7210):
This member should be called before start is called. Sets the number
of seconds libmilter will wait for an MTA connection before timing out a
socket. If setTimeout is not called, a default timeout of 7210
seconds is used. It is the responsibility of the programmer not to call
this function with an argument equal to 0.
- o
- char const *symval(std::string const &name) const:
This member returns the value of a specific sendmail macro. The name
parameter should be set to he name of a sendmail macro . Single letter
macros can optionally be enclosed in braces ({ and }),
longer macro names must be enclosed in braces, just as in a sendmail.cf
file.0 is returned if the macro is not defined. By default, the following
macros are valid in the given contexts:
for connect: daemon_name, if_name, if_addr, j, _;
for helo: tls_version, cipher, cipher_bits, cert_subject,
cert_issuer;
for sender: i, auth_type, auth_authen, auth_ssf, auth_author,
mail_mailer, mail_host, mail_addr;
for recipient: rcpt_mailer, rcpt_host, rcpt_addr.
All macros stay in effect from the point they are received until the end of
the connection for the first two sets, the end of the message for the
third (sender), and just for each recipient for the final set
(recipient).
The following macros may be specified in the sendmail.mc configuration file:
define(`confMILTER_MACROS_CONNECT’, `m1’, ...),
define(`confMILTER_MACROS_HELO’, ...),
define(`confMILTER_MACROS_ENVFROM’, ...),
define(`confMILTER_MACROS_ENVRCPT’, ...), where
`m1’, ... represents a comma separated list of returnable
macros. Single letter macros can optionally be enclosed in braces
({ and }), longer macro names must be enclosed in
braces.
- o
- bool wait():
This member may only be called from eom and tells the MTA that the
filter is still working on a message, causing the MTA to re-start its
timeouts.
bobcat/milter - defines the class interface
bobcat(7), getpeername(2), listen(2),
http://www.milter.org (e.g.,
http://www.milter.org/developers/api)
http://sendmail.org/m4/readme.html
http://rfc.net/rfc821.html
http://rfc.net/rfc822.html
http://rfc.net/rfc1869.html
http://rfc.net/rfc1893.html
http://rfc.net/rfc2034.html
http://rfc.net/rfc2821.html
/usr/include/libmilter/mfapi.h
-lmilter must be specified before -lbobcat.
- o
- bobcat_4.08.06-x.dsc: detached signature;
- o
- bobcat_4.08.06-x.tar.gz: source archive;
- o
- bobcat_4.08.06-x_i386.changes: change log;
- o
- libbobcat1_4.08.06-x_*.deb: debian package holding the
libraries;
- o
- libbobcat1-dev_4.08.06-x_*.deb: debian package holding the
libraries, headers and manual pages;
- o
- http://sourceforge.net/projects/bobcat: public archive location;
Bobcat is an acronym of `Brokken’s Own Base Classes And
Templates’.
This is free software, distributed under the terms of the GNU
General Public License (GPL).
Frank B. Brokken (f.b.brokken@rug.nl).