NAME¶

filter_api_loop, filter_api_accept, filter_api_reject, filter_api_reject_code, filter_api_writeln, filter_api_on_connect, filter_api_on_helo, filter_api_on_mail, filter_api_on_rcpt, filter_api_on_data, filter_api_on_dataline, filter_api_on_eom, filter_api_on_reset, filter_api_on_disconnect, filter_api_on_commit, filter_api_on_rollback, filter_api_setugid, filter_api_set_chroot, filter_api_no_chroot, filter_api_set_udata, filter_api_get_udata, filter_api_sockaddr_to_text, filter_api_mailaddr_to_text —

SYNOPSIS¶

#include <smtpd-defines.h>
#include <smtpd-api.h> void
filter_api_loop(void); int
filter_api_accept(uint64_t id); int
filter_api_reject(uint64_t id, enum filter_status status); int
filter_api_reject_code(uint64_t id, enum filter_status status, uint32_t code, const char *line); void
filter_api_writeln(uint64_t id, const char * line); void
filter_api_on_connect(int(*cb)(uint64_t, struct filter_connect *)); void
filter_api_on_helo(int(*cb)(uint64_t, const char *)); void
filter_api_on_mail(int(*cb)(uint64_t, struct mailaddr *)); void
filter_api_on_rcpt(int(*cb)(uint64_t, struct mailaddr *)); void
filter_api_on_data(int(*cb)(uint64_t)); void
filter_api_on_dataline(void(*cb)(uint64_t, const char *)); void
filter_api_on_eom(int(*cb)(uint64_t, size_t)); void
filter_api_on_reset(void(*cb)(uint64_t)); void
filter_api_on_disconnect(void(*cb)(uint64_t)); void
filter_api_on_commit(void(*cb)(uint64_t)); void
filter_api_on_rollback(void(*cb)(uint64_t)); void
filter_api_setugid(uid_t uid, gid_t gid); void
filter_api_set_chroot(const char *rootpath); void
filter_api_no_chroot(void); void
filter_api_set_udata(uint64_t id, void *data); void *
filter_api_get_udata(uint64_t id); const char *
filter_api_sockaddr_to_text(const struct sockaddr *sa); const char *
filter_api_mailaddr_to_text(const struct mailaddr *maddr);

DESCRIPTION¶

filter_api is an interface intended to provide filter capabilities for the smtpd(8) daemon. filter_api is used in standalone filter programs, which setup callback functions to hook into the SMTP dialog. For example, each SMTP command can be intercepted with callback functions. The function filter_api_loop() is used to enter the filter loop, waiting for callback functions to be called. The function filter_api_accept() can be called to accept the current message with the given id from within a callback function. The functions filter_api_reject() and filter_api_reject_code() can be called to reject the current message with the given id from within a callback function. Both expect the status to be specified which should be one of the following values.

FILTER_FAIL

The filter failed and the message should not be accpeted.

FILTER_CLOSE

The filter is done and the message should not be accepted.

Morover, with the function filter_api_reject_code() a code and line can be specified, to reject the current message with a custom SMTP reply code and error message. The function filter_api_writeln() is intended to write (received) SMTP DATA command lines (back) from within a callback function. This might be used by a filter to add or modifiy DATA lines.

CALLBACK FUNCTIONS¶

The function filter_api_on_connect() is called on new SMTP connections. The callback can be used to accept or reject messages based on the given connection information. The function filter_api_on_helo() is called on SMTP HELO command. The callback can be used to accept or reject messages based on the given HELO string. The function filter_api_on_mail() is called on SMTP MAIL FROM command. The callback can be used to accept or reject messages based on the given MAIL FROM address. The function filter_api_on_rcpt() is called on SMTP RCPT TO command. The callback can be used to accept or reject messages based on the given RCPT TO address. The function filter_api_on_data() is called on SMTP DATA command. The callback might be used to setup data structures for filtering the upcoming DATA lines. The function filter_api_on_dataline() is called on each SMTP DATA line. The callback can be used to accept or reject messaged based on the (header or body) content of the current message. The function filter_api_on_eom() is called on the end (of DATA command) of the current message. The callback might be used to cleanup data structures and finalize the decision of accepting or rejecting the message. The function filter_api_on_reset() is called on SMTP RSET command. The callback might be used to reset the current filter state. The function filter_api_on_disconnect() is called on closed SMTP connections. The callback might be used to cleanup earlier setup data structures. The function filter_api_on_commit() is called on commit of the current message. The function filter_api_on_rollback() is called on rollback of the SMTP session. The callback might be used to cleanup earlier setup data structures.

HELPER FUNCTIONS¶

The function filter_api_setugid() can be called using uid and gid to set the running user and group of the filter. The function filter_api_set_chroot() can be called using rootpath to set the chroot path of the filter. The function filter_api_no_chroot() can be called to disable chroot for the filter. The function filter_api_set_udata() can be called for the current message with the given id to set a user data pointer data from within a callback function. The function filter_api_get_udata() can be called to get the user data pointer for the current message with the given id from within a callback function. The function filter_api_sockaddr_to_text() can be called to convert a socket address sa to a string. The function filter_api_mailaddr_to_text() can be called to convert a mail address maddr to a string.

RETURN VALUES¶

The functions filter_api_accept(), filter_api_reject(), and filter_api_reject_code(), return 1, intended to be used in a return statement of a callback function. The function filter_api_get_udata() returns a pointer to the user data set for the current message. The functions filter_api_sockaddr_to_text() and filter_api_mailaddr_to_text() return a pointer to a static buffer containing the string representation. The buffer remains valid until the next call to the conversion functions. In case of error, the function filter_api_sockaddr_to_text() returns the static string “(unknown)” and the function filter_api_mailaddr_to_text() returns NULL.

ERRORS¶

The function filter_api_sockaddr_to_text() may fail for any of the errors specified for the routine getnameinfo(3) and listed in gai_strerror(3).

EXAMPLES¶

filter-stub(8) which ships with OpenSMTPD-extras is intended to provide an example code template.

SEE ALSO¶

smtpd.conf(5), smtpd(8), filter-stub(8)