\input texinfo @c -*-texinfo-*  -
@setfilename pop3.info
@setchapternewpage off
@finalout

@comment This is part of the GNU Mailutils manual.
@comment Copyright (C) 1999,2000,2001,2002,2003,2004 Free Software Foundation, Inc.
@comment See file mailutils.texi for copying conditions.
@comment *******************************************************************

@smallexample
@code{/* Prefix  "mu_pop3_" is reserved */}
@code{#include <mailutils/pop3.h>}

@end smallexample

The purpose of the Post Office Protocol Version 3 (POP3) is to permit a client
to download a maildrop from a remote server,  the protocol does not provide
complex or extensive operation on the maildrop.  When the client successfully
authenticates, the server acquires an exclusive access lock on the mailbox
and holds it the entire duration of the session.  After the authentication,
the session enters transaction state and the client may issues commands to
access messages in the mailbox.

@itemize @bullet
@item
Authorization state
  @itemize @bullet
  @item
  USER
  @item
  PASS
  @item
  QUIT
  @item
  CAPA (extension)
  @item
  AUTH (extension)
  @end itemize
@item
Transaction state
  @itemize @bullet
  @item
  STAT
  @item
  LIST
  @item
  RETR
  @item
  DELE
  @item
  NOOP
  @item
  RSET
  @item
  TOP
  @item
  UIDL (extension)
  @item
  QUIT
  @item
  CAPA (extension)
  @end itemize
@end itemize

When the command QUIT is issue the session enters the update state;
the server removes all messages marked deleted, releases the exclusive lock
and closes the TCP connection.

@subsection Commands
@cindex mu_pop3_t

An opaque structure @code{mu_pop3_t} is use as a handle for the session, it is allocated and initialize by
calling @code{mu_pop3_create()}.  All Functions will wait for a reply from the POP3 server before returning.
The duration of the wait can be set by calling @code{mu_pop3_set_timeout()}, the default is 2 minutes.
On the server side, there is also an idle timeout of 10 minutes before the POP3 server closes the connection,
although the @cite{RFC 1939} specifies that the minimum
default timeout to be ten minutes, many servers have shorter idle period, care should be taken to at least send a
@code{mu_pop3_noop()} between lengthy period of idle time.  Once a successful connection is established with
@code{mu_pop3_connect()}, two built-ins authentications are provided @code{mu_pop3_apop ()} or
@code{mu_pop3_user()}/@code{mu_pop3_pass()}.  The @code{mu_pop3_stat()} and @code{mu_pop3_list ()} functions can be use to
get the number and size of messages. The functions @code{mu_pop3_list_all()}, @code{mu_pop3_uidl_all ()} and
@code{mu_pop3_capa()} save the information in an @code{iterator_t}.  Downloading of messages is done
via a two methods @code{mu_pop3_retr()} or @code{mu_pop3_top()};
@strong{Caution: Some Internet Service Providers do not permit to leave mail on server and the message will be
deleted once downloaded}.
POP3 provides only a single channel for operation, it means only one operation can be done at a time,
all the functions will return @code{EINPROGRESS} if an other operation is in progress.


@subsubsection Callbacks
The POP3 library does not provide any callbacks, the approach is to leave flow control and policy outside of the
library.  The functions do minimal state checking, for example when sending RETR with @code{mu_pop3_retr()}
it is the responsibility of the user to go through the entire buffer of the stream to terminate the RETR command,
any other operation will fail, while the RETR is in progress.
To reset the state or break the downloading, the user should disconnect @code{mu_pop3_disconnect()} and reconnect
@code{mu_pop3_connect()}, after a sufficient waiting period, @strong{Some POP3 server, move the maildrop to a different
location after a sudden disconnect, it may be necessary to wait before working on the same mailbox, if not the user may
receive a ``Mailbox busy'' error code}.

@smallexample
@group
/* Example on how to implement a callback mechanism on top of the library. */
int pop3_list_cb (mu_pop3_t pop3, int msgno, int (*callback_list)(int msgno, size_t octet))
@{
   size_t octet = 0;
   int status = mu_pop3_list (pop3, msgno, &octet);
   if (status == 0)
    @{
        callback_retr (msgno, octect);
    @}
   return status;
@}
@end group
@end smallexample

@subsubsection Initialization
@cindex POP3 Initialization

@deftypefun int mu_pop3_create (mu_pop3_t *@var{pop3})

Allocate and initialize a @var{pop3} session, only memory is allocated.

Errors:
@table @code
@item ENOMEM
@item EINVAL
@end table
@end deftypefun

@deftypefun void mu_pop3_destroy (mu_pop3_t *@var{pop3})

When a POP3 session is finished, any data use by the library is release.
@end deftypefun

@deftypefun int mu_pop3_connect (mu_pop3_t @var{pop3}) 

A connection is established on the carrier,  if there was any previous connection it is close first.  If non-blocking the
function should be recall until the return value is not EAGAIN or EINPROGRESS.

Errors:
@table @code
@item ENOMEM
@item EAGAIN
@item ETIMEDOUT
@item EIO
@item EINTR
@end table

@end deftypefun

@deftypefun int mu_pop3_disconnect (mu_pop3_t @var{pop3})

Disconnect an established POP3 session.

Errors:
@table @code
@item EIO
@item EINTR
@end table

@end deftypefun

@deftypefun int mu_pop3_stls (mu_pop3_t @var{pop3})

Create a TLS stream from the carrier and sets it as the current carrier for the session.

Errors:
@table @code
@item EINVAL
@end table

@end deftypefun

@cindex POP3 carrier

@deftypefun int mu_pop3_set_carrier (mu_pop3_t @var{pop3}, stream_t @var{carrier})

Set the stream to be use as the carrier to the server , for example tcp_stream.

Errors:
@table @code
@item EINVAL
@end table

@end deftypefun

@subsubsection Authentication State
@cindex POP3 APOP

@deftypefun int mu_pop3_apop (mu_pop3_t @var{pop3}, const char *@var{user}, const char *@var{secret})

APOP offers an alternative to USER/PASS authentication.  For intermittent use of POP3, like checking for new mail, it is the
preferred way to authenticate.  It reduces the risk of password capture.  The @var{user} and the shared @var{secret} are pass
to @code{mu_pop3_apop()}, the MD5 digest is calculated by applying the time-stamp given by the server in the greeting
followed by the @var{secret}.

@end deftypefun

@cindex POP3 USER

@deftypefun int mu_pop3_user (mu_pop3_t @var{pop3}, const char *@var{user})

Sends the USER command.

Errors:
@table @code
@item EINVAL
@item EACCES
@end table
@end deftypefun

@cindex POP3 PASS

@deftypefun int mu_pop3_pass (mu_pop3_t @var{pop3}, const char *@var{passwd})

Sends the PASS, to authenticate after the USER command.

Errors:
@table @code
@item EINVAL
@item EACCES
@end table
@end deftypefun

@cindex POP3 CAPA

@deftypefun int mu_pop3_capa (mu_pop3_t @var{pop3}, iterator_t *@var{iterator})

The CAPA command is send to the server and the list of capabilities is retrieve by going through
the iterator, when done the user should call @code{iterator_destroy()}.

Errors:
@table @code
@item EINVAL
@item EACCES
@end table
@end deftypefun


@subsubsection Transaction State
@cindex POP3 DELE

@deftypefun int mu_pop3_dele (mu_pop3_t @var{pop3}, unsigned @var{msgno})

Sends a DELE to the servers who will mark the @var{msgno} for deletion. The @var{msgno} may not refer to a message already marked
deleted. If successful any future reference to @var{msgno} in other operations will be an error, unless unmarked by RSET.

Errors:
@table @code
@item EINVAL
@item EACCES
@item EINPROGRESS
@end table

@end deftypefun

@cindex POP3 LIST
@cindex struct mu_pop3_list

@deftypefun int mu_pop3_list (mu_pop3_t @var{pop3}, unsigned @var{msgno}, size_t *@var{size})

Sends a List for a specific @var{msgno} and returns the @var{size}.

Errors:
@table @code
@item EINVAL
@item EACCES
@item EINPROGRESS
@end table
@end deftypefun

@cindex POP3 NOOP

@deftypefun int mu_pop3_noop (mu_pop3_t @var{pop3})

Sends a NOOP, useful to reset the timeout on the server.

Errors:
@table @code
@item POP3_INVALID_PARAMETER
@item POP3_OPERATION_DENIED
@item POP3_OPERATION_IN_PROGRESS
@item any carrier errors.
@end table
@end deftypefun

@cindex POP3 RETR

@deftypefun int mu_pop3_retr (mu_pop3_t @var{pop3}, unsigned @var{msgno}, stream_t *@var{stream})

If successful @code{stream} should be call to download the message, byte-stuff lines or handle internally, CRLFs are
converted to LF. All other operations will fail until the downloaded is complete by the caller.

Errors:
@table @code
@item POP3_INVALID_PARAMETER
@item POP3_OPERATION_DENIED
@item POP3_OPERATION_IN_PROGRESS
@item any carrier errors.
@end table
@end deftypefun

@smallexample
#include <stdio.h>
#include <mailutils/pop3.h>

int
print_message (mu_pop3_t pop3, unsigned int msgno)
@{
   stream_t stream;
   int status = mu_pop3_retr (pop3, msgno, &stream);
   if (status == 0)
    @{
       size_t n = 0;
       char buf[128];
       while ((status = stream_readline (stream, buf, sizeof buf, &n)) == 0) && n > 0)
        @{
           printf ("%s", buf);
        @}
    @}
   return status;
@}
@end smallexample

@cindex POP3 TOP

@deftypefun int mu_pop3_top  (mu_pop3_t @var{pop3}, unsigned int @var{msgno}, unsigned int @var{lines}, stream_t *@var{stream})

If successful @code{stream} should be call to download the header, byte-stuff lines or handle internally, CRLFs are
converted to LF.  All other operations will failed until the operation is completed by the caller.

Errors:
@table @code
@item EINVAL
@item EACCES
@item EINPROGRESS
@end table
@end deftypefun

@smallexample
#include <stdio.h>
#include <mailutils/pop3.h>

int
print_top (mu_pop3_t pop3, unsigned int msgno, unsigned int lines)
@{
    stream_t stream;
    int status = mu_pop3_top (pop3, msgno, lines, &stream);
    if (status == 0)
     @{
        size_t n = 0;
        char buf[128];
        while ((status = stream_readline (stream, buf, sizeof buf, &n)) == 0) && n > 0)
          printf ("%s", buf);
     @}
  return status;
@}
@end smallexample


@cindex POP3 RSET

@deftypefun int mu_pop3_rset (mu_pop3_t @var{pop3})

Sends a RSET to unmarked the messages marked as deleted.

Errors:
@table @code
@item EINVAL
@item EACCES
@item EINPROGRESS
@end table
@end deftypefun

@cindex POP3 STAT

@deftypefun int mu_pop3_stat (mu_pop3_t @var{pop3}, unsigned @var{msgno}, unsigned *@var{msg_count}, size_t *@var{size})

The number of messages in the mailbox and the size of the mailbox in octets. @strong{Caution:} The size is in RFC822 where
line termination is CRLF, messages marked as deleted are not counted in either total.

Errors:
@table @code
@item EINVAL
@item EACCES
@item EINPROGRESS
@end table
@end deftypefun

@cindex POP3 UIDL

@deftypefun int mu_pop3_uidl (mu_pop3_t @var{pop3}, unsigned int @var{msgno}, char **@var{uidl})

The UIDL is return in @var{uidl}, the string must be @code{free ()}'ed, by the caller.

Errors:
@table @code
@item EINVAL
@item EACCES
@item EINPROGRESS
@item any carrier errors.
@end table
@end deftypefun

@deftypefun int mu_pop3_uidl_all (mu_pop3_t @var{pop3}, iterator_t *@var{iterator})

A UIDL command is executed.  The call should iterate through the @code{iterator} to fetch the response.

Errors:
@table @code
@item EINVAL
@item EACCES
@item EINPROGRESS
@end table
@end deftypefun

@smallexample
#include <stdio.h>
#include <stdlib.h>
#include <mailutils/pop3.h>

void print_uidl (mu_pop3_t pop3)
@{
   iterator_t itr;
   status = mu_pop3_uidl_all (pop3, &itr);
   if (status == 0)
    @{
       int rc;
   
       for (iterator_first (itr); !iterator_is_done (itr); iterator_next (itr))
          @{
              char *text;
 
              rc = iterator_current (itr, (void**) &text);
              if (rc)
                lperror ("iterator_current", rc);
              printf ("%s\n", text);
          @}
       iterator_destroy (&itr);
    @}
    
@}
@end smallexample


@subsubsection Update State
@cindex POP3 QUIT

@deftypefun int mu_pop3_quit (mu_pop3_t @var{pop3})

QUIT will be send to enter the update state, if the command is successful, the connection is close and any state
the library is cleared. On the server side, all messages marked deleted before closing the connection will be removed..

Errors:
@table @code
@item EINVAL
@item EACCES
@item EINPROGRESS
@end table
@end deftypefun


@subsubsection Help functions

@deftypefun int mu_pop3_writeline (mu_pop3_t @var{pop3}, const char *@var{format}, ...);

Copy in the internal buffer of @code{mu_pop3_t} the formatted string @var{format},
@code{mu_pop3_send()} should be called later to flush the string to the POP3 server.

Errors:
@table @code
@item EINVAL
@end table
@end deftypefun

@deftypefun int mu_pop3_sendline (mu_pop3_t @var{pop3}, const char *@var{cmd});

Cover function for @code{mu_pop3_writeline()} followed by a @code{mu_pop3_send()}.

Errors:
@table @code
@item EINVAL
@end table
@end deftypefun

@deftypefun int mu_pop3_send (mu_pop3_t @var{pop3});

Flushes out the strings written by @code{mu_pop3_writeline ()} in the internal buffer to the
stream carrier.

Errors:
@table @code
@item EINVAL
@end table
@end deftypefun

@deftypefun int mu_pop3_response (mu_pop3_t @var{pop3}, char *@var{buffer}, size_t @var{len}, size_t *@var{plen})

The last response from the last command is save and can be examine after a failure or success.

Errors:
@table @code
@item EINVAL
@end table
@end deftypefun

@subsubsection Timeout
@cindex Pop3 Timeout

@deftypefun int mu_pop3_set_timeout (mu_pop3_t @var{pop3}, int @var{timeout})

Set the timeout time for I/O on the carrier.  The default is 10 minutes. The @var{timeout} is given in milliseconds.

Errors:
@table @code
@item EINVAL
@end table
@end deftypefun

@deftypefun int mu_pop3_get_timeout (mu_pop3_t @var{pop3}, int *@var{timeout})

Get the timeout time for I/O on the carrier. The @var{timeout} is given in milliseconds.

Errors:
@table @code
@item EINVAL
@end table

@end deftypefun