[PATCH] PHP_IMAP New Function "imap_partialbody" to fetch chunks of a MIME attachment

How about the idea to make a function like "imap_getbodystream(...)" that
returns a PHP stream that can be read with fread() etc. and then closed by
fclose()?. This could be done by using Wez's PHP stream wrappers in PHP5
(even in PHP4.3).

Uwe

At 00:47 15.08.2004, you wrote:

This new function is intended to add "chunking" capability to fetching
attachments from an email using the IMAP library. Currently the attachment
fetch is done with imap_fetchbody , and is placed entirely in memory, ergo

• if the attachment is larger than the available memory it will fail.

This function has the following prototype - string
imap_partialbody(resource stream_id, int msg_no, int section, int start,
int len [, int options])
It's exactly like imap_fetchbody, except it adds the parameters start
(for the start position offset) and len (for the number of bytes to
retrieve). I've also made sure that the correct checks for message number
are in the code (as per the recent change to imap_fetchbody).

It uses the function "mail_partial_body" in the C Client, which doesn't
appear in any of the very dated documentation, but I found a few postings
by Mark Crispin explaining how to use it, and it's also been used in pine.
One complication is that it uses a callback to populate the buffer, but I
found some hints on how to use a "spare pointer " element in the IMAP
stream structure from a post by him in one of the online IMAP forums here

• http://www.webservertalk.com/message299504.html

Obviously the benefit is that a new attachment retrieval could be
implemented in webmail such as IMP that doesn't require the memlimit on
the server to be set to some absurd value, and would be less likely bring
the server to its knees when some idiot mails a 50M video to a group of
his friends. Note however c-client is still greedy about memory for its
cache (theres nothing that can be done about that) - but this doesn't
figure in the PHP memlimit.
A snippet of some resulting PHP using the function (struct is the return
from imap_fetchstructure - note I haven't put anything in to decode the
structure or errorcheck the return for brevity). CHUNKSIZE is how much to
fetch at a time (100K works quite well)
$size=$struct->parts[$partindex]->bytes;
$fp=fopen($attachfile,"w");
for ($i=0;$i<$size;$i+=CHUNKSIZE)
{
$len = (($size-$i)<CHUNKSIZE) ? $size-$i:CHUNKSIZE;
$pbody = imap_partialbody($imap,$msgno,$partno,$i,$len);
fwrite($fp,$pbody);
}

You will find this code works fine on a large attachment, and doesn't blow
the memlimit when its set to the default of 8M.
The next problem of course is that php/php_imap doesn't have a streamed
Base64 decoder - though I've used a simple command line one quite effectively.

I'm guessing if this is of interest, it will be of most interest to the
HORDE/IMP team?

Crispin Olson

Uwe Schindler
thetaphi@php.net - http://www.php.net
NSAPI SAPI developer
Erlangen, Germany