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Date: Sun, 15 Aug 2004 17:32:25 +0200
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Subject: Re: [PHP-DEV] [PATCH] PHP_IMAP New Function "imap_partialbody"
  to fetch chunks of a MIME attachment
From: thetaphi@php.net (Uwe Schindler)

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