Investigations into ACCVIO when using Ilohamail under VMS
---------------------------------------------------------
Rene Mendoza <mendoza a-commercial-at coloradomtn a-period edu> 23-FEB-2005

First a warning that I am no PHP expert. I just started playing with PHP and 
have only been using WASD for a few months, so I am a complete newbie with PHP 
and WASD but I have been doing programming for nearly 2 decades.

Tested under VMS 7.3-2, with latest critical patches as of about 20-Jan-2005, 
Multinet 5.0, and WASD 9.02 with 1.2-1 PHP from HP.

I followed the instructions on the WASD server page for installing Ilohamail. 
During the initial test I immediately noticed the ACCVIOs happening as
explained on the WASD Ilohamail installation page.

I was able to trace down where the ACCVIOs in Ilohamail were occurring through 
the liberal use of echo();flush(); statements.  In this case it is caused by a 
call to the PHP file() function in the read() function in Ilohamail's 
data_manager.fs.inc file.  It appears that the most likely time that the ACCVIO 
is likely to happen is when a zero length file is first accessed.  It will 
always occur when you reduce a file to zero length and then immediately access 
it again.  The one consistently reproducible process for causing an ACCVIO was 
to start with an empty contacts page, add a contact, then delete the one and 
only contact.

The source of the original read() is reproduced here.

--------begin
         function read(){
                 $filePath = $this->path;
                 $this->data = false;

                 $fp = fopen($filePath, "a");            //force create file
                 if ($fp) fclose($fp);

                 $lines = file($filePath);

                 if (is_array($lines)){
                         $i=1;
                         while ( list($key, $line) = each ($lines) ){
                                 $a = explode(",", chop($line));
                                 while ( list($k2, $data) = each($a) ){
                                         list($type, $string) = explode(":", $da`
                                         if ($type!="id") $string = base64_decod`
                                         //$string = base64_decode($string);
                                         $this->data[$i][$type] = $string;
                                 }
                                 $this->data[$i]["id"] = $i;
                                 $i++;
                         }
                 }else{
                         $this->error.= "Failed to read from: $filePath.\n";
                         $this->data = array();
                 }

                 return $this->data;
         }
---------end

This is my modified version of the read() changes highlighted with "|".

---------begin
         function read(){
                 $filePath = $this->path;
                 $this->data = false;

|                if (file_exists($filePath) ) {
|                        clearstatcache();
|                        if (filesize($filePath) > 0 ) {
|                                $lines = file($filePath);
|                        }
|                        else {
|                                $lines = "";
|                        }
|                }
|                else {
|                        $fp = fopen($filePath, "a");            //force create
|                        if ($fp) fclose($fp);
|                        $lines = "";
|                }

                 if (is_array($lines)){
                         $i=1;
                         while ( list($key, $line) = each ($lines) ){
                                 $a = explode(",", chop($line));
                                 while ( list($k2, $data) = each($a) ){
                                         list($type, $string) = explode(":", $da`
                                         if ($type!="id") $string = base64_decod`
                                         //$string = base64_decode($string);
                                         $this->data[$i][$type] = $string;
                                 }
                                 $this->data[$i]["id"] = $i;
                                 $i++;
                         }
                 }else{
                         $this->error.= "Failed to read from: $filePath.\n";
                         $this->data = array();
                 }

                 return $this->data;
         }
--------end

The change I made was to check if the file exists and if it does only read it 
with file() if its length is greater than zero.  clearstatcache() is called 
prior to checking the size so that the correct file size is returned.  I am 
uncertain if my handling of $lines is correct in this case and its affect on
the rest of the processing, although it appears to behave as you would expect
it to.

After making this change the ACCVIOs that I could reproduce consistently have 
stopped.  I can't say that it will stop all ACCVIOs though.

One final note, the ACCVIO output will be output immediately, so if the PHP 
script has done some output but it hasn't been flushed, you will have the
ACCVIO output prior to the unflushed PHP output.  This was a little confusing
at first and made it seem as if the ACCVIO was occurring at a different point
than it was.

[Note by Mark Daniel: When using PHPWASD 1.3.0 or later it is possible to
define a system-level logical name PHPWASD$WATCH_REMOTE_ADDR to the IP address
string of the accessing client and 'watch' the PHP-engine/WASD interactions. 
This can provide a better handle on exactly when such an ACCVIO or other issue
is occuring, as well as general insights into script behaviour.  See the
READMORE.HTML in the [SRC.PHP] directory.]