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cetlib.php
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cetlib.php
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<?php
/*
(c) 2022 Chris Royle
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
// THIS IS ALL WELL AND GOOD, BUT THE REAL DECODERS RESET THEIR SHIFT OFFSET TO 0 ON |A AT START OF FRAME...
// NEED TO ENCODE FRAME AT A TIME AFTER ALL - CAN'T DO THE WHOLE FILE BECAUSE WITH HEADER BLOCK WE CAN'T
// SAY PRECISELY HOW MUCH SPACE WE HAVE IN EACH FRAME
$cet_shift_offset = 0;
function cet_escape($c)
{
global $cet_shift_offset;
$orig = $c = ord($c);
if ($c == 125)
{
//printf("Input %02x Output |\\\n", $orig);
return "|".chr(125); // The 3/4 escape
}
if ($c == 0x7c) // | character
return "|E";
if ($c === 32)
$c = 125; // Spaces go to 3/4
if ($c < 32)
{
$ec = 1;
$c += 64;
}
else if ($c < 128)
$ec = 0;
else
{
$ec = intval(($c-64) / 32);
$c -= (32 * $ec);
}
$retval = chr($c);
if ($ec != $cet_shift_offset)
{
$cet_shift_offset = $ec;
$retval = "|".$ec.$retval;
}
//printf("Input %02x Output %s\n", $orig, $retval);
return $retval;
}
function cet_convert ($in_handle, $in_size, $offset = 0, $length = 880)
{
//$cet_shift_offset = 0; // Looks like Commstar might not re-set this at start of each frame?
$bytes_output = 0;
$retval = array("converted" => "", "processed" => 0);
$bytes_input = 0;
fseek($in_handle, $offset);
while (($bytes_input < $in_size) and (($length == -1) or ($bytes_output < $length)))
{
$in_c = fread($in_handle, 1);
if (feof($in_handle))
$out_c = "|F";
else
$out_c = cet_escape($in_c);
if (($length != -1) and ($bytes_output + strlen($out_c)) > $length) // If we'd exceed the length available, then don't output (so we don't split across a frame)
break;
$bytes_output += strlen($out_c);
if ($out_c != "|F") // We weren't at end of file
$bytes_input++;
$retval['converted'] .= $out_c;
if ($out_c == "|F") // End of file
break;
}
$retval['processed'] = $bytes_input;
return ($retval);
}
function cet_decode ($infile, $outfile)
{
global $cet_shift_offset;
$in_handle = fopen($infile, "r");
$out_handle = fopen($outfile, "w");
$cet_shift_offset = 0;
$fsize = filesize($infile);
//print "Input file size ".$fsize." bytes\n";
$bytes_read = 0;
$bytes_output = 0;
while ($bytes_read < $fsize)
{
$in_c = fread($in_handle, 1);
$bytes_read++;
$in_c = ord($in_c);
//printf ("Read byte %d - character %02x...", $bytes_read, $in_c);
if (chr($in_c) == "|") // Escape
{
$next_char = fread($in_handle, 1);
$bytes_read++;
//printf ("and %02x...", ord($next_char));
if (ord($next_char) == 0x5c)
{
fwrite($out_handle, chr(0x5c));
$bytes_output++;
}
else if (ord($next_char) == 69) // \E = |
{
fwrite($out_handle, chr(0x7c));
$bytes_output++;
}
else if (($next_char >= "0") and ($next_char <= "5"))
{
$cet_shift_offset = ord($next_char)-ord("0");
if ($cet_shift_offset > 5) $cet_shift_offset = 0; // Cope with invalid shifts.
}
//print "\n";
continue;
}
if ($cet_shift_offset == 1)
$out_c = $in_c - 64;
else
$out_c = $in_c + ($cet_shift_offset * 32); // works for offset 0.
if ($out_c == 125)
$out_c = 32; // Change 3/4 back to space
//printf ("Output %02x...", $out_c);
fwrite ($out_handle, chr($out_c));
$bytes_output++;
//print "Output byte $bytes_output\n";
}
fclose($in_handle); fclose($out_handle);
}
// Retrieve a remote file for CET purposes
// Return FALSE (couldn't get it)
// Return TRUE (it was there, but didn't need updating)
// Return timestamp (It was there, we retrieved it, and this is its last update time)
function cet_fileupdate($url, $localfile, $lastmodifiedtime, $cetid)
{
$headers = get_headers($url, 1);
$date = null;
$retval = false;
if ($headers && (strpos($headers[0], '200') !== FALSE))
{
$time = strtotime($headers['Last-Modified']);
if ($time > $lastmodifiedtime)
if(file_put_contents($localfile, file_get_contents($url)))
$retval = $time;
else $retval = false;
else $retval = true;
}
return $retval;
}
?>