PHP: gztell - Manual

(PHP 4, PHP 5, PHP 7, PHP 8)

gztell — Tell gz-file pointer read/write position

Description

Parameters

stream

The gz-file pointer. It must be valid, and must point to a file successfully opened by gzopen().

Return Values

The position of the file pointer or false if an error occurs.

See Also

• gzopen() - Open gz-file
• gzseek() - Seek on a gz-file pointer
• gzrewind() - Rewind the position of a gz-file pointer

ok so this function returns the gz file pointer as the uncompressed data byte length so if you are trying to put something in to specific size gzip files it won't work.

Example: 

<?
//some_file.sql  filesize = 2,048,000 bytes

$text_fp=fopen('some_file.sql','r');
$gz_fp=gzopen('some_file.sql.gz','wb9');
while(!feof($text_fp)){
    gzwrite($gz_fp,fread($text_fp,655360));
}
fclose($text_fp);
echo "gztell = ".gztell($gz_fp)."<BR>\n";
gzclose($gz_fp);
echo "filesize = ".filesize('some_file.sql.gz')."<BR>\n";
?>

Output:

gztell = 2048000
filesize = 249264

I will report this as a bug but post a note here for now