PHP: Why is this forced mime download adding 2 extra empty lines?

问题

I have a PHP script I wrote to create a .txt tab delimited file. I need to have this forced downloaded to the web browser. It does all this, but when I compare the file to the source the forced downloaded on contain two extra blank lines. Here is the code:

// Force download of the tab del .txt file to the web browser:

    header('Content-Type: application/download');
    header("Content-Disposition: attachment; filename=$tab_del_file");
    header("Content-Length: " . filesize($tab_del_file));

    $fp = fopen($tab_del_file, "r");
    fpassthru($fp);
    fclose($fp);

Linux Shell Command to compare the two files and show there are extra blank lines: $ diff example.txt /tmp/example.txt 25a26,27

I sftp'ed the downloaded example.txt to the /tmp directory so I could then do the diff on the server. Why are two blank lines being added to the downloaded version and what is the fix? Thanks!

回答1:

As the php code itself looks ok and does not produce that new lines, this can have only one reason. You have a closing ?> tag and extra new lines at the end of your file:

?>
<--- empty line
<--- empty line

Note the content outside the php tags will not be parsed by PHP and just forwarded to the browser.

Solution: remove the closing ?> tag or the extra new lines. I usually prefer just not using the ?>

Btw, I should mention that this:

$fp = fopen($tab_del_file, "r");
fpassthru($fp);
fclose($fp);

can be simplified by

readfile($tab_del_file);

回答2:

You most likely have an extra blank line after the closing ?>, which is being echoed with the data. The closing ?> is always optional at the end of a PHP file. Leaving it out is a good practice to prevent this sort of problem.

回答3:

Actually this is problem due to position of php closing Tag.. ?>.

Basically the PHP closing tag on a PHP document ?> is optional to the PHP parser. So if it is used in your script and you leave any whitespace after ?> then it can cause unwanted error or output. I believe In your case also you would have done the same mistake.

So for this reason, PHP script should OMIT the closing Tag and instead you should use a comment block to mark the end of script.

Here is small example:

INCORRECT:

<?php

echo "Hello World!";

?>

CORRECT:

<?php

echo "Hello World!";

/* End of file myfile.php */
/* Location: ./system/modules/mymodule/myfile.php */

I Hope this helps you..!!

来源：https://stackoverflow.com/questions/16372678/php-why-is-this-forced-mime-download-adding-2-extra-empty-lines

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php

mime