file io - PHP: headers already sent when using fwrite but not when using fputcsv -

i know theory behind error driving me crazy again. i'm using tonic in application. library redirect traffic dispatch.php script executes appropriate resource , resource return response displayed (output) dispatch.php.

the output method of response this:

/**  * output response  */ public function output() {     foreach ($this->headers $name => $value) {         header($name.': '.$value, true, $this->responsecode());     }     echo $this->body; } 

so afaik tells can't write php output in resource.

i have resource dynamically generates csv input csv , outputs browser (it converts 1 column of data different format).

$csv = fopen('php://output', 'w'); // sets header $response->__set('contentdisposition:', 'attachment; filename="' . $filename . '"'); while (($line = fgetcsv($filepointer, 0, ",", '"')) !== false) {     // generate line     fputcsv($csv, $line); } fclose($filepointer); return $response; 

this works 100% fine. no issue headers , correct file generated , offered download. confusing because writing output before headers set? fputcsv do?

i have second resource similar thing outputs custom file format (text file).

$output = fopen('php://output', 'w'); // sets header $response->__set('contentdisposition:', 'attachment; filename="' . $filename . '"'); while (($line = fgetcsv($filepointer, 0, ",", '"')) !== false) {     // generate record (multiple lines) not shown / snipped     fwrite($output, $record); } fclose($filepointer); return $response; 

the difference uses fwrite instead of fputcsv , bang

 headers sent by... // line number = fwrite() 

this confusing! imho should fail in both cases? why first 1 work? how can second 1 work? (i can generate huge string containing file , put responses body , works. files rather big (up 50 mb) , hence want avoid this.)

$record not set, generating error of level notice. if have error_reporting true, php put error in output before sending headers.

set error_reporting false , keep eye on logs instead.