Yii2 setDownloadHeaders() is not working - php

Question

Code
public function actionExport() {
ini_set('memory_limit','32M');
$whileAgo = date('Y-m-d', time() - 2*24*60*60); // 7-9 seems to be the limit for # days before the 30s timeout
$agkn = AdGroupKeywordNetwork::find()
->select(['field1', 'field2', ...])
->where(['>', 'event_date', $whileAgo])->asArray()->each(10000);
$dateStamp = date('Y-m-d');
Yii::$app->response->setDownloadHeaders("stats_$dateStamp.csv", 'text/csv');
echo 'id,ad_group_keyword_id,keyword,network_id,quality,event_date,clicks,cost,impressions,position,ebay_revenue,prosperent_revenue'.PHP_EOL;
// flush(); // gives us 55s more // doesn't work with gzip
foreach ($agkn as $row) {
echo join(',', $row).PHP_EOL;
// flush();
}
}
Tested:
$ time (curl -sv -b 'PHPSESSID=ckg8l603vpls8jgj6h49d32tq0' http://localhost:81/web/ad-group-keyword-network/export | head)
...
< HTTP/1.1 200 OK
< Transfer-Encoding: chunked
< Content-Type: text/html; charset=UTF-8
<
{ [8277 bytes data]
id,ad_group_keyword_id,keyword,network_id,quality,event_date,clicks,cost,impressions,position,ebay_revenue,prosperent_revenue
9690697,527322,ray ban predator,1,6,2015-11-22,0,0.00,1,5.0,,
It's not downloading a CSV file in the browser either. It's not setting the headers. What is wrong?
Reference: http://www.yiiframework.com/doc-2.0/yii-web-response.html#setDownloadHeaders()-detail

Answer 1

It's because php send header at first echo, before Yii does it.
There are some way to solve the issue.
Collect output to buffer, then send it.
Yii::$app->response->setDownloadHeaders("stats_$dateStamp.csv", 'text/csv');
$data = 'id,ad_group_keyword_id,keyword,network_id,quality,event_date,clicks,cost,impressions,position,ebay_revenue,prosperent_revenue'.PHP_EOL;
foreach ($agkn as $row) {
$data .= join(',', $row).PHP_EOL;
}
return $data;
If output is too large to fit in memory, then data may be stored to temp file. Then send file and delete temp file. There is no need to set header manually in this case.
$filePath = tempnam(sys_get_temp_dir(), 'export');
$fp = fopen($filePath, 'w');
if ($fp) {
fputs($fp, ...);
}
fclose($fp);
return Yii::$app->response->sendFile($filePath, "stats_$dateStamp.csv")
->on(\yii\web\Response::EVENT_AFTER_SEND, function($event) {
unlink($event->data);
}, $filePath);