Seems that when using HHVM, Piwik's API renderer sets wrong response format (XML).

PDF file format requires EOF to be used as file trailer, on the last line of the content.
This is done in https://github.com/tecnickcom/TCPDF/blob/develop/tcpdf.php#L9988

Piwik's API renderer appends XML response to valid PDF content, resulting in garbaged output:

... PDF content
0000413826 00000 n
0000414317 00000 n
0000414489 00000 n
0000414685 00000 n
0000414750 00000 n
0000414950 00000 n
0000419257 00000 n
trailer
<< /Size 24 /Root 23 0 R /Info 21 0 R /ID 
[ <8aeb203749d4538ab33be9cb9db12ceb> <8aeb203749d4538ab33be9cb9db12ceb> ] >>
startxref
419506
%%EOF
<?xml version="1.0" encoding="utf-8" ?>
<result></result>

Therefore, the browser cannot show the PDF content correctly, and shows you the XML error message instead.

Furthermore, when using HHVM instead of PHP engine, even though TCPDF is already setting correct Content-Type header when generating inline browser output (https://github.com/tecnickcom/TCPDF/blob/6.2.12/tcpdf.php#L7624), the actual header's value being sent is text/xml.

Content-Type: text/xml; charset=utf-8
X-Powered-By: HHVM/3.12.1
Cache-Control: private, must-revalidate, post-check=0, pre-check=0, max-age=1
Content-Disposition: inline; filename="All_Websites_-_Sunday_March_20_2016_-_test.pdf"

Correct response headers using PHP 5.6.19:

Content-Type: application/pdf
Cache-Control: private, must-revalidate, post-check=0, pre-check=0, max-age=1
Content-Disposition: inline; filename="All_Websites_-_Sunday_March_20_2016_-_test.pdf"

Temporary solution

You can bypass this behaviour by appending &format=original parameter into the PDF report URI. That will show the report in your browser correctly, by setting correct Content-Type response header and also disabling the additional XML output being appended.

LTS solution

This issue requires thorough investigation, but from what I can see so far, here would be some proposed solutions:

• Correct Content-Type should be set regardless of the library used for PDF generation (currently tecnickcom/TCPDF).
• Processing of the request should be stopped after the PDF content is returned to user in https://github.com/piwik/piwik/blob/master/plugins/ScheduledReports/API.php#L509 (the simplest solution would be exit(0) before the break.

That way we would ensure that there is no extra content appended to the inline browser PDF output.

@emirb thank you a lot for investigating and giving us insights into the problem. 👍 👍

I haven't tried to reproduce it but wonder if this PR maybe kind of fixed the content type issue: #9700

@kofispaceman or @emirb can you maybe try with latest beta version 2.16.1 (at least 2.16.1-b2 or master branch)

Hi @kofispaceman - do you still have the issue with our latest beta? please let us know http://piwik.org/faq/how-to-update/faq_159/

Hello @mattab and @tsteur,

I will test the latest beta and let you guys know. @emirb was right. HHVM was rendering the content as XML instead of PDF.

Hi @kofispaceman @emirb let us know if the issue is still here