I found this problem trying to serve a binary file.
The basic structure of this part of my script is:

header('Content-Type: ..');
header('Content-Length: ..');
<output file contents>

where <output file contents> would be readfile or similar. However I learned that the first byte of the served file was always a 0x0a (linefeed). I have used telnet to create  requests and log responses, and I have found that the response has the following structure:

<header><cr><lf>
..
<header><cr><lf>
<cr><lf>
<lf><body-part>

i.e. and extra <lf> prepended to the body part of the response. I have tested several different scenarios:

* no headers, echo some text
* set chunked transfer encoding, do a readfile
* set chunked transfer encoding, echo some text
* set chunked transfer encoding, use fwrite on php://stdout

All methods prepend the linefeed. The telnet dump verify that the headers are set correctly, so this should rule-out the possibility that the linefeed stems from any text before the <? -tag.

PHP is build with the following configuration line:

'./configure' '--with-apache=../apache_1.3.27' '--enable-safe-mode' '--with-mhash' '--enable-xslt' '--with-xslt-sablot' '--enable-sablot-errors-descriptive' '--with-pdflib' '--with-imap=/usr/local/imap' '--with-mcrypt' '--with-pspell' '--with-gettext' '--with-mysql=/usr/local' '--with-pgsql' '--with-gd' '--with-ttf' '--with-t1lib' '--with-png-dir' '--with-zlib-dir=/usr/local/zlib' '--enable-memory-limit' '--with-jpeg-dir' '--with-freetype-dir' '--enable-freetype-4bit-antialias-hack' '--with-tiff-dir' '--enable-exif' '--enable-calendar'

I think this problem may be related to #18740..

/David Holdt