Cannot output a big string block without break lines (nginx+php)

As you write

the server fails without an error

I presume you mean that the server sends a response to the client (status code: 200 - no error), but the response body (the content) is empty (this is the failure).

You should check this because if actually the server sends a response with content then the issue is not with php, nginx or buffering.

Otherwise (as suggested in comments) maybe the JSON instead of inside a <script> - </script> block may be wrapped between <pre> tags and this could be the problem (but I can't help unless you post more of your code).

From now on I assume the response sent from the server is empty

The code you posted is valid and is supposed to handle correctly the output string you're building up (that's far below PHP limits).

Said that it seems a weird buffering issue. I write "weird" because as far as I know (and I took time to do some research too) buffering should not be influenced by line breaks.

I have found that if I put line breaks in the JSON string, it's OK even if the string is 400k.

A quick workaround to solve your problem is to output a valid JSON with line breaks. You just need to specify an option to json_encode:

echo 'var config = ' . json_encode( $config, JSON_PRETTY_PRINT ) . ';' . PHP_EOL;

JSON_PRETTY_PRINT tells json_encode to format the json to be more readable and doing so will add line breaks.

(Note that this option is available for PHP 5.4.0 and above)

I hope the above solution works for you.

Anyway I strongly suggest you to investigate further the issue in order to let the original code too to work.

First you should ensure you're running a recent and stable version of both nginx and php.

Then I would check nginx configuration file, php-fpm configuration (if you're using php-fpm) and finally php configuration.

Also check php, nginx, and php-fpm error logs.

try using php heredoc for echoing http://www.php.net/manual/en/language.types.string.php#language.types.string.syntax.heredoc

In case you don't have PHP version > 5.4.0 installed on your server a quick workaround could be something like this. The below snippet works for a test array. Initial test was with an array of 250Kb. Since i can't post the actual test array here is a test link with a smaller example. It is as the result of JSON_PRETTY_PRINT though.

$out = json_encode($arr,JSON_FORCE_OBJECT);$out = str_replace( ':{', ':' . PHP_EOL . '    ' . '{', $out );$out = str_replace( '},', PHP_EOL . '    },', $out );$out = str_replace( ',', ',' . PHP_EOL  . '     ', $out );$out = str_replace( '},' . PHP_EOL . '     ', '},' . PHP_EOL . ' ', $out );$out = str_replace( '}}', PHP_EOL . '    }' . PHP_EOL . '}', $out );echo $out;