json_decode from https url JSON validation on https - php

Question

Can anyone shed any light on why
http://jsonlint.com/
and
http://jsonformatter.curiousconcept.com/
is giving invalid json from URL 1 below but not URL 2? They are both the same JSON generating code. The only difference is one is HTTPs and one is HTTP.
https://www.discussthemarket.com/dev/
JSON.parse: unexpected character at line 1 column 1 of the JSON data
and also
http://www.lambwatch.co.uk/json.htm
Valid JSON
Both have the same JSON generating code behind them, exact same code, but when I put the URLs into
http://jsonlint.com/
for validation, the https site is coming back with a parse error!?
Also, when I do
$json = json_decode(file_get_contents("https://www.discussthemarket.com/dev/"));
$json is NULL
However
$json = json_decode(file_get_contents("http://www.lambwatch.co.uk/json.htm"));
$json is the object as you'd expect
Can anyone shed any light on this?

Answer 1

Your problem is that the HTTPS server is adding a UTF8 BOM character to the start of the output, therefore invalidating the expected JSON response. Without seeing the code, it's unclear why, but it's likely a header issue.
If you're unable to solve it server-side, you can always simply remove it at the other end. Here is an example
<?php
$response = file_get_contents('https://www.discussthemarket.com/dev/');
$json = remove_utf8_bom($response);
var_dump(json_decode($json));
function remove_utf8_bom($text) {
$bom = pack('H*', 'EFBBBF');
$text = preg_replace("/^$bom/", '', $text);
return $text;
}