preg_match removes escaping from json string - php

Question

I am trying to parse some json data using json_decode function of php. However, I need to remove certain leading and trailing characters from this long string before decoding. Therefore, I am using preg_match to remove those characters prior to decode. For some reason, preg_match is changing escaping when it encounters following substring (in the middle of the string)
{content: \\\"\\200B\\\"}
After preg_match the above string looks like this:
{content: \\"\200B\\"}
Because of this, json_decode fails.
FYI, the preg_match pattern looks like this:
(?<=remove_these_leading_char)(.*)(?=remove_these_trailing_char)
OK, so here is the additional information based on the questions being asked:
Why triple escaping? fix triple escpaing etc. The answer is that I don't have any control over it. It is not generated by my code.
The original string is not fully json compliant. It has several leading and trailing characters that need to be removed. Therefore I have to use regex. The format of that string is like this:
returnedHTMLdata({json_object},xx);
It looks like this behavior is not limited to preg_match only. Even substr also does this.

Answer 1

It looks like you've got some JSON with padding. To remove the function name and parenthesis, leaving the (unescaped) json object, you can do something like this:
$str = <<<'EOS'
returnedHTMLdata({content: \\\"\\200B\\\", foo: \\\"bar\\\", \"baz\": \\\"fez\\\"},xx);
EOS;
$str = preg_replace('/.+?({.+}).+/','$1', $str);
echo $str;
Output:
{content: \\\"\\200B\\\", foo: \\\"bar\\\", \"baz\": \\\"fez\\\"}
Please note that even if you manage to successfully unescape this string, json_decode requires that keys - e.g. "content" - are enclosed in double quotes, so you will need to modify the JSON string/object before calling that function. Or I guess you could instead use something like the old Services_JSON package to decode it, which I believe does not have that requirement.