500 error from call to XMLHttpRequest()

valid point. My problem might be a need to set a Content-Length in the header. 

I added:

->set_header("Content-Length: 1000")

And it still gives me a 500 error, but at least the error in the error log went away. How do I get the actual length of a json encoded structure (instead of 1000)?

strlen(json_encode($table));
??