is_file() / file_exists error with wordpress - php

Question

I am having problems with both is_file() and file_exists(), i am trying to verify a featured image exists in the wp uploads folder....both output sets of characters and create multiple errors for each thumbnail size
fopen(http://www.xxx.gf/wp-content/uploads/2014/09/1-150x150.jpg): failed to open stream: HTTP wrapper does not support writeable connections in /home/tserv/public_html/wp-includes/class-wp-image-editor.php on line 396
This is odd because i am passing a correct server path to both functions and the functions works for files outside the uploads folder. Also the filename is 1.jpg and its appending - 150x150 and a few other sizes which are the thumbnail sizes for wordpress.
update: server path is being passed: e.g. home/user/etc.., the error is saying fopen... but im not calling fopen directly nor passing a url to file_exists, is_file.
Since starting this i realize i'm mad for trying to verify it like this when i can check it using wp_functions but i would like to figure out why this is happening!
php code
if($x= is_file($upload_path.$filename) )
server- linux debian wheezy vps
open_basedir= None
safemode- off
folder permissions - 777 (temp)

Answer 1

You can't open the file using fopen using http and expect to write to the file. You will want to use fopen and specify the second option as "r" for read only or you can keep using this code but actually access it using the servers path and not http:// . You can also use file get contents.
try using http://codex.wordpress.org/Function_Reference/wp_upload_dir when accessing the upload
$upload_dir = wp_upload_dir(); // Array of key => value pairs
//base dir
$base_dir = $upload_dir['basedir'];