Note that the first regex in the loop

for($response_xml){
    s/^s*//;
    s/\s*$//;
}
[download]

should be

    s/^\s*//;
[download]

Or better yet, both regexes should perhaps be

    s/^\s+//;
    s/\s+$//;
[download]

since there is little point in replacing zero whitespace with nothing.