@return array

should be return string|null

This tool would benefit (see next comment) to be structured with:

• a controller logic
• a form view
• a timeline view

At this stage, $client could be null, if the address is invalid.

the text to clean

Style to improve:

• comments are third person (returns, encodes)
• we generally use $matches instead of $captures
• we generaly explicitely name callback functions as as callback
• concatenation is a . b, not a.b

This betrays the import of a sample 3rd party code by the way, the source must be documented. In this case, Markus Jarderot should be credited according http://stackoverflow.com/a/1401716/1930997