Max Cutler

Uses PHP’s output buffering to buffer XML-RPC responses and strip superfluous whitespace.
Plugins, themes, and any other files executed during the WordPress load process can unintentionally emit whitespace, 
such as by including a newline character after an explicit closing “?>” PHP tag instead of letting PHP auto-close the 
file.

XML-RPC De-whitespacer

Removes leading and trailing whitespace from XML-RPC responses that can break some XML-RPC clients.

Joseph Scott

Work around for some versions of libxml2 2.7.x that strip out brackets when parsing XML. This plugin fixes XML-RPC requests that are mangled because of this problem. The real fix for this (making the use of this plugin unnecessary) is to use PHP 5.2.9+ with libxml2 2.7.3+.
For more information about this problem see <a href="https://core.trac.wordpress.org/ticket/7771" rel="nofollow ugc">https://core.trac.wordpress.org/ticket/7771</a>.

LibXML2 Fix

Work around for some versions of libxml2 2.7.x that strip out brackets when parsing XML.  This plugin fixes XML-RPC requests that are mangled because  …

XML-RPC De-whitespacer vs LibXML2 Fix