retrieve-http-utf8.js

        var body = [];
        var body_length = 0;

        sourceResponse.on('data', function(chunk)
        {
            body.push(chunk);
            body_length += chunk.length;
        });
        sourceResponse.on('end', function()
        {
            clientPool.returnToPool(sourceResponse.client); // it's from my clientPool implementation, not required!
            var full_body;
            if (body.length == 1)
            {
                full_body = body[0];
            }
            else
            {
                full_body = new Buffer(body_length);
                var position = 0;
                for (var i = 0; i < body.length; i++)
                {
                    body[i].copy(full_body, position, 0);
                    position += body[i].length;
                }
            }
            body = null;
            callback(null, full_body.toString('utf8'));
        });

Take a note that convertion to utf8 string done after concatenation of all chunks together. This is because chunks can divide utf8 characters (up to 4 bytes each) between them.