Throw an error if a specified value does not exist in the prior header

// Get the Message that immediately precedes this Script.
var msg = $context.currentItem.previousItem;

var header = msg.getResponse(msg.RESPONSE_HTTP_HEADER, "X-Core-Value");
$context.result.postMessage($context.result.LEVEL_INFO, "Cookie = "+ header);

// Was there a header?
if (header == null)
{
// There was no header.

// Output an informational message.
$context.result.postMessage($context.result.LEVEL_INFO, "No header to validate");
}
else
{
// There was a response.

// string to find; hard coded
var stringToFind = "Family";

// Determine if the value exists in the header.
var searchIndex = header.indexOf(stringToFind);

// If the value does not exist in the header, output an error.
if (searchIndex == -1)
{
var details = "Response:\n" + header + "\n\nValue searched for:\n" + stringToFind;
$context.result.postMessage($context.result.LEVEL_ERROR, "Expected value not found in '" + msg.name + "' message header", details);
}
}

msg.clearResponse();