CSW Harvester: Inconsistent and Incorrect Metrics under certain conditions

[tobias-hotz]

Describe the bug
The CSW harvester of the geonetwork sometimes increments two metrics for a single record. This is not desired and does not happen in other harvesters AFAICT.
This can happen if a new or existing record cannot be retrived, validated or is a duplicate. In both addMetadata and updatingLocalMetadata, the function retriveMetadata is called.

core-geonetwork/harvesters/src/main/java/org/fao/geonet/kernel/harvest/harvester/csw/Aligner.java

Line 504 in a79641b

private Element retrieveMetadata(String uuid) {

This function increments one of the metrics and returns null if retrival or validation fails or if the record is a duplicate.
The error is that the calling functions also increment either unretrievable in case of new metadata or unchanged in case of updating existing metadata when null is returned, which causes the erronious behavior:

core-geonetwork/harvesters/src/main/java/org/fao/geonet/kernel/harvest/harvester/csw/Aligner.java

Lines 280 to 290 in a79641b

	private void addMetadata(RecordInfo ri, String uuidToAssign) throws Exception {
	if (cancelMonitor.get()) {
	return;
	}
	Element md = retrieveMetadata(ri.uuid);
	if (md == null) {
	result.unretrievable++;
	return;
	}

core-geonetwork/harvesters/src/main/java/org/fao/geonet/kernel/harvest/harvester/csw/Aligner.java

Lines 441 to 447 in a79641b

	boolean updatingLocalMetadata(RecordInfo ri, String id, Boolean force) throws Exception {
	Element md = retrieveMetadata(ri.uuid);
	if (md == null) {
	result.unchangedMetadata++;
	return false;
	}

The solution seems to just not increment any counter if retriveMetadata return null

To Reproduce
Steps to reproduce the behavior:

1. Add a harvester that harvests a CSW with known-unretrivable records or records that dont validate
2. Run the harvester
3. Notice that the number of total records is smaller than all added + doesNotValidate + unretrievable

Expected behavior
A single record only increments the number of total records and one of the other status metrics.

Screenshots

The count of all other metrics besides total combined in this screenshot is 2969, which is 4 entries more than should be possible

Desktop (please complete the following information):

• GeoNetwork Version 4.2.5 (but latest main branch affected as well)

Additional context
This bug makes the metrics way less useful, as you cannot say for certain what errors occured and what is just a byproduct of the current behaviour, which makes automated monitoring of these metrics impossible.