Etag support for S/4 EX - sap-cloud-sdk

Question

Etag is supported in SDK: https://sap.github.io/cloud-sdk/docs/java/features/odata/use-typed-odata-v4-client-in-sap-cloud-sdk-for-java/#handling-of-etags
So experimenting it by using BusinessPartner entity in S/4 EX.
But seems there's no If-Match header:
How come the header doesn't show up - any prerequisite with etag?
(entering on behalf of the implementation partner team)
I checked the VersionIdentifier of the response and it was not set to a value.
I also checked the response's JSON __metadeta and header, but there were no values that appeared to correspond to the ETag value.
[Code]
BusinessPartner bp1 = new DefaultBusinessPartnerService().getBusinessPartnerByKey(bpId).execute(dest);
log.debug("get 1: {}", bp1);
log.debug("get 1 VersionIdentifier: {}", bp1.getVersionIdentifier());
bp1.setOrganizationBPName1("SCP Update 1st:" + System.currentTimeMillis());
ODataUpdateResult result1 = new DefaultBusinessPartnerService().updateBusinessPartner(bp1).execute(dest);
log.debug("Update1 Http Status: {}", result1.getHttpStatusCode());
bp1.setOrganizationBPName1("SCP Update 2nd:" + System.currentTimeMillis());
bp1.setVersionIdentifier("dummy");
ODataUpdateResult result2 = new DefaultBusinessPartnerService().updateBusinessPartner(bp1).execute(dest);
log.debug("Update2 Http Status: {}", result2.getHttpStatusCode());
[Log]
get 1: BusinessPartner(super=VdmObject(customFields={}, changedOriginal...
get 1 VersionIdentifier: None
Update1 Http Status: 204
Update2 Http Status: 204
[GET Response JSON(__metadata) / Response Header]
(It has masked the IP address.)
"__metadata": {
"id": "https://xxx.xxx.xxx.xxx:xxxxxx/sap/opu/odata/sap/API_BUSINESS_PARTNER/A_BusinessPartner('1000001')",
"uri": "https://xxx.xxx.xxx.xxx:xxxxxx/sap/opu/odata/sap/API_BUSINESS_PARTNER/A_BusinessPartner('1000001')",
"type": "API_BUSINESS_PARTNER.A_BusinessPartnerType"
},
HTTP/1.1 200 OK
content-type: application/json; charset=utf-8
content-length: 3152
dataserviceversion: 2.0
sap-metadata-last-modified: Thu, 14 May 2020 23:58:07 GMT
cache-control: no-store, no-cache
sap-processing-info: ODataBEP=,crp=,RAL=,st=,MedCacheHub=SHM,codeployed=X,softstate=
sap-server: true
sap-perf-fesrec: 243070.000000
I tried setting the VersionIdentifier to a meaningless value in my test code (2nd update).
The update process seems to be successful, although the request header now has "If-Match" added to it.
(I was expecting the update to fail because the values never match, so I was hoping the update would fail.)
[2nd Update(setVersionIdenfifier)]
(It has masked some of the values.)
PATCH http://xxx.xxx.xxx.xxx:xxxxxx/sap/opu/odata/sap/API_BUSINESS_PARTNER/A_BusinessPartner(BusinessPartner='1000001') HTTP/1.1
x-csrf-token: xxx
Content-Type: application/json
Accept: application/json
If-Match: dummy
Authorization: Basic xxx
SAP-Connectivity-SCC-Location_ID: xxx
Proxy-Authorization: Bearer xxx
sap-language: en
sap-client: xxx
Content-Length: 55

Answer 1

If ETags are not part of OData service responses, then you should approach the IT/administrators who maintain the S/4 backend. The SAP Cloud SDK is only consuming the OData service. Unfortunately it can't leverage ETag support if it's disabled.