Implement /eth/v1/validator/{beacon,sync}_committee_selections Beacon API end-points (#4760)

beacon_chain/rpc/rest_constants.nim

@@ -226,3 +226,5 @@ const
     "Invalid BLS to execution change; it won't validate, so it's rejected"
   BlsToExecutionChangeValidationSuccess* =
     "BLS to execution change was broadcast"
+  AggregationSelectionNotImplemented* =
+    "Attestation and sync committee aggreggation selection are not implemented"

beacon_chain/rpc/rest_validator_api.nim

@@ -993,3 +993,27 @@ proc installValidatorApiHandlers*(router: var RestRouter, node: BeaconNode) =
         )
       )
     return RestApiResponse.jsonResponse(response)
+
+  # https://github.com/ethereum/beacon-APIs/blob/f087fbf2764e657578a6c29bdf0261b36ee8db1e/apis/validator/beacon_committee_selections.yaml
+  router.api(MethodPost, "/eth/v1/validator/beacon_committee_selections") do (
+    contentBody: Option[ContentBody]) -> RestApiResponse:
+    # "Consensus clients need not support this endpoint and may return a 501."
+    # https://github.com/ethereum/beacon-APIs/pull/224: "This endpoint need not
+    # be implemented on the CL side. Once a validator client is aware of it and
+    # able to use it when a feature flag is turned on, the intercepting
+    # middleware can handle and swallow the request. I suggest a CL either
+    # returns 501 Not Implemented [or] 400 Bad Request."
+    return RestApiResponse.jsonError(
+      Http501, AggregationSelectionNotImplemented)
+
+  # https://github.com/ethereum/beacon-APIs/blob/f087fbf2764e657578a6c29bdf0261b36ee8db1e/apis/validator/sync_committee_selections.yaml
+  router.api(MethodPost, "/eth/v1/validator/sync_committee_selections") do (
+    contentBody: Option[ContentBody]) -> RestApiResponse:
+    # "Consensus clients need not support this endpoint and may return a 501."
+    # https://github.com/ethereum/beacon-APIs/pull/224: "This endpoint need not
+    # be implemented on the CL side. Once a validator client is aware of it and
+    # able to use it when a feature flag is turned on, the intercepting
+    # middleware can handle and swallow the request. I suggest a CL either
+    # returns 501 Not Implemented [or] 400 Bad Request."
+    return RestApiResponse.jsonError(
+      Http501, AggregationSelectionNotImplemented)

ncli/resttest-rules.json

@@ -3333,6 +3333,32 @@
       "body": [{"operator": "jstructcmpns", "value": {"code": 400, "message": ""}}]
     }
   },
+  {
+    "topics": ["validator", "beacon_committee_selections"],
+    "request": {
+      "url": "/eth/v1/validator/beacon_committee_selections",
+      "method": "POST",
+      "headers": {"Accept": "application/json"}
+    },
+    "response": {
+      "status": {"operator": "equals", "value": "501"},
+      "headers": [{"key": "Content-Type", "value": "application/json", "operator": "equals"}],
+      "body": [{"operator": "jstructcmpns", "value": {"code": 501, "message": ""}}]
+    }
+  },
+  {
+    "topics": ["validator", "sync_committee_selections"],
+    "request": {
+      "url": "/eth/v1/validator/sync_committee_selections",
+      "method": "POST",
+      "headers": {"Accept": "application/json"}
+    },
+    "response": {
+      "status": {"operator": "equals", "value": "501"},
+      "headers": [{"key": "Content-Type", "value": "application/json", "operator": "equals"}],
+      "body": [{"operator": "jstructcmpns", "value": {"code": 501, "message": ""}}]
+    }
+  },
   {
     "topics": ["validator", "register_validators"],
     "request": {