Add extension to agent decom

SingularityClient/src/main/java/com/hubspot/singularity/client/SingularityClient.java

@@ -136,6 +136,8 @@ public class SingularityClient {
   private static final String AGENT_DETAIL_FORMAT = AGENTS_FORMAT + "/agent/%s/details";
   private static final String AGENTS_DECOMISSION_FORMAT =
     AGENTS_FORMAT + "/agent/%s/decommission";
+  private static final String UPDATE_AGENTS_DECOMISSION_FORMAT =
+    AGENTS_FORMAT + "/agent/%s/decommission/update";
   private static final String AGENTS_FREEZE_FORMAT = AGENTS_FORMAT + "/agent/%s/freeze";
   private static final String AGENTS_ACTIVATE_FORMAT =
     AGENTS_FORMAT + "/agent/%s/activate";
@@ -1718,6 +1720,20 @@ public void decommissionAgent(
     );
   }
 
+  public void updateDecommissionedAgent(
+    String agentId,
+    Optional<SingularityMachineChangeRequest> machineChangeRequest
+  ) {
+    final Function<String, String> requestUri = host ->
+      String.format(UPDATE_AGENTS_DECOMISSION_FORMAT, getApiBase(host), agentId);
+
+    post(
+      requestUri,
+      String.format("update decommission agent %s", agentId),
+      Optional.of(machineChangeRequest.orElse(SingularityMachineChangeRequest.empty()))
+    );
+  }
+
   @Deprecated
   public void freezeSlave(
     String agentId,

SingularityService/src/main/java/com/hubspot/singularity/resources/AbstractMachineResource.java

@@ -132,6 +132,24 @@ protected void decommission(
     saveExpiring(decommissionRequest, user, objectId);
   }
 
+  public void updateDecommissionAgent(
+    SingularityUser user,
+    String agentId,
+    SingularityMachineChangeRequest changeRequest
+  ) {
+    authorizationHelper.checkAdminAuthorization(user);
+    final Optional<SingularityMachineChangeRequest> maybeChangeRequest = Optional.ofNullable(
+      changeRequest
+    );
+    validator.checkActionEnabled(SingularityAction.ACTIVATE_AGENT);
+    validator.checkActionEnabled(SingularityAction.DECOMMISSION_AGENT);
+
+    if (manager.getExpiringObject(agentId).isPresent()) {
+      manager.deleteExpiringObject(agentId);
+      saveExpiring(maybeChangeRequest, user, agentId);
+    }
+  }
+
   protected void freeze(
     String objectId,
     Optional<SingularityMachineChangeRequest> freezeRequest,

SingularityService/src/main/java/com/hubspot/singularity/resources/AgentResource.java

@@ -173,6 +173,31 @@ public void decommissionAgent(
     );
   }
 
+  @POST
+  @Path("/agent/{agentId}/decommission/update")
+  @Operation(summary = "Update decommission of a specific active agent")
+  @Consumes({ MediaType.APPLICATION_JSON })
+  public Response updateDecommissionAgent(
+    @Context HttpServletRequest requestContext,
+    @Parameter(hidden = true) @Auth SingularityUser user,
+    @Parameter(required = true, description = "Active agentId") @PathParam(
+      "agentId"
+    ) String agentId,
+    @RequestBody(
+      description = "Settings related to changing the state of a agent"
+    ) SingularityMachineChangeRequest changeRequest
+  ) {
+    return maybeProxyToLeader(
+      requestContext,
+      Response.class,
+      changeRequest,
+      () -> {
+        super.updateDecommissionAgent(user, agentId, changeRequest);
+        return Response.ok().build();
+      }
+    );
+  }
+
   @POST
   @Path("/agent/{agentId}/freeze")
   @Operation(summary = "Freeze tasks on a specific agent")