Lagom 1.2: how to invoke service calls with headers

[sallad...@gmail.com]

Hello,

I am currently using the Lagom Message Broker API and I want to do some treatments (=> emit service calls). My problem is that the service I want to call is a HeaderServiceCall, which needs to be invoked with headers. Is there a pattern, a simple method to do this? Here is my implementation:

organizationService.organizationsTopic().subscribe().atLeastOnce(Flow.fromFunction[OrganizationMessage, Done] {
  case x: OrganizationCreatedMessage =>
    x.operatorId.fold[Done] {
      throw new RuntimeException("Operator doesn't exist")
    } { realOperatorId => {
      val addOrganizationCall = addOrganization(realOperatorId).invoke(
        AddOrganizationRequest(
          organizationId = x.entityId
        ))
      val addPermissionsCall = addPermissions(realOperatorId).invoke(
        AddPermissionsRequest(
          permissions = Set(Permission(x.entityId, EntityType.ORGANIZATION, Action.values))
            ++ Set(Permission(x.entityId, EntityType.USER, Action.values)
          )
        ))
      for {
        _ <- addOrganizationCall
        _ <- addPermissionsCall
      } yield Done
      Done
    }
    }
})

[Tim Moore]

Hi,

You can call handleRequestHeader on the ServiceCall before calling invoke. It takes a function that transforms the request, and you can add headers, etc. in that function.

Here is the Javadoc with more details:

http://www.lagomframework.com/documentation/1.2.x/java/api/com/lightbend/lagom/javadsl/api/ServiceCall.html#handleRequestHeader-java.util.function.Function-

This method is useful when the content of the header depend on the context of the request.

However, for services that always require a particular header to be added, it can be better to use a HeaderFilter, which can be declared on the service descriptor and automatically applied on both the client and server side. This is good for things such as authentication, where the headers can be derived from the Principal already available in the request.

http://www.lagomframework.com/documentation/1.2.x/java/api/com/lightbend/lagom/javadsl/api/transport/HeaderFilter.html

You can see an example of this in use in https://github.com/lagom/online-auction-java

This filter adds the current user ID to a header on the client request and extracts it on the server:

https://github.com/lagom/online-auction-java/blob/master/security/src/main/java/com/example/auction/security/SecurityHeaderFilter.java

And these service descriptors apply the filter:

https://github.com/lagom/online-auction-java/blob/37272136f6c250ac12522d7a46849f20f44bb0f3/bidding-api/src/main/java/com/example/auction/bidding/api/BiddingService.java#L59

https://github.com/lagom/online-auction-java/blob/c470cbc90805c459c01f59813aa9cd81d3d9436b/item-api/src/main/java/com/example/auction/item/api/ItemService.java#L89

It looks like we haven't covered this in the docs yet, so I added an issue to follow that up: https://github.com/lagom/lagom/issues/286

Cheers,

Tim Moore

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Tim Moore

Senior Engineer, Lagom, Lightbend, Inc.

tim....@lightbend.com
+61 420 981 589
Skype: timothy.m.moore