This document contains information on the overall structure of the code, and how particularly important pieces of the system are implemented.

Gradle build system

Gradle is used to build and test the Nomulus codebase.

Nomulus, for the most part, uses fairly standard Gradle task naming for building and running tests, with the various tasks defined in various build.gradle files.

Dependencies and their version restrictions are defined in the dependencies.gradle file. Within each subproject's build.gradle file, the actual dependencies used by that subproject are listed along with the type of dependency (e.g. implementation, testImplementation). Versions of each dependency are locked to avoid frequent dependency churn, with the locked versions stored in the various gradle.lockfile files. To update these versions, run any Gradle command (e.g. ./gradlew build) with the --write-locks argument.

Generating WAR archives for deployment

The jetty project is the main entry point for building the Nomulus WAR files, and one can use the war gradle task to build the base WAR file. The various deployment/release files use Docker to deploy this, in a system that is too Google-specialized to replicate directly here.

Subprojects

Within the Nomulus repository there are a few notable subprojects:

• util contains tools that don't depend on any of our other code, e.g. libraries or raw utilities
• db contains database-related code, managing the schema and deployment/testing of the database.
• integration contains tests to make sure that schema rollouts won't break Nomulus, that code versions and schema versions are cross-compatible
• console-webapp contains the Typescript/HTML/CSS/Angular code for the registrar console frontend
• proxy contains code for the EPP proxy, which relays port 700 requests to the core EPP services
• core contains the bulk of the core Nomulus code, including request handling+serving, backend, actions, etc

Cursors

Cursors are DateTime pointers used to ensure rolling transactional isolation of various reporting and other maintenance operations. Utilizing a Cursor within an operation ensures that instances in time are processed exactly once for a given task, and that tasks can catch up from any failure states at any time.

Cursors are rolled forward at the end of successful tasks, are not rolled forward in the case of failure, and can be manually set backwards using the nomulus update_cursors command to reprocess a past action.

The following cursor types are defined:

• BRDA - BRDA (thin) escrow deposits
• RDE_REPORT - XML RDE report uploads
• RDE_STAGING - RDE (thick) escrow deposit staging
• RDE_UPLOAD - RDE (thick) escrow deposit upload
• RDE_UPLOAD_SFTP - Cursor that tracks the last time we talked to the escrow provider's SFTP server for a given TLD.
• RECURRING_BILLING - Expansion of BillingRecurrence (renew) billing events into one-time BillingEvents.
• SYNC_REGISTRAR_SHEET - Tracks the last time the registrar spreadsheet was successfully synced.

All Cursor entities in the database contain a DateTime that represents the next timestamp at which an operation should resume processing and a CursorType that identifies which operation the cursor is associated with. In many cases, there are multiple cursors per operation; for instance, the cursors related to RDE reporting, staging, and upload are per-TLD cursors. To accomplish this, each Cursor also has a scope, a string to which the particular cursor applies (this can be anything, but in practice is either a TLD or GLOBAL for cross-TLD cursors. Cursors are singleton entities by type and scope.

Guava

The Nomulus codebase makes extensive use of the Guava libraries. These libraries provide idiomatic, well-tested, and performant add-ons to the JDK. There are several libraries in particular that you should familiarize yourself with, as they are used extensively throughout the codebase:

• Immutable Collections: Immutable collections are a useful defensive programming technique. When an Immutable collection type is used as a parameter type, it immediately indicates that the given collection will not be modified in the method. Immutable collections are also more memory-efficient than their mutable counterparts, and are inherently thread-safe.

  Immutable collections are constructed one of three ways:

  • Using a Builder: used when the collection will be built iteratively in a loop.
  • With the of method: used when constructing the collection with a handful of elements. Most commonly used when creating collections representing constants, like lookup tables or allow lists.
  • With the copyOf method: used when constructing the method from a reference to another collection. Used to defensively copy a mutable collection (like a return value from an external library) to an immutable collection.

• Optional: The Optional<T> class is used as a container for nullable values. It is most often used as return value, as an explicit indicator that the return value may be absent, thereby making a null return value an obvious error.

• Preconditions: Preconditions are used defensively, in order to validate parameters and state upon entry to a method.

In addition to Guava, the codebase also extensively uses AutoValue value classes. AutoValue value type objects are immutable and have sane default implementations of toString, hashCode, and equals. They are often used as parameters and return values to encapsulate related values together.

EPP resources

EppResource is the base class for objects allocated within a registry via EPP. The classes that extend EppResource (along with the RFCs that define them) are as follows:

• Domain (RFC 5731)
• Host (RFC 5732)

All EppResource entities use a Repository Object Identifier (ROID) as its unique id, in the format specified by RFC 5730 and defined in EppResourceUtils.createRoid().

Each entity also tracks a number of timestamps related to its lifecycle (in particular, creation time, past or future deletion time, and last update time). The way in which an EPP resource's active/deleted status is determined is by comparing clock time against a resource's creation and deletion time, rather than relying on an automated job (or similar) to flip an active bit on a resource when it is deleted.

There are a number of other useful utility methods for interacting with EPP resources in the EppResourceUtils class, many of which deal with inspecting the status of a resource at a given point in time.

Foreign key indexes

Domain and Host each are foreign-keyed, meaning we often wish to query them by their foreign keys (fully-qualified domain name and fully-qualified host name, respectively).

Since all EppResource entities are indexed on ROID (which is also unique, but not as useful as the resource's name), the ForeignKeyUtils provides a way to look up the resources using another key which is also unique during the lifetime of the resource (though not for all time).

It is important to note that throughout the lifecycle of an EppResource, the underlying entity is never hard-deleted; its deletion time is set to the time at which the EPP command to delete the resource was set, and it remains in the database. Other resources with that same name can then be created.

History entries

A HistoryEntry is a record of a mutation of an EPP resource. There are various events that are recorded as history entries, including:

• Creates
• Deletes
• Delete failures
• Pending deletes
• Updates
• Domain allocation
• Domain renews
• Domain restores
• Application status updates
• Domain and contact transfer status changes
  • Approval
  • Cancellation
  • Rejection
  • Requests

The full list is captured in the HistoryEntry.Type enum.

Each HistoryEntry has a reference to a singular EPP resource that was mutated by the event. A HistoryEntry will also contain the complete EPP XML command that initiated the mutation, stored as a byte array to be agnostic of encoding.

A HistoryEntry also captures other event metadata, such as the DateTime of the change, whether the change was created by a superuser, and the ID of the registrar that sent the command.

Poll messages

Poll messages are the mechanism by which EPP handles asynchronous communication between the registry and registrars. Refer to RFC 5730 Section 2.9.2.3 for their protocol specification.

Poll messages are stored by the system as entities in the database. All poll messages have an event time at which they become active; any poll request before that time will not return the poll message. For example, every domain when created enqueues a speculative poll message for the automatic renewal of the domain a year later. This poll message won't be delivered until that year elapses, and if some change to the domain occurs prior to that point, such as it being deleted, then the speculative poll message will be deleted and thus never delivered. Other poll messages are effective immediately, e.g. the poll message generated for the owning registrar when another registrar requests the transfer of a domain. These messages are written out with an event time of when they were created, and will thus be delivered whenever the registrar next polls for messages.

PollMessage is the abstract base class for the two different types of poll messages that extend it:

• Autorenew - A poll message corresponding to an automatic renewal of a domain. It recurs annually.
• OneTime - A one-time poll message used for everything else.

Queries for poll messages by the registrar are handled in PollRequestFlow, and poll messages are ACKed (and thus deleted) in PollAckFlow.

Billing events

Billing events capture all events in a domain's lifecycle for which a registrar will be charged. A one-time BillingEvent will (or can) be created for the following reasons (the full list of which is represented by BillingBase.Reason):

• Domain creates
• Domain renewals
• Domain restores
• Server status changes
• Domain transfers

There are 4 types of billing events, all of which extend the abstract BillingBase base class:

• BillingEvent, a one-time billing event.
• BillingRecurrence, a recurring billing event (used for events such as domain renewals).
• BillingCancellation, which represents the cancellation of either a BillingEvent or BillingRecurrence billing event. This is implemented as a distinct event to preserve the immutability of billing events.

A BillingBase can also contain one or more BillingBase.Flag flags that provide additional metadata about the billing event (e.g. the application phase during which the domain was applied for).

All BillingBase entities contain reference to a given ROID (EppResource reference) to identify the mutation that spawned the BillingBase.