google-nomulus/docs/code-structure.md

Code structure

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

Dagger dependency injection

Bazel build system

Flows

Commit logs and backups

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 Recurring (renew) billing events into OneTime events.

All Cursor entities in Datastore 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 Key<ImmutableObject> to which the particular cursor applies (this can be e.g. a Registry or any other ImmutableObject in datastore, depending on the operation). If the Cursor applies to the entire registry environment, it is considered a global cursor and has a scope of EntityGroupRoot.getCrossTldKey().

Cursors are singleton entities by type and scope. The id for a Cursor is a deterministic string that consists of the websafe string of the Key of the scope object concatenated with the name of the name of the cursor type, separated by an underscore.

Mapreduces

Nomulus uses the App Engine MapReduce framework extensively, both for a variety of regularly scheduled background tasks and for one-off maintenance tasks. The MapReduce framework comes with a web UI for viewing the status of ongoing and completed tasks.

Most MapReduces in Nomulus work by mapping over all entities of a given set of Datastore kind(s) (e.g. domains, contacts, etc.). All of the MapReduces in Nomulus are run by the MapreduceRunner class, which provides a standard set of ways to set the number of mapper and reducer shards. It is common to run map-only MapReduces when reducers aren't needed; these are supported as well.

The main complication with MapReduces is that the mapper and reducer classes are required to be serializable as a consequence of how work is sharded out, pasued/resumed, and moved around. All fields on these classes must therefore be either Serializable or transient. This also means that dependency injection is of limited use -- the best you can do is to @Inject serializable fields on the entire MapReduce Action, and then set them manually on the mapper/reducer classes in their constructor.

Actions and servlets

Foreign key indexes

Point-in-time accuracy

Guava

EPP resource hierarchy

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 Datastore. 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.

Security