docs: Zinnia in Filecoin Station [ADR] (#121)

Signed-off-by: Miroslav Bajtoš <oss@bajtos.net>

docs/architecture-decision-records/2023-03-integration-with-station.md

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+# Zinnia in Filecoin Station
+
+<!--
+This is a minimal template. Feel free to add more sections as needed.
+
+Please review also the Design Doc template and add any relevant sections to your ADR:
+https://www.notion.so/pl-strflt/Writing-a-Design-Doc-aa6034be43c2434ba88a2fd844516e94
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+
+> Status: ACCEPTED
+
+<!--
+PROPOSED, ACCEPTED, REJECTED, DEPRECATED, SUPERSEDED BY {link-to-ADR}
+-->
+
+## Context
+
+Zinnia is a runtime for Filecoin Station modules. It's time to integrate Zinnia into the Station to
+enable the deployment of the first modules.
+
+Zinnia is designed to run multiple modules inside the same process, using V8 Isolates for keeping
+modules separated and sandboxed. The integration with libp2p (and later IPFS) is designed to allow
+multiple modules to share the same underlying set of network connections and block storage.
+
+Zinnia has two primary modes of operation:
+
+1. A developer tool for building a single module. We want to optimize for ease of use and a fast
+   feedback loop.
+
+   In this mode, Zinnia is typically started and stopped frequently, running for short periods at a
+   time, executing a single module only.
+
+   As a CLI tool, it reads the configuration from a config file (either user-level or
+   project-specific) or CLI arguments. There should be reasonable defaults tailored to developers
+   building a module - e.g. the state files should be stored in the project's working directory.
+
+2. A deployment platform, running modules inside Filecoin Station instances operated by
+   non-technical users. We want to optimize for a smooth user experience for Station operators
+   first, and easy troubleshooting of operations by module developers second.
+
+   In this mode, Zinnia is a long-running process executing multiple modules. It needs to support
+   reloading individual modules when a new version of a module is deployed. It also needs to report
+   various information back to the Station, e.g. activity log and the number of jobs completed.
+
+   As a service, it should read the configuration from environment variables (see
+   [The Twelve-Factor App](https://12factor.net/config)) and allow embedders to improve security
+   e.g. by keeping modules in a different place from the runtime state.
+
+### `zinniad`
+
+For the reasons above, I propose to build a new binary called `zinniad` that will execute Zinnia
+modules inside the Station.
+
+_(This is a strawman proposal, subject to changes during implementation.)_
+
+Configuration via environment variables:
+
+- `FIL_WALLET_ADDRESS`: Address of Station's built-in wallet (required).
+
+- `ROOT_DIR`: Directory where to keep state files (optional). Defaults to a platform-specific
+  location, e.g. `$XDG_STATE_HOME/zinniad` on Linux.
+
+Positional arguments:
+
+- Positional arguments specify which modules to run, where each module is a single JS file. We don't
+  make any assumptions about the directory layout of modules. Paths are resolved relatively to the
+  current working directory.
+
+Example invocation:
+
+```bash
+cd /Applications/Filecoin\ Station.app/Contents/Resources/zinnia-modules
+
+FIL_WALLET_ADDRESS=f1etc \
+ROOT_DIR=$HOME/Library/Caches/Filecoin\ Station/zinnia \
+zinniad \
+  saturn-l2/main.js \
+  ping.js \
+  retrieval-checker/dist/index.js
+```
+
+### Communication with Station (Core, Desktop):
+
+As explained above, I propose to use environment variables to pass configuration from the Station to
+Zinnia.
+
+For communicating information from Zinnia back to the Station, I propose that Zinnia prints
+newline-delimited JSON entries to `stdout` and uses `stderr` for general/debug logging. This format
+is easy to parse from Node.js code powering both Station variants.
+
+Example messages:
+
+- **Activity log - error**
+
+  `{"type": "activity:error", "module": "saturn", "message": "Cannot connect to the orchestrator."x }`
+
+  _Note: `"module": "saturn"` describes which module emitted the log._
+
+- **Activity log - info**
+
+  `{"type": "activity:info", "module": null, "message": "Zinnia is starting up..."}`
+
+  _Note: `"module": null` means the message comes from Zinnia runtime._
+
+- **Number of jobs completed:**
+
+  `{"type": "jobs-completed", "total": 123 }`
+
+  _Note: This message is emitted periodically, e.g. every 200ms._
+
+  In the future, we can easily extend this line to include per-module stats too:
+
+  `{"type": "jobs-completed", "total": 123, modules: {"saturn": 100, "retrieval-checker": 23}}`
+
+- Messages logged via Console APIs like `console.log` are printed to `stderr` without any
+  modifications.
+
+  ```text
+  Pinging /dnsaddr/bootstrap.libp2p.io/p2p/QmQCU2EcMqAqQPR2i9bChDtGNJchTbq5TbXJJ16u19uLTa
+  RTT: 1252ms
+  Cannot record stats: Error: InfluxDB API error 401
+  {"code":"unauthorized","message":"unauthorized access"}
+  ```
+
+### Module identifiers
+
+We need each module to have a unique identifier (a name) that we can use in the messages above. This
+id must remain unchanged across module version upgrades.
+
+For the initial version, these ids will be hard-coded human-readable names like `saturn-l2`.
+
+In the future, when we move towards untrusted modules deployed in a decentralized manner, we will
+need to find a different way how to derive these unique module ids. That's out of scope of the
+current work though. Adding new id types should be easy as long as our architecture supports
+arbitrary string ids.
+
+### Deploying and upgrading modules
+
+The initial version will not implement any upgrade mechanisms for modules. Both `zinniad` and all
+module sources will be bundled inside the Station. When a new module is added or an existing module
+is upgraded to a new version, we will publish a new version of the Station.
+
+### Zinnia API for module builders
+
+_(This is a strawman proposal, subject to changes during implementation.)_
+
+```ts
+namespace Zinnia {
+  // omitted: existing APIs like `peerId`
+
+  /** Get the wallet address, this value is typically provided by the Station. */
+  walletAddress: String;
+
+  /** Report activities to the Station. These messages are displayed in the main UI. */
+  activity: {
+    /** Report an informative status update, e.g. "Connecting to the network." */
+    info(message: string);
+
+    /** Report an error, e.g. "Cannot connect to the orchestrator." */
+    error(message: string);
+  }
+
+  /** Report completion of a single job */
+  jobCompleted();
+}
+```
+
+### Dev-mode in `zinnia`
+
+These APIs will behave differently when running a module via `zinnia` CLI in development.
+
+- In the initial version, the wallet address is hardcoded to a dummy testnet address
+  `t1abjxfbp274xpdqcpuaykwkfb43omjotacm2p3za`. This value is taken from
+  [Filecoin Lotus docs](https://lotus.filecoin.io/lotus/manage/manage-fil/#public-key-address) with
+  the leading `"f"` replaced with `"t"`.
+
+  Later, we can implement reading of the wallet address from a configuration file, e.g.
+  `.zinnia/config.yaml` in the current working directory (typically the project root).
+
+- Activity logs are printed to stdout with human-readable formatting.
+  ```text
+  [10:30:20.000  INFO] Connecting to the network.
+  [10:30:21.000 ERROR] Cannot connect to the orchestrator.
+  ```
+- Job completions are printed to stdout but less frequently, e.g. every 500ms.
+
+  ```text
+  [10:30:20.000 STATS] Jobs completed: 123
+  [10:30:20.500 STATS] Jobs completed: 134
+  [10:30:21.000 STATS] Jobs completed: 146
+  ```
+
+## Options Considered
+
+1. Don't build a new binary, bundle the existing `zinnia` CLI inside the Station.
+
+   Pros:
+
+   - Less work to ship the first version. Less yak-shaving like setting up CI/CD workflows.
+
+   Cons:
+
+   - Zinnia modules cannot share libp2p & IPFS resources (network connection, peer address book,
+     block store).
+
+   - To meet the requirements of both module builders and the Station runtime, we would need to
+     implement extra configuration options to get different behaviour in different settings.
+
+   - Most of the Station work will be discarded later, once we need `zinniad` to allow running
+     multiple modules inside the same runtime process.
+
+2. Don't push job stats via stdout, let the station pull the stats via HTTP API. (The current
+   saturn-l2 module uses this model.)
+
+   Pros:
+
+   - We already have code in Station to deal with this.
+   - Less cluttered `stdout`
+
+   Cons:
+
+   - More complex implementation in Zinnia for little benefits. Since `zinniad` routes all
+     `console.log` messages to `stderr`, no humans should be reading `stdout`, therefore extra
+     clutter does not matter.
+
+   - More complex integration between Station and Zinnia: Zinnia needs to report URL where the stats
+     API is available, the Station needs to parse that URL from Zinnia's `stdout`.
+
+3. Include a timestamp in the JSON messages printed to `stdout` for the Station. We decided this is
+   not needed now and can be easily added later if such a need arises.
+
+   Our current goal is integration with the Station. The Station (Core or Desktop) and the Zinnia
+   runtime will initially sit on the same machine. If the log consumer sits on the same machine, it
+   shouldn't matter who will attach the timestamp.
+
+4. Use `XDG_STATE_HOME` to configure where should `zinniad` keep the state files.
+
+   The major difference between `XDG_STATE_HOME` and `ROOT_DIR` is that `XDG_STATE_HOME` provides a
+   system (or user) wide directory, we need to append a zinnia-specific segment to that path to
+   obtain `ROOT_DIR`.
+
+   I prefer to give the user full control over the location by providing them `ROOT_DIR` config
+   option.
+
+   This becomes relevant when Zinnia is running inside the Station. If we use `XDG_STATE_HOME`, then
+   we will keep the state in `XDG_STATE_HOME/zinnia`, a different place from where Station keeps its
+   files. We could make this path Station specific, but that feels hacky to me and incorrect in the
+   situation when Zinnia runs outside of the Station
+
+   However, I think it's a good idea to make `ROOT_DIR` an optional configuration option and use
+   `XDG_STATE_HOME/zinnia` as the default value.
+
+   Few more thoughts:
+
+   - `XDG_STATE_HOME` is specific to Linux. Windows uses something like `%LOCALAPPDATA%`, macOS
+     something else.
+
+   - We already provide `ROOT_DIR` for trusted modules, quoting from
+     [module interface docs](https://github.com/filecoin-station/desktop/blob/596b16704347c5c6e09c621f475cd20291938b77/docs/MODULE_INTERFACE.md?plain=1#L27-L29):
+
+     > `ROOT_DIR` The long-lived working directory on disk. The module must store all of its files
+     > inside (subdirectories of) this directory. The directory isn't expected to be backed up or
+     > shared across machines in any way.
+
+<!--
+What are the different options we considered? What are their pros & cons?
+-->
+
+## Decision
+
+<!--
+What is the change that we're proposing and/or doing?
+-->
+
+Build `zinniad` and add new `Zinnia` APIs as described above.
+
+## Consequences
+
+<!--
+What becomes easier or more challenging to do because of this change?
+-->
+
+After we implement the architecture described above and integrate Zinnia into the Station, we will
+have a solid foundation that's easily extensible and should not require major updates for a long
+time.
+
+<!--
+## Links &amp; References
+
+Link to other ADRs, GitHub issues, documentation, etc.
+-->