docs: Verify and document append-only immutability guarantees #136

HugoNijhuis · 2026-01-13T20:45:34Z

HugoNijhuis commented

2026-01-13 20:45:34 +00:00

Summary

This PR completes issue #60 by documenting and verifying that the Aether event store provides immutability guarantees at multiple levels: interface design, storage implementation, and tests.

The EventStore interface is append-only by design - it provides no Update or Delete methods. JetStreamEventStore implements this with file-based storage and a limits-based retention policy that ensures events are immutable during their lifetime.

Changes

event.go: Enhanced EventStore interface documentation to explicitly document the immutability guarantee and explain the absence of Update/Delete methods
store/jetstream.go: Added detailed retention policy documentation showing how MaxAge and file-based storage enforce immutability at the storage layer
store/immutability_test.go: New test file with comprehensive immutability verification tests covering:
- Event persistence cannot be modified after saving
- No Update/Delete methods exist on the interface
- Version enforcement ensures monotonic ordering
- Events cannot be deleted through the API
README.md: Added detailed "Events are immutable" section explaining:
- Interface-level append-only guarantee
- Storage-level immutability mechanisms
- Audit trail reliability guarantees
- Pattern for handling corrections (append new event vs modify)

Testing

All immutability tests pass:

TestEventImmutability_MemoryStore
TestEventImmutability_NoUpdateMethod
TestEventImmutability_VersionOnlyGoesUp
TestEventImmutability_EventCannotBeDeleted

All existing tests continue to pass with no regressions.

Closes #60

Co-Authored-By: Claude Code noreply@anthropic.com

## Summary This PR completes issue #60 by documenting and verifying that the Aether event store provides immutability guarantees at multiple levels: interface design, storage implementation, and tests. The EventStore interface is append-only by design - it provides no Update or Delete methods. JetStreamEventStore implements this with file-based storage and a limits-based retention policy that ensures events are immutable during their lifetime. ## Changes - **event.go**: Enhanced EventStore interface documentation to explicitly document the immutability guarantee and explain the absence of Update/Delete methods - **store/jetstream.go**: Added detailed retention policy documentation showing how MaxAge and file-based storage enforce immutability at the storage layer - **store/immutability_test.go**: New test file with comprehensive immutability verification tests covering: - Event persistence cannot be modified after saving - No Update/Delete methods exist on the interface - Version enforcement ensures monotonic ordering - Events cannot be deleted through the API - **README.md**: Added detailed "Events are immutable" section explaining: - Interface-level append-only guarantee - Storage-level immutability mechanisms - Audit trail reliability guarantees - Pattern for handling corrections (append new event vs modify) ## Testing All immutability tests pass: - TestEventImmutability_MemoryStore - TestEventImmutability_NoUpdateMethod - TestEventImmutability_VersionOnlyGoesUp - TestEventImmutability_EventCannotBeDeleted All existing tests continue to pass with no regressions. Closes #60 Co-Authored-By: Claude Code <noreply@anthropic.com>

HugoNijhuis added 1 commit 2026-01-13 20:45:35 +00:00

docs: Verify and document append-only immutability guarantees

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Details

78aaea9330

Document that EventStore interface has no Update/Delete methods, enforcing
append-only semantics by design. Events are immutable once persisted.

Changes:
- Update EventStore interface documentation in event.go to explicitly state
  immutability guarantee and explain why Update/Delete methods are absent
- Add detailed retention policy documentation to JetStreamConfig showing
  how MaxAge limits enforce automatic expiration without manual deletion
- Document JetStreamEventStore's immutability guarantee with storage-level
  explanation of file-based storage and limits-based retention
- Add comprehensive immutability tests verifying:
  - Events cannot be modified after persistence
  - No Update or Delete methods exist on EventStore interface
  - Versions are monotonically increasing
  - Events cannot be deleted through the API
- Update README with detailed immutability section explaining:
  - Interface-level append-only guarantee
  - Storage-level immutability through JetStream configuration
  - Audit trail reliability
  - Pattern for handling corrections (append new event)

Closes #60

Co-Authored-By: Claude Code <noreply@anthropic.com>

HugoNijhuis commented

2026-01-13 20:59:37 +00:00

Code Review: Changes Requested

Issues:

store/memory.go:30-32 - Errors from json.Marshal and json.Unmarshal are silently discarded. While Event should always be JSON-marshallable, ignoring errors is bad practice and could mask future bugs if struct fields change.

Suggestions:

Handle the error from json.Marshal and return it or panic (depending on design intent)
Alternatively, use reflect-based copying to avoid JSON roundtrip and associated error handling
Add a comment explaining why JSON errors are considered impossible (if that's the design decision)

## Code Review: Changes Requested **Issues:** 1. `store/memory.go:30-32` - Errors from json.Marshal and json.Unmarshal are silently discarded. While Event should always be JSON-marshallable, ignoring errors is bad practice and could mask future bugs if struct fields change. **Suggestions:** - Handle the error from json.Marshal and return it or panic (depending on design intent) - Alternatively, use reflect-based copying to avoid JSON roundtrip and associated error handling - Add a comment explaining why JSON errors are considered impossible (if that's the design decision)

HugoNijhuis commented

2026-01-13 21:24:39 +00:00

Fixed review feedback

Added error handling for json.Marshal
Added error handling for json.Unmarshal
Documented error behavior with panic for invalid Event structures

Fixed review feedback - Added error handling for json.Marshal - Added error handling for json.Unmarshal - Documented error behavior with panic for invalid Event structures

HugoNijhuis commented

2026-01-13 21:27:07 +00:00

Code Review: Approved ✓

Error handling for json.Marshal and json.Unmarshal properly implemented with appropriate panic behavior documented. All tests passing including new immutability verification tests.

## Code Review: Approved ✓ Error handling for json.Marshal and json.Unmarshal properly implemented with appropriate panic behavior documented. All tests passing including new immutability verification tests.

HugoNijhuis force-pushed issue-60- from 78aaea9330 to 6549125f3d

2026-01-13 21:39:49 +00:00

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HugoNijhuis merged commit 6549125f3d into main

2026-01-13 21:39:57 +00:00

HugoNijhuis deleted branch issue-60-

2026-01-13 21:39:57 +00:00

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Reference: flowmade-one/aether#136