prosgarz35 opened a new pull request, #3228:
URL: https://github.com/apache/james-project/pull/3228
## Summary
This PR integrates **Google Jimfs** (`com.google.jimfs:jimfs:1.3.2`) into
Apache James test infrastructure and introduces a reusable JUnit 5 extension
(`JimfsExtension`) to drastically speed up file-related unit and integration
tests while eliminating native OS file locking issues (especially on Windows /
CI).
## Rationale & Problem Statement
Currently, many tests in Apache James that test configuration hierarchies,
MIME/RFC-822 stream parsing, or cryptographic certificates rely on disk-backed
temporary folders (`@TempDir`, `Files.createTempDirectory`, or
`TemporaryFolderExtension`).
On physical disks (and particularly under Windows or loaded CI builders like
Jenkins):
1. **I/O bottleneck & High latency:** Disk write/flush/read/delete cycles
are bounded by OS filesystem metadata flushes (10–15 MB/s on average with ~7 ms
per-operation latency).
2. **File locking & Flaky tests:** Native OS file locks frequently cause
`AccessDeniedException` during `@AfterEach` directory cleanup when background
threads hold file handles.
3. **OS-specific paths:** Windows paths (`\`) vs. UNIX POSIX paths (`/`) can
cause non-deterministic behavior across development environments and Linux CI
containers.
## Solution
We introduce Google Jimfs as an in-memory Java NIO FileSystem provider
conforming to POSIX/Unix filesystem semantics:
1. **`pom.xml` (root):**
- Added property `<jimfs.version>1.3.2</jimfs.version>`.
- Added `com.google.jimfs:jimfs` to `<dependencyManagement>` in exact
alphabetical order.
2. **`server/testing/pom.xml`:**
- Added `com.google.jimfs:jimfs` dependency (managed version).
3. **`server/testing/.../JimfsExtension.java`:**
- A lightweight, idiomatic JUnit 5 extension (`ParameterResolver`,
`BeforeEachCallback`, `AfterEachCallback`).
- Automatically provides an isolated in-memory Unix
`java.nio.file.FileSystem` or `java.nio.file.Path` to test methods.
- Non-intrusive: explicitly yields parameter resolution when `@TempDir`
is present to prevent collisions.
- Automatically closes and frees the in-memory filesystem upon test
completion (`afterEach`).
4. **`server/testing/.../JimfsExtensionTest.java`:**
- Full test coverage for parameter injection (`FileSystem` and `Path`).
- Validates memory-backed configuration parsing (`conf/smtpserver.xml`).
- Validates in-memory RFC-822 email payload stream processing.
- Verifies test isolation across executions.
- Includes a direct comparative benchmark against disk-backed `@TempDir`.
## Measured Benchmark Results
Benchmarking 1,000 cycles (create $\to$ write 64 KB payload $\to$ read $\to$
delete) directly within `JimfsExtensionTest`:
| Metric | Physical Disk (`@TempDir`) | Jimfs In-Memory (`JimfsExtension`) |
Improvement / Advantage |
| :--- | :--- | :--- | :--- |
| **Execution Time** | **8 280 ms** | **223 ms** | **37.1x faster** (97.3%
time saved) |
| **Throughput (Read + Write)** | **15.10 MB/s** | **560.54 MB/s** | **37.1x
higher throughput** |
| **Latency p50 (Median)** | **7 330.00 µs** (~7.3 ms) | **45.50 µs**
(~0.045 ms) | **161.1x lower latency** |
| **Latency p95** | **11 734.80 µs** (~11.7 ms) | **366.30 µs** (~0.36 ms) |
**32.0x lower latency** |
## Design Principles Adherence
- **KISS:** Zero custom annotation boilerplate required; simply
`@ExtendWith(JimfsExtension.class)` and inject standard `Path` or `FileSystem`.
- **DRY:** Centralized in `james-server-testing`, immediately available
across all 60+ server submodules without modifying individual POMs.
- **YAGNI:** Kept strictly minimal (85 LOC), avoiding premature abstractions
or changes to legacy `java.io.File` subsystems.
- **Checkstyle & Standards:** 0 Checkstyle violations, formatted per Apache
James rules, full ALv2 license headers included.
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