Untangle layering: move FairnessConfig from connection to fairness module

[coderabbitai]

Problem

FairnessConfig is currently defined in the connection module (src/connection.rs:82) but is consumed by the fairness module (src/fairness.rs:10). This creates a layering violation where a lower-level module depends on configuration defined in a higher-level module.

Desired Outcome

Move FairnessConfig into src/fairness.rs:1 where it logically belongs, and pub use it from the connection module to maintain the existing public API surface and avoid breaking changes.

Context

Raised by @leynos in PR #424: #424
Comment: #424 (comment)

[traycerai]

Plan

Observations

The codebase has a layering violation where FairnessConfig is defined in file:src/connection.rs (lines 82-95) but is consumed by the lower-level file:src/fairness.rs module (line 10). The fairness module is currently private (not exposed in file:src/lib.rs), while connection is public. FairnessConfig is part of the public API, accessible as wireframe::connection::FairnessConfig and used in multiple test files. The struct includes a Default implementation (lines 111-118) and is used to configure the FairnessTracker within the connection actor.

Approach

Move FairnessConfig and its Default implementation from file:src/connection.rs to file:src/fairness.rs, then re-export it from file:src/connection.rs using pub use to maintain backward compatibility. This resolves the layering violation by placing the configuration type in the module that consumes it, while preserving the existing public API surface. The change requires updating the import in file:src/fairness.rs and adding a re-export in file:src/connection.rs.

Implementation Steps

1. Move FairnessConfig to the fairness module

In file:src/fairness.rs:

• Remove the import statement at line 10: use crate::connection::FairnessConfig;
• Add the FairnessConfig struct definition at the beginning of the file (after the module documentation and before the Clock trait definition, around line 10)
• Include the complete struct definition with:
  • Documentation comments (lines 82-95 from connection.rs)
  • #[derive(Clone, Copy, Debug)] attribute
  • Both public fields: max_high_before_low: usize and time_slice: Option<Duration>
• Add the Default implementation for FairnessConfig (lines 111-118 from connection.rs)
• Ensure the struct is declared as pub struct FairnessConfig to make it accessible for re-export

2. Re-export FairnessConfig from the connection module

In file:src/connection.rs:

• Remove the FairnessConfig struct definition (lines 82-95)
• Remove the Default implementation for FairnessConfig (lines 111-118)
• Add a re-export statement near the top of the file (after the existing use statements, around line 62): pub use crate::fairness::FairnessConfig;
• This maintains the public API path wireframe::connection::FairnessConfig that existing code depends on

3. Verify no other changes are needed

Check the following:

• The test files (file:tests/connection_actor_fairness.rs, file:tests/multi_packet.rs, file:tests/multi_packet_streaming.rs) should continue to work without modification since they import from wireframe::connection::FairnessConfig
• The ConnectionActor implementation in file:src/connection.rs will continue to access FairnessConfig through the re-export
• No changes needed to file:src/lib.rs since the fairness module remains private and FairnessConfig is still accessible via the public connection module

sequenceDiagram
    participant Dev as Developer
    participant Fairness as src/fairness.rs
    participant Connection as src/connection.rs
    participant Tests as Test Files
    
    Dev->>Fairness: 1. Move FairnessConfig struct
    Dev->>Fairness: 2. Move Default impl
    Dev->>Fairness: 3. Remove import of FairnessConfig
    Dev->>Connection: 4. Remove FairnessConfig definition
    Dev->>Connection: 5. Remove Default impl
    Dev->>Connection: 6. Add pub use fairness::FairnessConfig
    Tests->>Connection: Import FairnessConfig (unchanged)
    Connection->>Fairness: Re-export from fairness module
    Fairness->>Tests: Provide FairnessConfig

Loading

4. Build and test verification

• Run cargo build to ensure the code compiles without errors
• Run cargo test to verify all tests pass, particularly:
  • tests/connection_actor_fairness.rs tests
  • tests/multi_packet.rs tests
  • tests/multi_packet_streaming.rs tests
  • Unit tests in file:src/fairness.rs
• Run cargo clippy to ensure no new warnings are introduced
• Verify documentation builds correctly with cargo doc

Import In IDE

🤖 Prompt for AI Agents

## Observations

The codebase has a layering violation where `FairnessConfig` is defined in `file:src/connection.rs` (lines 82-95) but is consumed by the lower-level `file:src/fairness.rs` module (line 10). The `fairness` module is currently private (not exposed in `file:src/lib.rs`), while `connection` is public. `FairnessConfig` is part of the public API, accessible as `wireframe::connection::FairnessConfig` and used in multiple test files. The struct includes a `Default` implementation (lines 111-118) and is used to configure the `FairnessTracker` within the connection actor.

## Approach

Move `FairnessConfig` and its `Default` implementation from `file:src/connection.rs` to `file:src/fairness.rs`, then re-export it from `file:src/connection.rs` using `pub use` to maintain backward compatibility. This resolves the layering violation by placing the configuration type in the module that consumes it, while preserving the existing public API surface. The change requires updating the import in `file:src/fairness.rs` and adding a re-export in `file:src/connection.rs`.

## Implementation Steps

### 1. Move `FairnessConfig` to the fairness module

**In `file:src/fairness.rs`:**

- Remove the import statement at line 10: `use crate::connection::FairnessConfig;`
- Add the `FairnessConfig` struct definition at the beginning of the file (after the module documentation and before the `Clock` trait definition, around line 10)
- Include the complete struct definition with:
  - Documentation comments (lines 82-95 from connection.rs)
  - `#[derive(Clone, Copy, Debug)]` attribute
  - Both public fields: `max_high_before_low: usize` and `time_slice: Option<Duration>`
- Add the `Default` implementation for `FairnessConfig` (lines 111-118 from connection.rs)
- Ensure the struct is declared as `pub struct FairnessConfig` to make it accessible for re-export

### 2. Re-export `FairnessConfig` from the connection module

**In `file:src/connection.rs`:**

- Remove the `FairnessConfig` struct definition (lines 82-95)
- Remove the `Default` implementation for `FairnessConfig` (lines 111-118)
- Add a re-export statement near the top of the file (after the existing `use` statements, around line 62): `pub use crate::fairness::FairnessConfig;`
- This maintains the public API path `wireframe::connection::FairnessConfig` that existing code depends on

### 3. Verify no other changes are needed

**Check the following:**

- The test files (`file:tests/connection_actor_fairness.rs`, `file:tests/multi_packet.rs`, `file:tests/multi_packet_streaming.rs`) should continue to work without modification since they import from `wireframe::connection::FairnessConfig`
- The `ConnectionActor` implementation in `file:src/connection.rs` will continue to access `FairnessConfig` through the re-export
- No changes needed to `file:src/lib.rs` since the `fairness` module remains private and `FairnessConfig` is still accessible via the public `connection` module

```mermaid
sequenceDiagram
    participant Dev as Developer
    participant Fairness as src/fairness.rs
    participant Connection as src/connection.rs
    participant Tests as Test Files
    
    Dev->>Fairness: 1. Move FairnessConfig struct
    Dev->>Fairness: 2. Move Default impl
    Dev->>Fairness: 3. Remove import of FairnessConfig
    Dev->>Connection: 4. Remove FairnessConfig definition
    Dev->>Connection: 5. Remove Default impl
    Dev->>Connection: 6. Add pub use fairness::FairnessConfig
    Tests->>Connection: Import FairnessConfig (unchanged)
    Connection->>Fairness: Re-export from fairness module
    Fairness->>Tests: Provide FairnessConfig
```

### 4. Build and test verification

- Run `cargo build` to ensure the code compiles without errors
- Run `cargo test` to verify all tests pass, particularly:
  - `tests/connection_actor_fairness.rs` tests
  - `tests/multi_packet.rs` tests  
  - `tests/multi_packet_streaming.rs` tests
  - Unit tests in `file:src/fairness.rs`
- Run `cargo clippy` to ensure no new warnings are introduced
- Verify documentation builds correctly with `cargo doc`

---

Execution Information

Branch: main
Commit: 9b4ea6e

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