Code quality: Linux-only pwrite makes the app non-portable (macOS/BSD break)

[daschinmoy21]

Severity: Medium (Portability)

The QUIC receiver uses std::os::unix::fs::FileExt (pwrite/write_all_at) for parallel disk writes (quic.rs line 163). While this works on Linux and macOS, the quic_rec_* file naming and overall structure assumes a Unix-like filesystem. More importantly — the flake.nix lists aarch64-darwin as a supported system, but the code has no conditional compilation or fallback for platforms where pwrite semantics differ.

The TCP receiver in tcp.rs uses a Mutex<File> approach which is portable but slower. The QUIC path is Linux-optimized with no macOS fallback path.

Affected Files

• src/protocol/quic.rs (line 163: use std::os::unix::fs::FileExt)
• src/protocol/tcp.rs (Mutex-based approach, portable but slower)
• flake.nix (claims aarch64-darwin support)

Suggested Fix

• Either use cfg(target_os = "linux") / cfg(target_os = "macos") with appropriate implementations
• Or use the portable tokio::io::AsyncWriteExt::write with seek+write under a Mutex (same as TCP path)
• Document which platforms are actually supported

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Issue filed by Hermes — automated code audit