Design

A hexagon, all the way through. ports.rs holds every interface the core talks through: Tree and Sink for a storage location (list, read as segments of data and holes, create_file, kernel_copy, metadata, attributes), Digests for the content hash, Throttle for the read rate, Log for debug lines, Names for user and group ids, and Batches for a worker fleet; Runtime bundles the cross-cutting ones. The core (plan.rs, transfer.rs, scan.rs, catalog.rs, filter.rs) is written against those ports only and keeps no process-wide state: plan.rs turns listings into actions with no I/O, so the resume, sync and hard-link rules are unit-tested in microseconds, and transfer.rs and scan.rs run the use cases. The driven adapters are LocalTree (with uring.rs as its fast engine), NfsTree and Nfs4Tree, S3Tree, HdfsTree, the two digests, the token bucket, the stderr log, the system name tables and the ssh fleet, each taking its settings at construction; anytree.rs is the static dispatch over the trees and Transports the settings of every remote kind. The driving adapter is the CLI in main.rs: it parses the options, assembles a Runtime and Transports, opens the trees and calls the use cases; a library caller starts from Runtime::plain(). tests/hexagon.rs reads the source and fails when a core module names an adapter or keeps a static, with a control that plants an offense and checks the scan sees it. unsafe is the syscalls a copy needs – tree, uring, gss, xattr – plus seven libc declarations in five other modules: setsid and kill (jobs), signal (cluster and main), prctl and getppid (mcp), isatty (lib). Hand-kept versions of this sentence go wrong easily: naming only the four modules, miscounting the declarations, or attributing a fork to cluster, which this crate does not call anywhere. The list above came from grep -rn 'extern "C"' src/, and so should the next one: a hand-kept inventory of the code is the code’s second copy, and the second copy is the one that rots. The protocol code (nfs/: XDR, SUN RPC, NFSv3; s3/: HTTP, SigV4, the XML that the service speaks) is written against the standard library and tested against in-process stand-in servers that speak the real wire formats.