pstore

pstore — go-ruby-pstore

A pure-Go (no cgo) reimplementation of the transaction engine at the heart of Ruby's PStore — MRI 4.0.5's transactional, Marshal-backed object store (the pstore-0.2.1 gem). It runs the load → transaction-body → commit/abort state machine over a Hash "table" and serialises that table with go-ruby-marshal, so the on-disk bytes are byte-compatible with a file written by MRI's PStore — without any Ruby runtime.

It is the PStore backend for go-embedded-ruby, but is a standalone, reusable module — a sibling of go-ruby-marshal, go-ruby-yaml, go-ruby-regexp, and go-ruby-erb.

What it is — and isn't. The transactional core — load the table, run the body, commit on normal exit (skipping the write when nothing changed), abort or commit early, forbid writes in a read-only transaction, refuse a nested transaction, raise outside one — is fully deterministic and needs no interpreter, so it lives here as pure Go over the Marshal codec. The file half — opening the store file (O_CREAT), flock(LOCK_SH/LOCK_EX), the atomic-rename / rewind-truncate save strategies — is the host's job, injected as a two-method Backend. rbgo wires the real os.File + syscall.Flock; tests use an in-memory backend, so the whole suite is deterministic and Ruby-free.

Features

Faithful port of PStore's transaction semantics, validated against the ruby binary on every supported platform:

• Commit on normal exit — a read-write transaction whose body returns normally Marshal-dumps the table back through the backend, only if the bytes changed (MRI's checksum/size guard); an unchanged transaction performs no write.
• Commit / Abort early exit — return t.Commit() or t.Abort() from the body to exit it early (MRI's throw :pstore_abort_transaction); Abort discards every change, Commit persists the work so far. The body does not continue past either.
• Read-only transactions — Set and Delete raise PStore::Error ("in read-only transaction") and the backend is never written.
• The error taxonomy — a single *pstore.Error (Ruby's PStore::Error) with MRI's exact messages: "not in transaction", "in read-only transaction", "nested transaction", "undefined key '…'", and "PStore file seems to be corrupted.".
• The on-disk Marshal format — the table is Marshal.dump/loaded via go-ruby-marshal, so a file this engine commits is read back unchanged by MRI's PStore, and vice-versa (a real ruby -rpstore file loads here).

CGO-free, 100% test coverage, gofmt + go vet clean, and green across the six 64-bit Go targets (amd64, arm64, riscv64, loong64, ppc64le, s390x) and three OSes (Linux, macOS, Windows).

Install

go get github.com/go-ruby-pstore/pstore

Usage

package main

import (
	"fmt"

	"github.com/go-ruby-marshal/marshal"
	"github.com/go-ruby-pstore/pstore"
)

func main() {
	// The host supplies the file seam (real os.File + flock in rbgo); here an
	// in-memory backend stands in.
	be := &mem{}
	store := pstore.New(be)

	// A read-write transaction: writes commit on normal return.
	store.Transaction(false, func(t *pstore.Tx) error {
		t.Set(marshal.Symbol("foo"), marshal.NewInt(0))
		t.Set(marshal.NewString("baz"), &marshal.Array{
			Elems: []marshal.Value{marshal.NewInt(1), marshal.NewInt(2)},
		})
		return nil // commit
	})

	// A read-only transaction: reads only; a write here would raise PStore::Error.
	store.Transaction(true, func(t *pstore.Tx) error {
		roots, _ := t.Roots()           // [:foo, "baz"]
		v, ok, _ := t.Get(marshal.Symbol("foo"))
		fmt.Println(roots, v, ok)
		return nil
	})
}

type mem struct{ b []byte }

func (m *mem) Load() ([]byte, error)  { return m.b, nil }
func (m *mem) Store(b []byte) error   { m.b = b; return nil }

API

// New returns a Store over an injected Backend.
func New(b Backend) *Store

// Backend is the file seam the host injects (real os.File + flock in rbgo).
type Backend interface {
	Load() ([]byte, error)   // current store bytes (empty == fresh store)
	Store(data []byte) error // overwrite with the marshalled table
}

// Transaction loads the table, runs body, and — on a committing read-write
// transaction whose table changed — Marshal-dumps it back to the backend.
// body returns t.Commit()/t.Abort() to exit early, any other error to propagate
// (no commit), or nil to finish (a read-write transaction then commits).
func (s *Store) Transaction(readOnly bool, body func(t *Tx) error) error

// In-transaction API (mirrors PStore#[], #[]=, #delete, #fetch, #roots/#keys,
// #root?/#key?, #commit, #abort). Keys and values are go-ruby-marshal Values.
func (t *Tx) Get(key marshal.Value) (marshal.Value, bool, error)            // PStore#[]
func (t *Tx) Set(key, val marshal.Value) error                             // PStore#[]=
func (t *Tx) Delete(key marshal.Value) (marshal.Value, error)              // PStore#delete
func (t *Tx) Fetch(key marshal.Value, def marshal.Value) (marshal.Value, error) // PStore#fetch
func (t *Tx) Roots() ([]marshal.Value, error)                              // PStore#roots
func (t *Tx) RootQ(key marshal.Value) (bool, error)                        // PStore#root?
func (t *Tx) Commit() error                                                // PStore#commit
func (t *Tx) Abort() error                                                 // PStore#abort

// Error is PStore::Error.
type Error struct{ /* … */ }

The table's keys and values are go-ruby-marshal Values (marshal.Symbol, *marshal.Str, marshal.Int, *marshal.Array, *marshal.Hash, …) — the same typed model the rest of the go-embedded-ruby stack speaks, so a host binds its own Ruby objects to and from this engine exactly as it does for Marshal.

Tests & coverage

The suite pairs deterministic, ruby-free tests over the in-memory backend (which alone hold coverage at 100%, so the qemu cross-arch and Windows lanes pass the gate) with a differential MRI oracle: it writes a store with the real ruby -rpstore, loads its file bytes here, and round-trips the table both directions (MRI→Go and Go→MRI), plus replays MRI's own commit / abort / read-only sequence and asserts the engine produces the identical persisted roots. The oracle scripts $stdout.binmode so Windows text-mode never corrupts the raw Marshal bytes, and skip themselves where ruby is absent.

COVERPKG=$(go list ./... | paste -sd, -)
go test -race -coverpkg="$COVERPKG" -coverprofile=cover.out ./...
go tool cover -func=cover.out | tail -1   # 100.0%

License

BSD-3-Clause — see LICENSE. Copyright the go-ruby-pstore/pstore authors.

WebAssembly

Being pure Go (CGO=0), this library also compiles to WebAssembly — both GOOS=js GOARCH=wasm (browser / Node.js) and GOOS=wasip1 GOARCH=wasm (WASI). CI builds both targets on every push, alongside the six 64-bit native/qemu arches.

GOOS=js     GOARCH=wasm go build ./...   # browser / Node
GOOS=wasip1 GOARCH=wasm go build ./...   # WASI (wasmtime, wasmer, wasmedge, …)