Initial

Signed-off-by: Paweł Gronowski <[email protected]>

go.mod

@@ -0,0 +1,16 @@
+module woland.xyz/livefile
+
+go 1.21
+
+require (
+	github.com/rs/zerolog v1.33.0
+	gotest.tools v2.2.0+incompatible
+)
+
+require (
+	github.com/google/go-cmp v0.6.0 // indirect
+	github.com/mattn/go-colorable v0.1.13 // indirect
+	github.com/mattn/go-isatty v0.0.19 // indirect
+	github.com/pkg/errors v0.9.1 // indirect
+	golang.org/x/sys v0.12.0 // indirect
+)

go.sum

@@ -0,0 +1,20 @@
+github.com/coreos/go-systemd/v22 v22.5.0/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
+github.com/godbus/dbus/v5 v5.0.4/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/mattn/go-colorable v0.1.13 h1:fFA4WZxdEF4tXPZVKMLwD8oUnCTTo08duU7wxecdEvA=
+github.com/mattn/go-colorable v0.1.13/go.mod h1:7S9/ev0klgBDR4GtXTXX8a3vIGJpMovkB8vQcUbaXHg=
+github.com/mattn/go-isatty v0.0.16/go.mod h1:kYGgaQfpe5nmfYZH+SKPsOc2e4SrIfOl2e/yFXSvRLM=
+github.com/mattn/go-isatty v0.0.19 h1:JITubQf0MOLdlGRuRq+jtsDlekdYPia9ZFsB8h/APPA=
+github.com/mattn/go-isatty v0.0.19/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
+github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
+github.com/rs/xid v1.5.0/go.mod h1:trrq9SKmegXys3aeAKXMUTdJsYXVwGY3RLcfgqegfbg=
+github.com/rs/zerolog v1.33.0 h1:1cU2KZkvPxNyfgEmhHAz/1A9Bz+llsdYzklWFzgp0r8=
+github.com/rs/zerolog v1.33.0/go.mod h1:/7mN4D5sKwJLZQ2b/znpjC3/GQWY/xaDXUM0kKWRHss=
+golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.12.0 h1:CM0HF96J0hcLAwsHPJZjfdNzs0gftsLfgKt57wWHJ0o=
+golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+gotest.tools v2.2.0+incompatible h1:VsBPFP1AI068pPrMxtb/S8Zkgf9xEmTLJjfM+P5UIEo=
+gotest.tools v2.2.0+incompatible/go.mod h1:DsYFclhRJ6vuDpmuTbkuFWG+y2sxOXAzmJt81HFBacw=

statefile.go

@@ -0,0 +1,162 @@
+package statefile
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"io"
+	"os"
+	"path"
+	"path/filepath"
+	"sync"
+	"time"
+
+	"github.com/rs/zerolog/log"
+)
+
+var BaseDir string
+
+type StateFile[StateT any] struct {
+	path string
+
+	lastModTime time.Time
+	cached      StateT
+	mutex       sync.Mutex
+
+	defaultFunc func() StateT
+}
+
+func New[T any](path string, def func() T) *StateFile[T] {
+	if !filepath.IsAbs(path) && BaseDir != "" {
+		path = filepath.Join(BaseDir, path)
+	}
+	return &StateFile[T]{
+		path:        path,
+		defaultFunc: def,
+		cached:      def(),
+	}
+}
+
+func (ps *StateFile[T]) Peek(ctx context.Context) T {
+	ps.mutex.Lock()
+	ps.ensure(ctx)
+	c := ps.cached
+	ps.mutex.Unlock()
+	return c
+}
+
+func (ps *StateFile[T]) ensure(ctx context.Context) {
+	file, err := os.Open(ps.path)
+	if err != nil {
+		if !errors.Is(err, os.ErrNotExist) {
+			panic(err)
+		}
+	} else {
+		ps.loadIfUpdated(ctx, file)
+		file.Close()
+	}
+}
+
+func (ps *StateFile[T]) View(ctx context.Context, f func(state *T)) {
+	ps.mutex.Lock()
+	defer ps.mutex.Unlock()
+
+	ps.ensure(ctx)
+	f(&ps.cached)
+}
+
+func (ps *StateFile[T]) loadIfUpdated(ctx context.Context, file *os.File) {
+	stat, err := file.Stat()
+	if err != nil {
+		panic(err)
+	}
+
+	if stat.Size() == 0 {
+		return
+	}
+
+	modTime := stat.ModTime()
+	if modTime.After(ps.lastModTime) {
+		ps.forceLoad(ctx, file)
+		ps.lastModTime = modTime
+	}
+}
+
+func (ps *StateFile[T]) forceLoad(ctx context.Context, file *os.File) {
+	_, err := file.Seek(0, io.SeekStart)
+	if err != nil {
+		panic(err)
+	}
+
+	decoder := json.NewDecoder(file)
+	err = decoder.Decode(&ps.cached)
+
+	// File empty
+	if err == io.EOF && decoder.InputOffset() == 0 {
+		ps.cached = ps.defaultFunc()
+		err = nil
+	}
+	log.Ctx(ctx).Debug().
+		Err(err).
+		Any("data", ps.cached).
+		Str("path", ps.path).
+		Time("lastMod", ps.lastModTime).
+		Time("timestamp", time.Now()).
+		Msg("loaded")
+
+	if err != nil {
+		panic(err)
+	}
+}
+
+func (ps *StateFile[T]) Update(ctx context.Context, f func(state *T) error) error {
+	ps.mutex.Lock()
+	defer ps.mutex.Unlock()
+
+	ps.ensure(ctx)
+
+	file, err := os.OpenFile(ps.path, os.O_RDWR|os.O_CREATE, 0o660)
+	if errors.Is(err, os.ErrNotExist) {
+		err = os.MkdirAll(path.Dir(ps.path), 0o770)
+		if err != nil {
+			return err
+		}
+		file, err = os.OpenFile(ps.path, os.O_RDWR|os.O_CREATE, 0o660)
+	}
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	ps.loadIfUpdated(ctx, file)
+	err = f(&ps.cached)
+	if err != nil {
+		log.Ctx(ctx).Error().Err(err).Msg("update failed, rolling back")
+		ps.forceLoad(ctx, file)
+		return err
+	}
+
+	err = file.Truncate(0)
+	if err != nil {
+		return err
+	}
+
+	enc := json.NewEncoder(file)
+	enc.SetIndent("", "  ")
+
+	err = enc.Encode(ps.cached)
+	if err != nil {
+		return err
+	}
+
+	err = file.Sync()
+	if err != nil {
+		return err
+	}
+
+	stat, err := file.Stat()
+	if err == nil {
+		ps.lastModTime = stat.ModTime()
+	}
+	return err
+}