ps -> lf

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

Author: vvoland

go.mod

@@ -2,15 +2,9 @@ module woland.xyz/livefile
 
 go 1.21
 
-require (
-	github.com/rs/zerolog v1.33.0
-	gotest.tools v2.2.0+incompatible
-)
+require 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

@@ -1,20 +1,6 @@
-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=

livefile.go

@@ -0,0 +1,173 @@
+package livefile
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path"
+	"path/filepath"
+	"sync"
+	"time"
+)
+
+type LiveFile[StateT any] struct {
+	path string
+
+	lastModTime time.Time
+	cached      StateT
+	mutex       sync.Mutex
+
+	defaultFunc func() StateT
+	error       func(context.Context, error)
+}
+
+// The default error handler used for all LiveFile instances created without an
+// explicit [WithDefault] option.
+var DefaultErrorHandler = func(_ context.Context, err error) {
+	panic(err)
+}
+
+// BaseDir is the base directory for the relative paths passed to the [New]
+// function.
+var BaseDir string
+
+func New[T any](path string, opts ...Opt[T]) *LiveFile[T] {
+	if !filepath.IsAbs(path) && BaseDir != "" {
+		path = filepath.Join(BaseDir, path)
+	}
+	lf := &LiveFile[T]{
+		path:  path,
+		error: DefaultErrorHandler,
+	}
+
+	for _, opt := range opts {
+		opt(lf)
+	}
+	if lf.defaultFunc == nil {
+		lf.defaultFunc = func() T {
+			var zero T
+			return zero
+		}
+	}
+	lf.cached = lf.defaultFunc()
+	return lf
+}
+
+func (lf *LiveFile[T]) Peek(ctx context.Context) T {
+	lf.mutex.Lock()
+	lf.ensure(ctx)
+	c := lf.cached
+	lf.mutex.Unlock()
+	return c
+}
+
+func (lf *LiveFile[T]) ensure(ctx context.Context) {
+	file, err := os.Open(lf.path)
+	if err != nil {
+		if !errors.Is(err, os.ErrNotExist) {
+			lf.error(ctx, err)
+		}
+	} else {
+		lf.loadIfUpdated(ctx, file)
+		file.Close()
+	}
+}
+
+func (lf *LiveFile[T]) View(ctx context.Context, f func(state *T)) {
+	lf.mutex.Lock()
+	defer lf.mutex.Unlock()
+
+	lf.ensure(ctx)
+	f(&lf.cached)
+}
+
+func (lf *LiveFile[T]) loadIfUpdated(ctx context.Context, file *os.File) {
+	stat, err := file.Stat()
+	if err != nil {
+		lf.error(ctx, fmt.Errorf("stat failed: %w", err))
+	}
+
+	if stat.Size() == 0 {
+		return
+	}
+
+	modTime := stat.ModTime()
+	if modTime.After(lf.lastModTime) {
+		lf.forceLoad(ctx, file)
+		lf.lastModTime = modTime
+	}
+}
+
+func (lf *LiveFile[T]) forceLoad(ctx context.Context, file *os.File) {
+	_, err := file.Seek(0, io.SeekStart)
+	if err != nil {
+		lf.error(ctx, fmt.Errorf("failed to rewind file: %w", err))
+	}
+
+	decoder := json.NewDecoder(file)
+	err = decoder.Decode(&lf.cached)
+
+	// File empty
+	if err == io.EOF && decoder.InputOffset() == 0 {
+		lf.cached = lf.defaultFunc()
+		err = nil
+	}
+	if err != nil {
+		lf.error(ctx, fmt.Errorf("invalid JSON: %w", err))
+	}
+}
+
+func (lf *LiveFile[T]) Update(ctx context.Context, f func(state *T) error) error {
+	lf.mutex.Lock()
+	defer lf.mutex.Unlock()
+
+	lf.ensure(ctx)
+
+	file, err := os.OpenFile(lf.path, os.O_RDWR|os.O_CREATE, 0o660)
+	if errors.Is(err, os.ErrNotExist) {
+		err = os.MkdirAll(path.Dir(lf.path), 0o770)
+		if err != nil {
+			return err
+		}
+		file, err = os.OpenFile(lf.path, os.O_RDWR|os.O_CREATE, 0o660)
+	}
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	lf.loadIfUpdated(ctx, file)
+	err = f(&lf.cached)
+	if err != nil {
+		// Update failed, rollback changes.
+		lf.forceLoad(ctx, file)
+		return err
+	}
+
+	err = file.Truncate(0)
+	if err != nil {
+		return err
+	}
+
+	enc := json.NewEncoder(file)
+	enc.SetIndent("", "  ")
+
+	err = enc.Encode(lf.cached)
+	if err != nil {
+		return err
+	}
+
+	err = file.Sync()
+	if err != nil {
+		return err
+	}
+
+	stat, err := file.Stat()
+	if err == nil {
+		lf.lastModTime = stat.ModTime()
+	}
+	return err
+}

statefile_test.go livefile_test.gostatefile_test.go renamed to livefile_test.go

@@ -1,4 +1,4 @@
-package statefile
+package livefile
 
 import (
 	"context"
@@ -25,9 +25,9 @@ type TestData struct {
 func TestSimple(t *testing.T) {
 	path := testFilePath(t)
 	ctx := context.Background()
-	f := New(path, func() TestData {
+	f := New(path, WithDefault(func() TestData {
 		return TestData{Value: 42, Name: "test"}
-	})
+	}))
 
 	t.Run("View", func(t *testing.T) {
 		f.View(ctx, func(state *TestData) {
@@ -59,9 +59,9 @@ func TestSimple(t *testing.T) {
 func TestFileIsntCreatedBeforeFirstUpdate(t *testing.T) {
 	path := testFilePath(t)
 	ctx := context.Background()
-	f := New(path, func() TestData {
+	f := New(path, WithDefault(func() TestData {
 		return TestData{Value: 42, Name: "test"}
-	})
+	}))
 
 	_, err := os.Stat(path)
 	assert.Check(t, errors.Is(err, os.ErrNotExist))
@@ -86,9 +86,9 @@ func TestFileIsntCreatedBeforeFirstUpdate(t *testing.T) {
 func TestUpdateErrorWillRollbackChanges(t *testing.T) {
 	path := testFilePath(t)
 	ctx := context.Background()
-	f := New(path, func() TestData {
+	f := New(path, WithDefault(func() TestData {
 		return TestData{Value: 42, Name: "test"}
-	})
+	}))
 
 	err := f.Update(ctx, func(data *TestData) error {
 		data.Name = "updated"
@@ -126,9 +126,9 @@ func TestFileExists(t *testing.T) {
 	ctx := context.Background()
 
 	assert.NilError(t, os.WriteFile(path, []byte(`{"Value": 1337, "Name": "foobar"}`), 0o600))
-	f := New(path, func() TestData {
+	f := New(path, WithDefault(func() TestData {
 		return TestData{Value: 42, Name: "test"}
-	})
+	}))
 
 	data := f.Peek(ctx)
 	assert.Check(t, cmp.Equal(data.Value, 1337))
@@ -139,9 +139,9 @@ func TestFileExternalChange(t *testing.T) {
 	path := testFilePath(t)
 	ctx := context.Background()
 
-	f := New(path, func() TestData {
+	f := New(path, WithDefault(func() TestData {
 		return TestData{Value: 42, Name: "test"}
-	})
+	}))
 
 	data := f.Peek(ctx)
 	assert.Check(t, cmp.Equal(data.Value, 42))
@@ -158,9 +158,9 @@ func TestFileExternalChangeDuringView(t *testing.T) {
 	path := testFilePath(t)
 	ctx := context.Background()
 
-	f := New(path, func() TestData {
+	f := New(path, WithDefault(func() TestData {
 		return TestData{Value: 42, Name: "test"}
-	})
+	}))
 
 	doWrite := make(chan struct{})
 	doRead := make(chan struct{})
@@ -182,9 +182,9 @@ func TestFileExternalChangeDuringUpdate(t *testing.T) {
 	path := testFilePath(t)
 	ctx := context.Background()
 
-	f := New(path, func() TestData {
+	f := New(path, WithDefault(func() TestData {
 		return TestData{Value: 42, Name: "test"}
-	})
+	}))
 
 	doWrite := make(chan struct{})
 	doRead := make(chan struct{})

opts.go

@@ -0,0 +1,22 @@
+package livefile
+
+import "context"
+
+type Opt[T any] func(s *LiveFile[T])
+
+// WithDefault sets the function that will be called to get the default value of
+// the file data.
+// If not set, the default value will be the zero value of the type.
+func WithDefault[T any](f func() T) Opt[T] {
+	return func(s *LiveFile[T]) {
+		s.defaultFunc = f
+	}
+}
+
+// WithErrorHandler sets the function that will be called when an error occurs.
+// If not set, the default error handler will panic.
+func WithErrorHandler[T any](f func(context.Context, error)) Opt[T] {
+	return func(s *LiveFile[T]) {
+		s.error = f
+	}
+}