high level event exporter & cursor helpers (#47370)

lib/events/export/cursor.go

@@ -0,0 +1,276 @@
+/*
+ * Teleport
+ * Copyright (C) 2024  Gravitational, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package export
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"path/filepath"
+	"slices"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/gravitational/trace"
+
+	"github.com/gravitational/teleport"
+)
+
+const (
+	// completedName is the completed file name
+	completedName = "completed-chunks"
+
+	// chunkSuffix is the suffix for per-chunk cursor files
+	chunkSuffix = ".chunk"
+)
+
+// CursorConfig configures a cursor.
+type CursorConfig struct {
+	// Dir is the cursor directory. This directory will be created if it does not exist
+	// and should not be used for any other purpose.
+	Dir string
+}
+
+// CheckAndSetDefaults validates configuration and sets default values for optional parameters.
+func (c *CursorConfig) CheckAndSetDefaults() error {
+	if c.Dir == "" {
+		return trace.BadParameter("missing required parameter Dir in CursorConfig")
+	}
+
+	return nil
+}
+
+// Cursor manages an event export cursor directory and keeps a copy of its state in-memory,
+// improving the efficiency of updates by only writing diffs to disk. the cursor directory
+// contains a sub-directory per date. each date's state is tracked using an append-only list
+// of completed chunks, along with a per-chunk cursor file. cursor directories are not intended
+// for true concurrent use, but concurrent use in the context of a graceful restart won't have
+// any consequences more dire than duplicate events.
+type Cursor struct {
+	cfg   CursorConfig
+	mu    sync.Mutex
+	state ExporterState
+}
+
+// NewCursor creates a new cursor, loading any preexisting state from disk.
+func NewCursor(cfg CursorConfig) (*Cursor, error) {
+	if err := cfg.CheckAndSetDefaults(); err != nil {
+		return nil, trace.Wrap(err)
+	}
+
+	state, err := loadInitialState(cfg.Dir)
+	if err != nil {
+		return nil, trace.Wrap(err)
+	}
+	return &Cursor{
+		cfg:   cfg,
+		state: *state,
+	}, nil
+}
+
+// GetState gets the current state as seen by this cursor.
+func (c *Cursor) GetState() ExporterState {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	return c.state.Clone()
+}
+
+// Sync synchronizes the cursor's in-memory state with the provided state, writing any diffs to disk.
+func (c *Cursor) Sync(newState ExporterState) error {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	for d, s := range newState.Dates {
+		if err := c.syncDate(d, s); err != nil {
+			return trace.Wrap(err)
+		}
+	}
+
+	for d := range c.state.Dates {
+		if _, ok := newState.Dates[d]; !ok {
+			if err := c.deleteDate(d); err != nil {
+				return trace.Wrap(err)
+			}
+		}
+	}
+
+	return nil
+}
+
+func (c *Cursor) syncDate(date time.Time, state DateExporterState) error {
+	// ensure date directory exists. the existence of the date directory
+	// is meaningful even if it contains no files.
+	dateDir := filepath.Join(c.cfg.Dir, date.Format(time.DateOnly))
+	if err := os.MkdirAll(dateDir, teleport.SharedDirMode); err != nil {
+		return trace.ConvertSystemError(err)
+	}
+
+	// open completed file in append mode
+	completedFile, err := os.OpenFile(filepath.Join(dateDir, completedName), os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+	if err != nil {
+		return trace.ConvertSystemError(err)
+	}
+	defer completedFile.Close()
+
+	current, ok := c.state.Dates[date]
+	if !ok {
+		current = DateExporterState{
+			Cursors: make(map[string]string),
+		}
+	}
+	defer func() {
+		c.state.Dates[date] = current
+	}()
+
+	for _, chunk := range state.Completed {
+		if slices.Contains(current.Completed, chunk) {
+			// already written to disk
+			continue
+		}
+
+		// add chunk to completed file
+		if _, err := fmt.Fprintln(completedFile, chunk); err != nil {
+			return trace.ConvertSystemError(err)
+		}
+
+		// ensure chunk is flushed to disk successfully before removing the cursor file
+		// and updating in-memory state.
+		if err := completedFile.Sync(); err != nil {
+			return trace.ConvertSystemError(err)
+		}
+
+		// delete cursor file if it exists
+		if err := os.Remove(filepath.Join(dateDir, chunk+chunkSuffix)); err != nil && !os.IsNotExist(err) {
+			return trace.ConvertSystemError(err)
+		}
+
+		// update current state
+		current.Completed = append(current.Completed, chunk)
+		delete(current.Cursors, chunk)
+	}
+
+	for chunk, cursor := range state.Cursors {
+		if current.Cursors[chunk] == cursor {
+			continue
+		}
+
+		// write cursor file
+		if err := os.WriteFile(filepath.Join(dateDir, chunk+chunkSuffix), []byte(cursor), 0644); err != nil {
+			return trace.ConvertSystemError(err)
+		}
+
+		// update current state
+		current.Cursors[chunk] = cursor
+	}
+
+	return nil
+}
+
+func (c *Cursor) deleteDate(date time.Time) error {
+	if _, ok := c.state.Dates[date]; !ok {
+		return nil
+	}
+
+	// delete the date directory and all its contents
+	if err := os.RemoveAll(filepath.Join(c.cfg.Dir, date.Format(time.DateOnly))); err != nil {
+		return trace.ConvertSystemError(err)
+	}
+
+	delete(c.state.Dates, date)
+
+	return nil
+}
+
+func loadInitialState(dir string) (*ExporterState, error) {
+	state := ExporterState{
+		Dates: make(map[time.Time]DateExporterState),
+	}
+	// list subdirectories of the cursors v2 directory
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return &state, nil
+		}
+		return nil, trace.ConvertSystemError(err)
+	}
+
+	for _, entry := range entries {
+		if !entry.IsDir() {
+			// ignore non-directories
+			continue
+		}
+
+		// attempt to parse dir name as date
+		date, err := time.Parse(time.DateOnly, entry.Name())
+		if err != nil {
+			// ignore non-date directories
+			continue
+		}
+
+		dateState := DateExporterState{
+			Cursors: make(map[string]string),
+		}
+
+		dateEntries, err := os.ReadDir(filepath.Join(dir, entry.Name()))
+		if err != nil {
+			return nil, trace.ConvertSystemError(err)
+		}
+
+		for _, dateEntry := range dateEntries {
+			if dateEntry.IsDir() {
+				continue
+			}
+
+			if dateEntry.Name() == completedName {
+				// load the completed file
+				b, err := os.ReadFile(filepath.Join(dir, entry.Name(), completedName))
+				if err != nil {
+					return nil, trace.ConvertSystemError(err)
+				}
+
+				// split the completed file into whitespace-separated chunks
+				dateState.Completed = strings.Fields(string(b))
+				continue
+			}
+
+			if !strings.HasSuffix(dateEntry.Name(), chunkSuffix) {
+				continue
+			}
+
+			chunk := strings.TrimSuffix(dateEntry.Name(), chunkSuffix)
+			b, err := os.ReadFile(filepath.Join(dir, entry.Name(), dateEntry.Name()))
+			if err != nil {
+				return nil, trace.ConvertSystemError(err)
+			}
+
+			if cc := bytes.TrimSpace(b); len(cc) != 0 {
+				dateState.Cursors[chunk] = string(cc)
+			}
+		}
+
+		// note that some dates may not contain any chunks. we still want to track the
+		// fact that these dates have had their dirs initialized since that still indicates
+		// how far we've gotten in the export process.
+		state.Dates[date] = dateState
+	}
+
+	return &state, nil
+}