Add simple tool for examining WAL files

db/wal/walr/main.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"os"
+
+	"github.com/rqlite/rqlite/db/wal"
+)
+
+const name = `walr`
+const desc = `walr is a tool for displaying information about WAL files.`
+
+func init() {
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, "\n%s\n\n", desc)
+		fmt.Fprintf(os.Stderr, "Usage: %s <Path to WAL file>\n", name)
+		flag.PrintDefaults()
+	}
+}
+
+func main() {
+	flag.Parse()
+
+	if flag.NArg() == 0 {
+		flag.Usage()
+		os.Exit(1)
+	}
+	walPath := flag.Args()[0]
+
+	walFD, err := os.Open(walPath)
+	if err != nil {
+		fmt.Println("failed to open WAL file:", err)
+		os.Exit(1)
+	}
+
+	r := wal.NewWALReader(walFD)
+	if err := r.ReadHeader(); err != nil {
+		fmt.Println("failed to read WAL header:", err)
+		os.Exit(1)
+	}
+	fmt.Println("WAL page size: ", r.PageSize())
+
+	nFrames := 0
+	nCommits := 0
+	uniquePgs := make(map[uint32]struct{})
+	buf := make([]byte, r.PageSize())
+	for {
+		pgno, commit, err := r.ReadFrame(buf)
+		if err == io.EOF {
+			break
+		} else if err != nil {
+			fmt.Println("failed to read WAL frame:", err)
+			os.Exit(1)
+		}
+		uniquePgs[pgno] = struct{}{}
+		nFrames++
+
+		if commit != 0 {
+			nCommits++
+		}
+	}
+
+	fmt.Printf("Found %d WAL frames, %d unique pages, %d commit frames\n", nFrames, len(uniquePgs), nCommits)
+}