diff --git a/cmd/server/cmd.go b/cmd/server/cmd.go
index da7a16d..cb7b7a9 100644
--- a/cmd/server/cmd.go
+++ b/cmd/server/cmd.go
@@ -2,7 +2,6 @@ package server
 
 import (
 	"context"
-	"errors"
 	"flag"
 	"fmt"
 	"io"
@@ -11,6 +10,7 @@ import (
 	"os"
 	"os/signal"
 	"syscall"
+	"time"
 
 	"github.com/ikawaha/kagome-dict/dict"
 	"github.com/ikawaha/kagome-dict/ipa"
@@ -106,8 +106,9 @@ func command(ctx context.Context, opt *option) error {
 	mux.Handle("/", &TokenizeDemoHandler{tokenizer: t})
 	mux.Handle("/tokenize", &TokenizeHandler{tokenizer: t})
 	srv := http.Server{
-		Addr:    opt.http,
-		Handler: mux,
+		Addr:              opt.http,
+		Handler:           mux,
+		ReadHeaderTimeout: 20 * time.Second,
 	}
 	ch := make(chan error)
 	go func() {
@@ -132,17 +133,15 @@ func Run(ctx context.Context, args []string) error {
 	if err := opt.parse(args); err != nil {
 		Usage()
 		PrintDefaults(flag.ContinueOnError)
-		return errors.New("")
+		return fmt.Errorf("option parse error: %w", err)
 	}
 	ctx, cancel := context.WithCancel(ctx)
 	defer cancel()
 	go func() {
 		c := make(chan os.Signal, 1)
 		signal.Notify(c, syscall.SIGHUP, syscall.SIGINT, syscall.SIGTERM)
-		select {
-		case <-c:
-			cancel()
-		}
+		<-c
+		cancel()
 	}()
 	return command(ctx, opt)
 }
diff --git a/sample/_example/db_search/main.go b/sample/_example/db_search/main.go
index bc2ca32..b79aad4 100644
--- a/sample/_example/db_search/main.go
+++ b/sample/_example/db_search/main.go
@@ -37,6 +37,7 @@ import (
 	"errors"
 	"fmt"
 	"log"
+	"os"
 	"strings"
 
 	"github.com/ikawaha/kagome-dict/ipa"
@@ -45,6 +46,13 @@ import (
 )
 
 func main() {
+	if err := run(); err != nil {
+		log.Println(err)
+		os.Exit(1)
+	}
+}
+
+func run() error {
 	// Contents to be inserted into the database. Each element represents a line
 	// of text and will be inserted into a row of the database.
 	lines := []string{
@@ -58,26 +66,30 @@ func main() {
 
 	// Create a database. In-memory database is used for simplicity.
 	db, err := sql.Open("sqlite3", ":memory:")
-	PanicOnError(err)
-
+	if err != nil {
+		return err
+	}
 	defer db.Close()
 
 	// Create tables.
 	// The first table "contents_fts" is for storing the original content, and
 	// the second table "fts" is for storing the tokenized content.
-	_, err = db.Exec(`
+	if _, err = db.Exec(`
 		CREATE TABLE IF NOT EXISTS contents_fts(docid INTEGER PRIMARY KEY AUTOINCREMENT, content TEXT);
 		CREATE VIRTUAL TABLE IF NOT EXISTS fts USING fts4(words);
-	`)
-	PanicOnError(err)
+	`); err != nil {
+		return err
+	}
 
 	// Insert contents
 	for _, line := range lines {
 		rowID, err := insertContent(db, line)
-		PanicOnError(err)
-
-		err = insertSearchToken(db, rowID, line)
-		PanicOnError(err)
+		if err != nil {
+			return err
+		}
+		if err := insertSearchToken(db, rowID, line); err != nil {
+			return err
+		}
 	}
 
 	// Search by word.
@@ -98,7 +110,9 @@ func main() {
 		fmt.Println("Searching for:", searchWord)
 
 		rowIDsFound, err := searchFTS4(db, searchWord)
-		PanicOnError(err)
+		if err != nil {
+			return err
+		}
 
 		if len(rowIDsFound) == 0 {
 			fmt.Println("  No results found")
@@ -108,8 +122,9 @@ func main() {
 		// Print search results
 		for _, rowID := range rowIDsFound {
 			cont, err := retrieveContent(db, rowID)
-			PanicOnError(err)
-
+			if err != nil {
+				return err
+			}
 			fmt.Printf("  Found content: %s at line: %v\n", cont, rowID)
 		}
 	}
@@ -124,6 +139,8 @@ func main() {
 	//   Found content: 北方の海の色は、青うございました。 at line: 3
 	// Searching for: 北
 	//   Found content: 北の海にも棲んでいたのであります。 at line: 2
+
+	return nil
 }
 
 func insertContent(db *sql.DB, content string) (int64, error) {
@@ -142,7 +159,9 @@ func insertSearchToken(db *sql.DB, rowID int64, content string) error {
 	// This example uses the IPA dictionary, but it may be more efficient to use
 	// the 'Uni' dictionary if memory is available.
 	tknzr, err := tokenizer.New(ipa.Dict(), tokenizer.OmitBosEos())
-	PanicOnError(err)
+	if err != nil {
+		return err
+	}
 
 	seg := tknzr.Wakati(content)
 	tokenizedContent := strings.Join(seg, " ")
@@ -156,13 +175,6 @@ func insertSearchToken(db *sql.DB, rowID int64, content string) error {
 	return err
 }
 
-// PanicOnError exits the program with panic if the given error is not nil.
-func PanicOnError(err error) {
-	if err != nil {
-		log.Panic(err)
-	}
-}
-
 func retrieveContent(db *sql.DB, rowID int) (string, error) {
 	rows, err := db.Query(
 		`SELECT rowid, content FROM contents_fts WHERE rowid=?`,