Improve server shutdown

Less likely to corrupt data now.

LICENSE

@@ -1,8 +1,7 @@
-Copyright (c) 2017, Přemysl Janouch <p.janouch@gmail.com>
+Copyright (c) 2017, Přemysl Janouch <p@janouch.name>
 
 Permission to use, copy, modify, and/or distribute this software for any
-purpose with or without fee is hereby granted, provided that the above
+purpose with or without fee is hereby granted.
-copyright notice and this permission notice appear in all copies.
 
 THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF

db.go

@@ -12,20 +12,20 @@ import (
 var ErrClosed = errors.New("database has been closed")
 
 type DB struct {
-	sync.RWMutex                   // Locking
+	sync.RWMutex                   // locking
-	data         map[string]string // Current state of the database
+	data         map[string]string // current state of the database
-	file         *os.File          // Data storage
+	file         *os.File          // data storage
 }
 
-// Open an existing database file, loading the contents to memory
+// OpenDB opens an existing database file, loading the contents to memory.
 func OpenDB(path string) (*DB, error) {
 	file, err := os.OpenFile(path, os.O_RDWR, 0 /* not used */)
 	if err != nil {
 		return nil, err
 	}
 
-	// TODO we might want a recover flag that just reads as much as it can
+	// TODO: We might want a recover flag that just reads as much as it can
-	//   instead of returning io.ErrUnexpectedEOF
+	// instead of returning io.ErrUnexpectedEOF.
 	db := &DB{data: make(map[string]string), file: file}
 	for {
 		var header struct{ KeyLen, ValueLen int32 }
@@ -64,7 +64,7 @@ func OpenDB(path string) (*DB, error) {
 	return db, nil
 }
 
-// Create a new database, overwriting any previous contents of the file
+// CreateDB creates a new database, overwriting any previous file contents.
 func CreateDB(path string) (*DB, error) {
 	file, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
 	if err != nil {
@@ -73,7 +73,7 @@ func CreateDB(path string) (*DB, error) {
 	return &DB{data: make(map[string]string), file: file}, nil
 }
 
-// Retrieve the value corresponding to the given key
+// Get retrieves the value corresponding to the given key.
 func (db *DB) Get(key string) (string, bool, error) {
 	db.RLock()
 	defer db.RUnlock()
@@ -106,7 +106,7 @@ func put(file *os.File, key, value string) error {
 	return nil
 }
 
-// Save a key-value pair in the database storage
+// Put saves a key-value pair in the database storage.
 func (db *DB) Put(key, value string) error {
 	db.Lock()
 	defer db.Unlock()
@@ -127,7 +127,7 @@ func (db *DB) Put(key, value string) error {
 	return nil
 }
 
-// Delete a key from the database storage
+// Delete deletes a key from the database storage.
 func (db *DB) Delete(key string) error {
 	db.Lock()
 	defer db.Unlock()
@@ -157,7 +157,7 @@ func (db *DB) Delete(key string) error {
 	return nil
 }
 
-// Get rid of historical data in the database file
+// Checkpoint gets rid of historical data in the database file.
 func (db *DB) Checkpoint() error {
 	db.Lock()
 	defer db.Unlock()
@@ -194,7 +194,7 @@ func (db *DB) Checkpoint() error {
 	return nil
 }
 
-// Close the database file, rendering the object unusable
+// Close closes the database file, rendering the object unusable.
 func (db *DB) Close() error {
 	db.Lock()
 	defer db.Unlock()

main.go

@@ -1,4 +1,4 @@
-// Demos a trivial key-value database backed by a file
+// Demos a trivial key-value database backed by a file.
 package main
 
 import (
@@ -14,7 +14,7 @@ import (
 
 func main() {
 	if len(os.Args) != 3 {
-		log.Fatalln("usage: %s LISTEN-ADDRESS DATABASE-FILE", os.Args[0])
+		log.Fatalf("Usage: %s LISTEN-ADDRESS DATABASE-FILE\n", os.Args[0])
 	}
 
 	listenAddr, dbFilename := os.Args[1], os.Args[2]
@@ -66,18 +66,18 @@ func main() {
 	})
 
 	server := &http.Server{Addr: listenAddr}
-	go func() {
+	errs := make(chan error, 1)
-		if err := http.ListenAndServe(listenAddr, nil); err != nil &&
+	go func() { errs <- server.ListenAndServe() }()
-			err != http.ErrServerClosed {
-			log.Fatalln(err)
-		}
-	}()
 
 	sig := make(chan os.Signal)
 	signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
-	<-sig
+	select {
+	case <-sig:
+	case err := <-errs:
+		log.Println(err)
+	}
 
-	// For simplicity, we'll wait for everything to finish, including snapshots
+	// For simplicity, we'll wait for everything to finish, including snapshots.
 	if err := server.Shutdown(context.Background()); err != nil {
 		log.Fatalln(err)
 	}