Initial commit
The most basic REST database you'll find.
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commit
4c71bc58e9
GPG Key ID:
B715679E3A361BE6
1
.gitignore
vendored
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1
.gitignore
vendored
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/tinydb
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209
db.go
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209
db.go
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package main
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import (
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"encoding/binary"
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"errors"
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"fmt"
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"io"
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"os"
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"sync"
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)
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var ErrClosed = errors.New("database has been closed")
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type DB struct {
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sync.RWMutex // Locking
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data map[string]string // Current state of the database
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file *os.File // Data storage
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}
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// Open an existing database file, loading the contents to memory
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func OpenDB(path string) (*DB, error) {
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file, err := os.OpenFile(path, os.O_RDWR, 0 /* not used */)
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if err != nil {
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return nil, err
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}
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// TODO we might want a recover flag that just reads as much as it can
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// instead of returning io.ErrUnexpectedEOF
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db := &DB{data: make(map[string]string), file: file}
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for {
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var header struct{ KeyLen, ValueLen int32 }
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err := binary.Read(db.file, binary.LittleEndian, &header)
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if err == io.EOF {
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break
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} else if err != nil {
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return nil, err
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}
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if header.KeyLen < 0 {
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return nil, fmt.Errorf("invalid key length: %d", header.KeyLen)
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}
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key := make([]byte, header.KeyLen)
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if n, err := file.Read(key); err != nil {
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return nil, err
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} else if n != len(key) {
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return nil, io.ErrUnexpectedEOF
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}
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if header.ValueLen < 0 {
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delete(db.data, string(key))
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continue
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}
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value := make([]byte, header.ValueLen)
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if n, err := file.Read(value); err != nil {
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return nil, err
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} else if n != len(value) {
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return nil, io.ErrUnexpectedEOF
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}
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db.data[string(key)] = string(value)
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}
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// We've been successful, clean up after failed snapshots
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os.Remove(path + ".1")
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return db, nil
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}
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// Create a new database, overwriting any previous contents of the file
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func CreateDB(path string) (*DB, error) {
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file, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
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if err != nil {
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return nil, err
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}
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return &DB{data: make(map[string]string), file: file}, nil
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}
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// Retrieve the value corresponding to the given key
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func (db *DB) Get(key string) (string, bool, error) {
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db.RLock()
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defer db.RUnlock()
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if db.file == nil {
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return "", false, ErrClosed
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}
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value, ok := db.data[key]
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return value, ok, nil
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}
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func put(file *os.File, key, value string) error {
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header := [2]int32{int32(len(key)), int32(len(value))}
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if err := binary.Write(file, binary.LittleEndian, &header); err != nil {
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return err
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}
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if n, err := file.WriteString(key); err != nil {
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return err
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} else if n != len(key) {
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return io.ErrShortWrite
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}
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if n, err := file.WriteString(value); err != nil {
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return err
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} else if n != len(value) {
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return io.ErrShortWrite
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}
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return nil
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}
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// Save a key-value pair in the database storage
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func (db *DB) Put(key, value string) error {
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db.Lock()
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defer db.Unlock()
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if db.file == nil {
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return ErrClosed
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}
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// XXX we should check whether the key and the value fit
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if err := put(db.file, key, value); err != nil {
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return err
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}
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if err := db.file.Sync(); err != nil {
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return err
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}
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db.data[key] = value
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return nil
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}
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// Delete a key from the database storage
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func (db *DB) Delete(key string) error {
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db.Lock()
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defer db.Unlock()
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if db.file == nil {
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return ErrClosed
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}
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// Like put(), just without the "value"
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header := [2]int32{int32(len(key)), -1}
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if err := binary.Write(db.file, binary.LittleEndian, &header); err != nil {
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return err
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}
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if n, err := db.file.WriteString(key); err != nil {
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return err
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} else if n != len(key) {
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return io.ErrShortWrite
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}
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if err := db.file.Sync(); err != nil {
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return err
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}
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// TODO maybe return an indication whether anything was actually deleted
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delete(db.data, key)
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return nil
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}
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// Get rid of historical data in the database file
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func (db *DB) Checkpoint() error {
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db.Lock()
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defer db.Unlock()
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if db.file == nil {
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return ErrClosed
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}
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checkpoint, err := os.OpenFile(db.file.Name()+".1",
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os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
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if err != nil {
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return err
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}
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// The checkpoint is made of the current value of every present key
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for key, value := range db.data {
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if err := put(checkpoint, key, value); err != nil {
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return err
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}
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}
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if err := checkpoint.Sync(); err != nil {
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return err
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}
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// Atomically move the checkpoint over the old database file
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if err := os.Rename(checkpoint.Name(), db.file.Name()); err != nil {
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// Not sure how much sense this makes--when do we get here?
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_ = os.Remove(checkpoint.Name())
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return err
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}
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// The old file now points to unlinked storage, replace it with the new one
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_ = db.file.Close()
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db.file = checkpoint
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return nil
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}
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// Close the database file, rendering the object unusable
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func (db *DB) Close() error {
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db.Lock()
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defer db.Unlock()
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if db.file != nil {
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return nil
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}
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err := db.file.Close()
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db.file = nil
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return err
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}
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87
main.go
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87
main.go
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@ -0,0 +1,87 @@
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// Demos a trivial key-value database backed by a file
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package main
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import (
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"context"
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"io/ioutil"
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"log"
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"net/http"
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"os"
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"os/signal"
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"strings"
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"syscall"
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)
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func main() {
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if len(os.Args) != 3 {
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log.Fatalln("usage: %s LISTEN-ADDRESS DATABASE-FILE", os.Args[0])
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}
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listenAddr, dbFilename := os.Args[1], os.Args[2]
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db, err := OpenDB(dbFilename)
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if err != nil && os.IsNotExist(err) {
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log.Println("database file does not exist, creating")
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db, err = CreateDB(dbFilename)
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}
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if err != nil {
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log.Fatalln(err)
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}
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http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
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if _, ok := r.URL.Query()["checkpoint"]; ok && r.Method == "GET" {
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if err := db.Checkpoint(); err != nil {
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w.WriteHeader(http.StatusInternalServerError)
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}
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return
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}
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byteValue, err := ioutil.ReadAll(r.Body)
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if err != nil {
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w.WriteHeader(http.StatusInternalServerError)
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return
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}
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key, value := strings.TrimPrefix(r.URL.Path, "/"), string(byteValue)
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switch r.Method {
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case "GET":
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if value, ok, err := db.Get(key); err != nil {
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w.WriteHeader(http.StatusInternalServerError)
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} else if ok {
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w.WriteHeader(http.StatusOK)
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w.Write([]byte(value))
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} else {
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w.WriteHeader(http.StatusNotFound)
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}
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case "PUT":
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if err := db.Put(key, value); err != nil {
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w.WriteHeader(http.StatusInternalServerError)
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}
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case "DELETE":
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if err := db.Delete(key); err != nil {
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w.WriteHeader(http.StatusInternalServerError)
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}
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default:
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w.WriteHeader(http.StatusMethodNotAllowed)
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}
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})
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server := &http.Server{Addr: listenAddr}
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go func() {
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if err := http.ListenAndServe(listenAddr, nil); err != nil &&
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err != http.ErrServerClosed {
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log.Fatalln(err)
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}
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}()
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sig := make(chan os.Signal)
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signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
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<-sig
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// For simplicity, we'll wait for everything to finish, including snapshots
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if err := server.Shutdown(context.Background()); err != nil {
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log.Fatalln(err)
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}
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if err := db.Close(); err != nil {
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log.Fatalln(err)
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}
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}
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