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|
package main
import (
"encoding/json"
"errors"
"fmt"
"os"
"time"
)
type Series struct {
Prefix string // PK: prefix
Description string // what kind of containers this is for
}
type Container struct {
Series string // PK: what series does this belong to
Number uint // PK: order within the series
Parent ContainerId // the container we're in, if any, otherwise ""
Description string // description and/or contents of this container
}
type ContainerId string
func (c *Container) Id() ContainerId {
return ContainerId(fmt.Sprintf("%s%s%d", db.Prefix, c.Series, c.Number))
}
type Database struct {
Password string // password for web users
Prefix string // prefix for all container IDs
Series []*Series // all known series
Containers []*Container // all known containers
}
var (
dbPath string
db Database
dbLast Database
dbLog *os.File
indexSeries = map[string]*Series{}
indexContainer = map[ContainerId]*Container{}
indexChildren = map[ContainerId][]*Container{}
)
// TODO: Some functions to add, remove and change things in the database.
// Indexes must be kept valid, just like any invariants.
// TODO: A function for fulltext search in series (1. Prefix, 2. Description).
// TODO: A function for fulltext search in containers (1. Id, 2. Description).
func dbCommit() error {
// Write a timestamp.
e := json.NewEncoder(dbLog)
e.SetIndent("", " ")
if err := e.Encode(time.Now().Format(time.RFC3339)); err != nil {
return err
}
// Back up the current database contents.
if err := e.Encode(&dbLast); err != nil {
return err
}
if err := dbLog.Sync(); err != nil {
return err
}
// Atomically replace the current database file.
tempPath := dbPath + ".new"
temp, err := os.OpenFile(tempPath, os.O_WRONLY|os.O_CREATE, 0644)
if err != nil {
return err
}
defer temp.Close()
e = json.NewEncoder(temp)
e.SetIndent("", " ")
if err := e.Encode(&db); err != nil {
return err
}
if err := os.Rename(tempPath, dbPath); err != nil {
return err
}
dbLast = db
return nil
}
// loadDatabase loads the database from a simple JSON file. We do not use
// any SQL stuff or even external KV storage because there is no real need
// for our trivial use case, with our general amount of data.
func loadDatabase() error {
dbFile, err := os.Open(dbPath)
if err != nil {
return err
}
if err := json.NewDecoder(dbFile).Decode(&db); err != nil {
return err
}
// Further validate the database.
if db.Prefix == "" {
return errors.New("misconfigured prefix")
}
// Construct indexes for primary keys, validate against duplicates.
for _, pv := range db.Series {
if _, ok := indexSeries[pv.Prefix]; ok {
return fmt.Errorf("duplicate series: %s", pv.Prefix)
}
indexSeries[pv.Prefix] = pv
}
for _, pv := range db.Containers {
id := pv.Id()
if _, ok := indexContainer[id]; ok {
return fmt.Errorf("duplicate container: %s", id)
}
indexContainer[id] = pv
}
// Construct an index that goes from parent containers to their children.
for _, pv := range db.Containers {
if pv.Parent == "" {
continue
}
if _, ok := indexContainer[pv.Parent]; !ok {
return fmt.Errorf("container %s has a nonexistent parent %s",
pv.Id(), pv.Parent)
}
indexChildren[pv.Parent] = append(indexChildren[pv.Parent], pv)
}
// Validate that no container is a parent of itself on any level.
// This could probably be optimized but it would stop being obvious.
for _, pv := range db.Containers {
parents := map[ContainerId]bool{pv.Id(): true}
for pv.Parent != "" {
if parents[pv.Parent] {
return fmt.Errorf("%s contains itself", pv.Parent)
}
parents[pv.Parent] = true
pv = indexContainer[pv.Parent]
}
}
// Open database log file for appending.
if dbLog, err = os.OpenFile(dbPath+".log",
os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644); err != nil {
return err
}
// Remember the current state of the database.
dbLast = db
return nil
}
|
