github.com/hugh712/snapd@v0.0.0-20200910133618-1a99902bd583/advisor/backend.go

// -*- Mode: Go; indent-tabs-mode: t -*-

/*
 * Copyright (C) 2018 Canonical Ltd
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 3 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

package advisor

import (
	"encoding/json"
	"os"
	"path/filepath"
	"time"

	"github.com/snapcore/bolt"

	"github.com/snapcore/snapd/dirs"
	"github.com/snapcore/snapd/osutil"
	"github.com/snapcore/snapd/randutil"
)

var (
	cmdBucketKey = []byte("Commands")
	pkgBucketKey = []byte("Snaps")
)

type writer struct {
	fn        string
	db        *bolt.DB
	tx        *bolt.Tx
	cmdBucket *bolt.Bucket
	pkgBucket *bolt.Bucket
}

type CommandDB interface {
	// AddSnap adds the entries for commands pointing to the given
	// snap name to the commands database.
	AddSnap(snapName, version, summary string, commands []string) error
	// Commit persist the changes, and closes the database. If the
	// database has already been committed/rollbacked, does nothing.
	Commit() error
	// Rollback aborts the changes, and closes the database. If the
	// database has already been committed/rollbacked, does nothing.
	Rollback() error
}

// Create opens the commands database for writing, and starts a
// transaction that drops and recreates the buckets. You should then
// call AddSnap with each snap you wish to add, and them Commit the
// results to make the changes live, or Rollback to abort; either of
// these closes the database again.
func Create() (CommandDB, error) {
	var err error
	t := &writer{
		fn: dirs.SnapCommandsDB + "." + randutil.RandomString(12) + "~",
	}

	t.db, err = bolt.Open(t.fn, 0644, &bolt.Options{Timeout: 1 * time.Second})
	if err != nil {
		return nil, err
	}

	t.tx, err = t.db.Begin(true)
	if err == nil {
		t.cmdBucket, err = t.tx.CreateBucket(cmdBucketKey)
		if err == nil {
			t.pkgBucket, err = t.tx.CreateBucket(pkgBucketKey)
		}

		if err != nil {
			t.tx.Rollback()
		}
	}

	if err != nil {
		t.db.Close()
		return nil, err
	}

	return t, nil
}

func (t *writer) AddSnap(snapName, version, summary string, commands []string) error {
	for _, cmd := range commands {
		var sil []Package

		bcmd := []byte(cmd)
		row := t.cmdBucket.Get(bcmd)
		if row != nil {
			if err := json.Unmarshal(row, &sil); err != nil {
				return err
			}
		}
		// For the mapping of command->snap we do not need the summary, nothing is using that.
		sil = append(sil, Package{Snap: snapName, Version: version})
		row, err := json.Marshal(sil)
		if err != nil {
			return err
		}
		if err := t.cmdBucket.Put(bcmd, row); err != nil {
			return err
		}
	}

	// TODO: use json here as well and put the version information here
	bj, err := json.Marshal(Package{
		Snap:    snapName,
		Version: version,
		Summary: summary,
	})
	if err != nil {
		return err
	}
	if err := t.pkgBucket.Put([]byte(snapName), bj); err != nil {
		return err
	}

	return nil
}

func (t *writer) Commit() error {
	// either everything worked, and therefore this will fail, or something
	// will fail, and that error is more important than this one if this one
	// then fails as well. So, ignore the error.
	defer os.Remove(t.fn)

	if err := t.done(true); err != nil {
		return err
	}

	dir, err := os.Open(filepath.Dir(dirs.SnapCommandsDB))
	if err != nil {
		return err
	}
	defer dir.Close()

	if err := os.Rename(t.fn, dirs.SnapCommandsDB); err != nil {
		return err
	}

	return dir.Sync()
}

func (t *writer) Rollback() error {
	e1 := t.done(false)
	e2 := os.Remove(t.fn)
	if e1 == nil {
		return e2
	}
	return e1
}

func (t *writer) done(commit bool) error {
	var e1, e2 error

	t.cmdBucket = nil
	t.pkgBucket = nil
	if t.tx != nil {
		if commit {
			e1 = t.tx.Commit()
		} else {
			e1 = t.tx.Rollback()
		}
		t.tx = nil
	}
	if t.db != nil {
		e2 = t.db.Close()
		t.db = nil
	}
	if e1 == nil {
		return e2
	}
	return e1
}

// DumpCommands returns the whole database as a map. For use in
// testing and debugging.
func DumpCommands() (map[string]string, error) {
	db, err := bolt.Open(dirs.SnapCommandsDB, 0644, &bolt.Options{
		ReadOnly: true,
		Timeout:  1 * time.Second,
	})
	if err != nil {
		return nil, err
	}
	defer db.Close()

	tx, err := db.Begin(false)
	if err != nil {
		return nil, err
	}
	defer tx.Rollback()

	b := tx.Bucket(cmdBucketKey)
	if b == nil {
		return nil, nil
	}

	m := map[string]string{}
	c := b.Cursor()
	for k, v := c.First(); k != nil; k, v = c.Next() {
		m[string(k)] = string(v)
	}

	return m, nil
}

type boltFinder struct {
	*bolt.DB
}

// Open the database for reading.
func Open() (Finder, error) {
	// Check for missing file manually to workaround bug in bolt.
	// bolt.Open() is using os.OpenFile(.., os.O_RDONLY |
	// os.O_CREATE) even if ReadOnly mode is used. So we would get
	// a misleading "permission denied" error without this check.
	if !osutil.FileExists(dirs.SnapCommandsDB) {
		return nil, os.ErrNotExist
	}
	db, err := bolt.Open(dirs.SnapCommandsDB, 0644, &bolt.Options{
		ReadOnly: true,
		Timeout:  1 * time.Second,
	})
	if err != nil {
		return nil, err
	}

	return &boltFinder{db}, nil
}

func (f *boltFinder) FindCommand(command string) ([]Command, error) {
	tx, err := f.Begin(false)
	if err != nil {
		return nil, err
	}
	defer tx.Rollback()

	b := tx.Bucket(cmdBucketKey)
	if b == nil {
		return nil, nil
	}

	buf := b.Get([]byte(command))
	if buf == nil {
		return nil, nil
	}
	var sil []Package
	if err := json.Unmarshal(buf, &sil); err != nil {
		return nil, err
	}
	cmds := make([]Command, len(sil))
	for i, si := range sil {
		cmds[i] = Command{
			Snap:    si.Snap,
			Version: si.Version,
			Command: command,
		}
	}

	return cmds, nil
}

func (f *boltFinder) FindPackage(pkgName string) (*Package, error) {
	tx, err := f.Begin(false)
	if err != nil {
		return nil, err
	}
	defer tx.Rollback()

	b := tx.Bucket(pkgBucketKey)
	if b == nil {
		return nil, nil
	}

	bj := b.Get([]byte(pkgName))
	if bj == nil {
		return nil, nil
	}
	var si Package
	err = json.Unmarshal(bj, &si)
	if err != nil {
		return nil, err
	}

	return &Package{Snap: pkgName, Version: si.Version, Summary: si.Summary}, nil
}