tailscale/tka/tailchonk.go

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// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package tka
import (
"bytes"
"encoding/base32"
"encoding/hex"
"fmt"
"io/ioutil"
"os"
"path/filepath"
"sync"
"github.com/fxamacker/cbor/v2"
"tailscale.com/atomicfile"
)
// Chonk implementations provide durable storage for AUMs and other
// TKA state.
//
// All methods must be thread-safe.
//
// The name 'tailchonk' was coined by @catzkorn.
type Chonk interface {
// AUM returns the AUM with the specified digest.
//
// If the AUM does not exist, then os.ErrNotExist is returned.
AUM(hash AUMHash) (AUM, error)
// ChildAUMs returns all AUMs with a specified previous
// AUM hash.
ChildAUMs(prevAUMHash AUMHash) ([]AUM, error)
// CommitVerifiedAUMs durably stores the provided AUMs.
// Callers MUST ONLY provide AUMs which are verified (specifically,
// a call to aumVerify() must return a nil error).
// as the implementation assumes that only verified AUMs are stored.
CommitVerifiedAUMs(updates []AUM) error
// Heads returns AUMs for which there are no children. In other
// words, the latest AUM in all possible chains (the 'leaves').
Heads() ([]AUM, error)
// SetLastActiveAncestor is called to record the oldest-known AUM
// that contributed to the current state. This value is used as
// a hint on next startup to determine which chain to pick when computing
// the current state, if there are multiple distinct chains.
SetLastActiveAncestor(hash AUMHash) error
// LastActiveAncestor returns the oldest-known AUM that was (in a
// previous run) an ancestor of the current state. This is used
// as a hint to pick the correct chain in the event that the Chonk stores
// multiple distinct chains.
LastActiveAncestor() (*AUMHash, error)
}
// Mem implements in-memory storage of TKA state, suitable for
// tests.
//
// Mem implements the Chonk interface.
type Mem struct {
l sync.RWMutex
aums map[AUMHash]AUM
parentIndex map[AUMHash][]AUMHash
lastActiveAncestor *AUMHash
}
func (c *Mem) SetLastActiveAncestor(hash AUMHash) error {
c.l.Lock()
defer c.l.Unlock()
c.lastActiveAncestor = &hash
return nil
}
func (c *Mem) LastActiveAncestor() (*AUMHash, error) {
c.l.RLock()
defer c.l.RUnlock()
return c.lastActiveAncestor, nil
}
// Heads returns AUMs for which there are no children. In other
// words, the latest AUM in all chains (the 'leaf').
func (c *Mem) Heads() ([]AUM, error) {
c.l.RLock()
defer c.l.RUnlock()
out := make([]AUM, 0, 6)
// An AUM is a 'head' if there are no nodes for which it is the parent.
for _, a := range c.aums {
if len(c.parentIndex[a.Hash()]) == 0 {
out = append(out, a)
}
}
return out, nil
}
// AUM returns the AUM with the specified digest.
func (c *Mem) AUM(hash AUMHash) (AUM, error) {
c.l.RLock()
defer c.l.RUnlock()
aum, ok := c.aums[hash]
if !ok {
return AUM{}, os.ErrNotExist
}
return aum, nil
}
// Orphans returns all AUMs which do not have a parent.
func (c *Mem) Orphans() ([]AUM, error) {
c.l.RLock()
defer c.l.RUnlock()
out := make([]AUM, 0, 6)
for _, a := range c.aums {
if _, ok := a.Parent(); !ok {
out = append(out, a)
}
}
return out, nil
}
// ChildAUMs returns all AUMs with a specified previous
// AUM hash.
func (c *Mem) ChildAUMs(prevAUMHash AUMHash) ([]AUM, error) {
c.l.RLock()
defer c.l.RUnlock()
out := make([]AUM, 0, 6)
for _, entry := range c.parentIndex[prevAUMHash] {
out = append(out, c.aums[entry])
}
return out, nil
}
// CommitVerifiedAUMs durably stores the provided AUMs.
// Callers MUST ONLY provide well-formed and verified AUMs,
// as the rest of the TKA implementation assumes that only
// verified AUMs are stored.
func (c *Mem) CommitVerifiedAUMs(updates []AUM) error {
c.l.Lock()
defer c.l.Unlock()
if c.aums == nil {
c.parentIndex = make(map[AUMHash][]AUMHash, 64)
c.aums = make(map[AUMHash]AUM, 64)
}
updateLoop:
for _, aum := range updates {
aumHash := aum.Hash()
c.aums[aumHash] = aum
parent, ok := aum.Parent()
if ok {
for _, exists := range c.parentIndex[parent] {
if exists == aumHash {
continue updateLoop
}
}
c.parentIndex[parent] = append(c.parentIndex[parent], aumHash)
}
}
return nil
}
// FS implements filesystem storage of TKA state.
//
// FS implements the Chonk interface.
type FS struct {
base string
mu sync.RWMutex
}
// fsHashInfo describes how information about an AUMHash is represented
// on disk.
//
// The CBOR-serialization of this struct is stored to base/hex(hash[0])/base32(hash[1:])
//
// CBOR was chosen because we are already using it and it serializes
// much smaller than JSON for AUMs. The 'keyasint' thing isn't essential
// but again it saves a bunch of bytes.
type fsHashInfo struct {
Children []AUMHash `cbor:"1,keyasint"`
AUM *AUM `cbor:"2,keyasint"`
}
func (c *FS) dirPrefix(h AUMHash) string {
return filepath.Join(c.base, hex.EncodeToString(h[:1]))
}
func (c *FS) filename(h AUMHash) string {
return base32.StdEncoding.WithPadding(base32.NoPadding).EncodeToString(h[1:])
}
// AUM returns the AUM with the specified digest.
//
// If the AUM does not exist, then os.ErrNotExist is returned.
func (c *FS) AUM(hash AUMHash) (AUM, error) {
c.mu.RLock()
defer c.mu.RUnlock()
info, err := c.get(hash)
if err != nil {
return AUM{}, err
}
if info.AUM == nil {
return AUM{}, os.ErrNotExist
}
return *info.AUM, nil
}
// AUM returns any known AUMs with a specific parent hash.
func (c *FS) ChildAUMs(prevAUMHash AUMHash) ([]AUM, error) {
c.mu.RLock()
defer c.mu.RUnlock()
info, err := c.get(prevAUMHash)
if err != nil {
if os.IsNotExist(err) {
// not knowing about this hash is not an error
return nil, nil
}
return nil, err
}
out := make([]AUM, len(info.Children))
for i, h := range info.Children {
c, err := c.get(h)
if err != nil {
// We expect any AUM recorded as a child on its parent to exist.
return nil, fmt.Errorf("reading child %d of %x: %v", i, h, err)
}
if c.AUM == nil {
return nil, fmt.Errorf("child %d of %x: AUM not stored", i, h)
}
out[i] = *c.AUM
}
return out, nil
}
func (c *FS) get(h AUMHash) (*fsHashInfo, error) {
f, err := os.Open(filepath.Join(c.dirPrefix(h), c.filename(h)))
if err != nil {
return nil, err
}
defer f.Close()
var out fsHashInfo
if err := cbor.NewDecoder(f).Decode(&out); err != nil {
return nil, err
}
return &out, nil
}
// Heads returns AUMs for which there are no children. In other
// words, the latest AUM in all possible chains (the 'leaves').
//
// Heads is expected to be called infrequently compared to AUM() or
// ChildAUMs(), so we haven't put any work into maintaining an index.
// Instead, the full set of AUMs is scanned.
func (c *FS) Heads() ([]AUM, error) {
c.mu.RLock()
defer c.mu.RUnlock()
out := make([]AUM, 0, 6) // 6 is arbitrary.
err := c.scanHashes(func(info *fsHashInfo) {
if len(info.Children) == 0 && info.AUM != nil {
out = append(out, *info.AUM)
}
})
return out, err
}
func (c *FS) scanHashes(eachHashInfo func(*fsHashInfo)) error {
prefixDirs, err := os.ReadDir(c.base)
if err != nil {
return fmt.Errorf("reading prefix dirs: %v", err)
}
for _, prefix := range prefixDirs {
if !prefix.IsDir() {
continue
}
pb, err := hex.DecodeString(prefix.Name())
if err != nil || len(pb) != 1 {
return fmt.Errorf("invalid prefix directory %q: %v", prefix.Name(), err)
}
files, err := os.ReadDir(filepath.Join(c.base, prefix.Name()))
if err != nil {
return fmt.Errorf("reading prefix dir: %v", err)
}
for _, file := range files {
remainingHash, err := base32.StdEncoding.WithPadding(base32.NoPadding).DecodeString(file.Name())
if err != nil {
return fmt.Errorf("invalid aum file %s/%s: %v", prefix.Name(), file.Name(), err)
}
var h AUMHash
h[0] = pb[0]
copy(h[1:], remainingHash)
info, err := c.get(h)
if err != nil {
return fmt.Errorf("reading %x: %v", h, err)
}
eachHashInfo(info)
}
}
return nil
}
// SetLastActiveAncestor is called to record the oldest-known AUM
// that contributed to the current state. This value is used as
// a hint on next startup to determine which chain to pick when computing
// the current state, if there are multiple distinct chains.
func (c *FS) SetLastActiveAncestor(hash AUMHash) error {
c.mu.Lock()
defer c.mu.Unlock()
return atomicfile.WriteFile(filepath.Join(c.base, "last_active_ancestor"), hash[:], 0644)
}
// LastActiveAncestor returns the oldest-known AUM that was (in a
// previous run) an ancestor of the current state. This is used
// as a hint to pick the correct chain in the event that the Chonk stores
// multiple distinct chains.
//
// Nil is returned if no last-active ancestor is set.
func (c *FS) LastActiveAncestor() (*AUMHash, error) {
c.mu.RLock()
defer c.mu.RUnlock()
hash, err := ioutil.ReadFile(filepath.Join(c.base, "last_active_ancestor"))
if err != nil {
if os.IsNotExist(err) {
return nil, nil // Not exist == none set.
}
return nil, err
}
var out AUMHash
if len(hash) != len(out) {
return nil, fmt.Errorf("stored hash is of wrong length: %d != %d", len(hash), len(out))
}
copy(out[:], hash)
return &out, nil
}
// CommitVerifiedAUMs durably stores the provided AUMs.
// Callers MUST ONLY provide AUMs which are verified (specifically,
// a call to aumVerify must return a nil error), as the
// implementation assumes that only verified AUMs are stored.
func (c *FS) CommitVerifiedAUMs(updates []AUM) error {
c.mu.Lock()
defer c.mu.Unlock()
for i, aum := range updates {
h := aum.Hash()
// We keep track of children against their parent so that
// ChildAUMs() do not need to scan all AUMs.
parent, hasParent := aum.Parent()
if hasParent {
err := c.commit(parent, func(info *fsHashInfo) {
// Only add it if its not already there.
for i := range info.Children {
if info.Children[i] == h {
return
}
}
info.Children = append(info.Children, h)
})
if err != nil {
return fmt.Errorf("committing update[%d] to parent %x: %v", i, parent, err)
}
}
err := c.commit(h, func(info *fsHashInfo) {
info.AUM = &aum
})
if err != nil {
return fmt.Errorf("committing update[%d] (%x): %v", i, h, err)
}
}
return nil
}
// commit calls the provided updater function to record changes relevant
// to the given hash. The caller is expected to update the AUM and
// Children fields, as relevant.
func (c *FS) commit(h AUMHash, updater func(*fsHashInfo)) error {
toCommit := fsHashInfo{}
existing, err := c.get(h)
switch {
case os.IsNotExist(err):
case err != nil:
return err
default:
toCommit = *existing
}
updater(&toCommit)
if toCommit.AUM != nil && toCommit.AUM.Hash() != h {
return fmt.Errorf("cannot commit AUM with hash %x to %x", toCommit.AUM.Hash(), h)
}
if err := os.MkdirAll(c.dirPrefix(h), 0755); err != nil && !os.IsExist(err) {
return fmt.Errorf("creating directory: %v", err)
}
var buff bytes.Buffer
if err := cbor.NewEncoder(&buff).Encode(toCommit); err != nil {
return fmt.Errorf("encoding: %v", err)
}
return atomicfile.WriteFile(filepath.Join(c.dirPrefix(h), c.filename(h)), buff.Bytes(), 0644)
}