syncthing/lib/fs/fakefs.go

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// Copyright (C) 2018 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.
package fs
import (
"context"
"errors"
"fmt"
"hash/fnv"
"io"
"io/ioutil"
"math/rand"
"net/url"
"os"
"path/filepath"
"strconv"
"strings"
"sync"
"time"
)
// see readShortAt()
const randomBlockShift = 14 // 128k
// fakefs is a fake filesystem for testing and benchmarking. It has the
// following properties:
//
// - File metadata is kept in RAM. Specifically, we remember which files and
// directories exist, their dates, permissions and sizes. Symlinks are
// not supported.
//
// - File contents are generated pseudorandomly with just the file name as
// seed. Writes are discarded, other than having the effect of increasing
// the file size. If you only write data that you've read from a file with
// the same name on a different fakefs, you'll never know the difference...
//
// - We totally ignore permissions - pretend you are root.
//
// - The root path can contain URL query-style parameters that pre populate
// the filesystem at creation with a certain amount of random data:
//
// files=n to generate n random files (default 0)
// maxsize=n to generate files up to a total of n MiB (default 0)
// sizeavg=n to set the average size of random files, in bytes (default 1<<20)
// seed=n to set the initial random seed (default 0)
//
// - Two fakefs:s pointing at the same root path see the same files.
//
type fakefs struct {
mut sync.Mutex
root *fakeEntry
}
var (
fakefsMut sync.Mutex
fakefsFs = make(map[string]*fakefs)
)
func newFakeFilesystem(root string) *fakefs {
fakefsMut.Lock()
defer fakefsMut.Unlock()
var params url.Values
uri, err := url.Parse(root)
if err == nil {
root = uri.Path
params = uri.Query()
}
if fs, ok := fakefsFs[root]; ok {
// Already have an fs at this path
return fs
}
fs := &fakefs{
root: &fakeEntry{
name: "/",
isdir: true,
mode: 0700,
mtime: time.Now(),
children: make(map[string]*fakeEntry),
},
}
files, _ := strconv.Atoi(params.Get("files"))
maxsize, _ := strconv.Atoi(params.Get("maxsize"))
sizeavg, _ := strconv.Atoi(params.Get("sizeavg"))
seed, _ := strconv.Atoi(params.Get("seed"))
if sizeavg == 0 {
sizeavg = 1 << 20
}
if files > 0 || maxsize > 0 {
// Generate initial data according to specs. Operations in here
// *look* like file I/O, but they are not. Do not worry that they
// might fail.
rng := rand.New(rand.NewSource(int64(seed)))
var createdFiles int
var writtenData int64
for (files == 0 || createdFiles < files) && (maxsize == 0 || writtenData>>20 < int64(maxsize)) {
dir := filepath.Join(fmt.Sprintf("%02x", rng.Intn(255)), fmt.Sprintf("%02x", rng.Intn(255)))
file := fmt.Sprintf("%016x", rng.Int63())
fs.MkdirAll(dir, 0755)
fd, _ := fs.Create(filepath.Join(dir, file))
createdFiles++
fsize := int64(sizeavg/2 + rng.Intn(sizeavg))
fd.Truncate(fsize)
writtenData += fsize
ftime := time.Unix(1000000000+rng.Int63n(10*365*86400), 0)
fs.Chtimes(filepath.Join(dir, file), ftime, ftime)
}
}
// Also create a default folder marker for good measure
fs.Mkdir(".stfolder", 0700)
fakefsFs[root] = fs
return fs
}
// fakeEntry is an entry (file or directory) in the fake filesystem
type fakeEntry struct {
name string
isdir bool
size int64
mode FileMode
mtime time.Time
children map[string]*fakeEntry
}
func (fs *fakefs) entryForName(name string) *fakeEntry {
name = filepath.ToSlash(name)
if name == "." || name == "/" {
return fs.root
}
name = strings.Trim(name, "/")
comps := strings.Split(name, "/")
entry := fs.root
for _, comp := range comps {
var ok bool
entry, ok = entry.children[comp]
if !ok {
return nil
}
}
return entry
}
func (fs *fakefs) Chmod(name string, mode FileMode) error {
fs.mut.Lock()
defer fs.mut.Unlock()
entry := fs.entryForName(name)
if entry == nil {
return os.ErrNotExist
}
entry.mode = mode
return nil
}
func (fs *fakefs) Chtimes(name string, atime time.Time, mtime time.Time) error {
fs.mut.Lock()
defer fs.mut.Unlock()
entry := fs.entryForName(name)
if entry == nil {
return os.ErrNotExist
}
entry.mtime = mtime
return nil
}
func (fs *fakefs) Create(name string) (File, error) {
fs.mut.Lock()
defer fs.mut.Unlock()
if entry := fs.entryForName(name); entry != nil {
if entry.isdir {
return nil, os.ErrExist
}
entry.size = 0
entry.mtime = time.Now()
entry.mode = 0666
return &fakeFile{fakeEntry: entry}, nil
}
dir := filepath.Dir(name)
base := filepath.Base(name)
entry := fs.entryForName(dir)
if entry == nil {
return nil, os.ErrNotExist
}
new := &fakeEntry{
name: base,
mode: 0666,
mtime: time.Now(),
}
entry.children[base] = new
return &fakeFile{fakeEntry: new}, nil
}
func (fs *fakefs) CreateSymlink(target, name string) error {
return errors.New("not implemented")
}
func (fs *fakefs) DirNames(name string) ([]string, error) {
fs.mut.Lock()
defer fs.mut.Unlock()
entry := fs.entryForName(name)
if entry == nil {
return nil, os.ErrNotExist
}
names := make([]string, 0, len(entry.children))
for name := range entry.children {
names = append(names, name)
}
return names, nil
}
func (fs *fakefs) Lstat(name string) (FileInfo, error) {
fs.mut.Lock()
defer fs.mut.Unlock()
entry := fs.entryForName(name)
if entry == nil {
return nil, os.ErrNotExist
}
return &fakeFileInfo{*entry}, nil
}
func (fs *fakefs) Mkdir(name string, perm FileMode) error {
fs.mut.Lock()
defer fs.mut.Unlock()
dir := filepath.Dir(name)
base := filepath.Base(name)
entry := fs.entryForName(dir)
if entry == nil {
return os.ErrNotExist
}
if _, ok := entry.children[base]; ok {
return os.ErrExist
}
entry.children[base] = &fakeEntry{
name: base,
isdir: true,
mode: perm,
mtime: time.Now(),
children: make(map[string]*fakeEntry),
}
return nil
}
func (fs *fakefs) MkdirAll(name string, perm FileMode) error {
name = filepath.ToSlash(name)
name = strings.Trim(name, "/")
comps := strings.Split(name, "/")
entry := fs.root
for _, comp := range comps {
next, ok := entry.children[comp]
if !ok {
new := &fakeEntry{
name: comp,
isdir: true,
mode: perm,
mtime: time.Now(),
children: make(map[string]*fakeEntry),
}
entry.children[comp] = new
next = new
} else if !next.isdir {
return errors.New("not a directory")
}
entry = next
}
return nil
}
func (fs *fakefs) Open(name string) (File, error) {
fs.mut.Lock()
defer fs.mut.Unlock()
entry := fs.entryForName(name)
if entry == nil {
return nil, os.ErrNotExist
}
return &fakeFile{fakeEntry: entry}, nil
}
func (fs *fakefs) OpenFile(name string, flags int, mode FileMode) (File, error) {
fs.mut.Lock()
defer fs.mut.Unlock()
if flags&os.O_CREATE == 0 {
return fs.Open(name)
}
dir := filepath.Dir(name)
base := filepath.Base(name)
entry := fs.entryForName(dir)
if entry == nil {
return nil, os.ErrNotExist
}
if flags&os.O_EXCL != 0 {
if _, ok := entry.children[base]; ok {
return nil, os.ErrExist
}
}
newEntry := &fakeEntry{
name: base,
mode: mode,
mtime: time.Now(),
}
entry.children[base] = newEntry
return &fakeFile{fakeEntry: newEntry}, nil
}
func (fs *fakefs) ReadSymlink(name string) (string, error) {
return "", errors.New("not implemented")
}
func (fs *fakefs) Remove(name string) error {
fs.mut.Lock()
defer fs.mut.Unlock()
entry := fs.entryForName(name)
if entry == nil {
return os.ErrNotExist
}
if len(entry.children) != 0 {
return errors.New("not empty")
}
entry = fs.entryForName(filepath.Dir(name))
delete(entry.children, filepath.Base(name))
return nil
}
func (fs *fakefs) RemoveAll(name string) error {
fs.mut.Lock()
defer fs.mut.Unlock()
entry := fs.entryForName(filepath.Dir(name))
if entry == nil {
return os.ErrNotExist
}
// RemoveAll is easy when the file system uses garbage collection under
// the hood... We even get the correct semantics for open fd:s for free.
delete(entry.children, filepath.Base(name))
return nil
}
func (fs *fakefs) Rename(oldname, newname string) error {
fs.mut.Lock()
defer fs.mut.Unlock()
p0 := fs.entryForName(filepath.Dir(oldname))
if p0 == nil {
return os.ErrNotExist
}
entry := p0.children[filepath.Base(oldname)]
if entry == nil {
return os.ErrNotExist
}
p1 := fs.entryForName(filepath.Dir(newname))
if p1 == nil {
return os.ErrNotExist
}
dst, ok := p1.children[filepath.Base(newname)]
if ok && dst.isdir {
return errors.New("is a directory")
}
p1.children[filepath.Base(newname)] = entry
delete(p0.children, filepath.Base(oldname))
return nil
}
func (fs *fakefs) Stat(name string) (FileInfo, error) {
return fs.Lstat(name)
}
func (fs *fakefs) SymlinksSupported() bool {
return false
}
func (fs *fakefs) Walk(name string, walkFn WalkFunc) error {
return errors.New("not implemented")
}
func (fs *fakefs) Watch(path string, ignore Matcher, ctx context.Context, ignorePerms bool) (<-chan Event, error) {
return nil, ErrWatchNotSupported
}
func (fs *fakefs) Hide(name string) error {
return nil
}
func (fs *fakefs) Unhide(name string) error {
return nil
}
func (fs *fakefs) Glob(pattern string) ([]string, error) {
// gnnh we don't seem to actually require this in practice
return nil, errors.New("not implemented")
}
func (fs *fakefs) Roots() ([]string, error) {
return []string{"/"}, nil
}
func (fs *fakefs) Usage(name string) (Usage, error) {
return Usage{}, errors.New("not implemented")
}
func (fs *fakefs) Type() FilesystemType {
return FilesystemTypeFake
}
func (fs *fakefs) URI() string {
return "fake://" + fs.root.name
}
func (fs *fakefs) SameFile(fi1, fi2 FileInfo) bool {
return fi1.Name() == fi1.Name()
}
// fakeFile is the representation of an open file. We don't care if it's
// opened for reading or writing, it's all good.
type fakeFile struct {
*fakeEntry
mut sync.Mutex
rng io.Reader
seed int64
offset int64
seedOffs int64
}
func (f *fakeFile) Close() error {
return nil
}
func (f *fakeFile) Read(p []byte) (int, error) {
f.mut.Lock()
defer f.mut.Unlock()
return f.readShortAt(p, f.offset)
}
func (f *fakeFile) ReadAt(p []byte, offs int64) (int, error) {
f.mut.Lock()
defer f.mut.Unlock()
// ReadAt is spec:ed to always read a full block unless EOF or failure,
// so we must loop. It's also not supposed to affect the seek position,
// but that would make things annoying or inefficient in terms of
// generating the appropriate RNG etc so I ignore that. In practice we
// currently don't depend on that aspect of it...
var read int
for {
n, err := f.readShortAt(p[read:], offs+int64(read))
read += n
if err != nil {
return read, err
}
if read == len(p) {
return read, nil
}
}
}
func (f *fakeFile) readShortAt(p []byte, offs int64) (int, error) {
// Here be a certain amount of magic... We want to return pseudorandom,
// predictable data so that a read from the same offset in the same file
// always returns the same data. But the RNG is a stream, and reads can
// be random.
//
// We split the file into "blocks" numbered by "seedNo", where each
// block becomes an instantiation of the RNG, seeded with the hash of
// the file number plus the seedNo (block number). We keep the RNG
// around in the hope that the next read will be sequential to this one
// and we can continue reading from the same RNG.
//
// When that's not the case we create a new RNG for the block we are in,
// read as many bytes from it as necessary to get to the right offset,
// and then serve the read from there. We limit the length of the read
// to the end of the block, as another RNG needs to be created to serve
// the next block.
//
// The size of the blocks are a matter of taste... Larger blocks give
// better performance for sequential reads, but worse for random reads
// as we often need to generate and throw away a lot of data at the
// start of the block to serve a given read. 128 KiB blocks fit
// reasonably well with the type of IO Syncthing tends to do.
if f.isdir {
return 0, errors.New("is a directory")
}
if offs >= f.size {
return 0, io.EOF
}
// Lazily calculate our main seed, a simple 64 bit FNV hash our file
// name.
if f.seed == 0 {
hf := fnv.New64()
hf.Write([]byte(f.name))
f.seed = int64(hf.Sum64())
}
// Check whether the read is a continuation of an RNG we already have or
// we need to set up a new one.
seedNo := offs >> randomBlockShift
minOffs := seedNo << randomBlockShift
nextBlockOffs := (seedNo + 1) << randomBlockShift
if f.rng == nil || f.offset != offs || seedNo != f.seedOffs {
// This is not a straight read continuing from a previous one
f.rng = rand.New(rand.NewSource(f.seed + seedNo))
// If the read is not at the start of the block, discard data
// accordingly.
diff := offs - minOffs
if diff > 0 {
lr := io.LimitReader(f.rng, diff)
io.Copy(ioutil.Discard, lr)
}
f.offset = offs
f.seedOffs = seedNo
}
size := len(p)
// Don't read past the end of the file
if offs+int64(size) > f.size {
size = int(f.size - offs)
}
// Don't read across the block boundary
if offs+int64(size) > nextBlockOffs {
size = int(nextBlockOffs - offs)
}
f.offset += int64(size)
return f.rng.Read(p[:size])
}
func (f *fakeFile) Seek(offset int64, whence int) (int64, error) {
f.mut.Lock()
defer f.mut.Unlock()
if f.isdir {
return 0, errors.New("is a directory")
}
f.rng = nil
switch whence {
case io.SeekCurrent:
f.offset += offset
case io.SeekEnd:
f.offset = f.size - offset
case io.SeekStart:
f.offset = offset
}
if f.offset < 0 {
f.offset = 0
return f.offset, errors.New("seek before start")
}
if f.offset > f.size {
f.offset = f.size
return f.offset, io.EOF
}
return f.offset, nil
}
func (f *fakeFile) Write(p []byte) (int, error) {
return f.WriteAt(p, f.offset)
}
func (f *fakeFile) WriteAt(p []byte, off int64) (int, error) {
f.mut.Lock()
defer f.mut.Unlock()
if f.isdir {
return 0, errors.New("is a directory")
}
f.rng = nil
f.offset = off + int64(len(p))
if f.offset > f.size {
f.size = f.offset
}
return len(p), nil
}
func (f *fakeFile) Name() string {
return f.name
}
func (f *fakeFile) Truncate(size int64) error {
f.mut.Lock()
defer f.mut.Unlock()
f.rng = nil
f.size = size
if f.offset > size {
f.offset = size
}
return nil
}
func (f *fakeFile) Stat() (FileInfo, error) {
return &fakeFileInfo{*f.fakeEntry}, nil
}
func (f *fakeFile) Sync() error {
return nil
}
// fakeFileInfo is the stat result.
type fakeFileInfo struct {
fakeEntry // intentionally a copy of the struct
}
func (f *fakeFileInfo) Name() string {
return f.name
}
func (f *fakeFileInfo) Mode() FileMode {
return f.mode
}
func (f *fakeFileInfo) Size() int64 {
return f.size
}
func (f *fakeFileInfo) ModTime() time.Time {
return f.mtime
}
func (f *fakeFileInfo) IsDir() bool {
return f.isdir
}
func (f *fakeFileInfo) IsRegular() bool {
return !f.isdir
}
func (f *fakeFileInfo) IsSymlink() bool {
return false
}