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datastore_file.go
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datastore_file.go
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/*
Copyright (c) 2016-2017 VMware, Inc. All Rights Reserved.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package object
import (
"bytes"
"context"
"errors"
"fmt"
"io"
"net/http"
"os"
"path"
"sync"
"time"
"github.com/vmware/govmomi/vim25/soap"
)
// DatastoreFile implements io.Reader, io.Seeker and io.Closer interfaces for datastore file access.
type DatastoreFile struct {
d Datastore
ctx context.Context
name string
buf io.Reader
body io.ReadCloser
length int64
offset struct {
read, seek int64
}
}
// Open opens the named file relative to the Datastore.
func (d Datastore) Open(ctx context.Context, name string) (*DatastoreFile, error) {
return &DatastoreFile{
d: d,
name: name,
length: -1,
ctx: ctx,
}, nil
}
// Read reads up to len(b) bytes from the DatastoreFile.
func (f *DatastoreFile) Read(b []byte) (int, error) {
if f.offset.read != f.offset.seek {
// A Seek() call changed the offset, we need to issue a new GET
_ = f.Close()
f.offset.read = f.offset.seek
} else if f.buf != nil {
// f.buf + f behaves like an io.MultiReader
n, err := f.buf.Read(b)
if err == io.EOF {
f.buf = nil // buffer has been drained
}
if n > 0 {
return n, nil
}
}
body, err := f.get()
if err != nil {
return 0, err
}
n, err := body.Read(b)
f.offset.read += int64(n)
f.offset.seek += int64(n)
return n, err
}
// Close closes the DatastoreFile.
func (f *DatastoreFile) Close() error {
var err error
if f.body != nil {
err = f.body.Close()
f.body = nil
}
f.buf = nil
return err
}
// Seek sets the offset for the next Read on the DatastoreFile.
func (f *DatastoreFile) Seek(offset int64, whence int) (int64, error) {
switch whence {
case io.SeekStart:
case io.SeekCurrent:
offset += f.offset.seek
case io.SeekEnd:
if f.length < 0 {
_, err := f.Stat()
if err != nil {
return 0, err
}
}
offset += f.length
default:
return 0, errors.New("Seek: invalid whence")
}
// allow negative SeekStart for initial Range request
if offset < 0 {
return 0, errors.New("Seek: invalid offset")
}
f.offset.seek = offset
return offset, nil
}
type fileStat struct {
file *DatastoreFile
header http.Header
}
func (s *fileStat) Name() string {
return path.Base(s.file.name)
}
func (s *fileStat) Size() int64 {
return s.file.length
}
func (s *fileStat) Mode() os.FileMode {
return 0
}
func (s *fileStat) ModTime() time.Time {
return time.Now() // no Last-Modified
}
func (s *fileStat) IsDir() bool {
return false
}
func (s *fileStat) Sys() interface{} {
return s.header
}
func statusError(res *http.Response) error {
if res.StatusCode == http.StatusNotFound {
return os.ErrNotExist
}
return errors.New(res.Status)
}
// Stat returns the os.FileInfo interface describing file.
func (f *DatastoreFile) Stat() (os.FileInfo, error) {
// TODO: consider using Datastore.Stat() instead
u, p, err := f.d.downloadTicket(f.ctx, f.name, &soap.Download{Method: "HEAD"})
if err != nil {
return nil, err
}
res, err := f.d.Client().DownloadRequest(f.ctx, u, p)
if err != nil {
return nil, err
}
if res.StatusCode != http.StatusOK {
return nil, statusError(res)
}
f.length = res.ContentLength
return &fileStat{f, res.Header}, nil
}
func (f *DatastoreFile) get() (io.Reader, error) {
if f.body != nil {
return f.body, nil
}
u, p, err := f.d.downloadTicket(f.ctx, f.name, nil)
if err != nil {
return nil, err
}
if f.offset.read != 0 {
p.Headers = map[string]string{
"Range": fmt.Sprintf("bytes=%d-", f.offset.read),
}
}
res, err := f.d.Client().DownloadRequest(f.ctx, u, p)
if err != nil {
return nil, err
}
switch res.StatusCode {
case http.StatusOK:
f.length = res.ContentLength
case http.StatusPartialContent:
var start, end int
cr := res.Header.Get("Content-Range")
_, err = fmt.Sscanf(cr, "bytes %d-%d/%d", &start, &end, &f.length)
if err != nil {
f.length = -1
}
case http.StatusRequestedRangeNotSatisfiable:
// ok: Read() will return io.EOF
default:
return nil, statusError(res)
}
if f.length < 0 {
_ = res.Body.Close()
return nil, errors.New("unable to determine file size")
}
f.body = res.Body
return f.body, nil
}
func lastIndexLines(s []byte, line *int, include func(l int, m string) bool) (int64, bool) {
i := len(s) - 1
done := false
for i > 0 {
o := bytes.LastIndexByte(s[:i], '\n')
if o < 0 {
break
}
msg := string(s[o+1 : i+1])
if !include(*line, msg) {
done = true
break
} else {
i = o
*line++
}
}
return int64(i), done
}
// Tail seeks to the position of the last N lines of the file.
func (f *DatastoreFile) Tail(n int) error {
return f.TailFunc(n, func(line int, _ string) bool { return n > line })
}
// TailFunc will seek backwards in the datastore file until it hits a line that does
// not satisfy the supplied `include` function.
func (f *DatastoreFile) TailFunc(lines int, include func(line int, message string) bool) error {
// Read the file in reverse using bsize chunks
const bsize = int64(1024 * 16)
fsize, err := f.Seek(0, io.SeekEnd)
if err != nil {
return err
}
if lines == 0 {
return nil
}
chunk := int64(-1)
buf := bytes.NewBuffer(make([]byte, 0, bsize))
line := 0
for {
var eof bool
var pos int64
nread := bsize
offset := chunk * bsize
remain := fsize + offset
if remain < 0 {
if pos, err = f.Seek(0, io.SeekStart); err != nil {
return err
}
nread = bsize + remain
eof = true
} else if pos, err = f.Seek(offset, io.SeekEnd); err != nil {
return err
}
if _, err = io.CopyN(buf, f, nread); err != nil {
if err != io.EOF {
return err
}
}
b := buf.Bytes()
idx, done := lastIndexLines(b, &line, include)
if done {
if chunk == -1 {
// We found all N lines in the last chunk of the file.
// The seek offset is also now at the current end of file.
// Save this buffer to avoid another GET request when Read() is called.
buf.Next(int(idx + 1))
f.buf = buf
return nil
}
if _, err = f.Seek(pos+idx+1, io.SeekStart); err != nil {
return err
}
break
}
if eof {
if remain < 0 {
// We found < N lines in the entire file, so seek to the start.
_, _ = f.Seek(0, io.SeekStart)
}
break
}
chunk--
buf.Reset()
}
return nil
}
type followDatastoreFile struct {
r *DatastoreFile
c chan struct{}
i time.Duration
o sync.Once
}
// Read reads up to len(b) bytes from the DatastoreFile being followed.
// This method will block until data is read, an error other than io.EOF is returned or Close() is called.
func (f *followDatastoreFile) Read(p []byte) (int, error) {
offset := f.r.offset.seek
stop := false
for {
n, err := f.r.Read(p)
if err != nil && err == io.EOF {
_ = f.r.Close() // GET request body has been drained.
if stop {
return n, err
}
err = nil
}
if n > 0 {
return n, err
}
select {
case <-f.c:
// Wake up and stop polling once the body has been drained
stop = true
case <-time.After(f.i):
}
info, serr := f.r.Stat()
if serr != nil {
// Return EOF rather than 404 if the file goes away
if serr == os.ErrNotExist {
_ = f.r.Close()
return 0, io.EOF
}
return 0, serr
}
if info.Size() < offset {
// assume file has be truncated
offset, err = f.r.Seek(0, io.SeekStart)
if err != nil {
return 0, err
}
}
}
}
// Close will stop Follow polling and close the underlying DatastoreFile.
func (f *followDatastoreFile) Close() error {
f.o.Do(func() { close(f.c) })
return nil
}
// Follow returns an io.ReadCloser to stream the file contents as data is appended.
func (f *DatastoreFile) Follow(interval time.Duration) io.ReadCloser {
return &followDatastoreFile{
r: f,
c: make(chan struct{}),
i: interval,
}
}