// Copyright 2016 Google LLC
//
// 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 storage
import (
"context"
"errors"
"fmt"
"hash/crc32"
"io"
"io/ioutil"
"net/http"
"net/url"
"reflect"
"strconv"
"strings"
"time"
"cloud.google.com/go/internal/trace"
"google.golang.org/api/googleapi"
)
var crc32cTable = crc32.MakeTable(crc32.Castagnoli)
// ReaderObjectAttrs are attributes about the object being read. These are populated
// during the New call. This struct only holds a subset of object attributes: to
// get the full set of attributes, use ObjectHandle.Attrs.
//
// Each field is read-only.
type ReaderObjectAttrs struct {
// Size is the length of the object's content.
Size int64
// ContentType is the MIME type of the object's content.
ContentType string
// ContentEncoding is the encoding of the object's content.
ContentEncoding string
// CacheControl specifies whether and for how long browser and Internet
// caches are allowed to cache your objects.
CacheControl string
// LastModified is the time that the object was last modified.
LastModified time.Time
// Generation is the generation number of the object's content.
Generation int64
// Metageneration is the version of the metadata for this object at
// this generation. This field is used for preconditions and for
// detecting changes in metadata. A metageneration number is only
// meaningful in the context of a particular generation of a
// particular object.
Metageneration int64
}
// NewReader creates a new Reader to read the contents of the
// object.
// ErrObjectNotExist will be returned if the object is not found.
//
// The caller must call Close on the returned Reader when done reading.
func (o *ObjectHandle) NewReader(ctx context.Context) (*Reader, error) {
return o.NewRangeReader(ctx, 0, -1)
}
// NewRangeReader reads part of an object, reading at most length bytes
// starting at the given offset. If length is negative, the object is read
// until the end.
func (o *ObjectHandle) NewRangeReader(ctx context.Context, offset, length int64) (r *Reader, err error) {
ctx = trace.StartSpan(ctx, "cloud.google.com/go/storage.Object.NewRangeReader")
defer func() { trace.EndSpan(ctx, err) }()
if err := o.validate(); err != nil {
return nil, err
}
if offset < 0 {
return nil, fmt.Errorf("storage: invalid offset %d < 0", offset)
}
if o.conds != nil {
if err := o.conds.validate("NewRangeReader"); err != nil {
return nil, err
}
}
u := &url.URL{
Scheme: "https",
Host: "storage.googleapis.com",
Path: fmt.Sprintf("/%s/%s", o.bucket, o.object),
}
verb := "GET"
if length == 0 {
verb = "HEAD"
}
req, err := http.NewRequest(verb, u.String(), nil)
if err != nil {
return nil, err
}
req = req.WithContext(ctx)
if o.userProject != "" {
req.Header.Set("X-Goog-User-Project", o.userProject)
}
if o.readCompressed {
req.Header.Set("Accept-Encoding", "gzip")
}
if err := setEncryptionHeaders(req.Header, o.encryptionKey, false); err != nil {
return nil, err
}
gen := o.gen
// Define a function that initiates a Read with offset and length, assuming we
// have already read seen bytes.
reopen := func(seen int64) (*http.Response, error) {
start := offset + seen
if length < 0 && start > 0 {
req.Header.Set("Range", fmt.Sprintf("bytes=%d-", start))
} else if length > 0 {
// The end character isn't affected by how many bytes we've seen.
req.Header.Set("Range", fmt.Sprintf("bytes=%d-%d", start, offset+length-1))
}
// We wait to assign conditions here because the generation number can change in between reopen() runs.
req.URL.RawQuery = conditionsQuery(gen, o.conds)
var res *http.Response
err = runWithRetry(ctx, func() error {
res, err = o.c.hc.Do(req)
if err != nil {
return err
}
if res.StatusCode == http.StatusNotFound {
res.Body.Close()
return ErrObjectNotExist
}
if res.StatusCode < 200 || res.StatusCode > 299 {
body, _ := ioutil.ReadAll(res.Body)
res.Body.Close()
return &googleapi.Error{
Code: res.StatusCode,
Header: res.Header,
Body: string(body),
}
}
if start > 0 && length != 0 && res.StatusCode != http.StatusPartialContent {
res.Body.Close()
return errors.New("storage: partial request not satisfied")
}
// If a generation hasn't been specified, and this is the first response we get, let's record the
// generation. In future requests we'll use this generation as a precondition to avoid data races.
if gen < 0 && res.Header.Get("X-Goog-Generation") != "" {
gen64, err := strconv.ParseInt(res.Header.Get("X-Goog-Generation"), 10, 64)
if err != nil {
return err
}
gen = gen64
}
return nil
})
if err != nil {
return nil, err
}
return res, nil
}
res, err := reopen(0)
if err != nil {
return nil, err
}
var (
size int64 // total size of object, even if a range was requested.
checkCRC bool
crc uint32
)
if res.StatusCode == http.StatusPartialContent {
cr := strings.TrimSpace(res.Header.Get("Content-Range"))
if !strings.HasPrefix(cr, "bytes ") || !strings.Contains(cr, "/") {
return nil, fmt.Errorf("storage: invalid Content-Range %q", cr)
}
size, err = strconv.ParseInt(cr[strings.LastIndex(cr, "/")+1:], 10, 64)
if err != nil {
return nil, fmt.Errorf("storage: invalid Content-Range %q", cr)
}
} else {
size = res.ContentLength
// Check the CRC iff all of the following hold:
// - We asked for content (length != 0).
// - We got all the content (status != PartialContent).
// - The server sent a CRC header.
// - The Go http stack did not uncompress the file.
// - We were not served compressed data that was uncompressed on download.
// The problem with the last two cases is that the CRC will not match -- GCS
// computes it on the compressed contents, but we compute it on the
// uncompressed contents.
if length != 0 && !res.Uncompressed && !uncompressedByServer(res) {
crc, checkCRC = parseCRC32c(res)
}
}
remain := res.ContentLength
body := res.Body
if length == 0 {
remain = 0
body.Close()
body = emptyBody
}
var metaGen int64
if res.Header.Get("X-Goog-Generation") != "" {
metaGen, err = strconv.ParseInt(res.Header.Get("X-Goog-Metageneration"), 10, 64)
if err != nil {
return nil, err
}
}
var lm time.Time
if res.Header.Get("Last-Modified") != "" {
lm, err = http.ParseTime(res.Header.Get("Last-Modified"))
if err != nil {
return nil, err
}
}
attrs := ReaderObjectAttrs{
Size: size,
ContentType: res.Header.Get("Content-Type"),
ContentEncoding: res.Header.Get("Content-Encoding"),
CacheControl: res.Header.Get("Cache-Control"),
LastModified: lm,
Generation: gen,
Metageneration: metaGen,
}
return &Reader{
Attrs: attrs,
body: body,
size: size,
remain: remain,
wantCRC: crc,
checkCRC: checkCRC,
reopen: reopen,
}, nil
}
func uncompressedByServer(res *http.Response) bool {
// If the data is stored as gzip but is not encoded as gzip, then it
// was uncompressed by the server.
return res.Header.Get("X-Goog-Stored-Content-Encoding") == "gzip" &&
res.Header.Get("Content-Encoding") != "gzip"
}
func parseCRC32c(res *http.Response) (uint32, bool) {
const prefix = "crc32c="
for _, spec := range res.Header["X-Goog-Hash"] {
if strings.HasPrefix(spec, prefix) {
c, err := decodeUint32(spec[len(prefix):])
if err == nil {
return c, true
}
}
}
return 0, false
}
var emptyBody = ioutil.NopCloser(strings.NewReader(""))
// Reader reads a Cloud Storage object.
// It implements io.Reader.
//
// Typically, a Reader computes the CRC of the downloaded content and compares it to
// the stored CRC, returning an error from Read if there is a mismatch. This integrity check
// is skipped if transcoding occurs. See https://cloud.google.com/storage/docs/transcoding.
type Reader struct {
Attrs ReaderObjectAttrs
body io.ReadCloser
seen, remain, size int64
checkCRC bool // should we check the CRC?
wantCRC uint32 // the CRC32c value the server sent in the header
gotCRC uint32 // running crc
reopen func(seen int64) (*http.Response, error)
}
// Close closes the Reader. It must be called when done reading.
func (r *Reader) Close() error {
return r.body.Close()
}
func (r *Reader) Read(p []byte) (int, error) {
n, err := r.readWithRetry(p)
if r.remain != -1 {
r.remain -= int64(n)
}
if r.checkCRC {
r.gotCRC = crc32.Update(r.gotCRC, crc32cTable, p[:n])
// Check CRC here. It would be natural to check it in Close, but
// everybody defers Close on the assumption that it doesn't return
// anything worth looking at.
if err == io.EOF {
if r.gotCRC != r.wantCRC {
return n, fmt.Errorf("storage: bad CRC on read: got %d, want %d",
r.gotCRC, r.wantCRC)
}
}
}
return n, err
}
func (r *Reader) readWithRetry(p []byte) (int, error) {
n := 0
for len(p[n:]) > 0 {
m, err := r.body.Read(p[n:])
n += m
r.seen += int64(m)
if !shouldRetryRead(err) {
return n, err
}
// Read failed, but we will try again. Send a ranged read request that takes
// into account the number of bytes we've already seen.
res, err := r.reopen(r.seen)
if err != nil {
// reopen already retries
return n, err
}
r.body.Close()
r.body = res.Body
}
return n, nil
}
func shouldRetryRead(err error) bool {
if err == nil {
return false
}
return strings.HasSuffix(err.Error(), "INTERNAL_ERROR") && strings.Contains(reflect.TypeOf(err).String(), "http2")
}
// Size returns the size of the object in bytes.
// The returned value is always the same and is not affected by
// calls to Read or Close.
//
// Deprecated: use Reader.Attrs.Size.
func (r *Reader) Size() int64 {
return r.Attrs.Size
}
// Remain returns the number of bytes left to read, or -1 if unknown.
func (r *Reader) Remain() int64 {
return r.remain
}
// ContentType returns the content type of the object.
//
// Deprecated: use Reader.Attrs.ContentType.
func (r *Reader) ContentType() string {
return r.Attrs.ContentType
}
// ContentEncoding returns the content encoding of the object.
//
// Deprecated: use Reader.Attrs.ContentEncoding.
func (r *Reader) ContentEncoding() string {
return r.Attrs.ContentEncoding
}
// CacheControl returns the cache control of the object.
//
// Deprecated: use Reader.Attrs.CacheControl.
func (r *Reader) CacheControl() string {
return r.Attrs.CacheControl
}
// LastModified returns the value of the Last-Modified header.
//
// Deprecated: use Reader.Attrs.LastModified.
func (r *Reader) LastModified() (time.Time, error) {
return r.Attrs.LastModified, nil
}
