forked from google/weasel
/
object.go
271 lines (244 loc) · 6.88 KB
/
object.go
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// Copyright 2015 Google 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 weasel
import (
"fmt"
"io/ioutil"
"net/http"
"path"
"path/filepath"
"strconv"
"strings"
"time"
"golang.org/x/net/context"
"golang.org/x/oauth2"
"golang.org/x/oauth2/google"
"google.golang.org/appengine/log"
"google.golang.org/appengine/memcache"
"google.golang.org/appengine/urlfetch"
)
const (
// defaultIndex is the trailing part of GCS object name
// when none is specified in an in-flight request.
defaultIndex = "index.html"
// object custom metadata
metaRedirect = "x-goog-meta-redirect"
metaRedirectCode = "x-goog-meta-redirect-code"
// GCS OAuth2 scopes
scopeStorageRead = "https://www.googleapis.com/auth/devstorage.read_only"
scopeStorageOwner = "https://www.googleapis.com/auth/devstorage.full_control"
)
var (
// gcsBase is the GCS base URL for fetching objects.
// defined as var for easier testing.
gcsBase = "https://storage.googleapis.com"
// objectHeaders is a slice of headers propagated from a GCS object.
objectHeaders = []string{
"cache-control",
"content-disposition",
"content-type",
"etag",
"last-modified",
}
)
// object represents a single GCS object.
type object struct {
Meta map[string]string
Body []byte
}
func (o *object) redirect() string {
return o.Meta[metaRedirect]
}
func (o *object) redirectCode() int {
c, err := strconv.Atoi(o.Meta[metaRedirectCode])
if err != nil {
c = http.StatusMovedPermanently
}
return c
}
// getFile abstracts getObject and treats object name like a file path.
func getFile(ctx context.Context, bucket, name string) (*object, error) {
if name == "" || strings.HasSuffix(name, "/") {
name += defaultIndex
}
// stat /dir/index.html if name is /dir, concurrently
var (
stat *object
statErr error
donec = make(chan struct{})
)
idxname := path.Join(name, defaultIndex)
if !strings.HasSuffix(name, defaultIndex) && filepath.Ext(name) == "" {
go func() {
stat, statErr = statObject(ctx, bucket, idxname)
close(donec)
}()
} else {
close(donec)
}
// get the original object meanwhile
o, err := getObject(ctx, bucket, name)
if err == nil {
return o, nil
}
// return non-404 errors right away
if ferr, ok := err.(*fetchError); ok && ferr.code != http.StatusNotFound {
return nil, err
}
// wait for stat obj
select {
case <-time.After(5 * time.Second):
log.Errorf(ctx, "statObject(%q, %q): timeout", bucket, idxname)
case <-donec:
// done stat-ing obj
}
if statErr != nil || stat == nil {
// it's not a "directory" either; return the original error
return nil, err
}
if stat.redirect() == "" {
stat = &object{Meta: map[string]string{
metaRedirect: "/" + idxname[:len(idxname)-len(defaultIndex)],
}}
}
return stat, nil
}
// getObject retrieves GCS object obj of the bucket from cache or network.
// Objects fetched from the network are cached before returning
// from this function.
func getObject(ctx context.Context, bucket, obj string) (*object, error) {
key := path.Join(bucket, obj)
o, err := getObjectCache(ctx, key)
if err != nil {
o, err = fetchObject(ctx, bucket, obj)
if err == nil {
putObjectCache(ctx, key, o)
}
}
return o, err
}
// statObject is similar to fetchObject except the returned object.Body
// may be nil.
func statObject(ctx context.Context, bucket, obj string) (*object, error) {
if o, err := getObjectCache(ctx, path.Join(bucket, obj)); err == nil {
return o, nil
}
u := fmt.Sprintf("%s/%s", gcsBase, path.Join(bucket, obj))
req, err := http.NewRequest("HEAD", u, nil)
if err != nil {
return nil, err
}
res, err := httpClient(ctx, scopeStorageRead).Do(req)
if err != nil {
return nil, err
}
defer res.Body.Close()
if res.StatusCode != http.StatusOK {
b, _ := ioutil.ReadAll(res.Body)
return nil, &fetchError{
msg: fmt.Sprintf("%s: %s", res.Status, b),
code: res.StatusCode,
}
}
meta := make(map[string]string)
for _, k := range objectHeaders {
if v := res.Header.Get(k); v != "" {
meta[k] = v
}
}
return &object{Meta: meta}, nil
}
// fetchObject retrieves object obj from the given GCS bucket.
// The returned error will be of type fetchError if the storage responds
// with an error code.
func fetchObject(ctx context.Context, bucket, obj string) (*object, error) {
u := fmt.Sprintf("%s/%s", gcsBase, path.Join(bucket, obj))
req, err := http.NewRequest("GET", u, nil)
if err != nil {
return nil, err
}
res, err := httpClient(ctx, scopeStorageRead).Do(req)
if err != nil {
return nil, err
}
defer res.Body.Close()
// error status code takes precedence over i/o errors
b, err := ioutil.ReadAll(res.Body)
if res.StatusCode > 399 {
return nil, &fetchError{
msg: fmt.Sprintf("%s: %s", res.Status, b),
code: res.StatusCode,
}
}
if err != nil { // i/o error
return nil, err
}
o := &object{
Body: b,
Meta: make(map[string]string),
}
for _, k := range objectHeaders {
if v := res.Header.Get(k); v != "" {
o.Meta[k] = v
}
}
return o, nil
}
// getObjectCache returns an object previously cached with the key.
func getObjectCache(ctx context.Context, key string) (*object, error) {
o := &object{}
_, err := memcache.Gob.Get(ctx, key, o)
if err != nil && err != memcache.ErrCacheMiss {
log.Errorf(ctx, "memcache.Gob.Get(%q): %v", key, err)
}
return o, err
}
// putObjectCache updates or creates cached copy of o with the key.
func putObjectCache(ctx context.Context, key string, o *object) error {
item := memcache.Item{
Key: key,
Object: o,
Expiration: 24 * time.Hour,
}
err := memcache.Gob.Set(ctx, &item)
if err != nil {
log.Errorf(ctx, "memcache.Gob.Set(%q): %v", key, err)
}
return err
}
// removeObjectCache removes cached object from memcache.
// It returns nil in case where memcache.Delete would result in ErrCacheMiss.
func removeObjectCache(ctx context.Context, bucket, obj string) error {
k := path.Join(bucket, obj)
err := memcache.Delete(ctx, k)
if err == memcache.ErrCacheMiss {
err = nil
}
return err
}
// httpClient returns an authenticated http client, suitable for App Engine.
func httpClient(c context.Context, scopes ...string) *http.Client {
t := &oauth2.Transport{
Source: google.AppEngineTokenSource(c, scopes...),
Base: &urlfetch.Transport{Context: c},
}
return &http.Client{Transport: t}
}
type fetchError struct {
msg string
code int
}
func (e *fetchError) Error() string {
return fmt.Sprintf("fetchError %d: %s", e.code, e.msg)
}