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object.go
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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 (
"bytes"
"context"
"io"
"net/http"
"strconv"
"time"
"google.golang.org/appengine/log"
"google.golang.org/appengine/memcache"
)
const (
// object custom metadata
metaRedirect = "x-goog-meta-redirect"
metaRedirectCode = "x-goog-meta-redirect-code"
// memcache settings
cacheItemMax = 1 << 20 // max size per item, in bytes
cacheItemExpiry = 24 * time.Hour
)
// objectHeaders is a slice of headers propagated from a GCS object.
var objectHeaders = []string{
"cache-control",
"content-disposition",
"content-type",
"etag",
"last-modified",
metaRedirect,
metaRedirectCode,
}
// Object represents a single GCS object.
type Object struct {
Meta map[string]string
Body io.ReadCloser
}
// Redirect returns o's redirect URL, zero string otherwise.
func (o *Object) Redirect() string {
return o.Meta[metaRedirect]
}
// RedirectCode returns o's HTTP response code for redirect.
// It defaults to http.StatusMovedPermanently.
func (o *Object) RedirectCode() int {
c, err := strconv.Atoi(o.Meta[metaRedirectCode])
if err != nil {
c = http.StatusMovedPermanently
}
return c
}
// objectBuf implements io.ReadCloser for Object.Body.
// It stores all r.Read results in its buf and caches exported fields
// in memcache when Read returns io.EOF.
type objectBuf struct {
Meta map[string]string
Body []byte // set after rc returns io.EOF
r io.Reader
buf bytes.Buffer
key string // cache key
ctx context.Context // memcache context
}
func (b *objectBuf) Read(p []byte) (int, error) {
n, err := b.r.Read(p)
if n > 0 && b.buf.Len() < cacheItemMax {
b.buf.Write(p[:n])
}
if err == io.EOF && b.buf.Len() < cacheItemMax {
b.Body = b.buf.Bytes()
item := memcache.Item{
Key: b.key,
Object: b,
Expiration: cacheItemExpiry,
}
if err := memcache.Gob.Set(b.ctx, &item); err != nil {
log.Errorf(b.ctx, "memcache.Gob.Set(%q): %v", b.key, err)
}
}
return n, err
}
func (b *objectBuf) Close() error {
if c, ok := b.r.(io.Closer); ok {
return c.Close()
}
return nil
}