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writer.go
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writer.go
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// Copyright 2014 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 (
"cloud.google.com/go/internal/trace"
"context"
"errors"
"fmt"
"io"
"sync"
"time"
"unicode/utf8"
)
// A Writer writes a Cloud Storage object.
type Writer struct {
// ObjectAttrs are optional attributes to set on the object. Any attributes
// must be initialized before the first Write call. Nil or zero-valued
// attributes are ignored.
ObjectAttrs
// SendCRC32C specifies whether to transmit a CRC32C field. It should be set
// to true in addition to setting the Writer's CRC32C field, because zero
// is a valid CRC and normally a zero would not be transmitted.
// If a CRC32C is sent, and the data written does not match the checksum,
// the write will be rejected.
//
// Note: SendCRC32C must be set to true BEFORE the first call to
// Writer.Write() in order to send the checksum. If it is set after that
// point, the checksum will be ignored.
SendCRC32C bool
// ChunkSize controls the maximum number of bytes of the object that the
// Writer will attempt to send to the server in a single request. Objects
// smaller than the size will be sent in a single request, while larger
// objects will be split over multiple requests. The value will be rounded up
// to the nearest multiple of 256K. The default ChunkSize is 16MiB.
//
// Each Writer will internally allocate a buffer of size ChunkSize. This is
// used to buffer input data and allow for the input to be sent again if a
// request must be retried.
//
// If you upload small objects (< 16MiB), you should set ChunkSize
// to a value slightly larger than the objects' sizes to avoid memory bloat.
// This is especially important if you are uploading many small objects
// concurrently. See
// https://cloud.google.com/storage/docs/json_api/v1/how-tos/upload#size
// for more information about performance trade-offs related to ChunkSize.
//
// If ChunkSize is set to zero, chunking will be disabled and the object will
// be uploaded in a single request without the use of a buffer. This will
// further reduce memory used during uploads, but will also prevent the writer
// from retrying in case of a transient error from the server or resuming an
// upload that fails midway through, since the buffer is required in order to
// retry the failed request.
//
// ChunkSize must be set before the first Write call.
ChunkSize int
// ChunkRetryDeadline sets a per-chunk retry deadline for multi-chunk
// resumable uploads.
//
// For uploads of larger files, the Writer will attempt to retry if the
// request to upload a particular chunk fails with a transient error.
// If a single chunk has been attempting to upload for longer than this
// deadline and the request fails, it will no longer be retried, and the error
// will be returned to the caller. This is only applicable for files which are
// large enough to require a multi-chunk resumable upload. The default value
// is 32s. Users may want to pick a longer deadline if they are using larger
// values for ChunkSize or if they expect to have a slow or unreliable
// internet connection.
//
// To set a deadline on the entire upload, use context timeout or
// cancellation.
ChunkRetryDeadline time.Duration
// ProgressFunc can be used to monitor the progress of a large write
// operation. If ProgressFunc is not nil and writing requires multiple
// calls to the underlying service (see
// https://cloud.google.com/storage/docs/json_api/v1/how-tos/resumable-upload),
// then ProgressFunc will be invoked after each call with the number of bytes of
// content copied so far.
//
// ProgressFunc should return quickly without blocking.
ProgressFunc func(int64)
ctx context.Context
o *ObjectHandle
opened bool
pw *io.PipeWriter
donec chan struct{} // closed after err and obj are set.
obj *ObjectAttrs
mu sync.Mutex
err error
}
// Write appends to w. It implements the io.Writer interface.
//
// Since writes happen asynchronously, Write may return a nil
// error even though the write failed (or will fail). Always
// use the error returned from Writer.Close to determine if
// the upload was successful.
//
// Writes will be retried on transient errors from the server, unless
// Writer.ChunkSize has been set to zero.
func (w *Writer) Write(p []byte) (n int, err error) {
w.mu.Lock()
werr := w.err
w.mu.Unlock()
if werr != nil {
return 0, werr
}
if !w.opened {
if err := w.openWriter(); err != nil {
return 0, err
}
}
n, err = w.pw.Write(p)
if err != nil {
w.mu.Lock()
werr := w.err
w.mu.Unlock()
// Preserve existing functionality that when context is canceled, Write will return
// context.Canceled instead of "io: read/write on closed pipe". This hides the
// pipe implementation detail from users and makes Write seem as though it's an RPC.
if errors.Is(werr, context.Canceled) || errors.Is(werr, context.DeadlineExceeded) {
return n, werr
}
}
return n, err
}
// Close completes the write operation and flushes any buffered data.
// If Close doesn't return an error, metadata about the written object
// can be retrieved by calling Attrs.
func (w *Writer) Close() error {
if !w.opened {
if err := w.openWriter(); err != nil {
return err
}
}
// Closing either the read or write causes the entire pipe to close.
if err := w.pw.Close(); err != nil {
return err
}
<-w.donec
w.mu.Lock()
defer w.mu.Unlock()
trace.EndSpan(w.ctx, w.err)
return w.err
}
func (w *Writer) openWriter() (err error) {
if err := w.validateWriteAttrs(); err != nil {
return err
}
if w.o.gen != defaultGen {
return fmt.Errorf("storage: generation not supported on Writer, got %v", w.o.gen)
}
isIdempotent := w.o.conds != nil && (w.o.conds.GenerationMatch >= 0 || w.o.conds.DoesNotExist == true)
opts := makeStorageOpts(isIdempotent, w.o.retry, w.o.userProject)
params := &openWriterParams{
ctx: w.ctx,
chunkSize: w.ChunkSize,
chunkRetryDeadline: w.ChunkRetryDeadline,
bucket: w.o.bucket,
attrs: &w.ObjectAttrs,
conds: w.o.conds,
encryptionKey: w.o.encryptionKey,
sendCRC32C: w.SendCRC32C,
donec: w.donec,
setError: w.error,
progress: w.progress,
setObj: func(o *ObjectAttrs) { w.obj = o },
}
if err := w.ctx.Err(); err != nil {
return err // short-circuit
}
w.pw, err = w.o.c.tc.OpenWriter(params, opts...)
if err != nil {
return err
}
w.opened = true
go w.monitorCancel()
return nil
}
// monitorCancel is intended to be used as a background goroutine. It monitors the
// context, and when it observes that the context has been canceled, it manually
// closes things that do not take a context.
func (w *Writer) monitorCancel() {
select {
case <-w.ctx.Done():
w.mu.Lock()
werr := w.ctx.Err()
w.err = werr
w.mu.Unlock()
// Closing either the read or write causes the entire pipe to close.
w.CloseWithError(werr)
case <-w.donec:
}
}
// CloseWithError aborts the write operation with the provided error.
// CloseWithError always returns nil.
//
// Deprecated: cancel the context passed to NewWriter instead.
func (w *Writer) CloseWithError(err error) error {
if !w.opened {
return nil
}
return w.pw.CloseWithError(err)
}
// Attrs returns metadata about a successfully-written object.
// It's only valid to call it after Close returns nil.
func (w *Writer) Attrs() *ObjectAttrs {
return w.obj
}
func (w *Writer) validateWriteAttrs() error {
attrs := w.ObjectAttrs
// Check the developer didn't change the object Name (this is unfortunate, but
// we don't want to store an object under the wrong name).
if attrs.Name != w.o.object {
return fmt.Errorf("storage: Writer.Name %q does not match object name %q", attrs.Name, w.o.object)
}
if !utf8.ValidString(attrs.Name) {
return fmt.Errorf("storage: object name %q is not valid UTF-8", attrs.Name)
}
if attrs.KMSKeyName != "" && w.o.encryptionKey != nil {
return errors.New("storage: cannot use KMSKeyName with a customer-supplied encryption key")
}
if w.ChunkSize < 0 {
return errors.New("storage: Writer.ChunkSize must be non-negative")
}
return nil
}
// progress is a convenience wrapper that reports write progress to the Writer
// ProgressFunc if it is set and progress is non-zero.
func (w *Writer) progress(p int64) {
if w.ProgressFunc != nil && p != 0 {
w.ProgressFunc(p)
}
}
// error acquires the Writer's lock, sets the Writer's err to the given error,
// then relinquishes the lock.
func (w *Writer) error(err error) {
w.mu.Lock()
w.err = err
w.mu.Unlock()
}