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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package gensupport
import (
"bytes"
"io"
"google.golang.org/api/googleapi"
)
// MediaBuffer buffers data from an io.Reader to support uploading media in retryable chunks.
type MediaBuffer struct {
media io.Reader
chunk []byte // The current chunk which is pending upload. The capacity is the chunk size.
err error // Any error generated when populating chunk by reading media.
// The absolute position of chunk in the underlying media.
off int64
}
func NewMediaBuffer(media io.Reader, chunkSize int) *MediaBuffer {
return &MediaBuffer{media: media, chunk: make([]byte, 0, chunkSize)}
}
// Chunk returns the current buffered chunk, the offset in the underlying media
// from which the chunk is drawn, and the size of the chunk.
// Successive calls to Chunk return the same chunk between calls to Next.
func (mb *MediaBuffer) Chunk() (chunk io.Reader, off int64, size int, err error) {
// There may already be data in chunk if Next has not been called since the previous call to Chunk.
if mb.err == nil && len(mb.chunk) == 0 {
mb.err = mb.loadChunk()
}
return bytes.NewReader(mb.chunk), mb.off, len(mb.chunk), mb.err
}
// loadChunk will read from media into chunk, up to the capacity of chunk.
func (mb *MediaBuffer) loadChunk() error {
bufSize := cap(mb.chunk)
mb.chunk = mb.chunk[:bufSize]
read := 0
var err error
for err == nil && read < bufSize {
var n int
n, err = mb.media.Read(mb.chunk[read:])
read += n
}
mb.chunk = mb.chunk[:read]
return err
}
// Next advances to the next chunk, which will be returned by the next call to Chunk.
// Calls to Next without a corresponding prior call to Chunk will have no effect.
func (mb *MediaBuffer) Next() {
mb.off += int64(len(mb.chunk))
mb.chunk = mb.chunk[0:0]
}
type readerTyper struct {
io.Reader
googleapi.ContentTyper
}
// ReaderAtToReader adapts a ReaderAt to be used as a Reader.
// If ra implements googleapi.ContentTyper, then the returned reader
// will also implement googleapi.ContentTyper, delegating to ra.
func ReaderAtToReader(ra io.ReaderAt, size int64) io.Reader {
r := io.NewSectionReader(ra, 0, size)
if typer, ok := ra.(googleapi.ContentTyper); ok {
return readerTyper{r, typer}
}
return r
}
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