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