1// Copyright 2016 The Go Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style 3// license that can be found in the LICENSE file. 4 5package gensupport 6 7import ( 8 "bytes" 9 "io" 10 11 "google.golang.org/api/googleapi" 12) 13 14// MediaBuffer buffers data from an io.Reader to support uploading media in retryable chunks. 15type MediaBuffer struct { 16 media io.Reader 17 18 chunk []byte // The current chunk which is pending upload. The capacity is the chunk size. 19 err error // Any error generated when populating chunk by reading media. 20 21 // The absolute position of chunk in the underlying media. 22 off int64 23} 24 25func NewMediaBuffer(media io.Reader, chunkSize int) *MediaBuffer { 26 return &MediaBuffer{media: media, chunk: make([]byte, 0, chunkSize)} 27} 28 29// Chunk returns the current buffered chunk, the offset in the underlying media 30// from which the chunk is drawn, and the size of the chunk. 31// Successive calls to Chunk return the same chunk between calls to Next. 32func (mb *MediaBuffer) Chunk() (chunk io.Reader, off int64, size int, err error) { 33 // There may already be data in chunk if Next has not been called since the previous call to Chunk. 34 if mb.err == nil && len(mb.chunk) == 0 { 35 mb.err = mb.loadChunk() 36 } 37 return bytes.NewReader(mb.chunk), mb.off, len(mb.chunk), mb.err 38} 39 40// loadChunk will read from media into chunk, up to the capacity of chunk. 41func (mb *MediaBuffer) loadChunk() error { 42 bufSize := cap(mb.chunk) 43 mb.chunk = mb.chunk[:bufSize] 44 45 read := 0 46 var err error 47 for err == nil && read < bufSize { 48 var n int 49 n, err = mb.media.Read(mb.chunk[read:]) 50 read += n 51 } 52 mb.chunk = mb.chunk[:read] 53 return err 54} 55 56// Next advances to the next chunk, which will be returned by the next call to Chunk. 57// Calls to Next without a corresponding prior call to Chunk will have no effect. 58func (mb *MediaBuffer) Next() { 59 mb.off += int64(len(mb.chunk)) 60 mb.chunk = mb.chunk[0:0] 61} 62 63type readerTyper struct { 64 io.Reader 65 googleapi.ContentTyper 66} 67 68// ReaderAtToReader adapts a ReaderAt to be used as a Reader. 69// If ra implements googleapi.ContentTyper, then the returned reader 70// will also implement googleapi.ContentTyper, delegating to ra. 71func ReaderAtToReader(ra io.ReaderAt, size int64) io.Reader { 72 r := io.NewSectionReader(ra, 0, size) 73 if typer, ok := ra.(googleapi.ContentTyper); ok { 74 return readerTyper{r, typer} 75 } 76 return r 77} 78