buffer.go

Documentation: google.golang.org/api/internal/gensupport

     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  
     5  package gensupport
     6  
     7  import (
     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
    15  // retryable chunks. It should be created with NewMediaBuffer.
    16  type MediaBuffer struct {
    17  	media io.Reader
    18  
    19  	chunk []byte // The current chunk which is pending upload.  The capacity is the chunk size.
    20  	err   error  // Any error generated when populating chunk by reading media.
    21  
    22  	// The absolute position of chunk in the underlying media.
    23  	off int64
    24  }
    25  
    26  // NewMediaBuffer initializes a MediaBuffer.
    27  func NewMediaBuffer(media io.Reader, chunkSize int) *MediaBuffer {
    28  	return &MediaBuffer{media: media, chunk: make([]byte, 0, chunkSize)}
    29  }
    30  
    31  // Chunk returns the current buffered chunk, the offset in the underlying media
    32  // from which the chunk is drawn, and the size of the chunk.
    33  // Successive calls to Chunk return the same chunk between calls to Next.
    34  func (mb *MediaBuffer) Chunk() (chunk io.Reader, off int64, size int, err error) {
    35  	// There may already be data in chunk if Next has not been called since the previous call to Chunk.
    36  	if mb.err == nil && len(mb.chunk) == 0 {
    37  		mb.err = mb.loadChunk()
    38  	}
    39  	return bytes.NewReader(mb.chunk), mb.off, len(mb.chunk), mb.err
    40  }
    41  
    42  // loadChunk will read from media into chunk, up to the capacity of chunk.
    43  func (mb *MediaBuffer) loadChunk() error {
    44  	bufSize := cap(mb.chunk)
    45  	mb.chunk = mb.chunk[:bufSize]
    46  
    47  	read := 0
    48  	var err error
    49  	for err == nil && read < bufSize {
    50  		var n int
    51  		n, err = mb.media.Read(mb.chunk[read:])
    52  		read += n
    53  	}
    54  	mb.chunk = mb.chunk[:read]
    55  	return err
    56  }
    57  
    58  // Next advances to the next chunk, which will be returned by the next call to Chunk.
    59  // Calls to Next without a corresponding prior call to Chunk will have no effect.
    60  func (mb *MediaBuffer) Next() {
    61  	mb.off += int64(len(mb.chunk))
    62  	mb.chunk = mb.chunk[0:0]
    63  }
    64  
    65  type readerTyper struct {
    66  	io.Reader
    67  	googleapi.ContentTyper
    68  }
    69  
    70  // ReaderAtToReader adapts a ReaderAt to be used as a Reader.
    71  // If ra implements googleapi.ContentTyper, then the returned reader
    72  // will also implement googleapi.ContentTyper, delegating to ra.
    73  func ReaderAtToReader(ra io.ReaderAt, size int64) io.Reader {
    74  	r := io.NewSectionReader(ra, 0, size)
    75  	if typer, ok := ra.(googleapi.ContentTyper); ok {
    76  		return readerTyper{r, typer}
    77  	}
    78  	return r
    79  }
    80
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