github.com/aavshr/aws-sdk-go@v1.41.3/service/s3/s3manager/buffered_read_seeker.go (about)

     1  package s3manager
     2  
     3  import (
     4  	"io"
     5  
     6  	"github.com/aavshr/aws-sdk-go/internal/sdkio"
     7  )
     8  
     9  // BufferedReadSeeker is buffered io.ReadSeeker
    10  type BufferedReadSeeker struct {
    11  	r                 io.ReadSeeker
    12  	buffer            []byte
    13  	readIdx, writeIdx int
    14  }
    15  
    16  // NewBufferedReadSeeker returns a new BufferedReadSeeker
    17  // if len(b) == 0 then the buffer will be initialized to 64 KiB.
    18  func NewBufferedReadSeeker(r io.ReadSeeker, b []byte) *BufferedReadSeeker {
    19  	if len(b) == 0 {
    20  		b = make([]byte, 64*1024)
    21  	}
    22  	return &BufferedReadSeeker{r: r, buffer: b}
    23  }
    24  
    25  func (b *BufferedReadSeeker) reset(r io.ReadSeeker) {
    26  	b.r = r
    27  	b.readIdx, b.writeIdx = 0, 0
    28  }
    29  
    30  // Read will read up len(p) bytes into p and will return
    31  // the number of bytes read and any error that occurred.
    32  // If the len(p) > the buffer size then a single read request
    33  // will be issued to the underlying io.ReadSeeker for len(p) bytes.
    34  // A Read request will at most perform a single Read to the underlying
    35  // io.ReadSeeker, and may return < len(p) if serviced from the buffer.
    36  func (b *BufferedReadSeeker) Read(p []byte) (n int, err error) {
    37  	if len(p) == 0 {
    38  		return n, err
    39  	}
    40  
    41  	if b.readIdx == b.writeIdx {
    42  		if len(p) >= len(b.buffer) {
    43  			n, err = b.r.Read(p)
    44  			return n, err
    45  		}
    46  		b.readIdx, b.writeIdx = 0, 0
    47  
    48  		n, err = b.r.Read(b.buffer)
    49  		if n == 0 {
    50  			return n, err
    51  		}
    52  
    53  		b.writeIdx += n
    54  	}
    55  
    56  	n = copy(p, b.buffer[b.readIdx:b.writeIdx])
    57  	b.readIdx += n
    58  
    59  	return n, err
    60  }
    61  
    62  // Seek will position then underlying io.ReadSeeker to the given offset
    63  // and will clear the buffer.
    64  func (b *BufferedReadSeeker) Seek(offset int64, whence int) (int64, error) {
    65  	n, err := b.r.Seek(offset, whence)
    66  
    67  	b.reset(b.r)
    68  
    69  	return n, err
    70  }
    71  
    72  // ReadAt will read up to len(p) bytes at the given file offset.
    73  // This will result in the buffer being cleared.
    74  func (b *BufferedReadSeeker) ReadAt(p []byte, off int64) (int, error) {
    75  	_, err := b.Seek(off, sdkio.SeekStart)
    76  	if err != nil {
    77  		return 0, err
    78  	}
    79  
    80  	return b.Read(p)
    81  }