82 lines
1.9 KiB
Go
82 lines
1.9 KiB
Go
package s3manager
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import (
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"io"
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"github.com/aws/aws-sdk-go/internal/sdkio"
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)
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// BufferedReadSeeker is buffered io.ReadSeeker
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type BufferedReadSeeker struct {
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r io.ReadSeeker
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buffer []byte
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readIdx, writeIdx int
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}
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// NewBufferedReadSeeker returns a new BufferedReadSeeker
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// if len(b) == 0 then the buffer will be initialized to 64 KiB.
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func NewBufferedReadSeeker(r io.ReadSeeker, b []byte) *BufferedReadSeeker {
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if len(b) == 0 {
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b = make([]byte, 64*1024)
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}
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return &BufferedReadSeeker{r: r, buffer: b}
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}
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func (b *BufferedReadSeeker) reset(r io.ReadSeeker) {
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b.r = r
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b.readIdx, b.writeIdx = 0, 0
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}
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// Read will read up len(p) bytes into p and will return
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// the number of bytes read and any error that occurred.
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// If the len(p) > the buffer size then a single read request
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// will be issued to the underlying io.ReadSeeker for len(p) bytes.
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// A Read request will at most perform a single Read to the underlying
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// io.ReadSeeker, and may return < len(p) if serviced from the buffer.
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func (b *BufferedReadSeeker) Read(p []byte) (n int, err error) {
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if len(p) == 0 {
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return n, err
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}
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if b.readIdx == b.writeIdx {
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if len(p) >= len(b.buffer) {
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n, err = b.r.Read(p)
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return n, err
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}
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b.readIdx, b.writeIdx = 0, 0
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n, err = b.r.Read(b.buffer)
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if n == 0 {
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return n, err
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}
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b.writeIdx += n
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}
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n = copy(p, b.buffer[b.readIdx:b.writeIdx])
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b.readIdx += n
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return n, err
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}
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// Seek will position then underlying io.ReadSeeker to the given offset
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// and will clear the buffer.
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func (b *BufferedReadSeeker) Seek(offset int64, whence int) (int64, error) {
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n, err := b.r.Seek(offset, whence)
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b.reset(b.r)
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return n, err
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}
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// ReadAt will read up to len(p) bytes at the given file offset.
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// This will result in the buffer being cleared.
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func (b *BufferedReadSeeker) ReadAt(p []byte, off int64) (int, error) {
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_, err := b.Seek(off, sdkio.SeekStart)
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if err != nil {
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return 0, err
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}
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return b.Read(p)
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}
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