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