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100 lines
2.1 KiB
100 lines
2.1 KiB
3 years ago
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package buffer
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import (
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"encoding/gob"
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"io"
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)
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type swap struct {
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A BufferAt
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B BufferAt
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}
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// NewSwap creates a Buffer which writes to a until you write past a.Cap()
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// then it io.Copy's from a to b and writes to b.
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// Once the Buffer is empty again, it starts over writing to a.
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// Note that if b.Cap() <= a.Cap() it will cause a panic, b is expected
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// to be larger in order to accommodate writes past a.Cap().
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func NewSwap(a, b Buffer) Buffer {
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return NewSwapAt(toBufferAt(a), toBufferAt(b))
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}
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// NewSwapAt creates a BufferAt which writes to a until you write past a.Cap()
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// then it io.Copy's from a to b and writes to b.
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// Once the Buffer is empty again, it starts over writing to a.
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// Note that if b.Cap() <= a.Cap() it will cause a panic, b is expected
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// to be larger in order to accommodate writes past a.Cap().
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func NewSwapAt(a, b BufferAt) BufferAt {
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if b.Cap() <= a.Cap() {
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panic("Buffer b must be larger than a.")
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}
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return &swap{A: a, B: b}
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}
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func (buf *swap) Len() int64 {
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return buf.A.Len() + buf.B.Len()
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}
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func (buf *swap) Cap() int64 {
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return buf.B.Cap()
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}
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func (buf *swap) Read(p []byte) (n int, err error) {
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if buf.A.Len() > 0 {
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return buf.A.Read(p)
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}
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return buf.B.Read(p)
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}
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func (buf *swap) ReadAt(p []byte, off int64) (n int, err error) {
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if buf.A.Len() > 0 {
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return buf.A.ReadAt(p, off)
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}
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return buf.B.ReadAt(p, off)
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}
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func (buf *swap) Write(p []byte) (n int, err error) {
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switch {
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case buf.B.Len() > 0:
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n, err = buf.B.Write(p)
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case buf.A.Len()+int64(len(p)) > buf.A.Cap():
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_, err = io.Copy(buf.B, buf.A)
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if err == nil {
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n, err = buf.B.Write(p)
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}
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default:
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n, err = buf.A.Write(p)
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}
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return n, err
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}
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func (buf *swap) WriteAt(p []byte, off int64) (n int, err error) {
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switch {
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case buf.B.Len() > 0:
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n, err = buf.B.WriteAt(p, off)
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case off+int64(len(p)) > buf.A.Cap():
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_, err = io.Copy(buf.B, buf.A)
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if err == nil {
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n, err = buf.B.WriteAt(p, off)
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}
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default:
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n, err = buf.A.WriteAt(p, off)
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}
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return n, err
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}
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func (buf *swap) Reset() {
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buf.A.Reset()
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buf.B.Reset()
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}
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func init() {
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gob.Register(&swap{})
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}
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