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186 lines
3.9 KiB
186 lines
3.9 KiB
3 years ago
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package buffer
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import (
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"bytes"
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"encoding/gob"
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"io"
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"math"
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)
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type chain struct {
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Buf BufferAt
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Next BufferAt
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}
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type nopBufferAt struct {
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Buffer
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}
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func (buf *nopBufferAt) ReadAt(p []byte, off int64) (int, error) {
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panic("ReadAt not implemented")
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}
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func (buf *nopBufferAt) WriteAt(p []byte, off int64) (int, error) {
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panic("WriteAt not implemented")
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}
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// toBufferAt converts a Buffer to a BufferAt with nop ReadAt and WriteAt funcs
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func toBufferAt(buf Buffer) BufferAt {
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return &nopBufferAt{Buffer: buf}
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}
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// NewMultiAt returns a BufferAt which is the logical concatenation of the passed BufferAts.
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// The data in the buffers is shifted such that there is no non-empty buffer following
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// a non-full buffer, this process is also run after every Read.
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// If no buffers are passed, the returned Buffer is nil.
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func NewMultiAt(buffers ...BufferAt) BufferAt {
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if len(buffers) == 0 {
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return nil
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} else if len(buffers) == 1 {
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return buffers[0]
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}
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buf := &chain{
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Buf: buffers[0],
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Next: NewMultiAt(buffers[1:]...),
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}
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buf.Defrag()
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return buf
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}
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// NewMulti returns a Buffer which is the logical concatenation of the passed buffers.
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// The data in the buffers is shifted such that there is no non-empty buffer following
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// a non-full buffer, this process is also run after every Read.
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// If no buffers are passed, the returned Buffer is nil.
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func NewMulti(buffers ...Buffer) Buffer {
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bufAt := make([]BufferAt, len(buffers))
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for i, buf := range buffers {
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bufAt[i] = toBufferAt(buf)
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}
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return NewMultiAt(bufAt...)
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}
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func (buf *chain) Reset() {
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buf.Next.Reset()
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buf.Buf.Reset()
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}
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func (buf *chain) Cap() (n int64) {
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Next := buf.Next.Cap()
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if buf.Buf.Cap() > math.MaxInt64-Next {
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return math.MaxInt64
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}
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return buf.Buf.Cap() + Next
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}
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func (buf *chain) Len() (n int64) {
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Next := buf.Next.Len()
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if buf.Buf.Len() > math.MaxInt64-Next {
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return math.MaxInt64
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}
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return buf.Buf.Len() + Next
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}
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func (buf *chain) Defrag() {
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for !Full(buf.Buf) && !Empty(buf.Next) {
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r := io.LimitReader(buf.Next, Gap(buf.Buf))
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if _, err := io.Copy(buf.Buf, r); err != nil && err != io.EOF {
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return
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}
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}
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}
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func (buf *chain) Read(p []byte) (n int, err error) {
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n, err = buf.Buf.Read(p)
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if len(p[n:]) > 0 && (err == nil || err == io.EOF) {
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m, err := buf.Next.Read(p[n:])
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n += m
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if err != nil {
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return n, err
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}
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}
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buf.Defrag()
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return n, err
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}
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func (buf *chain) ReadAt(p []byte, off int64) (n int, err error) {
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if buf.Buf.Len() < off {
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return buf.Next.ReadAt(p, off-buf.Buf.Len())
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}
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n, err = buf.Buf.ReadAt(p, off)
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if len(p[n:]) > 0 && (err == nil || err == io.EOF) {
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var m int
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m, err = buf.Next.ReadAt(p[n:], 0)
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n += m
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}
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return n, err
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}
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func (buf *chain) Write(p []byte) (n int, err error) {
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if n, err = buf.Buf.Write(p); err == io.ErrShortWrite {
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err = nil
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}
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p = p[n:]
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if len(p) > 0 && err == nil {
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m, err := buf.Next.Write(p)
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n += m
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if err != nil {
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return n, err
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}
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}
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return n, err
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}
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func (buf *chain) WriteAt(p []byte, off int64) (n int, err error) {
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switch {
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case buf.Buf.Cap() <= off: // past the end
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return buf.Next.WriteAt(p, off-buf.Buf.Cap())
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case buf.Buf.Cap() >= off+int64(len(p)): // fits in
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return buf.Buf.WriteAt(p, off)
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default: // partial fit
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n, err = buf.Buf.WriteAt(p, off)
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if len(p[n:]) > 0 && (err == nil || err == io.ErrShortWrite) {
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var m int
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m, err = buf.Next.WriteAt(p[n:], 0)
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n += m
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}
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return n, err
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}
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}
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func init() {
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gob.Register(&chain{})
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gob.Register(&nopBufferAt{})
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}
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func (buf *chain) MarshalBinary() ([]byte, error) {
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b := bytes.NewBuffer(nil)
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enc := gob.NewEncoder(b)
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if err := enc.Encode(&buf.Buf); err != nil {
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return nil, err
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}
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if err := enc.Encode(&buf.Next); err != nil {
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return nil, err
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}
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return b.Bytes(), nil
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}
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func (buf *chain) UnmarshalBinary(data []byte) error {
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b := bytes.NewBuffer(data)
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dec := gob.NewDecoder(b)
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if err := dec.Decode(&buf.Buf); err != nil {
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return err
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}
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if err := dec.Decode(&buf.Next); err != nil {
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return err
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}
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return nil
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}
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