70 lines
1.3 KiB
Go
70 lines
1.3 KiB
Go
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package ioext
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import (
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"errors"
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"io"
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)
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var ErrExceedLimit = errors.New("write exceed limit")
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func NewSectionWriter(w io.WriterAt, off int64, n int64) *SectionWriter {
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return &SectionWriter{w, off, off, off + n}
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}
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type SectionWriter struct {
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w io.WriterAt
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base int64
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off int64
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limit int64
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}
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func (s *SectionWriter) Write(p []byte) (n int, err error) {
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if s.off >= s.limit {
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return 0, ErrExceedLimit
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}
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if max := s.limit - s.off; int64(len(p)) > max {
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return 0, ErrExceedLimit
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}
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n, err = s.w.WriteAt(p, s.off)
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s.off += int64(n)
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return
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}
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var errWhence = errors.New("Seek: invalid whence")
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var errOffset = errors.New("Seek: invalid offset")
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func (s *SectionWriter) Seek(offset int64, whence int) (int64, error) {
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switch whence {
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default:
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return 0, errWhence
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case 0:
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offset += s.base
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case 1:
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offset += s.off
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case 2:
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offset += s.limit
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}
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if offset < s.base {
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return 0, errOffset
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}
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s.off = offset
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return offset - s.base, nil
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}
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func (s *SectionWriter) WriteAt(p []byte, off int64) (n int, err error) {
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if off < 0 || off >= s.limit-s.base {
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return 0, errOffset
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}
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off += s.base
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if max := s.limit - off; int64(len(p)) > max {
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return 0, ErrExceedLimit
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}
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return s.w.WriteAt(p, off)
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}
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// Size returns the size of the section in bytes.
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func (s *SectionWriter) Size() int64 { return s.limit - s.base }
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