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Support for creating Slices from diskbuffer
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,170 @@ | ||
| /* | ||
| * Copyright 2021 National Library of Norway. | ||
| * | ||
| * Licensed under the Apache License, Version 2.0 (the "License"); | ||
| * you may not use this file except in compliance with the License. | ||
| * You may obtain a copy of the License at | ||
| * | ||
| * http://www.apache.org/licenses/LICENSE-2.0 | ||
| * | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, | ||
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| * See the License for the specific language governing permissions and | ||
| * limitations under the License. | ||
| */ | ||
|
|
||
| package diskbuffer | ||
|
|
||
| import ( | ||
| "bytes" | ||
| "io" | ||
| ) | ||
|
|
||
| type Slice interface { | ||
| io.Reader | ||
| io.WriterTo | ||
| io.Closer | ||
| io.Seeker | ||
| ReadBytes(delim byte) (line []byte, err error) | ||
| ReadString(delim byte) (line string, err error) | ||
| Peek(n int) (p []byte, err error) | ||
| Size() int64 | ||
| } | ||
|
|
||
| // Slice returns a read only subset of a buffer. | ||
| func (b *buffer) Slice(offset, len int64) Slice { | ||
| if len <= 0 { | ||
| len = unlimited | ||
| } | ||
| return &slice{ | ||
| buf: b, | ||
| off: offset, | ||
| len: len, | ||
| } | ||
| } | ||
|
|
||
| type slice struct { | ||
| buf *buffer | ||
| len int64 // Lenght of slice | ||
| off int64 // Offset in buffer where this slice starts | ||
| pos int64 // Current position in slice | ||
| } | ||
|
|
||
| func (s *slice) ReadAtOffset(off int64, p []byte) (n int, err error) { | ||
| start := s.off + off | ||
| l := s.len - s.pos | ||
| if l <= 0 { | ||
| return 0, io.EOF | ||
| } | ||
|
|
||
| pp := p | ||
| if int64(len(p)) > l { | ||
| pp = p[:l] | ||
| } | ||
| n, err = s.buf.ReadAtOffset(start, pp) | ||
| return n, err | ||
| } | ||
|
|
||
| func (s *slice) Read(p []byte) (n int, err error) { | ||
| n, err = s.ReadAtOffset(s.pos, p) | ||
| s.pos += int64(n) | ||
| return | ||
| } | ||
|
|
||
| func (s *slice) WriteTo(w io.Writer) (n int64, err error) { | ||
| p := make([]byte, 32*1024) | ||
| for { | ||
| l1, e1 := s.Read(p) | ||
| l2, e2 := w.Write(p[:l1]) | ||
| n += int64(l2) | ||
| if e1 != nil { | ||
| if e1 != io.EOF { | ||
| err = e1 | ||
| return | ||
| } | ||
| } | ||
| if e2 != nil { | ||
| err = e2 | ||
| return | ||
| } | ||
| if l2 == 0 { | ||
| break | ||
| } | ||
| } | ||
| return | ||
| } | ||
|
|
||
| // Close closes the underlying buffer | ||
| func (s *slice) Close() error { | ||
| return s.buf.Close() | ||
| } | ||
|
|
||
| func (s *slice) Seek(offset int64, whence int) (int64, error) { | ||
| switch whence { | ||
| case io.SeekStart: | ||
| s.pos = offset | ||
| case io.SeekCurrent: | ||
| s.pos += offset | ||
| case io.SeekEnd: | ||
| s.pos = s.Size() - offset | ||
| } | ||
| return s.pos, nil | ||
| } | ||
|
|
||
| func (s *slice) ReadBytes(delim byte) (line []byte, err error) { | ||
| if s.len-s.pos <= 0 { | ||
| return []byte{}, io.EOF | ||
| } | ||
|
|
||
| p := make([]byte, 100) | ||
| off := s.pos | ||
| for { | ||
| var n int | ||
| n, err = s.ReadAtOffset(off, p) | ||
| if n > 0 { | ||
| i := bytes.IndexByte(p[:n], delim) | ||
| end := i + 1 | ||
| if i < 0 { | ||
| line = append(line, p[:n]...) | ||
| off += int64(n) | ||
| } else { | ||
| // found delim | ||
| line = append(line, p[:end]...) | ||
| off += int64(end) | ||
| err = nil | ||
| break | ||
| } | ||
| } | ||
| if err != nil { | ||
| break | ||
| } | ||
| } | ||
| s.pos = off | ||
| return line, err | ||
| } | ||
|
|
||
| func (s *slice) ReadString(delim byte) (line string, err error) { | ||
| var bytes []byte | ||
| bytes, err = s.ReadBytes(delim) | ||
| return string(bytes), err | ||
| } | ||
|
|
||
| func (s *slice) Peek(n int) (p []byte, err error) { | ||
| p = make([]byte, n) | ||
| n, err = s.ReadAtOffset(s.pos, p) | ||
| return p[:n], err | ||
| } | ||
|
|
||
| // Len returns the number of bytes of the unread portion of the slice; | ||
| func (s *slice) Len() int64 { | ||
| return s.Size() - s.pos | ||
| } | ||
|
|
||
| func (s *slice) Size() int64 { | ||
| if s.len == unlimited { | ||
| return s.buf.Size() - s.off | ||
| } else { | ||
| return s.len - s.off | ||
| } | ||
| } |
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