100 lines
2.3 KiB
Go
100 lines
2.3 KiB
Go
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/*
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Copyright 2017 The Kubernetes Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package tail
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import (
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"bytes"
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"io"
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"io/ioutil"
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"os"
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)
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const (
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// blockSize is the block size used in tail.
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blockSize = 1024
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)
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var (
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// eol is the end-of-line sign in the log.
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eol = []byte{'\n'}
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)
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// ReadAtMost reads at most max bytes from the end of the file identified by path or
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// returns an error. It returns true if the file was longer than max. It will
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// allocate up to max bytes.
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func ReadAtMost(path string, max int64) ([]byte, bool, error) {
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f, err := os.Open(path)
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if err != nil {
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return nil, false, err
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}
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defer f.Close()
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fi, err := f.Stat()
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if err != nil {
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return nil, false, err
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}
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size := fi.Size()
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if size == 0 {
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return nil, false, nil
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}
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if size < max {
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max = size
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}
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offset, err := f.Seek(-max, os.SEEK_END)
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if err != nil {
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return nil, false, err
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}
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data, err := ioutil.ReadAll(f)
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return data, offset > 0, err
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}
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// FindTailLineStartIndex returns the start of last nth line.
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// * If n < 0, return the beginning of the file.
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// * If n >= 0, return the beginning of last nth line.
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// Notice that if the last line is incomplete (no end-of-line), it will not be counted
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// as one line.
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func FindTailLineStartIndex(f io.ReadSeeker, n int64) (int64, error) {
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if n < 0 {
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return 0, nil
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}
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size, err := f.Seek(0, os.SEEK_END)
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if err != nil {
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return 0, err
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}
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var left, cnt int64
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buf := make([]byte, blockSize)
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for right := size; right > 0 && cnt <= n; right -= blockSize {
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left = right - blockSize
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if left < 0 {
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left = 0
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buf = make([]byte, right)
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}
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if _, err := f.Seek(left, os.SEEK_SET); err != nil {
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return 0, err
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}
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if _, err := f.Read(buf); err != nil {
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return 0, err
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}
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cnt += int64(bytes.Count(buf, eol))
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}
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for ; cnt > n; cnt-- {
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idx := bytes.Index(buf, eol) + 1
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buf = buf[idx:]
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left += int64(idx)
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}
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return left, nil
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}
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