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75 lines
2.2 KiB
75 lines
2.2 KiB
/*
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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 io
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import (
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"bytes"
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"errors"
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"fmt"
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"io"
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"io/ioutil"
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)
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// ErrLimitReached means that the read limit is reached.
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var ErrLimitReached = errors.New("the read limit is reached")
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// ConsistentRead repeatedly reads a file until it gets the same content twice.
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// This is useful when reading files in /proc that are larger than page size
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// and kernel may modify them between individual read() syscalls.
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func ConsistentRead(filename string, attempts int) ([]byte, error) {
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return consistentReadSync(filename, attempts, nil)
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}
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// consistentReadSync is the main functionality of ConsistentRead but
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// introduces a sync callback that can be used by the tests to mutate the file
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// from which the test data is being read
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func consistentReadSync(filename string, attempts int, sync func(int)) ([]byte, error) {
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oldContent, err := ioutil.ReadFile(filename)
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if err != nil {
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return nil, err
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}
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for i := 0; i < attempts; i++ {
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if sync != nil {
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sync(i)
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}
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newContent, err := ioutil.ReadFile(filename)
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if err != nil {
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return nil, err
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}
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if bytes.Compare(oldContent, newContent) == 0 {
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return newContent, nil
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}
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// Files are different, continue reading
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oldContent = newContent
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}
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return nil, fmt.Errorf("could not get consistent content of %s after %d attempts", filename, attempts)
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}
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// ReadAtMost reads up to `limit` bytes from `r`, and reports an error
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// when `limit` bytes are read.
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func ReadAtMost(r io.Reader, limit int64) ([]byte, error) {
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limitedReader := &io.LimitedReader{R: r, N: limit}
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data, err := ioutil.ReadAll(limitedReader)
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if err != nil {
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return data, err
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}
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if limitedReader.N <= 0 {
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return data, ErrLimitReached
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}
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return data, nil
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}
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