forked from elastic/beats
-
Notifications
You must be signed in to change notification settings - Fork 1
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
Adding a Debug reader to detect Null Bytes from the io.Reader (elasti…
…c#9210) When you are reading logs on a network volume like NFS or ZFS it is possible that the underlying filesystem return null bytes instead of returning concrete data, its not currently possible to detect that in all scenario unless events are eventually send to ES and you can inspect them and see \u0000 chars in the messages. This is a small proposal to add a Debug Reader which should only by used for debugging purpose it allow to log if any null bytes are present in the streams of bytes and will log surround values. It accepts an io.Reader as the source of data, a buffer size, a predicate to check the value of a byte and how much detection invokation it should do before disabling the check. Enable it with either of the following selectors: "*" or "detect_null_bytes"
- Loading branch information
Showing
5 changed files
with
368 additions
and
1 deletion.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,178 @@ | ||
| // Licensed to Elasticsearch B.V. under one or more contributor | ||
| // license agreements. See the NOTICE file distributed with | ||
| // this work for additional information regarding copyright | ||
| // ownership. Elasticsearch B.V. licenses this file to you 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 debug | ||
|
|
||
| import ( | ||
| "bytes" | ||
| "io" | ||
|
|
||
| "github.com/elastic/beats/libbeat/logp" | ||
| ) | ||
|
|
||
| const ( | ||
| offsetStart = 100 | ||
| offsetEnd = 100 | ||
| defaultMinBuffer = 16 * 1024 | ||
| defaultMaxFailures = 100 | ||
| ) | ||
|
|
||
| type state int | ||
|
|
||
| const ( | ||
| initial state = iota | ||
| running | ||
| stopped | ||
| ) | ||
|
|
||
| // CheckFunc func receive a slice of bytes and returns true if it match the predicate. | ||
| type CheckFunc func(offset int64, buf []byte) bool | ||
|
|
||
| // Reader is a debug reader used to check the values of specific bytes from an io.Reader, | ||
| // Is is useful is you want to detect if you have received garbage from a network volume. | ||
| type Reader struct { | ||
| log *logp.Logger | ||
| reader io.Reader | ||
| buffer bytes.Buffer | ||
| minBufferSize int | ||
| maxFailures int | ||
| failures int | ||
| predicate CheckFunc | ||
| state state | ||
| offset int64 | ||
| } | ||
|
|
||
| // NewReader returns a debug reader. | ||
| func NewReader( | ||
| log *logp.Logger, | ||
| reader io.Reader, | ||
| minBufferSize int, | ||
| maxFailures int, | ||
| predicate CheckFunc, | ||
| ) (*Reader, error) { | ||
| return &Reader{ | ||
| log: log, | ||
| minBufferSize: minBufferSize, | ||
| reader: reader, | ||
| maxFailures: maxFailures, | ||
| predicate: predicate, | ||
| }, nil | ||
| } | ||
|
|
||
| // Read will proxy the read call to the original reader and will periodically checks the values of | ||
| // bytes in the buffer. | ||
| func (r *Reader) Read(p []byte) (int, error) { | ||
| if r.state == stopped { | ||
| return r.reader.Read(p) | ||
| } | ||
|
|
||
| if r.state == running && r.failures > r.maxFailures { | ||
| // cleanup any remaining bytes in the buffer. | ||
| if r.buffer.Len() > 0 { | ||
| r.predicate(r.offset, r.buffer.Bytes()) | ||
| } | ||
| r.buffer = bytes.Buffer{} | ||
| r.log.Info("Stopping debug reader, max execution reached") | ||
| r.state = stopped | ||
| return r.reader.Read(p) | ||
| } | ||
|
|
||
| if r.state == initial { | ||
| r.log.Infof( | ||
| "Starting debug reader with a buffer size of %d and max failures of %d", | ||
| r.minBufferSize, | ||
| r.maxFailures, | ||
| ) | ||
| r.state = running | ||
| } | ||
|
|
||
| n, err := r.reader.Read(p) | ||
|
|
||
| if n != 0 { | ||
| r.buffer.Write(p[:n]) | ||
| if r.buffer.Len() >= r.minBufferSize { | ||
| if r.failures < r.maxFailures && r.predicate(r.offset, r.buffer.Bytes()) { | ||
| r.failures++ | ||
| } | ||
| r.buffer.Reset() | ||
| } | ||
| r.offset += int64(n) | ||
| } | ||
| return n, err | ||
| } | ||
|
|
||
| func makeNullCheck(log *logp.Logger, minSize int) CheckFunc { | ||
| // create a slice with null bytes to match on the buffer. | ||
| pattern := make([]byte, minSize, minSize) | ||
| return func(offset int64, buf []byte) bool { | ||
| idx := bytes.Index(buf, pattern) | ||
| if idx <= 0 { | ||
| offset += int64(len(buf)) | ||
| return false | ||
| } | ||
| reportNull(log, offset+int64(idx), idx, buf) | ||
| return true | ||
| } | ||
| } | ||
|
|
||
| func reportNull(log *logp.Logger, offset int64, idx int, buf []byte) { | ||
| relativePos, surround := summarizeBufferInfo(idx, buf) | ||
| log.Debugf( | ||
| "Matching null byte found at offset %d (position %d in surrounding string: %s, bytes: %+v", | ||
| offset, | ||
| relativePos, | ||
| string(surround), | ||
| surround) | ||
| } | ||
|
|
||
| func summarizeBufferInfo(idx int, buf []byte) (int, []byte) { | ||
| startAt := idx - offsetStart | ||
| var relativePos int | ||
| if startAt < 0 { | ||
| startAt = 0 | ||
| relativePos = idx | ||
| } else { | ||
| relativePos = offsetStart | ||
| } | ||
|
|
||
| endAt := idx + offsetEnd | ||
| if endAt >= len(buf) { | ||
| endAt = len(buf) | ||
| } | ||
| surround := buf[startAt:endAt] | ||
| return relativePos, surround | ||
| } | ||
|
|
||
| // AppendReaders look into the current enabled log selector and will add any debug reader that match | ||
| // the selectors. | ||
| func AppendReaders(reader io.Reader) (io.Reader, error) { | ||
| var err error | ||
|
|
||
| if logp.HasSelector("detect_null_bytes") || logp.HasSelector("*") { | ||
| log := logp.NewLogger("detect_null_bytes") | ||
| if reader, err = NewReader( | ||
| log, | ||
| reader, | ||
| defaultMinBuffer, | ||
| defaultMaxFailures, | ||
| makeNullCheck(log, 4), | ||
| ); err != nil { | ||
| return nil, err | ||
| } | ||
| } | ||
| return reader, nil | ||
| } |
Oops, something went wrong.