go-parsesyslog - a Go library to parse syslog messages

Supported formats

BSD syslog format (RFC3164)

go-parsesyslog fully implements the RFC3164 format including timestamp parsing and optional tags.

Please note: the RFC is not providing any message length definition and explicity states that there is "no ending delimiter to this part" for this reason we are using the newline (\n (ASCII: 10)) as delimiter. This will therefore truncate messages that have a newline in it. Additionally the RFC does specify a timestamp format that has not provide any information about the year. For this reason, we infer the year from current local time. If the parsed time is more than ~31 days in the future, assume it was from the previous year, otherwise we assume it is from the current year.

Available fields in the LogMsg:

• AppName: this represents the TAG part of TAG[pid]: format (if given in the message) that is often used for the name off the application or process logging
• ProcID: this represents the pid part of TAG[pid]: format (if given in the message) that is often used for the process ID
• HostName: this represents the hostname part of the RFC3164 message
• Priority: The Priority part of the message
• Facility: The facility calculated from the Priority part of the message
• Severity: The severity calculated from the Priority part of the message
• Timestamp: The parsed timestamp of the RFC3164 message as time.Time representation
• Message: The message part of the log message as bytes.Buffer
• MsgLength: The length of the Message (not including any header part)
• Type: This will be always set to RFC3164

IETF-syslog

go-parsesyslog is also fully (RFC5424) compliant. All available fields are parsed and represented accordingly in the LogMsg fields. Although the RFC5424 mandates a maximum length of 2048 bytes for a log message, go-parsesyslog does only obey the message length given in the header of the message.

Available fields in the LogMsg:

• Priority: this represents the PRI field of the header
• ProtoVersion: this represents the VERSION field of the header
• Timestamp: this represents the TIMESTAMP field of the header
• Hostname: this represents the HOSTNAME field of the header
• AppName: this represents the APP-NAME field of the header
• ProcID: this represents the PROCID field of the header
• MsgID: this represents the MSGID field of the header
• StructuredData this represents fully parsed structured data as described in the STRUCTURED-DATA section of the RFC
• HasBOM: is set to true if the log message starts with a BOM
• Facility: The facility calculated from the Priority part of the message
• Severity: The severity calculated from the Priority part of the message
• Message: The message part of the log message as bytes.Buffer
• MsgLength: The length of the Message (not including any header part)
• Type: This will be always set to RFC5424

Usage

go-parsesyslog implements an interface for various syslog formats, which makes it easy to extend your own log parser. As long as the Parser interface is satisfied, go-parsesyslog will be able to work.

The interface looks as following:

type Parser interface {
  ParseReader(io.Reader) (LogMsg, error)
  ParseString(string) (LogMsg, error)
}

Parsing logs

As you can see, the ParseReader() method expects an io.Reader interface as argument. This allows you to easily parse your logs from any kind of source (STDIN, a file, a network socket...). ParseString() instead takes a string and parses it accordingly.

Parsing RFC3164

This example code show how to parse a RFC3164 conformant message:

package main

import (
	"fmt"
	"github.com/wneessen/go-parsesyslog"
	"github.com/wneessen/go-parsesyslog/rfc3164"
	"os"
)

func main() {
	msg := "<34>Oct 11 22:14:15 mymachine su: 'su root' failed for lonvick on /dev/pts/8\n"
	p, err := parsesyslog.New(rfc3164.Type)
	if err != nil {
		fmt.Printf("failed to create RFC3164 parser: %s", err)
		os.Exit(1)
	}
	lm, err := p.ParseString(msg)
	if err != nil {
		panic(err)
	}
	fmt.Printf("Log message: %+v", lm)
}

Parsing RFC5424

This example code show how to parse a RFC5424 conformant message:

package main

import (
	"fmt"
	"github.com/wneessen/go-parsesyslog"
	"github.com/wneessen/go-parsesyslog/rfc5424"
	"os"
)

func main() {
	msg := `197 <165>1 2003-10-11T22:14:15.003Z mymachine.example.com evntslog - ID47 [exampleSDID@32473 iut="3" eventSource="Application" eventID="1011"][foo@1234 foo="bar" blubb="bluh"] \xEF\xBB\xBFAn application event log entry..."`
	p, err := parsesyslog.New(rfc5424.Type)
	if err != nil {
		fmt.Printf("failed to create RFC3164 parser: %s", err)
		os.Exit(1)
	}
	lm, err := p.ParseString(msg)
	if err != nil {
		panic(err)
	}
	fmt.Printf("Log message: %+v", lm)
}

An example implementation can be found in cmd/stdin-parser

$ $ echo -ne '197 <165>1 2003-10-11T22:14:15.003Z mymachine.example.com evntslog - ID47 [exampleSDID@32473 iut="3" eventSource="Application" eventID="1011"][foo@1234 foo="bar" blubb="bluh"] \xEF\xBB\xBFAn application event log entry...' | go run github.com/wneessen/go-parsesyslog/cmd/stdin-parser

This command will output:

Log message details:
+ Log format:         RFC5424
+ Header:
  - Priority:         165 (Facility: LOCAL4 / Severity: NOTICE)
  - Protocol Version: 1
  - Hostname:         mymachine.example.com
  - AppName:          evntslog
  - ProcID:
  - MsgID:            ID47
  - Timestamp (UTC):  2003-10-11 22:14:15.003 +0000 UTC
+ Structured Data:
  - ID:               exampleSDID@32473
    + Param 0:
      - Name:         iut
      - Value:        3
    + Param 1:
      - Name:         eventSource
      - Value:        Application
    + Param 2:
      - Name:         eventID
      - Value:        1011
  - ID:               foo@1234
    + Param 0:
      - Name:         foo
      - Value:        bar
    + Param 1:
      - Name:         blubb
      - Value:        bluh
+ Message has BOM:    true
+ Message Length:     25
+ Message:            An application event l

Log parsed in 18.745µs

Benchmark

As the main intention of this library was for me to use it in a network service that parses incoming syslog messages, quite some work has been invested to make go-parsesyslog fast and memory efficient. We are trying to allocate as less as possible and make use of buffered I/O where possible.

$ go test -run=X -bench=.\*ParseReader -benchtime=15s ./...
goos: linux
goarch: amd64
pkg: github.com/wneessen/go-parsesyslog
cpu: AMD Ryzen 9 3950X 16-Core Processor
BenchmarkRFC3164Msg_ParseReader/ParseReader-32     36575746       490 ns/op     64 B/op    1 allocs/op
BenchmarkRFC5424Msg_ParseReader/ParseReader-32     12615361      1433 ns/op    432 B/op    5 allocs/op
PASS