Multiline Parser (xm_multiline)

This module can be used for parsing log messages that span multiple lines. All lines in an event are joined to form a single NXLog Agent event record that can be processed further as required. Each multiline event is detected through some combination of header lines, footer lines, and fixed line counts, as configured. The name of the xm_multiline module instance is specified by the input module’s InputType directive.

The module maintains a separate context for each input source, allowing multiline messages to be processed correctly even when coming from multiple sources (specifically, multiple files or multiple network connections).

UDP is treated as a single source and all logs are processed under the same context. It is therefore not recommended to use this module with im_udp if messages will be received by multiple UDP senders (such as Syslog).

Configuration

The xm_multiline module accepts the following directives in addition to the common module directives. One of FixedLineCount and HeaderLine must be specified.

Required directives

The following directives are required for the module to start.

FixedLineCount

This directive takes a positive integer number defining the number of lines to concatenate. This is useful when receiving log messages spanning a fixed number of lines. When this number is defined, the module knows where the event message ends and will not hold a message in the buffers until the next message arrives.

HeaderLine

This directive takes a string or a regular expression literal. This will be matched against each line. When the match is successful, the successive lines are appended until the next header line is read. This directive is mandatory unless FixedLineCount is used.

Until a new message arrives with its associated header, the previous message is stored in the buffers because the module does not know where the message ends. The im_file module will forcibly flush this buffer after the configured PollInterval timeout. If this behavior is unacceptable, disable AutoFlush, use an end marker with EndLine, or switch to an encapsulation method (such as JSON).

The /s and /m regular expression modifiers may be used here, but they have no meaning, because HeaderLine is only checked against one input line at a time.

Optional directives

AutoFlush

If set to TRUE, this boolean directive specifies that the corresponding im_file module should forcibly flush the buffer after its configured PollInterval timeout. The default is TRUE. If EndLine is used, AutoFlush is automatically set to FALSE to disable this behavior. AutoFlush has no effect if xm_multiline is used with an input module other than im_file.

EndLine

This is similar to the HeaderLine directive. This optional directive also takes a string or a regular expression literal to be matched against each line. When the match is successful the message is considered complete.

Exec

This directive is almost identical to the behavior of the Exec directive used by the other modules with the following differences:

each line is passed in $raw_event as it is read, and the line terminator is included; and
other fields cannot be used, and captured strings can not be stored as separate fields.

This is mostly useful for rewriting lines or filtering out certain lines with the drop() procedure.

Examples

Example 1. Parsing multiline XML logs and converting to JSON

XML is commonly formatted as indented multiline to make it more readable. In the following configuration file the HeaderLine and EndLine directives are used to parse the events. The events are then converted to JSON after some timestamp normalization.

nxlog.conf

<Extension multiline>
    Module          xm_multiline
    HeaderLine      /^<event>/
    EndLine         /^<\/event>/
</Extension>

<Extension xmlparser>
    Module          xm_xml
</Extension>

<Extension json>
    Module          xm_json
</Extension>

<Input filein>
    Module          im_file
    File            "modules/extension/multiline/xm_multiline5.in"
    InputType       multiline
    <Exec>
        # Discard everything that doesn't seem to be an xml event
        if $raw_event !~ /^<event>/ drop();

        # Parse the xml event
        parse_xml();

        # Rewrite some fields
        $EventTime = parsedate($timestamp);
        delete($timestamp);
        delete($EventReceivedTime);

        # Convert to JSON
        to_json();
    </Exec>
</Input>

<Output fileout>
    Module          om_file
    File            'tmp/output'
</Output>

<Route parse_xml>
    Path            filein => fileout
</Route>

Input Sample

<?xml version="1.0" encoding="UTF-8">
<event>
  <timestamp>2012-11-23 23:00:00</timestamp>
  <severity>ERROR</severity>
  <message>
    Something bad happened.
    Please check the system.
  </message>
</event>
<event>
  <timestamp>2012-11-23 23:00:12</timestamp>
  <severity>INFO</severity>
  <message>
   System state is now back to normal.
  </message>
</event>

Output Sample

{"SourceModuleName":"filein","SourceModuleType":"im_file","severity":"ERROR","message":"\n    Something bad happened.\n    Please check the system.\n  ","EventTime":"2012-11-23 23:00:00"}
{"SourceModuleName":"filein","SourceModuleType":"im_file","severity":"INFO","message":"\n   System state is now back to normal.\n  ","EventTime":"2012-11-23 23:00:12"}

Example 2. Parsing DICOM Logs

Each log message has a header (TIMESTAMP INTEGER SEVERITY) which is used as the message boundary. A regular expression is defined for this with the HeaderLine directive. Each log message is prepended with an additional line containing dashes and is written to a file.

nxlog.conf

<Extension dicom_multi>
    Module          xm_multiline
    HeaderLine      /^\d\d\d\d-\d\d-\d\d\d\d:\d\d:\d\d\.\d+\s+\d+\s+\S+\s+/
</Extension>

<Input filein>
    Module          im_file
    File            "modules/extension/multiline/xm_multiline4.in"
    InputType       dicom_multi
</Input>

<Output fileout>
    Module          om_file
    File            'tmp/output'
    Exec    $raw_event = "--------------------------------------\n" + $raw_event;
</Output>

<Route parse_dicom>
    Path            filein => fileout
</Route>

Input Sample

2011-12-1512:22:51.000000  4296   INFO   Association Request Parameters:
Our Implementation Class UID:    2.16.124.113543.6021.2
Our Implementation Version Name: RZDCX_2_0_1_8
Their Implementation Class UID:   
Their Implementation Version Name:
Application Context Name:    1.2.840.10008.3.1.1.1
Requested Extended Negotiation: none
Accepted Extended Negotiation: none
2011-12-1512:22:51.000000  4296   DEBUG  Constructing Associate RQ PDU
2011-12-1512:22:51.000000  4296   DEBUG  WriteToConnection, length: 310, bytes written: 310, loop no: 1
2011-12-1512:22:51.015000  4296   DEBUG  PDU Type: Associate Accept, PDU Length: 216 + 6 bytes PDU header
  02  00  00  00  00  d8  00  01  00  00  50  41  43  53  20  20
  20  20  20  20  20  20  20  20  20  20  52  5a  44  43  58  20
  20  20  20  20  20  20  20  20  20  20  00  00  00  00  00  00
2011-12-1512:22:51.031000  4296   DEBUG  DIMSE sendDcmDataset: sending 146 bytes

Output Sample

--------------------------------------
2011-12-1512:22:51.000000  4296   INFO   Association Request Parameters:
Our Implementation Class UID:    2.16.124.113543.6021.2
Our Implementation Version Name: RZDCX_2_0_1_8
Their Implementation Class UID:   
Their Implementation Version Name:
Application Context Name:    1.2.840.10008.3.1.1.1
Requested Extended Negotiation: none
Accepted Extended Negotiation: none
--------------------------------------
2011-12-1512:22:51.000000  4296   DEBUG  Constructing Associate RQ PDU
--------------------------------------
2011-12-1512:22:51.000000  4296   DEBUG  WriteToConnection, length: 310, bytes written: 310, loop no: 1
--------------------------------------
2011-12-1512:22:51.015000  4296   DEBUG  PDU Type: Associate Accept, PDU Length: 216 + 6 bytes PDU header
  02  00  00  00  00  d8  00  01  00  00  50  41  43  53  20  20
  20  20  20  20  20  20  20  20  20  20  52  5a  44  43  58  20
  20  20  20  20  20  20  20  20  20  20  00  00  00  00  00  00
--------------------------------------
2011-12-1512:22:51.031000  4296   DEBUG  DIMSE sendDcmDataset: sending 146 bytes

Example 3. Multiline messages with a fixed string header

The following configuration will process messages having a fixed string header containing dashes. Each event is then prepended with a hash mark (#) and written to a file.

nxlog.conf

<Extension multiline>
    Module          xm_multiline
    HeaderLine      "---------------"
</Extension>

<Input filein>
    Module          im_file
    File            "modules/extension/multiline/xm_multiline1.in"
    InputType       multiline
    Exec            $raw_event = "#" + $raw_event;
</Input>

<Output fileout>
    Module          om_file
    File            'tmp/output'
</Output>

<Route parse_multiline>
    Path            filein => fileout
</Route>

Input Sample

---------------
1
---------------
1
2
---------------
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
ccccccccccccccccccccccccccccccccccccc
dddd
---------------

Output Sample

#---------------
1
#---------------
1
2
#---------------
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
ccccccccccccccccccccccccccccccccccccc
dddd
#---------------

Example 4. Multiline messages with fixed line count

The following configuration will process messages having a fixed line count of four. Lines containing only whitespace are ignored and removed. Each event is then prefixed with a hash mark (#) and written to a file.

nxlog.conf

<Extension multiline>
    Module          xm_multiline
    FixedLineCount  4
    Exec            if $raw_event =~ /^\s*$/ drop();
</Extension>

<Input filein>
    Module          im_file
    File            "modules/extension/multiline/xm_multiline2.in"
    InputType       multiline
</Input>

<Output fileout>
    Module          om_file
    File            'tmp/output'
    Exec            $raw_event = "#" + $raw_event;
</Output>

<Route parse_multiline>
    Path            filein => fileout
</Route>

Input Sample

1
2
3
4
1asd 

2asdassad
3ewrwerew
4xcbccvbc

1dsfsdfsd
2sfsdfsdrewrwe

3sdfsdfsew
4werwerwrwe

Output Sample

#1
2
3
4
#1asd 
2asdassad
3ewrwerew
4xcbccvbc
#1dsfsdfsd
2sfsdfsdrewrwe
3sdfsdfsew
4werwerwrwe

Example 5. Multiline messages with a Syslog header

Often, multiline messages are logged over Syslog and each line is processed as an event, with its own Syslog header. It is commonly necessary to merge these back into a single event message.

Input Sample

Nov 21 11:40:27 hostname app[26459]: Iface   MTU Met   RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
Nov 21 11:40:27 hostname app[26459]: eth2       1500 0  16936814      0      0 0      30486067      0      8      0 BMRU
Nov 21 11:40:27 hostname app[26459]: lo        16436 0  277217234      0      0 0      277217234      0      0      0 LRU
Nov 21 11:40:27 hostname app[26459]: tun0       1500 0    316943      0      0 0        368642      0      0      0 MOPRU
Nov 21 11:40:28 hostname app[26459]: Iface   MTU Met   RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
Nov 21 11:40:28 hostname app[26459]: eth2       1500 0  16945117      0      0 0      30493583      0      8      0 BMRU
Nov 21 11:40:28 hostname app[26459]: lo        16436 0  277217234      0      0 0      277217234      0      0      0 LRU
Nov 21 11:40:28 hostname app[26459]: tun0       1500 0    316943      0      0 0        368642      0      0      0 MOPRU
Nov 21 11:40:29 hostname app[26459]: Iface   MTU Met   RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
Nov 21 11:40:29 hostname app[26459]: eth2       1500 0  16945270      0      0 0      30493735      0      8      0 BMRU
Nov 21 11:40:29 hostname app[26459]: lo        16436 0  277217234      0      0 0      277217234      0      0      0 LRU
Nov 21 11:40:29 hostname app[26459]: tun0       1500 0    316943      0      0 0        368642      0      0      0 MOPRU

The following configuration strips the syslog header from the netstat output stored in the traditional Syslog formatted file, and each message is then printed again with a line of dashes used as a separator.

nxlog.conf

<Extension syslog>
    Module          xm_syslog
</Extension>

<Extension netstat>
    Module          xm_multiline
    FixedLineCount  4
    <Exec>
        parse_syslog_bsd();
        $raw_event = $Message + "\n";
    </Exec>
</Extension>

<Input filein>
    Module          im_file
    File            "modules/extension/multiline/xm_multiline3.in"
    InputType       netstat
</Input>

<Output fileout>
    Module          om_file
    File            'tmp/output'
    <Exec>
        $raw_event = "-------------------------------------------------------" +
                     "-----------------------------\n" + $raw_event;
    </Exec>
</Output>

<Route parse_multiline>
    Path            filein => fileout
</Route>

Output Sample

------------------------------------------------------------------------------------
Iface   MTU Met   RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
eth2       1500 0  16936814      0      0 0      30486067      0      8      0 BMRU
lo        16436 0  277217234      0      0 0      277217234      0      0      0 LRU
tun0       1500 0    316943      0      0 0        368642      0      0      0 MOPRU
------------------------------------------------------------------------------------
Iface   MTU Met   RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
eth2       1500 0  16945117      0      0 0      30493583      0      8      0 BMRU
lo        16436 0  277217234      0      0 0      277217234      0      0      0 LRU
tun0       1500 0    316943      0      0 0        368642      0      0      0 MOPRU
------------------------------------------------------------------------------------
Iface   MTU Met   RX-OK RX-ERR RX-DRP RX-OVR    TX-OK TX-ERR TX-DRP TX-OVR Flg
eth2       1500 0  16945270      0      0 0      30493735      0      8      0 BMRU
lo        16436 0  277217234      0      0 0      277217234      0      0      0 LRU
tun0       1500 0    316943      0      0 0        368642      0      0      0 MOPRU