Delimiter-Separated Values (xm_csv)

This module provides functions and procedures for working with data formatted as comma-separated values (CSV). CSV input can be parsed into fields whilst output can be generated as CSV. Delimiters other than the comma are also supported.

To examine the supported platforms, see the list of installer packages in the Available Modules chapter.

The pm_transformer module provides a simple interface to parse and generate CSV format, but the xm_csv module exports an API that can be used to solve more complex tasks involving CSV-formatted data.

It is possible to use more than one xm_csv module instance with different options in order to support different CSV formats in the same configuration file. For this reason, functions and procedures exported by this module are public and must be referenced by the module instance name.

Configuration

The xm_csv module accepts the following directives in addition to the common module directives. The Fields directive is required.

Fields

This mandatory directive accepts a comma-separated list of fields which will be populated when parsing the input data. Field names with or without the dollar sign ($) are accepted. The fields will be stored as strings unless their types are explicitly specified with the FieldTypes directive.


Delimiter

This optional directive specifies the character to be used as the delimiter to separate fields. See the section on Specifying Delimiter Characters for more information. The default delimiter character is the comma (,). Note that there should not be a delimiter after the last field.

EscapeChar

This optional directive specifies the character to be used to escape special characters. See the section on Specifying Escape Characters for more information. The escape character is used to prefix the following characters: the escape character itself, the quote character, and the delimiter character. If EscapeControl is TRUE, the newline (\n), carriage return (\r), tab (\t), and backspace (\b) control characters are also escaped. The default escape character is the backslash character (\).

EscapeControl

If this optional boolean directive is set to TRUE, control characters are also escaped. See the EscapeChar directive for details. The default is TRUE: control characters are escaped. Note that this is necessary to allow single line CSV field lists which contain line-breaks.

FieldTypes

This optional directive specifies a list of field types corresponding to the field names defined in the Fields directive. If specified it must match the same number of fields. If this directive is omitted, all fields will be stored as strings. This directive has no effect on the fields-to-CSV conversion.

QuoteChar

This optional directive specifies the character to be used to quote/enclose fields. See the section on Specifying Quote Characters for more information. If QuoteOptional is TRUE, then only string type fields are quoted. The default is the double-quote character (").

QuoteMethod

This optional directive accepts the following values:

All

All fields will be quoted.

None

None of the fields will be quoted. This can be problematic if a field value, which is typically text that can contain any character, contains the delimiter character. When using this option, make sure that if the delimiter is found in the field value it is escaped or replaced with another character.

String

Only string type fields will be quoted. This has the same effect as QuoteOptional set to TRUE and is the default behavior if the QuoteMethod directive is not specified.

Note that this directive only effects CSV generation when using to_csv(). The CSV parser can automatically detect the quotation.

QuoteOptional

This directive has been deprecated in favor of QuoteMethod, which should be used instead.

StrictMode

If this optional boolean directive is set to TRUE, the CSV parser will fail to parse CSV lines that do not contain the required number of fields. When this is set to FALSE and the input contains fewer fields than specified in the Fields directive, the rest of the fields will be unset. The default value is FALSE.

UndefValue

This optional directive specifies a string which will be treated as an undefined value. This is particularly useful when parsing the W3C format where the dash (-) marks an omitted field.

Specifying Quote, Escape, and Delimiter Characters

The QuoteChar, EscapeChar, and Delimiter directives can be specified in several ways.

Unquoted single character

Any printable character can be specified as an unquoted character, except for the backslash (\):

Delimiter ;
Control characters

The following non-printable characters can be specified with escape sequences:

\a

audible alert (bell)

\b

backspace

\t

horizontal tab

\n

newline

\v

vertical tab

\f

formfeed

\r

carriage return

For example, to use TAB delimiting:

Delimiter \t
A character in single quotes

The configuration parser strips whitespace, so it is not possible to define a space as the delimiter unless it is enclosed within quotes:

Delimiter ' '

Printable characters can also be enclosed:

Delimiter ';'

The backslash can be specified when enclosed within quotes:

Delimiter '\'
A character in double quotes

Double quotes can be used like single quotes:

Delimiter " "

The backslash can be specified when enclosed within double quotes:

Delimiter "\"
A hexadecimal ASCII code

Hexadecimal ASCII character codes can be used prefixed with 0x. For example, the space can be specified as:

Delimiter 0x20

This is equivalent to:

Delimiter " "

Functions

The following functions are exported by xm_csv.

string to_csv()

Convert the specified fields to a single CSV formatted string.

Procedures

The following procedures are exported by xm_csv.

parse_csv();

Parse the $raw_event field as CSV input.

parse_csv(string source);

Parse the given string as CSV format.

to_csv();

Format the specified fields as CSV and put this into the $raw_event field.

Creating and populating fields

The parse_csv() procedure parses a string containing delimiter-separated values into structured data. It expects the $raw_event field or the string passed as a parameter to be in the following format:

value1,value2,value3

Once a log record is parsed with this procedure, additional fields are created based on the Fields directive. The fields can be used for further log processing or to convert the log record to a different output format. For an example of how to parse and process CSV log records, see Parsing CSV below.

Input modules may create additional fields containing various information. When converting to a different format, such fields will be included in the output log record, which may consume additional memory and bandwidth. For efficient handling of log records, consult the Fields section in the documentation of input modules and test the configuration before deployment. To delete any unwanted fields, use the delete() procedure or the xm_rewrite extension.

Examples

Example 1. Parsing CSV

This configuration uses the im_file input module to collect CSV logs from file. Log records are parsed into structured data using the parse_csv() procedure. If the log record has a severity of INFO, the record is dropped. Otherwise, the log record is converted to JSON using the to_json() procedure.

nxlog.conf
<Extension csv>
    Module      xm_csv
    Fields      $EventTime, $Severity, $Message
    Delimiter   ,
</Extension>

<Extension json>
    Module      xm_json
</Extension>

<Input file_input>
    Module      im_file
    File        'path/to/log/file'
    <Exec>
        csv->parse_csv();

        if ($Severity == "INFO")
            drop();

        to_json();
    </Exec>
</Input>
Input sample
2021-11-04T10:27:45.919858+03:00,ERROR,File not found
Output sample in JSON format
{
  "EventReceivedTime": "2021-11-04T10:27:58.919858+03:00"
  "SourceModuleName": "file_input",
  "SourceModuleType": "im_file",
  "EventTime": "2021-11-04T10:27:45.919858+03:00",
  "Severity": "ERROR",
  "Message": "File not found"
}
Example 2. Complex CSV format conversion

This example shows that the xm_csv module can not only parse and create CSV formatted input and output, but with multiple xm_csv module instances it is also possible to reorder, add, remove, or modify fields to output data in a different CSV format.

nxlog.conf
<Extension csv1>
    Module      xm_csv
    Fields      $id, $name, $number
    FieldTypes  integer, string, integer
    Delimiter   ,
</Extension>

<Extension csv2>
    Module      xm_csv
    Fields      $id, $number, $name, $date
    Delimiter   ;
</Extension>

<Input in>
    Module      im_file
    File        "tmp/input"
    <Exec>
        csv1->parse_csv();
        $date = now();
        if not defined $number $number = 0;
        csv2->to_csv();
    </Exec>
</Input>

<Output out>
    Module      om_file
    File        "tmp/output"
</Output>
Input Sample
1,"John K.",42
2,"Joe F.",43
Output Sample
1;42;"John K.";2011-01-15 23:45:20
2;43;"Joe F.";2011-01-15 23:45:20