The XML parser comes with certain limitations.
Vector-like structures:
It is not possible to address each element of a vector-like structure individually. For example, take this input:
<vector>
<entry>value1</entry>
<entry>value2</entry>
...
<entry>valueN</entry>
</vector>
After parsing, the entries cannot be addressed individually. Instead, the text of the entries will be concatenated:
vector.entry = "value1value2...valueN"
Note that xmllint has the same behavior:
$ xmllint --xpath "/vector/entry/text()" test.xml
value1value2valueN%
CDATA:
The XML parser does not support CDATA. CDATA inside the XML input is ignored. This is true for the processing instructions as well.
Inherited limitations:
The XML parser is based on the glib XML subset parser, called "GMarkup" parser, which is not a full-scale XML parser. It is intended to parse a simple markup format that is a subset of XML. Some limitations are inherited:
-
Do not use the XML parser if you expect to interoperate with applications generating full-scale XML. Instead, use it for application data files, configuration files, log files, and so on, where you know your application will be the only one writing the file.
-
The XML parser is not guaranteed to display an error message in the case of invalid XML. It may accept invalid XML. However, it does not accept XML input that is not well-formed (a condition that is weaker than requiring XML to be valid).
No support for long keys:
If the key is longer than 255 characters, syslog-ng drops the entry and an error log is emitted. There is no chunking or any other way of recovering data, not even partial data. The entry will be replaced by an empty string.
The XML parser has the following options.
drop-invalid
| Synopsis: |
drop-invalid() |
| Format: |
yes|no |
| Default: |
no |
| Mandatory: |
no |
Description: If set, messages with an invalid XML will be dropped entirely.
exclude-tags
| Synopsis: |
exclude-tags() |
| Format: |
list of globs |
| Default: |
None
If not set, no filtering is done. |
| Mandatory: |
no |
Description: The XML parser matches tags against the listed globs. If there is a match, the given subtree of the XML will be omitted.
Example: Using exclude_tags
parser xml_parser {
xml(
template("$MSG")
exclude-tags("tag1", "tag2", "inner*")
);
};
From this XML input:
<tag1>Text1</tag1><tag2>Text2</tag2><tag3>Text3<innertag>TextInner</innertag></tag3>
The following output is generated:
{"_xml":{"tag3":"Text3"}}
prefix()
Description: Insert a prefix before the name part of the parsed name-value pairs to help further processing. For example:
-
To insert the my-parsed-data. prefix, use the prefix(my-parsed-data.) option.
-
To refer to a particular data that has a prefix, use the prefix in the name of the macro, for example, ${my-parsed-data.name}.
-
If you forward the parsed messages using the IETF-syslog protocol, you can insert all the parsed data into the SDATA part of the message using the prefix(.SDATA.my-parsed-data.) option.
Names starting with a dot (for example, .example) are reserved for use by syslog-ng OSE. If you use such a macro name as the name of a parsed value, it will attempt to replace the original value of the macro (note that only soft macros can be overwritten, see Hard versus soft macros for details). To avoid such problems, use a prefix when naming the parsed values, for example, prefix(my-parsed-data.)
The prefix() option is optional and its default value is ".xml".
strip-whitespaces
| Synopsis: |
strip-whitespaces() |
| Format: |
yes|no |
| Default: |
no |
| Mandatory: |
no |
Description: Strip the whitespaces from the XML text nodes before adding them to the message.
Example: Using strip-whitespaces
parser xml_parser {
xml(
template("$MSG")
strip-whitespaces(yes)
);
};
From this XML input:
<tag1> Tag </tag1>
The following output is generated:
{"_xml":{"tag1":"Tag"}}
template()
| Synopsis: |
template("${<macroname>}") |
Description: The macro that contains the part of the message that the parser will process. It can also be a macro created by a previous parser of the log path. By default, the parser processes the entire message (${MESSAGE}).
The date parser can extract dates from non-syslog messages. It operates by default on the ${MESSAGE} part of the log message, but can operate on any template or field provided. The parsed date will be available as the sender date (that is, the ${S_DATE}, ${S_ISODATE}, ${S_MONTH}, and so on, and related macros). (To store the parsed date as the received date, use the time-stamp(recvd) option.)
NOTE: Note that parsing will fail if the format string does not match the entire template or field. Since by default syslog-ng Open Source Edition (syslog-ng OSE) uses the ${MESSAGE} part of the log message, parsing will fail, unless the log message contains only a date, but that is unlikely, so practically you will have to segment the message (for example, using a csv-parser()) before using the date-parser(). You can also use date-parser() to parse dates received in a JSON or key-value-formatted log message.
Declaration
parser parser_name {
date-parser(
format("<format-string-for-the-date>")
template("<field-to-parse>'")
);
};
Example: Using the date-parser()
In the following example, syslog-ng OSE parses dates like 01/Jan/2016:13:05:05 PST from a field called MY_DATE using the following format string: format("%d/%b/%Y:%H:%M:%S %Z") (how you create this field from the incoming message is not shown in the example). In the destination template every message will begin with the timestamp in ISODATE format. Since the syslog parser is disabled, syslog-ng OSE will include the entire original message (including the original timestamp) in the ${MESSAGE} macro.
source s_file {
file("/tmp/input" flags(no-parse));
};
destination d_file {
file(
"/tmp/output"
template("${S_ISODATE} ${MESSAGE}\n")
);
};
log {
source(s_file);
parser { date-parser(format("%d/%b/%Y:%H:%M:%S %Z") template("${MY_DATE}")); };
destination(d_file);
};
In the template option, you can use template functions to specify which part of the message to parse with the format string. The following example selects the first 24 characters of the ${MESSAGE} macro.
date-parser(format("%d/%b/%Y:%H:%M:%S %Z") template("$(substr ${MESSAGE} 0 24)") );
In syslog-ng OSE version 3.23 and later, you can specify a comma-separated list of formats to parse multiple date formats with a single parser. For example:
date-parser(format(
"%FT%T.%f",
"%F %T,%f",
"%F %T"
));
If you need to modify or correct the timezone of the message after parsing, see Rewrite the timezone of a message.
The date-parser() parser has the following options.
format()
| Synopsis: |
format(string) |
| Default: |
|
Description: Specifies the format how syslog-ng OSE should parse the date. You can use the following format elements:
%% PERCENT
%a day of the week, abbreviated
%A day of the week
%b month abbr
%B month
%c MM/DD/YY HH:MM:SS
%C ctime format: Sat Nov 19 21:05:57 1994
%d numeric day of the month, with leading zeros (eg 01..31)
%e like %d, but a leading zero is replaced by a space (eg 1..31)
%f microseconds, leading 0's, extra digits are silently discarded
%D MM/DD/YY
%G GPS week number (weeks since January 6, 1980)
%h month, abbreviated
%H hour, 24 hour clock, leading 0's)
%I hour, 12 hour clock, leading 0's)
%j day of the year
%k hour
%l hour, 12 hour clock
%L month number, starting with 1
%m month number, starting with 01
%M minute, leading 0's
%n NEWLINE
%o ornate day of month -- "1st", "2nd", "25th", etc.
%p AM or PM
%P am or pm (Yes %p and %P are backwards :)
%q Quarter number, starting with 1
%r time format: 09:05:57 PM
%R time format: 21:05
%s seconds since the Epoch, UCT
%S seconds, leading 0's
%t TAB
%T time format: 21:05:57
%U week number, Sunday as first day of week
%w day of the week, numerically, Sunday == 0
%W week number, Monday as first day of week
%x date format: 11/19/94
%X time format: 21:05:57
%y year (2 digits)
%Y year (4 digits)
%Z timezone in ascii format (for example, PST), or in format -/+0000
%z timezone in ascii format (for example, PST), or in format -/+0000 (Required element)
|
|
CAUTION: When using the %z and %Z format elements, consider that while %z strictly expects a specified timezone, and triggers a warning if the timezone is not specified, %Z does not trigger a warning if the timezone is not specified.
For further information about the %z and %Z format elements, see the 'DESCRIPTION' section on the srtptime(3) - NetBSD Manual Pages. |
For example, for the date 01/Jan/2016:13:05:05 PST use the following format string: format("%d/%b/%Y:%H:%M:%S %Z")
In syslog-ng OSE version 3.23 and later, you can specify a comma-separated list of formats to parse multiple date formats with a single parser. For example:
date-parser(format(
"%FT%T.%f",
"%F %T,%f",
"%F %T"
));
template()
| Synopsis: |
template("${<macroname>}") |
Description: The macro that contains the part of the message that the parser will process. It can also be a macro created by a previous parser of the log path. By default, the parser processes the entire message (${MESSAGE}).
flags()
| Type: |
guess-timezone |
| Default: |
empty string |
guess-timezone: Attempt to guess the timezone of the message if this information is not available in the message. Works when the incoming message stream is close to real time, and the timezone information is missing from the timestamp. For example:
date-parser(flags(guess-timezone));
time-stamp()
| Synopsis: |
stamp | recvd |
| Default: |
stamp |
Description: Determines if the parsed date values are treated as sent or received date. If you use time-stamp(stamp), syslog-ng OSE adds the parsed date to the S_ macros (corresponding to the sent date). If you use time-stamp(recvd), syslog-ng OSE adds the parsed date to the R_ macros (corresponding to the received date).
time-zone()
| Synopsis: |
time-zone(string) |
| Default: |
|
Description: If this option is set, syslog-ng OSE assumes that the parsed timestamp refers to the specified timezone. The timezone set in the time-zone() option overrides any timezone information parsed from the timestamp.
The timezone can be specified by using the name, for example, time-zone("Europe/Budapest")), or as the timezone offset in +/-HH:MM format, for example, +01:00). On Linux and UNIX platforms, the valid timezone names are listed under the /usr/share/zoneinfo directory.
