The GrokReader Controller Service provides a means for parsing and structuring input that is made up of unstructured text, such as log files. Grok allows users to add a naming construct to Regular Expressions such that they can be composed in order to create expressions that are easier to manage and work with. This Controller Service consists of one Required Property and a few Optional Properties. The is named `Grok Pattern File` property specifies the filename of a file that contains Grok Patterns that can be used for parsing log data. If not specified, a default patterns file will be used. Its contents are provided below. There are also properties for specifying the schema to use when parsing data. The schema is not required. However, when data is parsed a Record is created that contains all of the fields present in the Grok Expression (explained below), and all fields are of type String. If a schema is chosen, the field can be declared to be a different, compatible type, such as number. Additionally, if the schema does not contain one of the fields in the parsed data, that field will be ignored. This can be used to filter out fields that are not of interest.

Note: a `_raw` field is also added to preserve the original message.

The Required Property is named `Grok Expression` and specifies how to parse each incoming record. This is done by providing a Grok Expression such as: `%{TIMESTAMP_ISO8601:timestamp} %{LOGLEVEL:level} \[%{DATA:thread}\] %{DATA:class} %{GREEDYDATA:message}`. This Expression will parse Apache NiFi log messages. This is accomplished by specifying that a line begins with the `TIMESTAMP_ISO8601` pattern (which is a Regular Expression defined in the default Grok Patterns File). The value that matches this pattern is then given the name `timestamp`. As a result, the value that matches this pattern will be assigned to a field named `timestamp` in the Record that produced by this Controller Service.

## No Match Behavior

If a line is encountered in the FlowFile that does not match the configured Grok Expression, it is assumed that the line is part of the previous message. If the line is the start of a stack trace, then the entire stack trace is read in and assigned to a field named `STACK_TRACE`. Otherwise, the line will be processed according to the value defined in the "No Match Behavior" property.

### Append to Previous Message

The line is appended to the last field defined in the Grok Expression. This is typically done because the last field is a 'message' type of field, which can consist of new-lines.

### Skip Line

The line is completely dismissed.

### Raw Line

The fields will be null except the `_raw` field that will contain the line allowing further processing downstream.

## Examples

Assuming two messages (`<6>Feb 28 12:00:00 192.168.0.1 aliyun[11111]: [error] Syslog test` and `This is a bad message...`) with the Grok Expression `<%{POSINT:priority}>%{SYSLOGTIMESTAMP:timestamp} %{SYSLOGHOST:hostname} %{WORD:ident}%{GREEDYDATA:message}` ; and assuming a JSON Writer, the following results will be generated:

### Append to Previous Message

``

    [ {
      "priority" : "6",
      "timestamp" : "Feb 28 12:00:00",
      "hostname" : "192.168.0.1",
      "ident" : "aliyun",
      "message" : "[11111]: [error] Syslog test\nThis is a bad message...",
      "stackTrace" : null,
      "_raw" : "<6>Feb 28 12:00:00 192.168.0.1 aliyun[11111]: [error] Syslog test\nThis is a bad message..."
    } ]

### Skip Line

``

    [ {
      "priority" : "6",
      "timestamp" : "Feb 28 12:00:00",
      "hostname" : "192.168.0.1",
      "ident" : "aliyun",
      "message" : "[11111]: [error] Syslog test",
      "stackTrace" : null,
      "_raw" : "<6>Feb 28 12:00:00 192.168.0.1 aliyun[11111]: [error] Syslog test"
    } ]

### Raw Line

``

    [ {
      "priority" : "6",
      "timestamp" : "Feb 28 12:00:00",
      "hostname" : "192.168.0.1",
      "ident" : "aliyun",
      "message" : "[11111]: [error] Syslog test",
      "stackTrace" : null,
      "_raw" : "<6>Feb 28 12:00:00 192.168.0.1 aliyun[11111]: [error] Syslog test"
    }, {
      "priority" : null,
      "timestamp" : null,
      "hostname" : null,
      "ident" : null,
      "message" : null,
      "stackTrace" : null,
      "_raw" : "This is a bad message..."
    } ]

## Schemas and Type Coercion

When a record is parsed from incoming data, it is separated into fields. Each of these fields is then looked up against the configured schema (by field name) in order to determine what the type of the data should be. If the field is not present in the schema, that field is omitted from the Record. If the field is found in the schema, the data type of the received data is compared against the data type specified in the schema. If the types match, the value of that field is used as-is. If the schema indicates that the field should be of a different type, then the Controller Service will attempt to coerce the data into the type specified by the schema. If the field cannot be coerced into the specified type, an Exception will be thrown.

The following rules apply when attempting to coerce a field value from one data type to another:

- Any data type can be coerced into a String type.
- Any numeric data type (Byte, Short, Int, Long, Float, Double) can be coerced into any other numeric data type.
- Any numeric value can be coerced into a Date, Time, or Timestamp type, by assuming that the Long value is the number of milliseconds since epoch (Midnight GMT, January 1, 1970).
- A String value can be coerced into a Date, Time, or Timestamp type, if its format matches the configured "Date Format," "Time Format," or "Timestamp Format."
- A String value can be coerced into a numeric value if the value is of the appropriate type. For example, the String value `8` can be coerced into any numeric type. However, the String value `8.2` can be coerced into a Double or Float type but not an Integer.
- A String value of "true" or "false" (regardless of case) can be coerced into a Boolean value.
- A String value that is not empty can be coerced into a Char type. If the String contains more than 1 character, the first character is used and the rest of the characters are ignored.
- Any "date/time" type (Date, Time, Timestamp) can be coerced into any other "date/time" type.
- Any "date/time" type can be coerced into a Long type, representing the number of milliseconds since epoch (Midnight GMT, January 1, 1970).
- Any "date/time" type can be coerced into a String. The format of the String is whatever DateFormat is configured for the corresponding property (Date Format, Time Format, Timestamp Format property).

If none of the above rules apply when attempting to coerce a value from one data type to another, the coercion will fail and an Exception will be thrown.

## Examples

As an example, consider that this Controller Service is configured with the following properties:

Property Name | Property Value
Grok Expression | `%{TIMESTAMP_ISO8601:timestamp} %{LOGLEVEL:level} \[%{DATA:thread}\] %{DATA:class} %{GREEDYDATA:message}`

Additionally, let's consider a FlowFile whose contents consists of the following:

`

    2016-08-04 13:26:32,473 INFO [Leader Election Notification Thread-1] o.a.n.c.l.e.CuratorLeaderElectionManager org.apache.nifi.controller.leader.election.CuratorLeaderElectionManager$ElectionListener@1fa27ea5 has been interrupted; no longer leader for role 'Cluster Coordinator'
    2016-08-04 13:26:32,474 ERROR [Leader Election Notification Thread-2] o.apache.nifi.controller.FlowController One
    Two
    Three
    org.apache.nifi.exception.UnitTestException: Testing to ensure we are able to capture stack traces
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_45]
    	at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [na:1.8.0_45]
            at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_45]
            at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [na:1.8.0_45]
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_45]
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_45]
            at java.lang.Thread.run(Thread.java:745) [na:1.8.0_45]
    Caused by: org.apache.nifi.exception.UnitTestException: Testing to ensure we are able to capture stack traces
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        ... 12 common frames omitted
    2016-08-04 13:26:35,475 WARN [Curator-Framework-0] org.apache.curator.ConnectionState Connection attempt unsuccessful after 3008 (greater than max timeout of 3000). Resetting connection and trying again with a new connection.

`

In this case, the result will be that this FlowFile consists of 3 different records. The first record will contain the following values:

Field Name | Field Value
timestamp | 2016-08-04 13:26:32,473
level | INFO
thread | Leader Election Notification Thread-1
class | o.a.n.c.l.e.CuratorLeaderElectionManager
message | org.apache.nifi.controller.leader.election.CuratorLeaderElectionManager$ElectionListener@1fa27ea5 has been interrupted; no longer leader for role 'Cluster Coordinator'
STACK_TRACE | null

The second record will contain the following values:

Field Name | Field Value
timestamp | 2016-08-04 13:26:32,474
level | ERROR
thread | Leader Election Notification Thread-2
class | o.apache.nifi.controller.FlowController
message | One Two Three
STACK_TRACE |
    org.apache.nifi.exception.UnitTestException: Testing to ensure we are able to capture stack traces
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
            at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_45]
    	at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [na:1.8.0_45]
            at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_45]
            at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [na:1.8.0_45]
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_45]
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_45]
            at java.lang.Thread.run(Thread.java:745) [na:1.8.0_45]
    Caused by: org.apache.nifi.exception.UnitTestException: Testing to ensure we are able to capture stack traces
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        at org.apache.nifi.cluster.coordination.node.NodeClusterCoordinator.getElectedActiveCoordinatorAddress(NodeClusterCoordinator.java:185)
        ... 12 common frames omitted

The third record will contain the following values:

Field Name | Field Value
timestamp | 2016-08-04 13:26:35,475
level | WARN
thread | Curator-Framework-0
class | org.apache.curator.ConnectionState
message | Connection attempt unsuccessful after 3008 (greater than max timeout of 3000). Resetting connection and trying again with a new connection.
STACK_TRACE | null

##

## Default Patterns

The following patterns are available in the default Grok Pattern File:

`

    # Log Levels
    LOGLEVEL ([Aa]lert|ALERT|[Tt]race|TRACE|[Dd]ebug|DEBUG|[Nn]otice|NOTICE|[Ii]nfo|INFO|[Ww]arn?(?:ing)?|WARN?(?:ING)?|[Ee]rr?(?:or)?|ERR?(?:OR)?|[Cc]rit?(?:ical)?|CRIT?(?:ICAL)?|[Ff]atal|FATAL|[Ss]evere|SEVERE|EMERG(?:ENCY)?|[Ee]merg(?:ency)?)|FINE|FINER|FINEST|CONFIG

    # Syslog Dates: Month Day HH:MM:SS
    SYSLOGTIMESTAMP %{MONTH} +%{MONTHDAY} %{TIME}
    PROG (?:[\w._/%-]+)
    SYSLOGPROG %{PROG:program}(?:\[%{POSINT:pid}\])?
    SYSLOGHOST %{IPORHOST}
    SYSLOGFACILITY <%{NONNEGINT:facility}.%{NONNEGINT:priority}>
    HTTPDATE %{MONTHDAY}/%{MONTH}/%{YEAR}:%{TIME} %{INT}

    # Months: January, Feb, 3, 03, 12, December
    MONTH \b(?:Jan(?:uary)?|Feb(?:ruary)?|Mar(?:ch)?|Apr(?:il)?|May|Jun(?:e)?|Jul(?:y)?|Aug(?:ust)?|Sep(?:tember)?|Oct(?:ober)?|Nov(?:ember)?|Dec(?:ember)?)\b
    MONTHNUM (?:0?[1-9]|1[0-2])
    MONTHNUM2 (?:0[1-9]|1[0-2])
    MONTHDAY (?:(?:0[1-9])|(?:[12][0-9])|(?:3[01])|[1-9])

    # Days: Monday, Tue, Thu, etc...
    DAY (?:Mon(?:day)?|Tue(?:sday)?|Wed(?:nesday)?|Thu(?:rsday)?|Fri(?:day)?|Sat(?:urday)?|Sun(?:day)?)

    # Years?
    YEAR (?>\d\d){1,2}
    HOUR (?:2[0123]|[01]?[0-9])
    MINUTE (?:[0-5][0-9])
    # '60' is a leap second in most time standards and thus is valid.
    SECOND (?:(?:[0-5]?[0-9]|60)(?:[:.,][0-9]+)?)
    TIME (?!<[0-9])%{HOUR}:%{MINUTE}(?::%{SECOND})(?![0-9])

    # datestamp is YYYY/MM/DD-HH:MM:SS.UUUU (or something like it)
    DATE_US_MONTH_DAY_YEAR %{MONTHNUM}[/-]%{MONTHDAY}[/-]%{YEAR}
    DATE_US_YEAR_MONTH_DAY %{YEAR}[/-]%{MONTHNUM}[/-]%{MONTHDAY}
    DATE_US %{DATE_US_MONTH_DAY_YEAR}|%{DATE_US_YEAR_MONTH_DAY}
    DATE_EU %{MONTHDAY}[./-]%{MONTHNUM}[./-]%{YEAR}
    ISO8601_TIMEZONE (?:Z|[+-]%{HOUR}(?::?%{MINUTE}))
    ISO8601_SECOND (?:%{SECOND}|60)
    TIMESTAMP_ISO8601 %{YEAR}-%{MONTHNUM}-%{MONTHDAY}[T ]%{HOUR}:?%{MINUTE}(?::?%{SECOND})?%{ISO8601_TIMEZONE}?
    DATE %{DATE_US}|%{DATE_EU}
    DATESTAMP %{DATE}[- ]%{TIME}
    TZ (?:[PMCE][SD]T|UTC)
    DATESTAMP_RFC822 %{DAY} %{MONTH} %{MONTHDAY} %{YEAR} %{TIME} %{TZ}
    DATESTAMP_RFC2822 %{DAY}, %{MONTHDAY} %{MONTH} %{YEAR} %{TIME} %{ISO8601_TIMEZONE}
    DATESTAMP_OTHER %{DAY} %{MONTH} %{MONTHDAY} %{TIME} %{TZ} %{YEAR}
    DATESTAMP_EVENTLOG %{YEAR}%{MONTHNUM2}%{MONTHDAY}%{HOUR}%{MINUTE}%{SECOND}

    POSINT \b(?:[1-9][0-9]*)\b
    NONNEGINT \b(?:[0-9]+)\b
    WORD \b\w+\b
    NOTSPACE \S+
    SPACE \s*
    DATA .*?
    GREEDYDATA .*
    QUOTEDSTRING (?>(?"(?>\\.|[^\\"]+)+"|""|(?>'(?>\\.|[^\\']+)+')|''|(?>`(?>\\.|[^\\`]+)+`)|``))
    UUID [A-Fa-f0-9]{8}-(?:[A-Fa-f0-9]{4}-){3}[A-Fa-f0-9]{12}

    USERNAME [a-zA-Z0-9._-]+
    USER %{USERNAME}
    INT (?:[+-]?(?:[0-9]+))
    BASE10NUM (?[+-]?(?:(?:[0-9]+(?:\.[0-9]+)?)|(?:\.[0-9]+)))
    NUMBER (?:%{BASE10NUM})
    BASE16NUM (?/(?>[\w_%!$@:.,-]+|\\.)*)+
    TTY (?:/dev/(pts|tty([pq])?)(\w+)?/?(?:[0-9]+))
    WINPATH (?>[A-Za-z]+:|\\)(?:\\[^\\?*]*)+
    URIPROTO [A-Za-z]+(\+[A-Za-z+]+)?
    URIHOST %{IPORHOST}(?::%{POSINT:port})?
    # uripath comes loosely from RFC1738, but mostly from what Firefox
    # doesn't turn into %XX
    URIPATH (?:/[A-Za-z0-9$.+!*'(){},~:;=@#%_\-]*)+
    #URIPARAM \?(?:[A-Za-z0-9]+(?:=(?:[^&]*))?(?:&(?:[A-Za-z0-9]+(?:=(?:[^&]*))?)?)*)?
    URIPARAM \?[A-Za-z0-9$.+!*'|(){},~@#%&/=:;_?\-\[\]]*
    URIPATHPARAM %{URIPATH}(?:%{URIPARAM})?
    URI %{URIPROTO}://(?:%{USER}(?::[^@]*)?@)?(?:%{URIHOST})?(?:%{URIPATHPARAM})?

    # Shortcuts
    QS %{QUOTEDSTRING}

    # Log formats
    SYSLOGBASE %{SYSLOGTIMESTAMP:timestamp} (?:%{SYSLOGFACILITY} )?%{SYSLOGHOST:logsource} %{SYSLOGPROG}:
    COMMONAPACHELOG %{IPORHOST:clientip} %{USER:ident} %{USER:auth} \[%{HTTPDATE:timestamp}\] "(?:%{WORD:verb} %{NOTSPACE:request}(?: HTTP/%{NUMBER:httpversion})?|%{DATA:rawrequest})" %{NUMBER:response} (?:%{NUMBER:bytes}|-)
    COMBINEDAPACHELOG %{COMMONAPACHELOG} %{QS:referrer} %{QS:agent}

`