parse_syslog

Parses a string as a Syslog message.

parse_syslog [octet_counting=bool, raw=bool, schema=string, selector=string,
              schema_only=bool, unflatten_separator=string]

Description

Parses a string as a Syslog message.

Tenzir supports reading syslog messages in both the standardized “Syslog Protocol” format (RFC 5424), and the older “BSD syslog Protocol” format (RFC 3164).

input: string

The string to parse as a syslog message.

octet_counting = bool (optional)

Controls handling of length-prefixed syslog messages as defined in RFC 6587. Some syslog implementations prepend the message length in bytes, followed by a space:

<length> <syslog-message>

For example, where 65 is the byte count of the syslog message that follows:

65 <165>1 2023-10-11T22:14:15.003Z host app 1234 ID01 - Test message

The parameter supports three modes:

• Not specified (default): Auto-detect. Treats the length prefix as a hint, not an authority. The parser first tries to parse the full message; if that fails and a valid prefix is present, it falls back to parsing the truncated message. This maximizes leniency for messages that happen to start with digits.
• octet_counting=true: Require and trust the length prefix. Emits a warning and returns null if the input lacks a valid prefix. If the message is longer than the stated length, truncates to the stated length before parsing.
• octet_counting=false: Never strip a length prefix. Parse the input as-is, treating any leading digits as part of the message.

raw = bool (optional)

Use only the raw types that are native to the parsed format. Fields that have a type specified in the chosen schema will still be parsed according to the schema.

schema = string (optional)

Provide the name of a schema to be used by the parser.

If a schema with a matching name is installed, the result will always have all fields from that schema.

• Fields that are specified in the schema, but did not appear in the input will be null.
• Fields that appear in the input, but not in the schema will also be kept. Use schema_only=true to reject fields that are not in the schema.

If the given schema does not exist, this option instead assigns the output schema name only.

The schema option is incompatible with the selector option.

selector = string (optional)

Designates a field value as schema name with an optional dot-separated prefix.

The string is parsed as <fieldname>[:<prefix>]. The prefix is optional and will be prepended to the field value to generate the schema name.

For example, the Suricata EVE JSON format includes a field event_type that contains the event type. Setting the selector to event_type:suricata causes an event with the value flow for the field event_type to map onto the schema suricata.flow.

The selector option is incompatible with the schema option.

schema_only = bool (optional)

When working with an existing schema, this option will ensure that the output schema has only the fields from that schema.

If the schema name is obtained via a selector and it does not exist, this has no effect.

This option requires either schema or selector to be set.

unflatten_separator = string (optional)

A delimiter that, if present in keys, causes values to be treated as values of nested records.

A popular example of this is the Zeek JSON format. It includes the fields id.orig_h, id.orig_p, id.resp_h, and id.resp_p at the top-level. The data is best modeled as an id record with four nested fields orig_h, orig_p, resp_h, and resp_p.

Without an unflatten separator, the data looks like this:

Without unflattening

{
  "id.orig_h": "1.1.1.1",
  "id.orig_p": 10,
  "id.resp_h": "1.1.1.2",
  "id.resp_p": 5
}

With the unflatten separator set to ., Tenzir reads the events like this:

With 'unflatten'

{
  "id": {
    "orig_h": "1.1.1.1",
    "orig_p": 10,
    "resp_h": "1.1.1.2",
    "resp_p": 5
  }
}

Duplicate Keys

If the parser encounters a duplicate key in an event, it will transparently upgrade the field to be a list of values instead.

For a simple example, consider this JSON file:

Duplicate Keys

{"key": 7}
{"key": 0.0, "key": 1}
{"key": 42}

{key: 7}
{key: [0.0, 1.0]}
{key: 42}

If the values are of different type, conversions to a common type will be attempted, such as to a common number type. Ultimately values will be stringified if they do not share a common type:

Type Conflict

{"key": 0.0, "key": "1.1.1.1", "key": "example.com"}

{key: ["0", "1.1.1.1", "example.com"]}

Examples

Parse a RFC5424 syslog string

from { input: r#"<165>8 2023-10-11T22:14:15.003Z mymachineexamplecom evntslog 1370 ID47 [exampleSDID@32473 eventSource="Application" eventID="1011"] Event log entry"#}
output = input.parse_syslog()

{
  input: "<165>8 2023-10-11T22:14:15.003Z mymachineexamplecom evntslog 1370 ID47 [exampleSDID@32473 eventSource=\"Application\" eventID=\"1011\"] Event log entry",
  output: {
    facility: 20,
    severity: 5,
    version: 8,
    timestamp: 2023-10-11T22:14:15.003Z,
    hostname: "mymachineexamplecom",
    app_name: "evntslog",
    process_id: "1370",
    message_id: "ID47",
    structured_data: {
      "exampleSDID@32473": {
        eventSource: "Application",
        eventID: 1011,
      },
    },
    message: "Event log entry",
  },
}

Parse an octet-counted syslog message

When dealing with syslog messages that use RFC 6587 octet counting, the function auto-detects and strips the length prefix:

from {
  input: "119 <165>1 2023-10-11T22:14:15.003Z mymachineexamplecom evntslog 1370 ID47 [exampleSDID@32473 iut=\"3\"] Event log entry"
}
output = input.parse_syslog()

{
  input: "119 <165>1 2023-10-11T22:14:15.003Z mymachineexamplecom evntslog 1370 ID47 [exampleSDID@32473 iut=\"3\"] Event log entry",
  output: {
    facility: 20,
    severity: 5,
    version: 1,
    timestamp: 2023-10-11T22:14:15.003Z,
    hostname: "mymachineexamplecom",
    app_name: "evntslog",
    process_id: "1370",
    message_id: "ID47",
    structured_data: {
      "exampleSDID@32473": {
        iut: 3,
      },
    },
    message: "Event log entry",
  },
}

Use octet_counting=true to require the prefix or octet_counting=false to disable auto-detection.

See Also

• read_syslog
• write_syslog
• Syslog