Stellar Language

Boolean Expressions

Variables may be used in boolean expressions and variables which are not explicitly boolean may be interpreted as booleans subject to the following rules:

• Similar to python and javascript, empty collections (e.g. []) will be interpreted as false
• Similar to python and javascript, missing variables will be interpreted as false
• Variables set to null will be interpreted as false

Otherwise, boolean variables will be interpreted as their values reflect.

Stellar Language Keywords

The following keywords need to be single quote escaped in order to be used in Stellar expressions:

Using parens such as: “foo” : “<ok>” requires escaping; “foo”: “'<ok>'”

Stellar Language Inclusion Checks (in and not in)

1. in supports string contains. e.g. 'foo' in 'foobar' == true
2. in supports collection contains. e.g. 'foo' in [ 'foo', 'bar' ] == true
3. in supports map key contains. e.g. 'foo' in { 'foo' : 5} == true
4. not in is the negation of the in expression. e.g. 'grok' not in 'foobar' == true

Stellar Language Comparisons (<, <=, >, >=)

1. If either side of the comparison is null then return false.
2. If both values being compared implement number then the following:
   • If either side is a double then get double value from both sides and compare using given operator.
   • Else if either side is a float then get float value from both sides and compare using given operator.
   • Else if either side is a long then get long value from both sides and compare using given operator.
   • Otherwise get the int value from both sides and compare using given operator.
3. If both sides are of the same type and are comparable then use the compareTo method to compare values.
4. If none of the above are met then an exception is thrown.

Stellar Language Equality Check (==, !=)

Below is how the == operator is expected to work:

1. If either side of the expression is null then check equality using Java’s == expression.
2. Else if both sides of the expression are of Java’s type Number then:
   • If either side of the expression is a double then use the double value of both sides to test equality.
   • Else if either side of the expression is a float then use the float value of both sides to test equality.
   • Else if either side of the expression is a long then use long value of both sides to test equality.
   • Otherwise use int value of both sides to test equality
3. Otherwise use equals method compare the left side with the right side.

The != operator is the negation of the above.

Stellar Language Lambda Expressions

Stellar provides the capability to pass lambda expressions to functions which wish to support that layer of indirection. The syntax is:

• (named_variables) -> stellar_expression : Lambda expression with named variables
  • For instance, the lambda expression which calls TO_UPPER on a named argument x could be be expressed as (x) -> TO_UPPER(x).
• var -> stellar_expression : Lambda expression with a single named variable, var
  • For instance, the lambda expression which calls TO_UPPER on a named argument x could be expressed as x -> TO_UPPER(x). Note, this is more succinct but equivalent to the example directly above.
• () -> stellar_expression : Lambda expression with no named variables.
  • If no named variables are needed, you may omit the named variable section. For instance, the lambda expression which returns a constant false would be () -> false

where

• named_variables is a comma separated list of variables to use in the Stellar expression
• stellar_expression is an arbitrary stellar expression

In the core language functions, we support basic functional programming primitives such as

• MAP - Applies a lambda expression over a list of input. For instance MAP([ 'foo', 'bar'], (x) -> TO_UPPER(x) ) returns [ 'FOO', 'BAR' ]
• FILTER - Filters a list by a predicate in the form of a lambda expression. For instance FILTER([ 'foo', 'bar'], (x ) -> x == 'foo' ) returns [ 'foo' ]
• REDUCE - Applies a function over a list of input. For instance REDUCE([ 1, 2, 3], (sum, x) -> sum + x, 0 ) returns 6

Stellar Language Match Expression

Stellar provides the capability to write match expressions, which are similar to switch statements commonly found in c like languages.

The syntax is:

• match{ logical_expression1 => evaluation expression1, logical_expression2 => evaluation_expression2, default => default_expression}

Where:

• logical_expression is a Stellar expression that evaluates to true or false. For instance var > 0 or var > 0 AND var2 == 'foo' or IF ... THEN ... ELSE
• evaluation_expression is a Stellar Expression
• default is a required default return value, should no logical expression match

default is required

Lambda expressions are supported, but they must be no argument lambdas such as () -> STATEMENT

• Only the first clause that evaluates to true will be executed.

APPEND_IF_MISSING

• Description: Appends the suffix to the end of the string if the string does not already end with any of the suffixes.
• Input:
  • string - The string to be appended.
  • suffix - The string suffix to append to the end of the string.
  • additionalsuffix - Optional - Additional string suffix that is a valid terminator.
• Returns: A new String if prefix was prepended, the same string otherwise.

ASN_GET

• Description: Look up an IPV4 address and returns Autonomous System Number information about it
• Input:
  • ip - The IPV4 address to lookup
  • fields - Optional list of ASN fields to grab. Options are network, autonomous_system_number, autonomous_system_organization.
• Returns: If a Single field is requested a string of the field, If multiple fields a map of string of the fields, and null otherwise

BLOOM_ADD

• Description: Adds an element to the bloom filter passed in
• Input:
  • bloom - The bloom filter
  • value(s) - The value(s) to add
• Returns: Bloom Filter

BLOOM_EXISTS

• Description: If the bloom filter contains the value
• Input:
  • bloom - The bloom filter
  • value - The value to check
• Returns: True if the filter might contain the value and false otherwise

BLOOM_INIT

• Description: Returns an empty bloom filter
• Input:
  • expectedInsertions - The expected insertions
  • falsePositiveRate - The false positive rate you are willing to tolerate
• Returns: Bloom Filter

BLOOM_MERGE

• Description: Returns a merged bloom filter
• Input:
  • bloomfilters - A list of bloom filters to merge
• Returns: Bloom Filter or null if the list is empty

CEILING

• Description: Returns the ceiling of a number.
• Input:
  • number - The number to take the ceiling of
• Returns: The ceiling of the number passed in.

COS

• Description: Returns the cosine of a number.
• Input:
  • number - The number to take the cosine of
• Returns: The cosine of the number passed in.

CHOP

• Description: Remove the last character from a String
• Input:
  • string - the String to chop last character from, may be null
• Returns: String without last character, null if null String input

CHOMP

• Description: Removes one newline from end of a String if it’s there, otherwise leave it alone. A newline is “\n”, “\r”, or “\r\n”
• Input:
  • string - the String to chomp a newline from, may be null
• Returns: String without newline, null if null String input

COUNT_MATCHES

• Description: Counts how many times the substring appears in the larger string.
• Input:
  • string - the CharSequence to check, may be null.
  • substring/character - the substring or character to count, may be null.
• Returns: the number of non-overlapping occurrences, 0 if either CharSequence is null.

DATE_FORMAT

• Description: Takes an epoch timestamp and converts it to a date format.
• Input:
  • format - DateTime format as a String.
  • timestampField - Optional epoch time in Long format. Defaults to now.
  • timezone - Optional timezone in String format.
• Returns: Formatted date.

DAY_OF_MONTH

• Description: The numbered day within the month. The first day within the month has a value of 1.
• Input:
  • dateTime - The datetime as a long representing the milliseconds since unix epoch
• Returns: The numbered day within the month.

DAY_OF_WEEK

• Description: The numbered day within the week. The first day of the week, Sunday, has a value of 1.
• Input:
  • dateTime - The datetime as a long representing the milliseconds since unix epoch
• Returns: The numbered day within the week.

DAY_OF_YEAR

• Description: The day number within the year. The first day of the year has value of 1.
• Input:
  • dateTime - The datetime as a long representing the milliseconds since unix epoch
• Returns: The day number within the year.

DECODE

• Description: Decodes the passed string with the provided encoding, which must be one of the encodings returned from GET_SUPPORTED_ENCODINGS
• Input:
  • string - the string to decode
  • encoding - the encoding to use, must be one of encodings returned from GET_SUPPORTED_ENCODINGS
  • verify - (optional), true or false to determine if string should be verified as being encoded with the passed encoding
• Returns:
  • The decoded string on success
  • The original string the string cannot be decoded
  • null on usage error

DOMAIN_REMOVE_SUBDOMAINS

• Description: Removes the subdomains from a domain.
• Input:
  • domain - Fully qualified domain name
• Returns: The domain without the subdomains. (for example, DOMAIN_REMOVE_SUBDOMAINS(‘mail.yahoo.com’) yields ‘yahoo.com’)

DOMAIN_REMOVE_TLD

• Description: Removes the top level domain (TLD) suffix from a domain.
• Input:
  • domain - Fully qualified domain name
• Returns: The domain without the TLD. (for example, DOMAIN_REMOVE_TLD(‘mail.yahoo.co.uk’) yields ‘mail.yahoo’)

DOMAIN_TO_TLD

• Description: Extracts the top level domain from a domain
• Input:
  • domain - Fully qualified domain name
• Returns: The TLD of the domain. (for example, DOMAIN_TO_TLD(‘mail.yahoo.co.uk’) yields ‘co.uk’)

ENCODE

• Description: Encodes the passed string with the provided encoding, which must be one of the encodings returned from GET_SUPPORTED_ENCODINGS
• Input:
  • string - the string to encode
  • encoding - the encoding to use, must be one of encodings returned from GET_SUPPORTED_ENCODINGS
• Returns:
  • The encoded string on success
  • null on error

ENDS_WITH

• Description: Determines whether a string ends with a specified suffix
• Input:
  • string - The string to test
  • suffix - The proposed suffix
• Returns: True if the string ends with the specified suffix and false if otherwise

ENRICHMENT_EXISTS

• Description: Interrogates the HBase table holding the simple hbase enrichment data and returns whether the enrichment type and indicator are in the table.
• Input:
  • enrichment_type - The enrichment type
  • indicator - The string indicator to look up
  • nosql_table - The NoSQL Table to use
  • column_family - The Column Family to use
• Returns: True if the enrichment indicator exists and false otherwise

ENRICHMENT_GET

• Description: Interrogates the HBase table holding the simple hbase enrichment data and retrieves the tabular value associated with the enrichment type and indicator.
• Input:
  • enrichment_type - The enrichment type
  • indicator - The string indicator to look up
  • nosql_table - The NoSQL Table to use
  • column_family - The Column Family to use
• Returns: A Map associated with the indicator and enrichment type. Empty otherwise.

EXP

• Description: Returns Euler’s number raised to the power of the argument.
• Input:
  • number - The power to which e is raised.
• Returns: Euler’s number raised to the power of the argument.

FILL_LEFT

• Description: Fills or pads a given string with a given character, to a given length on the left
• Input:
  • input - string
  • fill - the fill character
  • len - the required length
• Returns: the filled string

FILL_RIGHT

• Description: Fills or pads a given string with a given character, to a given length on the right
• Input:
  • input - string
  • fill - the fill character string
  • len - the required length
• Returns: Last element of the list

FILTER

• Description: Applies a filter in the form of a lambda expression to a list. e.g. FILTER( [ 'foo', 'bar' ] , (x) -> x == 'foo') would yield [ 'foo']
• Input:
  • list - List of arguments.
  • predicate - The lambda expression to apply. This expression is assumed to take one argument and return a boolean.
• Returns: The input list filtered by the predicate.

FLOOR

• Description: Returns the floor of a number.
• Input:
  • number - The number to take the floor of
• Returns: The floor of the number passed in.

FORMAT

• Description: Returns a formatted string using the specified format string and arguments. Uses Java’s string formatting conventions.
• Input:
  • format - string
  • arguments… - object(s)
• Returns: A formatted string.

FUZZY_LANGS

• Description: Returns a list of IETF BCP 47 available to the system, such as en, fr, de.
• Returns: A list of IEF BGP 47 language tag strings

FUZZY_SCORE

• Description: Returns the Fuzzy Score which indicates the similarity score between two strings. One point is given for every matched character. Subsequent matches yield two bonus points. A higher score indicates a higher similarity.
• Input:
  • string - The full term that should be matched against.
  • string - The query that will be matched against a term.
  • string - The IETF BCP 47 language code to use.
• Returns: An Integer representing the score.

GEO_GET

• Description: Look up an IPV4 address and returns geographic information about it
• Input:
  • ip - The IPV4 address to lookup
  • fields - Optional list of GeoIP fields to grab. Options are locID, country, city postalCode, dmaCode, latitude, longitude, location_point
• Returns: If a Single field is requested a string of the field, If multiple fields a map of string of the fields, and null otherwise

GEOHASH_CENTROID

• Description: Compute the centroid (geographic midpoint or center of gravity) of a set of geohashes
• Input:
  • hashes - A collection of geohashes or a map associating geohashes to numeric weights
  • character_precision? - The number of characters to use in the hash. Default is 12
• Returns: The geohash of the centroid

GEOHASH_DIST

• Description: Compute the distance between geohashes
• Input:
  • hash1 - The first point as a geohash
  • hash2 - The second point as a geohash
  • strategy? - The great circle distance strategy to use. One of HAVERSINE, LAW_OF_COSINES, or VICENTY. Haversine is default.
• Returns: The distance in kilometers between the hashes.

GEOHASH_FROM_LATLONG

• Description: Compute geohash given a lat/long
• Input:
  • latitude - The latitude
  • longitude - The longitude
  • character_precision? - The number of characters to use in the hash. Default is 12
• Returns: A geohash of the lat/long

GEOHASH_FROM_LOC

• Description: Compute geohash given a geo enrichment location
• Input:
  • map - the latitude and logitude in a map (the output of GEO_GET )
  • longitude - The longitude
  • character_precision? - The number of characters to use in the hash. Default is 12
• Returns: A geohash of the location

GEOHASH_MAX_DIST

• Description: Compute the maximum distance among a list of geohashes
• Input:
  • hashes - A set of geohashes
  • strategy? - The great circle distance strategy to use. One of HAVERSINE, LAW_OF_COSINES, or VICENTY. Haversine is default.
• Returns: The maximum distance in kilometers between any two locations

GEOHASH_TO_LATLONG

• Description: Compute the lat/long of a given geohash
• Input:
  • hash - The geohash
• Returns: A map containing the latitude and longitude of the hash (keys “latitude” and “longitude”)

GET

• Description: Returns the i’th element of the list
• Input:
  • input - List
  • i - The index (0-based)
• Returns: First element of the list

GET_FIRST

• Description: Returns the first element of the list
• Input:
  • input - List
• Returns: First element of the list

GET_HASHES_AVAILABLE

• Description: Will return all available hashing algorithms available to ‘HASH’.
• Returns: A list containing all supported hashing algorithms.

GET_LAST

• Description: Returns the last element of the list
• Input:
  • input - List
• Returns: Last element of the list

GET_SUPPORTED_ENCODINGS

• Description: Returns a list of the encodings that are currently supported.
• Returns: A List of String

HASH

• Description: Hashes a given value using the given hashing algorithm and returns a hex encoded string.
• Input:
  • toHash - value to hash.
  • hashType - A valid string representation of a hashing algorithm. See ‘GET_HASHES_AVAILABLE’.
  • config? - Configuration for the hash function in the form of a String to object map.
    • For forensic hash TLSH (see https://github.com/trendmicro/tlsh and Jonathan Oliver, Chun Cheng, and Yanggui Chen, TLSH - A Locality Sensitive Hash. 4th Cybercrime and Trustworthy Computing Workshop, Sydney, November 2013):
      • bucketSize : This defines the size of the hash created. Valid values are 128 (default) or 256 (the former results in a 70 character hash and latter results in 134 characters)
      • checksumBytes : This defines how many bytes are used to capture the checksum. Valid values are 1 (default) and 3
      • force : If true (the default) then a hash can be generated from as few as 50 bytes. If false, then at least 256 bytes are required. Insufficient variation or size in the bytes result in a null being returned.
      • hashes : You can compute a second hash for use in fuzzy clustering TLSH signatures. The number of hashes is the lever to adjust the size of those clusters and "fuzzy" the clusters are. If this is specified, then one or more bins are created based on the specified size and the function will return a Map containing the bins.
    • For all other hashes:
      • charset : The character set to use (UTF8 is default).
• Returns = A hex encoded string of a hashed value using the given algorithm. If ‘hashType’ is null then ‘00’, padded to the necessary length, will be returned. If ‘toHash’ is not able to be hashed or ‘hashType’ is null then null is returned.

IN_SUBNET

• Description: Returns true if an IP is within a subnet range.
• Input:
  • ip - The IP address in string form
  • cidr+ - One or more IP ranges specified in CIDR notation (for example 192.168.0.0/24)
• Returns: True if the IP address is within at least one of the network ranges and false if otherwise

IS_DATE

• Description: Determines if the date contained in the string conforms to the specified format.
• Input:
  • date - The date in string form
  • format - The format of the date
• Returns: True if the date is in the specified format and false if otherwise.

IS_DOMAIN

• Description: Tests if a string refers to a valid domain name. Domain names are evaluated according to the standards RFC1034 section 3, and RFC1123 section 2.1.
• Input:
  • address - The string to test
• Returns: True if the string refers to a valid domain name and false if otherwise

IS_EMAIL

• Description: Tests if a string is a valid email address
• Input:
  • address - The string to test
• Returns: True if the string is a valid email address and false if otherwise.

IS_EMPTY

• Description: Returns true if string or collection is empty or null and false if otherwise.
• Input:
  • Object of string or collection type (for example, list)
• Returns: True if the string or collection is empty or null and false if otherwise.

IS_ENCODING

• Description: Returns true if the passed string is encoded in one of the supported encodings and false if otherwise.
• Input:
  • string - The string to test
  • encoding - The name of the encoding as string. See GET_SUPPORTED_ENCODINGS.
• Returns: True if the passed string is encoded in one of the supported encodings and false if otherwise.

IS_INTEGER

• Description: Determines whether or not an object is an integer.
• Input:
  • x - The object to test
• Returns: True if the object can be converted to an integer and false if otherwise.

IS_IP

• Description: Determine if an string is an IP or not.
• Input:
  • ip - An object which we wish to test is an ip
  • type (optional) - Object of string or collection type (e.g. list) one of IPV4 or IPV6 or both. The default is IPV4.
• Returns: True if the string is an IP and false otherwise.

IS_NAN

• Description: Evaluates if the passed number is NaN. The number is evaluated as a double.
• Input:
  • number - number to evaluate"
• Returns: True if the number is NaN, false if it is

IS_URL

• Description: Tests if a string is a valid URL
• Input:
  • url - The string to test
• Returns: True if the string is a valid URL and false if otherwise.

JOIN

• Description: Joins the components in the list of strings with the specified delimiter.
• Input:
  • list - List of strings
  • delim - String delimiter
• Returns: String

KAFKA_GET

• Description: Retrieves messages from a Kafka topic. Subsequent calls will continue retrieving messages sequentially from the original offset.
• Input:
  • topic - The name of the Kafka topic.
  • count - The number of Kafka messages to retrieve.
  • config - Optional map of key/values that override any global properties.
• Returns: List of String

KAFKA_PROPS

• Description: Retrieves the Kafka properties that are used by other KAFKA_* functions like KAFKA_GET and KAFKA_PUT. The Kafka properties are compiled from a set of default properties, the global properties, and any overrides.
• Input:
  • config - An optional map of key/values that override any global properties.
• Returns: Map of key/value pairs

KAFKA_PUT

• Description: Sends messages to a Kafka topic.
• Input:
  • topic - The name of the Kafka topic.
  • messages - A list of messages to write.
  • config - Optional map of key/values that override any global properties.
• Returns: n/a

KAFKA_TAIL

• Description: etrieves messages from a Kafka topic always starting with the most recent message first.
• Input:
  • topic - The name of the Kafka topic.
  • count - The number of Kafka messages to retrieve.
  • config - Optional map of key/values that override any global properties.
• Returns: List of String

LENGTH

• Description: Returns the length of a string or size of a collection. Returns 0 for empty or null Strings
• Input:
  • input - Object of string or collection type (e.g. list)
• Returns: Integer

LIST_ADD

• Description: Adds an element to a list.
• Input:
  • list - List to add element to.
  • element - Element to add to list
• Returns: Resulting list with the item added at the end.

LOG2

• Description: Returns the log (base 2) of a number.
• Input:
  • number - The number to take the log (base 2) of
• Returns: The log (base 2) of the number passed in.

LOG10

• Description: Returns the log (base 10) of a number.
• Input:
  • number - The number to take the log (base 10) of
• Returns: The log (base 10) of the number passed in.

LN

• Description: Returns the natural log of a number.
• Input:
  • number - The number to take the natural log of
• Returns: The natural log of the number passed in.

MAAS_GET_ENDPOINT

• Description: Inspects ZooKeeper and returns a map containing the name, version and url for the model referred to by the input parameters.
• Input:
  • model_name - The name of the model
  • model_version - The optional version of the model. If the model version is not specified, the most current version is used.
• Returns: A map containing the name, version, and url for the REST endpoint (fields named name, version and url). Note that the output of this function is suitable for input into the first argument of MAAS_MODEL_APPLY.

MAAS_MODEL_APPLY

• Description: Returns the output of a model deployed via Model as a Service. NOTE: Results are cached locally for 10 minutes.
• Input:
  • endpoint - A map containing the name, version, and url for the REST endpoint
  • function - The optional endpoint path; default is ‘apply’
  • model_args - A Dictionary of arguments for the model (these become request params)
• Returns: The output of the model deployed as a REST endpoint in Map form. Assumes REST endpoint returns a JSON Map.

MAP

• Description: Applies lambda expression to a list of arguments. e.g. MAP( [ 'foo', 'bar' ] , (x) -> TO_UPPER(x) ) would yield [ 'FOO', 'BAR' ]
• Input:
  • list - List of arguments.
  • transform_expression - The lambda expression to apply. This expression is assumed to take one argument.
• Returns: The input list transformed item-wise by the lambda expression.

MAP_EXISTS

• Description: Checks for existence of a key in a map.
• Input:
  • key - The key to check for existence
  • map - The map to check for existence of the key
• Returns: True if the key is found in the map and false if otherwise.

MAP_GET

• Description: Gets the value associated with a key from a map
• Input:
  • key - The key
  • map - The map
  • default - Optionally the default value to return if the key is not in the map.
• Returns: The object associated with the key in the map. If no value is associated with the key and default is specified, then default is returned. If no value is associated with the key or default, then null is returned.

MAP_MERGE

• Description: Merges a list of maps
• Input:
  • maps - A collection of maps to merge. Last entry wins for overlapping keys.
• Returns: A Map. null if the list of maps is empty.

MAP_PUT

• Description: Adds a key/value pair to a map
• Input:
  • key - The key
  • value - The value
  • map - The map to perform the put on
• Returns: The original map modified with the key/value. If the map argument is null, a new map will be created and returned that contains the provided key and value - note: if the ‘map’ argument is null, only the returned map will be non-null and contain the key/value.

MAX

• Description: Returns the maximum value of a list of input values.
  • Input:
  • "list - List of arguments. The list may only contain objects that are mutually comparable / ordinal (implement java.lang.Comparable interface). Multi type numeric comparisons are supported: MAX([10,15L,15.3]) would return 15.3, but MAX([‘23’,25]) will fail and return null as strings and numbers can’t be compared.
• Returns: The maximum value of the list, or null if the list is empty or the input values were not comparable.

MIN

• Description: Returns the minimum value of a list of input values.
  • Input:
  • "list - List of arguments. The list may only contain objects that are mutually comparable / ordinal (implement java.lang.Comparable interface). Multi type numeric comparisons are supported: MIN([10,15L,15.3]) would return 10, but MIN([‘23’,25]) will fail and return null as strings and numbers can’t be compared.
• Returns: The minimum value of the list, or null if the list is empty or the input values were not comparable.

MONTH

• Description: The number representing the month. The first month, January, has a value of 0.
• Input:
  • dateTime - The datetime as a long representing the milliseconds since unix epoch
• Returns: The current month (0-based)

MULTISET_ADD

• Description: Adds to a multiset, which is a map associating objects to their instance counts.
• Input:
  • set - The multiset to add to
  • o - object to add to multiset
• Returns: A multiset

MULTISET_INIT

• Description: Creates an empty multiset, which is a map associating objects to their instance counts.
• Input:
  • input (optional) - An initialization of the multiset
• Returns: A multiset

MULTISET_MERGE

• Description: Merges a list of multisets, which is a map associating objects to their instance counts.
• Input:
  • sets - A collection of multisets to merge
• Returns: A multiset

MULTISET_REMOVE

• Description: Removes from a multiset, which is a map associating objects to their instance counts.
• Input:
  • set - The multiset to add to
  • o - object to remove from multiset
• Returns: A multiset

MULTISET_TO_SET

• Description: Create a set out of a multiset, which is a map associating objects to their instance counts.
• Input:
  • multiset - The multiset to convert.
• Returns: The set of objects in the multiset ignoring multiplicity

OBJECT_GET

• Description: Retrieve and deserialize a serialized object from HDFS. The cache can be specified via two properties in the global config: “object.cache.size” (default 1000), “object.cache.expiration.minutes” (default 1440). Note, if these are changed in global config, topology restart is required.
• Input:
  • path - The path in HDFS to the serialized object
• Returns: The deserialized object.

PREPEND_IF_MISSING

• Description: Prepends the prefix to the start of the string if the string does not already start with any of the prefixes.
• Input:
  • string - The string to be prepended.
  • prefix - The string prefix to prepend to the start of the string.
  • additionalprefix - Optional - Additional string prefix that is valid.
• Returns: A new String if prefix was prepended, the same string otherwise.

PROFILE_GET

• Description: Retrieves a series of values from a stored profile.
• Input:
  • profile - The name of the profile.
  • entity - The name of the entity.
  • periods - The list of profile periods to fetch. Use PROFILE_WINDOW or PROFILE_FIXED.
  • groups_list - Optional, must correspond to the ‘groupBy’ list used in profile creation - List (in square brackets) of groupBy values used to filter the profile. Default is the empty list, meaning groupBy was not used when creating the profile.
  • config_overrides - Optional - Map (in curly braces) of name:value pairs, each overriding the global config parameter of the same name. Default is the empty Map, meaning no overrides.
• Returns: The selected profile measurements.

PROFILE_VERBOSE

• Description: Retrieves a series of measurements from a stored profile. Returns a map containing the profile name, entity, period id, period start, period end for each profile measurement. Provides a more verbose view of each measurement than PROFILE_GET.
• Input:
  • profile - The name of the profile.
  • entity - The name of the entity.
  • periods - The list of profile periods to fetch. Use PROFILE_WINDOW or PROFILE_FIXED.
  • groups - Optional - The groups to retrieve. Must correspond to the ‘groupBy’ used during profile creation. Defaults to an empty list, meaning no groups.
• Returns: The selected profile measurements.

PROFILE_FIXED

• Description: The profile periods associated with a fixed lookback starting from now
• Input:
  • durationAgo - How long ago should values be retrieved from?
  • units - The units of ‘durationAgo’.
  • config_overrides - Optional - Map (in curly braces) of name:value pairs, each overriding the global config parameter of the same name. Default is the empty Map, meaning no overrides.
• Returns: The selected profile measurement timestamps. These are ProfilePeriod objects.

PROFILE_WINDOW

• Description: The profiler periods associated with a window selector statement from an optional reference timestamp.
• Input:
  • windowSelector - The statement specifying the window to select.
  • now - Optional - The timestamp to use for now.
  • config_overrides - Optional - Map (in curly braces) of name:value pairs, each overriding the global config parameter of the same name. Default is the empty Map, meaning no overrides.
• Returns: The selected profile measurement periods. These are ProfilePeriod objects.

PROTOCOL_TO_NAME

• Description: Converts the IANA protocol number to the protocol name
• Input:
  • IANA Number
• Returns: The protocol name associated with the IANA number.

REDUCE

• Description: Reduces a list by a binary lambda expression. That is, the expression takes two arguments. Usage example: REDUCE( [ 1, 2, 3 ] , (x, y) -> x + y, 0) would sum the input list, yielding 6.
• Input:
  • list - List of arguments.
  • binary_operation - The lambda expression function to apply to reduce the list. It is assumed that this takes two arguments, the first being the running total and the second being an item from the list.
  • initial_value - The initial value to use.
• Returns: The reduction of the list.

REGEXP_MATCH

• Description: Determines whether a regex matches a string. If a list of patterns is passed, then the matching is an OR operation
• Input:
  • string - The string to test
  • pattern - The proposed regex pattern or a list of patterns
• Returns: True if the regex pattern matches the string and false if otherwise.

REGEXP_GROUP_VAL

• Description: Returns the value of a group in a regex against a string
• Input:
  • string - The string to test
  • pattern - The proposed regex pattern
  • group - The integer that selects what group to select, starting at 1
• Returns: The value of the group, or null if not matched or no group at index.

REGEXP_REPLACE

• Description: Replace all occurences of the regex pattern within the string by value
• Input:
  • string - The input string
  • pattern - The proposed regex pattern
  • value - The value to replace the regex pattern
• Returns: The modified input string with replaced values

REST_GET

• Description: Performs a REST GET request and parses the JSON results into a map.
• Input:
  • url - URI to the REST service
  • rest_config - Optional - Map (in curly braces) of name:value pairs, each overriding the global config parameter of the same name. Default is the empty Map, meaning no overrides.
• Returns: JSON results as a Map

ROUND

• Description: Rounds a number to the nearest integer. This is half-up rounding.
• Input:
  • number - The number to round
• Returns: The nearest integer (based on half-up rounding).

SET_ADD

• Description: Adds to a set
• Input:
  • set - The set to add to
  • o - object to add to set
• Returns: A Set

SET_INIT

• Description: Creates an new set
• Input:
  • input (optional) - An initialization of the set
• Returns: A Set

SET_MERGE

• Description: Merges a list of sets
• Input:
  • sets - A collection of sets to merge
• Returns: A Set

SET_REMOVE

• Description: Removes from a set
• Input:
  • set - The set to add to
  • o - object to add to set
• Returns: A Set

SHELL_EDIT

• Description: Open an editor (optionally initialized with text) and return whatever is saved from the editor. The editor to use is pulled from EDITOR or VISUAL environment variable.
• Input:
  • string - (Optional) A string whose content is used to initialize the editor.
• Returns: The content that the editor saved after editor exit.

SHELL_GET_EXPRESSION

• Description: Get a stellar expression from a variable
• Input:
  • variable - variable name
• Returns: The stellar expression associated with the variable.

SHELL_LIST_VARS

• Description: Return the variables in a tabular form
• Input:
  • wrap : Length of string to wrap the columns
• Returns: A tabular representation of the variables.

SHELL_MAP2TABLE

• Description: Take a map and return a table
• Input:
  • map - Map
• Returns: The map in table form

SHELL_VARS2MAP

• Description: Take a set of variables and return a map
• Input:
  • variables* - variable names to use to create map
• Returns: A map associating the variable name with the stellar expression.

SIN

• Description: Returns the sine of a number.
• Input:
  • number - The number to take the sine of
• Returns: The sine of the number passed in.

SPLIT

• Description: Splits the string by the delimiter.
• Input:
  • input - String to split
  • delim - String delimiter
• Returns: List of strings

SQRT

• Description: Returns the square root of a number.
• Input:
  • number - The number to take the square root of
• Returns: The square root of the number passed in.

STRING_ENTROPY

• Description: Computes the base-2 shannon entropy of a string.
• Input:
  • input - String
• Returns: The base-2 shannon entropy of the string (https://en.wikipedia.org/wiki/Entropy_(information_theory)#Definition). The unit of this is bits.

STARTS_WITH

• Description: Determines whether a string starts with a prefix
• Input:
  • string - The string to test
  • prefix - The proposed prefix
• Returns: True if the string starts with the specified prefix and false if otherwise

SYSTEM_ENV_GET

• Description: Returns the value associated with an environment variable
• Input:
  • env_var - Environment variable name to get the value for
• Returns: String

SYSTEM_PROPERTY_GET

• Description: Returns the value associated with a Java system property
• Input:
  • key - Property to get the value for
• Returns: String

SUBSTRING

• Description: Returns the substring of a string
• Input:
  • input - The string to take the substring of
  • start - The starting position (0-based and inclusive)
  • end? - The ending position (0-based and exclusive)
• Returns: The substring of the input

TAN

• Description: Returns the tangent of a number.
• Input:
  • number - The number to take the tangent of
• Returns: The tangent of the number passed in.

TLSH_DIST

• Description: Will return the hamming distance between two TLSH hashes (note: must be computed with the same params). For more information, see https://github.com/trendmicro/tlsh and Jonathan Oliver, Chun Cheng, and Yanggui Chen, TLSH - A Locality Sensitive Hash. 4th Cybercrime and Trustworthy Computing Workshop, Sydney, November 2013. For a discussion of tradeoffs, see Table II on page 5 of https://github.com/trendmicro/tlsh/blob/master/TLSH_CTC_final.pdf
• Input:
  • hash1 - The first TLSH hash
  • hash2 - The first TLSH hash
  • includeLength? - Include the length in the distance calculation or not? Returns: An integer representing the distance between hash1 and hash2. The distance is roughly hamming distance, so 0 is very similar.

TO_DOUBLE

• Description: Transforms the first argument to a double precision number
• Input:
  • input - Object of string or numeric type
• Returns: Double version of the first argument

TO_EPOCH_TIMESTAMP

• Description: Returns the epoch timestamp of the dateTime in the specified format. If the format does not have a timestamp and you wish to assume a given timestamp, you may specify the timezone optionally.
• Input:
  • dateTime - DateTime in String format
  • format - DateTime format as a String
  • timezone - Optional timezone in String format
• Returns: Epoch timestamp

TO_FLOAT

• Description: Transforms the first argument to a float
• Input:
  • input - Object of string or numeric type
• Returns: Float version of the first argument

TO_INTEGER

• Description: Transforms the first argument to an integer
• Input:
  • input - Object of string or numeric type
• Returns: Integer version of the first argument

TO_JSON_LIST

• Description: Accepts JSON string as an input and returns a List object parsed by Jackson. You need to be aware of content of JSON string that is to be parsed. For e.g. GET_FIRST( TO_JSON_LIST( '[ "foo", 2]') would yield foo
• Input:
  • string - The JSON string to be parsed
• Returns: A parsed List object

TO_JSON_MAP

• Description: Accepts JSON string as an input and returns a Map object parsed by Jackson. You need to be aware of content of JSON string that is to be parsed. For e.g. MAP_GET( 'bar', TO_JSON_MAP( '{ "foo" : 1, "bar" : 2}' ) would yield 2
• Input:
  • string - The JSON string to be parsed
• Returns: A parsed Map object

TO_JSON_OBJECT

• Description: Accepts JSON string as an input and returns a JSON Object parsed by Jackson. You need to be aware of content of JSON string that is to be parsed. For e.g. MAP_GET( 'bar', TO_JSON_OBJECT( '{ "foo" : 1, "bar" : 2}' ) would yield 2
• Input:
  • string - The JSON string to be parsed
• Returns: A parsed JSON object

TO_LONG

• Description: Transforms the first argument to a long integer
• Input:
  • input - Object of string or numeric type
• Returns: Long version of the first argument

TO_LOWER

• Description: Transforms the first argument to a lowercase string
• Input:
  • input - String
• Returns: Lowercase string

TO_STRING

• Description: Transforms the first argument to a string
• Input:
  • input - Object
• Returns: String

TO_UPPER

• Description: Transforms the first argument to an uppercase string
• Input:
  • input - String
• Returns: Uppercase string

TRIM

• Description: Trims whitespace from both sides of a string.
• Input:
  • input - String
• Returns: String

URL_TO_HOST

• Description: Extract the hostname from a URL.
• Input:
  • url - URL in String form
• Returns: The hostname from the URL as a String. e.g. URL_TO_HOST(‘http://www.yahoo.com/foo’) would yield ‘www.yahoo.com’

URL_TO_PATH

• Description: Extract the path from a URL.
• Input:
  • url - URL in String form
• Returns: The path from the URL as a String. e.g. URL_TO_PATH(‘http://www.yahoo.com/foo’) would yield ‘foo’

URL_TO_PORT

• Description: Extract the port from a URL. If the port is not explicitly stated in the URL, then an implicit port is inferred based on the protocol.
• Input:
  • url - URL in string form
• Returns: The port used in the URL as an integer (for example, URL_TO_PORT(‘http://www.yahoo.com/foo’) would yield 80)

URL_TO_PROTOCOL

• Description: Extract the protocol from a URL.
• Input:
  • url - URL in String form
• Returns: The protocol from the URL as a String. e.g. URL_TO_PROTOCOL(‘http://www.yahoo.com/foo’) would yield ‘http’

WEEK_OF_MONTH

• Description: The numbered week within the month. The first week within the month has a value of 1.
• Input:
  • dateTime - The datetime as a long representing the milliseconds since unix epoch
• Returns: The numbered week within the month.

WEEK_OF_YEAR

• Description: The numbered week within the year. The first week in the year has a value of 1.
• Input:
  • dateTime - The datetime as a long representing the milliseconds since unix epoch
• Returns: The numbered week within the year.

YEAR

• Description: The number representing the year.
• Input:
  • dateTime - The datetime as a long representing the milliseconds since unix epoch
• Returns: The current year

ZIP

• Description: Zips lists into a single list where the ith element is an list containing the ith items from the constituent lists. See python and wikipedia for more context.
• Input:
  • list(s) - List(s) to zip.
• Returns: The zip of the lists. The returned list is the min size of all the lists. e.g. ZIP( [ 1, 2 ], [ 3, 4, 5] ) == [ [1, 3], [2, 4] ]

ZIP_LONGEST

• Description: Zips lists into a single list where the ith element is an list containing the ith items from the constituent lists. See python and wikipedia for more context.
• Input:
  • list(s) - List(s) to zip.
• Returns: The zip of the lists. The returned list is the max size of all the lists. Empty elements are null e.g. ZIP_LONGEST( [ 1, 2 ], [ 3, 4, 5] ) == [ [1, 3], [2, 4], [null, 5] ]

The following is an example query (i.e. a function which returns a boolean) which would be seen possibly in threat triage:

IN_SUBNET( ip, '192.168.0.0/24') or ip in [ '10.0.0.1', '10.0.0.2' ] or exists(is_local)

This evaluates to true precisely when one of the following is true:

• The value of the ip field is in the 192.168.0.0/24 subnet
• The value of the ip field is 10.0.0.1 or 10.0.0.2
• The field is_local exists

The following is an example transformation which might be seen in a field transformation:

TO_EPOCH_TIMESTAMP(timestamp, 'yyyy-MM-dd HH:mm:ss', MAP_GET(dc, dc2tz, 'UTC'))

For a message with a timestamp and dc field, we want to set the transform the timestamp to an epoch timestamp given a timezone which we will lookup in a separate map, called dc2tz.

This will convert the timestamp field to an epoch timestamp based on the

• Format yyyy-MM-dd HH:mm:ss
• The value in dc2tz associated with the value associated with field dc, defaulting to UTC

Environment Variables

When starting the REPL via $METRON_HOME/bin/stellar you can specify certain environment variables to customize the experience:

• JVMFLAGS - Arbitrary JVM flags to pass to the java command when starting the REPL.
• CONTRIB - Directory where jars with Stellar functions can be placed. The default is $METRON_HOME/contrib.

Getting Started

To run the Stellar Shell from within a deployed Metron cluster, run the following command on the host where Metron is installed.

$ $METRON_HOME/bin/stellar

Stellar, Go!
{es.clustername=metron, es.ip=node1, es.port=9300, es.date.format=yyyy.MM.dd.HH}

[Stellar]>>> %functions
BLOOM_ADD, BLOOM_EXISTS, BLOOM_INIT, BLOOM_MERGE, DAY_OF_MONTH, DAY_OF_WEEK, DAY_OF_YEAR, ...

[Stellar]>>> ?PROTOCOL_TO_NAME
PROTOCOL_TO_NAME
 desc: Convert the IANA protocol number to the protocol name       
 args: IANA Number                                                 
  ret: The protocol name associated with the IANA number.          

[Stellar]>>> ip.protocol := 6
6
[Stellar]>>> PROTOCOL_TO_NAME(ip.protocol)
TCP

Command Line Options

$ $METRON_HOME/bin/stellar -h
usage: stellar
 -h,--help              Print help
 -irc,--inputrc <arg>   File containing the inputrc if not the default
                        ~/.inputrc
 -v,--variables <arg>   File containing a JSON Map of variables
 -z,--zookeeper <arg>   Zookeeper URL fragment in the form [HOSTNAME|IPADDRESS]:PORT
 -na,--no_ansi          Make the input prompt not use ANSI colors.

$ $METRON_HOME/bin/stellar -z node1:2181
Stellar, Go!
{es.clustername=metron, es.ip=node1, es.port=9300, es.date.format=yyyy.MM.dd.HH}
[Stellar]>>> 

Variable Assignment

Stellar has no concept of variable assignment. For testing and debugging purposes, it is important to be able to create variables that simulate data contained within incoming messages. The REPL has created a means for a user to perform variable assignment outside of the core Stellar language. This is done via the := operator, such as foo := 1 + 1 would assign the result of the stellar expression 1 + 1 to the variable foo.

[Stellar]>>> foo := 2 + 2
4.0
[Stellar]>>> 2 + 2
4.0

Magic Commands

The REPL has a set of magic commands that provide the REPL user with information about the Stellar execution environment. The following magic commands are supported.

[Stellar]>>> %functions
BLOOM_ADD, BLOOM_EXISTS, BLOOM_INIT, BLOOM_MERGE, DAY_OF_MONTH, DAY_OF_WEEK, DAY_OF_YEAR, 
DECODE, DOMAIN_REMOVE_SUBDOMAINS, DOMAIN_REMOVE_TLD, DOMAIN_TO_TLD, ENDS_WITH, GET, GET_FIRST, 
GET_LAST, GET_ENCODINGS_LIST, IN_SUBNET, IS_DATE, IS_DOMAIN, IS_EMAIL, IS_EMPTY, IS_ENCODING, IS_INTEGER, IS_IP, IS_URL, 
JOIN, LENGTH, MAAS_GET_ENDPOINT, MAAS_MODEL_APPLY, MAP_EXISTS, MAP_GET, MONTH, PROTOCOL_TO_NAME, 
REGEXP_MATCH, SPLIT, STARTS_WITH, STATS_ADD, STATS_COUNT, STATS_GEOMETRIC_MEAN, STATS_INIT, 
STATS_KURTOSIS, STATS_MAX, STATS_MEAN, STATS_MERGE, STATS_MIN, STATS_PERCENTILE, 
STATS_POPULATION_VARIANCE, STATS_QUADRATIC_MEAN, STATS_SD, STATS_SKEWNESS, STATS_SUM, 
STATS_SUM_LOGS, STATS_SUM_SQUARES, STATS_VARIANCE, TO_DOUBLE, TO_EPOCH_TIMESTAMP, TO_FLOAT, 
TO_INTEGER, TO_LOWER, TO_STRING, TO_UPPER, TRIM, URL_TO_HOST, URL_TO_PATH, URL_TO_PORT, 
URL_TO_PROTOCOL, WEEK_OF_MONTH, WEEK_OF_YEAR, YEAR

[Stellar]>>> %functions NET
IN_SUBNET

[Stellar]>>> %vars
[Stellar]>>> foo := 2 + 2
4.0
[Stellar]>>> %vars
foo = 4.0

[Stellar]>>> %globals
{es.clustername=metron, es.ip=node1:9300, es.date.format=yyyy.MM.dd.HH, parser.error.topic=indexing, update.hbase.table=metron_update, update.hbase.cf=t}

[Stellar]>>> %define bootstrap.servers := "node1:6667"
node1:6667
[Stellar]>>> %globals
{bootstrap.servers=node1:6667}

[Stellar]>>> %undefine bootstrap.servers
[Stellar]>>> %globals
{}

[Stellar]>>> ?BLOOM_ADD
BLOOM_ADD
 desc: Adds an element to the bloom filter passed in               
 args: bloom - The bloom filter, value* - The values to add        
  ret: Bloom Filter                                                
[Stellar]>>> ?IS_EMAIL
IS_EMAIL
 desc: Tests if a string is a valid email address                  
 args: address - The String to test                                
  ret: True if the string is a valid email address and false otherwise.
[Stellar]>>> 

Advanced Usage

To run the Stellar Shell directly from the Metron source code, run a command like the following. Ensure that Metron has already been built and installed with mvn clean install -DskipTests.

$ mvn exec:java \
   -Dexec.mainClass="org.apache.metron.stellar.common.shell.cli.StellarShell" \
   -pl metron-platform/metron-enrichment
...
Stellar, Go!
Please note that functions are loading lazily in the background and will be unavailable until loaded fully.
[Stellar]>>> Functions loaded, you may refer to functions now...
[Stellar]>>> %functions
ABS, APPEND_IF_MISSING, BIN, BLOOM_ADD, BLOOM_EXISTS, BLOOM_INIT, BLOOM_MERGE, CHOMP, CHOP, COUNT_MATCHES, DAY_OF_MONTH, DAY_OF_WEEK, DAY_OF_YEAR, DOMAIN_REMOVE_SUBDOMAINS, DOMAIN_REMOVE_TLD, DOMAIN_TO_TLD, ENDS_WITH, ENRICHMENT_EXISTS, ENRICHMENT_GET, FILL_LEFT, FILL_RIGHT, FILTER, FORMAT, GEO_GET, GET, GET_FIRST, GET_LAST, HLLP_ADD, HLLP_CARDINALITY, HLLP_INIT, HLLP_MERGE, IN_SUBNET, IS_DATE, IS_DOMAIN, IS_EMAIL, IS_EMPTY, IS_INTEGER, IS_IP, IS_URL, JOIN, LENGTH, LIST_ADD, MAAS_GET_ENDPOINT, MAAS_MODEL_APPLY, MAP, MAP_EXISTS, MAP_GET, MONTH, OUTLIER_MAD_ADD, OUTLIER_MAD_SCORE, OUTLIER_MAD_STATE_MERGE, PREPEND_IF_MISSING, PROFILE_FIXED, PROFILE_GET, PROFILE_WINDOW, PROTOCOL_TO_NAME, REDUCE, REGEXP_MATCH, SPLIT, STARTS_WITH, STATS_ADD, STATS_BIN, STATS_COUNT, STATS_GEOMETRIC_MEAN, STATS_INIT, STATS_KURTOSIS, STATS_MAX, STATS_MEAN, STATS_MERGE, STATS_MIN, STATS_PERCENTILE, STATS_POPULATION_VARIANCE, STATS_QUADRATIC_MEAN, STATS_SD, STATS_SKEWNESS, STATS_SUM, STATS_SUM_LOGS, STATS_SUM_SQUARES, STATS_VARIANCE, STRING_ENTROPY, SYSTEM_ENV_GET, SYSTEM_PROPERTY_GET, TO_DOUBLE, TO_EPOCH_TIMESTAMP, TO_FLOAT, TO_INTEGER, TO_LONG, TO_LOWER, TO_STRING, TO_UPPER, TRIM, URL_TO_HOST, URL_TO_PATH, URL_TO_PORT, URL_TO_PROTOCOL, WEEK_OF_MONTH, WEEK_OF_YEAR, YEAR

Changing the project passed to the -pl argument will define which dependencies are included and ultimately which Stellar functions are available within the shell environment.

This can be useful for troubleshooting function resolution problems. The previous example defines which functions are available during Enrichment. For example, to determine which functions are available within the Profiler run the following.

 $ mvn exec:java \
   -Dexec.mainClass="org.apache.metron.stellar.common.shell.cli.StellarShell" \
   -pl metron-analytics/metron-profiler
...
Stellar, Go!
Please note that functions are loading lazily in the background and will be unavailable until loaded fully.
[Stellar]>>> Functions loaded, you may refer to functions now...
%functions
ABS, APPEND_IF_MISSING, BIN, BLOOM_ADD, BLOOM_EXISTS, BLOOM_INIT, BLOOM_MERGE, CHOMP, CHOP, COUNT_MATCHES, DAY_OF_MONTH, DAY_OF_WEEK, DAY_OF_YEAR, DOMAIN_REMOVE_SUBDOMAINS, DOMAIN_REMOVE_TLD, DOMAIN_TO_TLD, ENDS_WITH, FILL_LEFT, FILL_RIGHT, FILTER, FORMAT, GET, GET_FIRST, GET_LAST, HLLP_ADD, HLLP_CARDINALITY, HLLP_INIT, HLLP_MERGE, IN_SUBNET, IS_DATE, IS_DOMAIN, IS_EMAIL, IS_EMPTY, IS_INTEGER, IS_IP, IS_URL, JOIN, LENGTH, LIST_ADD, MAAS_GET_ENDPOINT, MAAS_MODEL_APPLY, MAP, MAP_EXISTS, MAP_GET, MONTH, OUTLIER_MAD_ADD, OUTLIER_MAD_SCORE, OUTLIER_MAD_STATE_MERGE, PREPEND_IF_MISSING, PROFILE_FIXED, PROFILE_GET, PROFILE_WINDOW, PROTOCOL_TO_NAME, REDUCE, REGEXP_MATCH, SPLIT, STARTS_WITH, STATS_ADD, STATS_BIN, STATS_COUNT, STATS_GEOMETRIC_MEAN, STATS_INIT, STATS_KURTOSIS, STATS_MAX, STATS_MEAN, STATS_MERGE, STATS_MIN, STATS_PERCENTILE, STATS_POPULATION_VARIANCE, STATS_QUADRATIC_MEAN, STATS_SD, STATS_SKEWNESS, STATS_SUM, STATS_SUM_LOGS, STATS_SUM_SQUARES, STATS_VARIANCE, STRING_ENTROPY, SYSTEM_ENV_GET, SYSTEM_PROPERTY_GET, TO_DOUBLE, TO_EPOCH_TIMESTAMP, TO_FLOAT, TO_INTEGER, TO_LONG, TO_LOWER, TO_STRING, TO_UPPER, TRIM, URL_TO_HOST, URL_TO_PATH, URL_TO_PORT, URL_TO_PROTOCOL, WEEK_OF_MONTH, WEEK_OF_YEAR, YEAR 

Implementation

The Stellar Shell can be executed both from the command line and from within a Stellar Notebook. The behavior and underlying implementation of the behavior is exactly the same across these two environments.

Configuration

The second argument is an optional Map of settings. The following settings are available:

• basic.auth.user - User name for basic authentication.
• basic.auth.password.path - Path to the basic authentication password file stored in HDFS.
• proxy.host - Proxy host.
• proxy.port - Proxy port.
• proxy.basic.auth.user - User name for proxy basic authentication.
• proxy.basic.auth.password.path - Path to the proxy basic authentication password file stored in HDFS.
• timeout - Stellar enforced hard timeout for the total request time. Defaults to 1000 ms. HttpClient timeouts alone are insufficient to guarantee the hard timeout.
• connect.timeout - Connect timeout exposed by the HttpClient object.
• connection.request.timeout - Connection request timeout exposed by the HttpClient object.
• socket.timeout - Socket timeout exposed by the HttpClient object.
• response.codes.allowed - A list of response codes that are allowed. All others will be treated as errors. Defaults to 200.
• empty.content.override - The default value that will be returned on a successful request with empty content. Defaults to null.
• error.value.override - The default value that will be returned on an error. Defaults to null.
• pooling.max.total - The maximum number of connections in the connection pool.
• pooling.default.max.per.route - The default maximum number of connections per route in the connection pool.

This Map of settings can also be stored in the global config stellar.rest.settings property. For example, to configure basic authentication settings you would add this property to the global config:

{
  "stellar.rest.settings": {
    "basic.auth.user": "user",
    "basic.auth.password.path": "/password/path"
  }
}

Any settings passed into the expression will take precedence over the global config settings. The global config settings will take precedence over the defaults.

For security purposes, passwords are read from a file in HDFS. Passwords are read as is including any new lines or spaces. Be careful not to include these in the file unless they are specifically part of the password.

Security

At this time, only basic authentication is supported.

Examples

Perform a simple GET request with no authentication:

[Stellar]>>> REST_GET('http://httpbin.org/get')
{args={}, headers={Accept=application/json, Accept-Encoding=gzip,deflate, Cache-Control=max-age=259200, Connection=close, Host=httpbin.org, User-Agent=Apache-HttpClient/4.3.2 (java 1.5)}, origin=127.0.0.1, 136.62.241.236, url=http://httpbin.org/get}

Perform a GET request using basic authentication:

[Stellar]>>> config := {'basic.auth.user': 'user', 'basic.auth.password.path': '/password/path'}
{basic.auth.user=user, basic.auth.password.path=/password/path}
[Stellar]>>> REST_GET('http://httpbin.org/basic-auth/user/passwd', config)
{authenticated=true, user=user}

Perform a GET request using a proxy:

[Stellar]>>> config := {'proxy.host': 'node1', 'proxy.port': 3128, 'proxy.basic.auth.user': 'user', 'proxy.basic.auth.password.path': '/proxy/password/path'}
{proxy.basic.auth.password.path=/proxy/password/path, proxy.port=3128, proxy.host=node1, proxy.basic.auth.user=user}
[Stellar]>>> REST_GET('http://httpbin.org/get', config)
{args={}, headers={Accept=application/json, Accept-Encoding=gzip,deflate, Cache-Control=max-age=259200, Connection=close, Host=httpbin.org, User-Agent=Apache-HttpClient/4.3.2 (java 1.5)}, origin=127.0.0.1, 136.62.241.236, url=http://httpbin.org/get}

Latency

Performing a REST request will introduce latency in a streaming pipeline. Therefore this function should only be used for low volume telemetries that are unlikely to be affected by higher latency operations. The timeout setting can be used to guarantee that requests complete within the configured time.

Response Handling

In cases of Http errors, timeouts, etc this function will log the error and return null. Only a status code of 200 is considered successful by default but this can be changed with the response.codes.allowed setting. Values returned on errors or emtpy content can be changed from the default value of null using the error.value.override and empty.content.override respectively.