Bloblang Functions
Functions can be placed anywhere and allow you to extract information from your environment, generate values, or access data from the underlying message being mapped:
root.doc.id = uuid_v4()
root.doc.received_at = now()
root.doc.host = hostname()
Functions support both named and nameless style arguments:
root.values_one = range(start: 0, stop: this.max, step: 2)
root.values_two = range(0, this.max, 2)
General
counter
This function is experimental and therefore breaking changes could be made to it outside of major version releases.
Returns a non-negative integer that increments each time it is resolved, yielding the minimum (1 by default) as the first value. Each instantiation of counter has its own independent count. Once the maximum integer (or max argument) is reached the counter resets back to the minimum.
Parameters
min <query expression, default 1> The minimum value of the counter, this is the first value that will be yielded. If this parameter is dynamic it will be resolved only once during the lifetime of the mapping.
max <query expression, default 9223372036854775807> The maximum value of the counter, once this value is yielded the counter will reset back to the min. If this parameter is dynamic it will be resolved only once during the lifetime of the mapping.
set <(optional) query expression> An optional mapping that when specified will be executed each time the counter is resolved. When this mapping resolves to a non-negative integer value it will cause the counter to reset to this value and yield it. If this mapping is omitted or doesn't resolve to anything then the counter will increment and yield the value as normal. If this mapping resolves to null then the counter is not incremented and the current value is yielded. If this mapping resolves to a deletion then the counter is reset to the min value.
Examples
root.id = counter()
# In: {}
# Out: {"id":1}
# In: {}
# Out: {"id":2}
It's possible to increment a counter multiple times within a single mapping invocation using a map.
map foos {
root = counter()
}
root.meow_id = null.apply("foos")
root.woof_id = null.apply("foos")
# In: {}
# Out: {"meow_id":1,"woof_id":2}
# In: {}
# Out: {"meow_id":3,"woof_id":4}
By specifying an optional set parameter it is possible to dynamically reset the counter based on input data.
root.consecutive_doggos = counter(min: 1, set: if !this.sound.lowercase().contains("woof") { 0 })
# In: {"sound":"woof woof"}
# Out: {"consecutive_doggos":1}
# In: {"sound":"woofer wooooo"}
# Out: {"consecutive_doggos":2}
# In: {"sound":"meow"}
# Out: {"consecutive_doggos":0}
# In: {"sound":"uuuuh uh uh woof uhhhhhh"}
# Out: {"consecutive_doggos":1}
The set parameter can also be utilised to peek at the counter without mutating it by returning null.
root.things = counter(set: if this.id == null { null })
# In: {"id":"a"}
# Out: {"things":1}
# In: {"id":"b"}
# Out: {"things":2}
# In: {"what":"just checking"}
# Out: {"things":2}
# In: {"id":"c"}
# Out: {"things":3}
deleted
A function that returns a result indicating that the mapping target should be deleted. Deleting, also known as dropping, messages will result in them being acknowledged as successfully processed to inputs in a Benthos pipeline. For more information about error handling patterns read here.
Examples
root = this
root.bar = deleted()
# In: {"bar":"bar_value","baz":"baz_value","foo":"foo value"}
# Out: {"baz":"baz_value","foo":"foo value"}
Since the result is a value it can be used to do things like remove elements of an array within map_each.
root.new_nums = this.nums.map_each(num -> if num < 10 { deleted() } else { num - 10 })
# In: {"nums":[3,11,4,17]}
# Out: {"new_nums":[1,7]}
ksuid
Generates a new ksuid each time it is invoked and prints a string representation.
Examples
root.id = ksuid()
nanoid
Generates a new nanoid each time it is invoked and prints a string representation.
Parameters
length <(optional) integer> An optional length.
alphabet <(optional) string> An optional custom alphabet to use for generating IDs. When specified the field length must also be present.
Examples
root.id = nanoid()
It is possible to specify an optional length parameter.
root.id = nanoid(54)
It is also possible to specify an optional custom alphabet after the length parameter.
root.id = nanoid(54, "abcde")
random_int
Generates a non-negative pseudo-random 64-bit integer. An optional integer argument can be provided in order to seed the random number generator.
Optional min and max arguments can be provided in order to only generate numbers within a range. Neither of these parameters can be set via a dynamic expression (i.e. from values taken from mapped data). Instead, for dynamic ranges extract a min and max manually using a modulo operator (random_int() % a + b).
Parameters
seed <query expression, default {"Value":0}> A seed to use, if a query is provided it will only be resolved once during the lifetime of the mapping.
min <integer, default 0> The minimum value the random generated number will have. The default value is 0.
max <integer, default 9223372036854775806> The maximum value the random generated number will have. The default value is 9223372036854775806 (math.MaxInt64 - 1).
Examples
root.first = random_int()
root.second = random_int(1)
root.third = random_int(max:20)
root.fourth = random_int(min:10, max:20)
root.fifth = random_int(timestamp_unix_nano(), 5, 20)
root.sixth = random_int(seed:timestamp_unix_nano(), max:20)
It is possible to specify a dynamic seed argument, in which case the argument will only be resolved once during the lifetime of the mapping.
root.first = random_int(timestamp_unix_nano())
range
The range function creates an array of integers following a range between a start, stop and optional step integer argument. If the step argument is omitted then it defaults to 1. A negative step can be provided as long as stop < start.
Parameters
start <integer> The start value.
stop <integer> The stop value.
step <integer, default 1> The step value.
Examples
root.a = range(0, 10)
root.b = range(start: 0, stop: this.max, step: 2) # Using named params
root.c = range(0, -this.max, -2)
# In: {"max":10}
# Out: {"a":[0,1,2,3,4,5,6,7,8,9],"b":[0,2,4,6,8],"c":[0,-2,-4,-6,-8]}
snowflake_id
Generate a new snowflake ID each time it is invoked and prints a string representation. I.e.: 1559229974454472704
Parameters
node_id <integer, default 1> It is possible to specify the node_id.
Examples
root.id = snowflake_id()
It is possible to specify the node_id.
root.id = snowflake_id(2)
throw
Throws an error similar to a regular mapping error. This is useful for abandoning a mapping entirely given certain conditions.
Parameters
why <string> A string explanation for why an error was thrown, this will be added to the resulting error message.
Examples
root.doc.type = match {
this.exists("header.id") => "foo"
this.exists("body.data") => "bar"
_ => throw("unknown type")
}
root.doc.contents = (this.body.content | this.thing.body)
# In: {"header":{"id":"first"},"thing":{"body":"hello world"}}
# Out: {"doc":{"contents":"hello world","type":"foo"}}
# In: {"nothing":"matches"}
# Out: Error("failed assignment (line 1): unknown type")
ulid
This function is experimental and therefore breaking changes could be made to it outside of major version releases.
Generate a random ULID.
Parameters
encoding <string, default "crockford"> The format to encode a ULID into. Valid options are: crockford, hex
random_source <string, default "secure_random"> The source of randomness to use for generating ULIDs. "secure_random" is recommended for most use cases. "fast_random" can be used if security is not a concern.
Examples
Using the defaults of Crockford Base32 encoding and secure random source
root.id = ulid()
ULIDs can be hex-encoded too.
root.id = ulid("hex")
They can be generated using a fast, but unsafe, random source for use cases that are not security-sensitive.
root.id = ulid("crockford", "fast_random")
uuid_v4
Generates a new RFC-4122 UUID each time it is invoked and prints a string representation.
Examples
root.id = uuid_v4()
Message Info
batch_index
Returns the index of the mapped message within a batch. This is useful for applying maps only on certain messages of a batch.
Examples
root = if batch_index() > 0 { deleted() }
batch_size
Returns the size of the message batch.
Examples
root.foo = batch_size()
content
Returns the full raw contents of the mapping target message as a byte array. When mapping to a JSON field the value should be encoded using the method encode, or cast to a string directly using the method string, otherwise it will be base64 encoded by default.
Examples
root.doc = content().string()
# In: {"foo":"bar"}
# Out: {"doc":"{\"foo\":\"bar\"}"}
error
If an error has occurred during the processing of a message this function returns the reported cause of the error as a string, otherwise null. For more information about error handling patterns read here.
Examples
root.doc.error = error()
errored
Returns a boolean value indicating whether an error has occurred during the processing of a message. For more information about error handling patterns read here.
Examples
root.doc.status = if errored() { 400 } else { 200 }
json
Returns the value of a field within a JSON message located by a dot path argument. This function always targets the entire source JSON document regardless of the mapping context.
Parameters
path <string, default ""> An optional dot path identifying a field to obtain.
Examples
root.mapped = json("foo.bar")
# In: {"foo":{"bar":"hello world"}}
# Out: {"mapped":"hello world"}
The path argument is optional and if omitted the entire JSON payload is returned.
root.doc = json()
# In: {"foo":{"bar":"hello world"}}
# Out: {"doc":{"foo":{"bar":"hello world"}}}
metadata
Returns the value of a metadata key from the input message, or null if the key does not exist. Since values are extracted from the read-only input message they do NOT reflect changes made from within the map, in order to query metadata mutations made within a mapping use the @.foo syntax. This function supports extracting metadata from other messages of a batch with the from method.
Parameters
key <string, default ""> An optional key of a metadata value to obtain.
Examples
root.topic = metadata("kafka_topic")
The key parameter is optional and if omitted the entire metadata contents are returned as an object.
root.all_metadata = metadata()
tracing_id
This function is experimental and therefore breaking changes could be made to it outside of major version releases.
Provides the message trace id. The returned value will be zeroed if the message does not contain a span.
Examples
meta trace_id = tracing_id()
tracing_span
This function is experimental and therefore breaking changes could be made to it outside of major version releases.
Provides the message tracing span (created via Open Telemetry APIs) as an object serialised via text map formatting. The returned value will be null if the message does not have a span.
Examples
root.headers.traceparent = tracing_span().traceparent
# In: {"some_stuff":"just can't be explained by science"}
# Out: {"headers":{"traceparent":"00-4bf92f3577b34da6a3ce929d0e0e4736-00f067aa0ba902b7-01"}}
Environment
env
Returns the value of an environment variable, or null if the environment variable does not exist.
Parameters
name <string> The name of an environment variable.
no_cache <bool, default false> Force the variable lookup to occur for each mapping invocation.
Examples
root.thing.key = env("key").or("default value")
root.thing.key = env(this.thing.key_name)
When the name parameter is static this function will only resolve once and yield the same result for each invocation as an optimisation, this means that updates to env vars during runtime will not be reflected. You can disable this cache with the optional parameter no_cache, which when set to true will cause the variable lookup to be performed for each execution of the mapping.
root.thing.key = env(name: "key", no_cache: true)
file
Reads a file and returns its contents. Relative paths are resolved from the directory of the process executing the mapping. In order to read files relative to the mapping file use the newer file_rel function
Parameters
path <string> The path of the target file.
no_cache <bool, default false> Force the file to be read for each mapping invocation.
Examples
root.doc = file(env("BENTHOS_TEST_BLOBLANG_FILE")).parse_json()
# In: {}
# Out: {"doc":{"foo":"bar"}}
When the path parameter is static this function will only read the specified file once and yield the same result for each invocation as an optimisation, this means that updates to files during runtime will not be reflected. You can disable this cache with the optional parameter no_cache, which when set to true will cause the file to be read for each execution of the mapping.
root.doc = file(path: env("BENTHOS_TEST_BLOBLANG_FILE"), no_cache: true).parse_json()
# In: {}
# Out: {"doc":{"foo":"bar"}}
file_rel
Reads a file and returns its contents. Relative paths are resolved from the directory of the mapping.
Parameters
path <string> The path of the target file.
no_cache <bool, default false> Force the file to be read for each mapping invocation.
Examples
root.doc = file_rel(env("BENTHOS_TEST_BLOBLANG_FILE")).parse_json()
# In: {}
# Out: {"doc":{"foo":"bar"}}
When the path parameter is static this function will only read the specified file once and yield the same result for each invocation as an optimisation, this means that updates to files during runtime will not be reflected. You can disable this cache with the optional parameter no_cache, which when set to true will cause the file to be read for each execution of the mapping.
root.doc = file_rel(path: env("BENTHOS_TEST_BLOBLANG_FILE"), no_cache: true).parse_json()
# In: {}
# Out: {"doc":{"foo":"bar"}}
hostname
Returns a string matching the hostname of the machine running Benthos.
Examples
root.thing.host = hostname()
now
Returns the current timestamp as a string in RFC 3339 format with the local timezone. Use the method ts_format in order to change the format and timezone.
Examples
root.received_at = now()
root.received_at = now().ts_format("Mon Jan 2 15:04:05 -0700 MST 2006", "UTC")
timestamp_unix
Returns the current unix timestamp in seconds.
Examples
root.received_at = timestamp_unix()
timestamp_unix_micro
Returns the current unix timestamp in microseconds.
Examples
root.received_at = timestamp_unix_micro()
timestamp_unix_milli
Returns the current unix timestamp in milliseconds.
Examples
root.received_at = timestamp_unix_milli()
timestamp_unix_nano
Returns the current unix timestamp in nanoseconds.
Examples
root.received_at = timestamp_unix_nano()
Fake Data Generation
fake
This function is mostly stable but breaking changes could still be made outside of major version releases if a fundamental problem with it is found.
Takes in a string that maps to a faker function and returns the result from that faker function. Returns an error if the given string doesn't match a supported faker function. Supported functions: latitude, longitude, unix_time, date, time_string, month_name, year_string, day_of_week, day_of_month, timestamp, century, timezone, time_period, email, mac_address, domain_name, url, username, ipv4, ipv6, password, jwt, word, sentence, paragraph, cc_type, cc_number, currency, amount_with_currency, title_male, title_female, first_name, first_name_male, first_name_female, last_name, name, gender, chinese_first_name, chinese_last_name, chinese_name, phone_number, toll_free_phone_number, e164_phone_number, uuid_hyphenated, uuid_digit. Refer to the faker docs for details on these functions.
Parameters
function <string, default ""> The name of the function to use to generate the value.
Examples
Use time_string to generate a time in the format 00:00:00:
root.time = fake("time_string")
Use email to generate a string in email address format:
root.email = fake("email")
Use jwt to generate a JWT token:
root.jwt = fake("jwt")
Use uuid_hyphenated to generate a hypenated UUID:
root.uuid = fake("uuid_hyphenated")
Deprecated
count
The count function is a counter starting at 1 which increments after each time it is called. Count takes an argument which is an identifier for the counter, allowing you to specify multiple unique counters in your configuration.
Parameters
name <string> An identifier for the counter.
Examples
root = this
root.id = count("bloblang_function_example")
# In: {"message":"foo"}
# Out: {"id":1,"message":"foo"}
# In: {"message":"bar"}
# Out: {"id":2,"message":"bar"}
meta
Returns the value of a metadata key from the input message as a string, or null if the key does not exist. Since values are extracted from the read-only input message they do NOT reflect changes made from within the map. In order to query metadata mutations made within a mapping use the root_meta function. This function supports extracting metadata from other messages of a batch with the from method.
Parameters
key <string, default ""> An optional key of a metadata value to obtain.
Examples
root.topic = meta("kafka_topic")
The key parameter is optional and if omitted the entire metadata contents are returned as an object.
root.all_metadata = meta()
root_meta
Returns the value of a metadata key from the new message being created as a string, or null if the key does not exist. Changes made to metadata during a mapping will be reflected by this function.
Parameters
key <string, default ""> An optional key of a metadata value to obtain.
Examples
root.topic = root_meta("kafka_topic")
The key parameter is optional and if omitted the entire metadata contents are returned as an object.
root.all_metadata = root_meta()