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:
Functions support both named and nameless style arguments:
General¶
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"}
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]}
¶
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
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
It is possible to specify an optional length parameter.
It is also possible to specify an optional custom alphabet after the length parameter.
¶
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 to make the generated numbers within a range.
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.
¶
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
It is possible to specify the node_id.
¶
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¶
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
ULIDs can be hex-encoded too.
They can be generated using a fast, but unsafe, random source for use cases that are not security-sensitive.
¶
uuid_v4¶
Generates a new RFC-4122 UUID each time it is invoked and prints a string representation.
Examples
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
¶
batch_size¶
Returns the size of the message batch.
Examples
¶
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
¶
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
¶
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
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
The path argument is optional and if omitted the entire JSON payload is returned.
¶
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
The key parameter is optional and if omitted the entire metadata contents are returned as an object.
tracing_id¶
Provides the message trace id. The returned value will be zeroed if the message does not contain a span.
Examples
tracing_span¶
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.
Examples
When the argument 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 work around this optimisation by using variables as the argument as this will force a new evaluation for each execution of the mapping.
¶
file¶
Reads a file and returns its contents. Relative paths are resolved from the directory of the process executing the mapping.
Parameters
path \<string> The path of the target file.
Examples
root.doc = file(env("BENTHOS_TEST_BLOBLANG_FILE")).parse_json()
# In: {}
# Out: {"doc":{"foo":"bar"}}
When the argument is static this function will only resolve 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 work around this optimisation by using variables as the argument as this will force a new file read for each execution of the mapping.
let env_key = "BENTHOS_TEST_BLOBLANG_FILE"
root.doc = file(env($env_key)).parse_json()
# In: {}
# Out: {"doc":{"foo":"bar"}}
¶
let env_key = "BENTHOS_TEST_BLOBLANG_FILE"
root.doc = file(env($env_key)).parse_json()
# In: {}
# Out: {"doc":{"foo":"bar"}}
hostname¶
Returns a string matching the hostname of the machine running Benthos.
Examples
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")
¶
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
timestamp_unix_micro¶
Returns the current unix timestamp in microseconds.
Examples
timestamp_unix_milli¶
Returns the current unix timestamp in milliseconds.
Examples
timestamp_unix_nano¶
Returns the current unix timestamp in nanoseconds.
Examples
Fake Data Generation¶
fake¶
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:
Use email to generate a string in email address format:
Use jwt to generate a JWT token:
Use uuid_hyphenated to generate a hypenated UUID:
Deprecated¶
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
The key parameter is optional and if omitted the entire metadata contents are returned as an object.
¶
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
The key parameter is optional and if omitted the entire metadata contents are returned as an object.