Language Reference

Language Reference Edit

This document is the authoritative specification of the Rego policy language (V1). All policies in OPA are written in Rego.

Built-in Functions

The built-in functions for the language provide basic operations to manipulate scalar values (e.g. numbers and strings), and aggregate functions that summarize complex types.

Comparison

Built-in	Description
`x == y`	`x` is equal to `y`
`x != y`	`x` is not equal to `y`
`x < y`	`x` is less than `y`
`x <= y`	`x` is less than or equal to `y`
`x > y`	`x` is greater than `y`
`x >= y`	`x` is greater than or equal to `y`

Numbers

Built-in	Description
`z := x + y`	`z` is the sum of `x` and `y`
`z := x - y`	`z` is the difference of `x` and `y`
`z := x * y`	`z` is the product of `x` and `y`
`z := x / y`	`z` is the quotient of `x` and `y`
`z := x % y`	`z` is the remainder from the division of `x` and `y`
`output := round(x)`	`output` is `x` rounded to the nearest integer
`output := abs(x)`	`output` is the absolute value of `x`

Aggregates

Built-in	Description
`output := count(collection_or_string)`	`output` is the length of the object, array, set, or string provided as input
`output := sum(array_or_set)`	`output` is the sum of the numbers in `array_or_set`
`output := product(array_or_set)`	`output` is the product of the numbers in `array_or_set`
`output := max(array_or_set)`	`output` is the maximum value in `array_or_set`
`output := min(array_or_set)`	`output` is the minimum value in `array_or_set`
`output := sort(array_or_set)`	`output` is the sorted `array` containing elements from `array_or_set`.
`output := all(array_or_set)`	`output` is `true` if all of the values in `array_or_set` are `true`. A collection of length 0 returns `true`.
`output := any(array_or_set)`	`output` is `true` if any of the values in `array_or_set` is `true`. A collection of length 0 returns `false`.

Arrays

Built-in	Description
`output := array.concat(array, array)`	`output` is the result of concatenating the two input arrays together.
`output := array.slice(array, startIndex, stopIndex)`	`output` is the part of the `array` from `startIndex` to `stopIndex` including the first but excluding the last. If `startIndex >= stopIndex` then `output == []`. If both `startIndex` and `stopIndex` are less than zero, `output == []`. Otherwise, `startIndex` and `stopIndex` are clamped to 0 and `count(array)` respectively.

Sets

Built-in	Description
`s3 := s1 & s2`	`s3` is the intersection of `s1` and `s2`.
`s3 := s1 \| s2`	`s3` is the union of `s1` and `s2`.
`s3 := s1 - s2`	`s3` is the difference between `s1` and `s2`, i.e., the elements in `s1` that are not in `s2`
`output := intersection(set[set])`	`output` is the intersection of the sets in the input set
`output := union(set[set])`	`output` is the union of the sets in the input set

Strings

Built-in	Description
`output := concat(delimiter, array_or_set)`	`output` is the result of joining together the elements of `array_or_set` with the string `delimiter`
`contains(string, search)`	true if `string` contains `search`
`endswith(string, search)`	true if `string` ends with `search`
`output := format_int(number, base)`	`output` is string representation of `number` in the given `base`
`output := indexof(string, search)`	`output` is the index inside `string` where `search` first occurs, or -1 if `search` does not exist
`output := lower(string)`	`output` is `string` after converting to lower case
`output := replace(string, old, new)`	`output` is a `string` representing `string` with all instances of `old` replaced by `new`
`output := split(string, delimiter)`	`output` is `array[string]` representing elements of `string` separated by `delimiter`
`output := sprintf(string, values)`	`output` is a `string` representing `string` formatted by the values in the `array` `values`.
`startswith(string, search)`	true if `string` begins with `search`
`output := substring(string, start, length)`	`output` is the portion of `string` from index `start` and having a length of `length`. If `length` is less than zero, `length` is the remainder of the `string`. If `start` is greater than the length of the string, `output` is empty. It is invalid to pass a negative offset to this function.
`output := trim(string, cutset)`	`output` is a `string` representing `string` with all leading and trailing instances of the characters in `cutset` removed.
`output := upper(string)`	`output` is `string` after converting to upper case

Regex

Built-in	Description
`re_match(pattern, value)`	true if the `value` matches the regex `pattern`
`output := regex.split(pattern, string)`	`output` is `array[string]` representing elements of `string` separated by `pattern`
`regex.globs_match(glob1, glob2)`	true if the intersection of regex-style globs `glob1` and `glob2` matches a non-empty set of non-empty strings. The set of regex symbols is limited for this builtin: only `.`, `*`, `+`, `[`, `-`, `]` and `\` are treated as special symbols.
`output := regex.template_match(patter, string, delimiter_start, delimiter_end)`	`output` is true if `string` matches `pattern`. `pattern` is a string containing `0..n` regular expressions delimited by `delimiter_start` and `delimiter_end`. Example `regex.template_match("urn:foo:{.*}", "urn:foo:bar:baz", "{", "}", x)` returns `true` for `x`.
`output := regex.find_n(pattern, string, number)`	`output` is an `array[string]` with the `number` of values matching the `pattern`. A `number` of `-1` means all matches.

Glob

Built-in	Description
`output := glob.match(pattern, delimiters, match)`	`output` is true if `match` can be found in `pattern` which is separated by `delimiters`. For valid patterns, check the table below. Argument `delimiters` is an array of single-characters (e.g. `[".", ":"]`). If `delimiters` is empty, it defaults to `["."]`.
`output := glob.quote_meta(pattern)`	`output` is the escaped string of `pattern`. Calling `glob.quote_meta(".github.com", output)` returns `\\.github.com` as `output`.

The following table shows examples of how glob.match works:

`call`	`output`	Description
`output := glob.match("*.github.com", [], "api.github.com")`	`true`	A glob with the default `["."]` delimiter.
`output := glob.match("*:github:com", [":"], "api:github:com")`	`true`	A glob with delimiters `[":"]`.
`output := glob.match("api.**.com", [], "api.github.com")`	`true`	A super glob.
`output := glob.match("api.**.com", [], "api.cdn.github.com")`	`true`	A super glob.
`output := glob.match("?at", [], "cat")`	`true`	A glob with a single character wildcard.
`output := glob.match("?at", [], "at")`	`false`	A glob with a single character wildcard.
`output := glob.match("[abc]at", [], "bat")`	`true`	A glob with character-list matchers.
`output := glob.match("[abc]at", [], "cat")`	`true`	A glob with character-list matchers.
`output := glob.match("[abc]at", [], "lat")`	`false`	A glob with character-list matchers.
`output := glob.match("[!abc]at", [], "cat")`	`false`	A glob with negated character-list matchers.
`output := glob.match("[!abc]at", [], "lat")`	`true`	A glob with negated character-list matchers.
`output := glob.match("[a-c]at", [], "cat")`	`true`	A glob with character-range matchers.
`output := glob.match("[a-c]at", [], "lat")`	`false`	A glob with character-range matchers.
`output := glob.match("[!a-c]at", [], "cat")`	`false`	A glob with negated character-range matchers.
`output := glob.match("[!a-c]at", [], "lat")`	`true`	A glob with negated character-range matchers.
`output := glob.match(""{cat,bat,[fr]at}", [], "cat")`	`true`	A glob with pattern-alternatives matchers.
`output := glob.match(""{cat,bat,[fr]at}", [], "bat")`	`true`	A glob with pattern-alternatives matchers.
`output := glob.match(""{cat,bat,[fr]at}", [], "rat")`	`true`	A glob with pattern-alternatives matchers.
`output := glob.match(""{cat,bat,[fr]at}", [], "at")`	`false`	A glob with pattern-alternatives matchers.

Types

Built-in	Description
`output := to_number(x)`	`output` is `x` converted to a number
`output := is_number(x)`	`output` is `true` if `x` is a number
`output := is_string(x)`	`output` is `true` if `x` is a string
`output := cast_string(x)`	`output` is `x` cast to a string
`output := is_boolean(x)`	`output` is `true` if `x` is a boolean
`output := cast_boolean(x)`	`output` is `x` cast to a boolean
`output := is_array(x)`	`output` is `true` if `x` is an array
`output := cast_array(x)`	`output` is `x` cast to an array
`output := is_set(x)`	`output` is `true` if `x` is a set
`output := cast_set(x)`	`output` is `x` cast to a set
`output := is_object(x)`	`output` is `true` if `x` is an object
`output := cast_object(x)`	`output` is `x` cast to an object
`output := is_null(x)`	`output` is `true` if `x` is null
`output := cast_null(x)`	`output` is `x` cast to null
`output := type_name(x)`	`output` is the type of `x`

Encoding

Built-in	Description
`output := base64.encode(x)`	`output` is `x` serialized to a base64 encoded string
`output := base64.decode(string)`	`output` is `x` deserialized from a base64 encoding string
`output := base64url.encode(x)`	`output` is `x` serialized to a base64url encoded string
`output := base64url.decode(string)`	`output` is `string` deserialized from a base64url encoding string
`output := urlquery.encode(string)`	`output` is `string` serialized to a URL query parameter encoded string
`output := urlquery.encode_object(object)`	`output` is `object` serialized to a URL query parameter encoded string
`output := urlquery.decode(string)`	`output` is `string` deserialized from a URL query parameter encoded string
`output := json.marshal(x)`	`output` is `x` serialized to a JSON string
`output := json.unmarshal(string)`	`output` is `string` deserialized to a term from a JSON encoded string
`output := yaml.marshal(x)`	`output` is `x` serialized to a YAML string
`output := yaml.unmarshal(string)`	`output` is `string` deserialized to a term from YAML encoded string

Tokens

Built-in	Description
`output := io.jwt.verify_rs256(string, certificate)`	`output` is `true` if the RS256 signature of the input token is valid. `certificate` is the PEM encoded certificate used to verify the RS256 signature
`output := io.jwt.verify_ps256(string, certificate)`	`output` is `true` if the PS256 signature of the input token is valid. `certificate` is the PEM encoded certificate used to verify the PS256 signature
`output := io.jwt.verify_es256(string, certificate)`	`output` is `true` if the ES256 signature of the input token is valid. `certificate` is the PEM encoded certificate used to verify the ES256 signature
`output := io.jwt.verify_hs256(string, secret)`	`output` is `true` if the Secret signature of the input token is valid. `secret` is a plain text secret used to verify the HS256 signature
`output := io.jwt.decode(string)`	`output` is of the form `[header, payload, sig]`. `header` and `payload` are `object`. `sig` is the hexadecimal representation of the signature on the token.
`output := io.jwt.decode_verify(string, constraints)`	`output` is of the form `[valid, header, payload]`. If the input token verifies and meets the requirements of `constraints` then `valid` is `true` and `header` and `payload` are objects containing the JOSE header and the JWT claim set. Otherwise, `valid` is `false` and `header` and `payload` are `{}`.

The input string is a JSON Web Token encoded with JWS Compact Serialization. JWE and JWS JSON Serialization are not supported. If nested signing was used, the header, payload and signature will represent the most deeply nested token.

For io.jwt.decode_verify, constraints is an object with the following members:

Name	Meaning	Required
`cert`	A PEM encoded certificate containing an RSA or ECDSA public key.	See below
`secret`	The secret key for HS256, HS384 and HS512 verification.	See below
`alg`	The JWA algorithm name to use. If it is absent then any algorithm that is compatible with the key is accepted.	Optional
`iss`	The issuer string. If it is present the only tokens with this issuer are accepted. If it is absent then any issuer is accepted.	Optional
`time`	The time in nanoseconds to verify the token at. If this is present then the `exp` and `nbf` claims are compared against this value. If it is absent then they are compared against the current time.	Optional
`aud`	The audience that the verifier identifies with. If this is present then the `aud` claim is checked against it. If it is absent then the `aud` claim must be absent too.	Optional

Exactly one of cert and secret must be present. If there are any unrecognized constraints then the token is considered invalid.

Time

Built-in	Description
`output := time.now_ns()`	`output` is `number` representing the current time since epoch in nanoseconds.
`output := time.parse_ns(layout, value)`	`output` is `number` representing the time `value` in nanoseconds since epoch. See the Go `time` package documentation for more details on `layout`.
`output := time.parse_rfc3339_ns(value)`	`output` is `number` representing the time `value` in nanoseconds since epoch.
`output := time.parse_duration_ns(duration)`	`output` is `number` representing the duration `duration` in nanoseconds. See the Go `time` package documentation for more details on `duration`.
`output := time.date(ns)`	`output` is of the form `[year, month, day]`, which includes the `year`, `month` (0-12), and `day` (0-31) as `number`s representing the date from the nanoseconds since epoch (`ns`).
`output := time.clock(ns)`	`output` is of the form `[hour, minute, second]`, which outputs the `hour`, `minute` (0-59), and `second` (0-59) as `number`s representing the time of day for the nanoseconds since epoch (`ns`).
`day := time.weekday(ns)`	outputs the `day` as `string` representing the day of the week for the nanoseconds since epoch (`ns`).

Multiple calls to the time.now_ns built-in function within a single policy evaluation query will always return the same value.

Cryptography

Built-in	Description
`output := crypto.x509.parse_certificates(string)`	`output` is an array of X.509 certificates represented as JSON objects.

Graphs

Built-in	Description
`walk(x, [path, value])`	`walk` is a relation that produces `path` and `value` pairs for documents under `x`. `path` is `array` representing a pointer to `value` in `x`. Queries can use `walk` to traverse documents nested under `x` (recursively).

HTTP

Built-in Description

http.send(request, output) http.send executes a HTTP request and returns the response.request is an object containing keys method, url and optionally body, enable_redirect, force_json_decode, headers, tls_use_system_certs, tls_ca_cert_file, tls_ca_cert_env_variable, tls_client_cert_env_variable, tls_client_key_env_variable or tls_client_cert_file, tls_client_key_file . For example, http.send({"method": "get", "url": "http://www.openpolicyagent.org/", "headers": {"X-Foo":"bar", "X-Opa": "rules"}}, output). output is an object containing keys status, status_code, body and raw_body which represent the HTTP status, status code, JSON value from the response body and response body as string respectively. Sample output, {"status": "200 OK", "status_code": 200, "body": {"hello": "world"}, "raw_body": "{\"hello\": \"world\"}"}. By default, HTTP redirects are not enabled. To enable, set enable_redirect to true. Also force_json_decode is set to false by default. This means if the HTTP server response does not specify the Content-type as application/json, the response body will not be JSON decoded ie. output’s body field will be null. To change this behaviour, set force_json_decode to true.

Built-in	Description
`http.send(request, output)`	`http.send` executes a HTTP request and returns the response.`request` is an object containing keys `method`, `url` and optionally `body`, `enable_redirect`, `force_json_decode`, `headers`, `tls_use_system_certs`, `tls_ca_cert_file`, `tls_ca_cert_env_variable`, `tls_client_cert_env_variable`, `tls_client_key_env_variable` or `tls_client_cert_file`, `tls_client_key_file` . For example, `http.send({"method": "get", "url": "http://www.openpolicyagent.org/", "headers": {"X-Foo":"bar", "X-Opa": "rules"}}, output)`. `output` is an object containing keys `status`, `status_code`, `body` and `raw_body` which represent the HTTP status, status code, JSON value from the response body and response body as string respectively. Sample output, `{"status": "200 OK", "status_code": 200, "body": {"hello": "world"}, "raw_body": "{\"hello\": \"world\"}"`}. By default, HTTP redirects are not enabled. To enable, set `enable_redirect` to `true`. Also `force_json_decode` is set to `false` by default. This means if the HTTP server response does not specify the `Content-type` as `application/json`, the response body will not be JSON decoded ie. output’s `body` field will be `null`. To change this behaviour, set `force_json_decode` to `true`.

HTTPs Usage

The following table explains the HTTPs objects

Object	Definition	Value
tls_use_system_certs	Use system certificate pool	true or false
tls_ca_cert_file	Path to file containing a root certificate in PEM encoded format	double-quoted string
tls_ca_cert_env_variable	Environment variable containing a root certificate in PEM encoded format	double-quoted string
tls_client_cert_env_variable	Environment variable containing a client certificate in PEM encoded format	double-quoted string
tls_client_key_env_variable	Environment variable containing a client key in PEM encoded format	double-quoted string
tls_client_cert_file	Path to file containing a client certificate in PEM encoded format	double-quoted string
tls_client_key_file	Path to file containing a key in PEM encoded format	double-quoted string

In order to trigger the use of HTTPs the user must provide one of the following combinations:

tls_client_cert_file, tls_client_key_file
tls_client_cert_env_variable, tls_client_key_env_variable

The user must also provide a trusted root CA through tls_ca_cert_file or tls_ca_cert_env_variable. Alternatively the user could set tls_use_system_certs to true and the system certificate pool will be used.

HTTPs Examples

Examples	Comments
Files containing TLS material	`http.send({"method": "get", "url": "https://127.0.0.1:65331", "tls_ca_cert_file": "testdata/ca.pem", "tls_client_cert_file": "testdata/client-cert.pem", "tls_client_key_file": "testdata/client-key.pem"}, output)`.
Environment variables containing TLS material	`http.send({"method": "get", "url": "https://127.0.0.1:65360", "tls_ca_cert_env_variable": "CLIENT_CA_ENV", "tls_client_cert_env_variable": "CLIENT_CERT_ENV", "tls_client_key_env_variable": "CLIENT_KEY_ENV"}, output)`.
Accessing Google using System Cert Pool	`http.send({"method": "get", "url": "https://www.google.com", "tls_use_system_certs": true, "tls_client_cert_file": "testdata/client-cert.pem", "tls_client_key_file": "testdata/client-key.pem"}, output)`

Net

Built-in	Description
`net.cidr_contains(cidr, cidr_or_ip)`	`output` is `true` if `cidr_or_ip` (e.g. `127.0.0.64/26` or `127.0.0.1`) is contained within `cidr` (e.g. `127.0.0.1/24`) and false otherwise. Supports both IPv4 and IPv6 notations.
`net.cidr_intersects(cidr1, cidr2)`	`output` is `true` if `cidr1` (e.g. `192.168.0.0/16`) overlaps with `cidr2` (e.g. `192.168.1.0/24`) and false otherwise. Supports both IPv4 and IPv6 notations.

Rego

Built-in	Description
`output := rego.parse_module(filename, string)`	`rego.parse_module` parses the input `string` as a Rego module and returns the AST as a JSON object `output`.

OPA

Built-in Description

output := opa.runtime() opa.runtime returns a JSON object output that describes the runtime environment where OPA is deployed. Caution: Policies that depend on the output of opa.runtime may return different answers depending on how OPA was started. If possible, prefer using an explicit input or data value instead of opa.runtime. The output of opa.runtime will include a "config" key if OPA was started with a configuration file. The output of opa.runtime will include a "env" key containing the environment variables that the OPA process was started with.

Built-in	Description
`output := opa.runtime()`	`opa.runtime` returns a JSON object `output` that describes the runtime environment where OPA is deployed. Caution: Policies that depend on the output of `opa.runtime` may return different answers depending on how OPA was started. If possible, prefer using an explicit `input` or `data` value instead of `opa.runtime`. The `output` of `opa.runtime` will include a `"config"` key if OPA was started with a configuration file. The `output` of `opa.runtime` will include a `"env"` key containing the environment variables that the OPA process was started with.

Debugging

Built-in	Description
`trace(string)`	`trace` outputs the debug message `string` as a `Note` event in the query explanation. For example, `trace("Hello There!")` includes `Note "Hello There!"` in the query explanation. To print variables, use sprintf. For example, `person := "Bob"; trace(sprintf("Hello There! %v", [person]))` will emit `Note "Hello There! Bob"`.

Reserved Names

The following words are reserved and cannot be used as variable names, rule names, or dot-access style reference arguments:

as
default
else
false
import
package
not
null
true
with

Grammar

Rego’s syntax is defined by the following grammar:

module          = package { import } policy
package         = "package" ref
import          = "import" package [ "as" var ]
policy          = { rule }
rule            = [ "default" ] rule-head { rule-body }
rule-head       = var [ "(" rule-args ")" ] [ "[" term "]" ] [ = term ]
rule-args       = term { "," term }
rule-body       = [ else [ = term ] ] "{" query "}"
query           = literal { ";" | [\r\n] literal }
literal         = ( some-decl | expr | "not" expr ) { with-modifier }
with-modifier   = "with" term "as" term
some-decl       = "some" var { "," var }
expr            = term | expr-built-in | expr-infix
expr-built-in   = var [ "." var ] "(" [ term { , term } ] ")"
expr-infix      = [ term "=" ] term infix-operator term
term            = ref | var | scalar | array | object | set | array-compr | object-compr | set-compr
array-compr     = "[" term "|" rule-body "]"
set-compr       = "{" term "|" rule-body "}"
object-compr    = "{" object-item "|" rule-body "}"
infix-operator  = bool-operator | arith-operator | bin-operator
bool-operator   = "=" | "!=" | "<" | ">" | ">=" | "<="
arith-operator  = "+" | "-" | "*" | "/"
bin-operator    = "&" | "|"
ref             = var { ref-arg }
ref-arg         = ref-arg-dot | ref-arg-brack
ref-arg-brack   = "[" ( scalar | var | array | object | set | "_" ) "]"
ref-arg-dot     = "." var
var             = ( ALPHA | "_" ) { ALPHA | DIGIT | "_" }
scalar          = string | NUMBER | TRUE | FALSE | NULL
string          = STRING | raw-string
raw-string      = "`" { CHAR-"`" } "`"
array           = "[" term { "," term } "]"
object          = "{" object-item { "," object-item } "}"
object-item     = ( scalar | ref | var ) ":" term
set             = empty-set | non-empty-set
non-empty-set   = "{" term { "," term } "}"
empty-set       = "set(" ")"

The grammar defined above makes use of the following syntax. See the Wikipedia page on EBNF for more details:

[]     optional (zero or one instances)
{}     repetition (zero or more instances)
|      alternation (one of the instances)
()     grouping (order of expansion)
STRING JSON string
NUMBER JSON number
TRUE   JSON true
FALSE  JSON false
NULL   JSON null
CHAR   Unicode character
ALPHA  ASCII characters A-Z and a-z
DIGIT  ASCII characters 0-9

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