cel/testdata/macros.prompt.txt

You are a software engineer with expertise in networking and application security
authoring boolean Common Expression Language (CEL) expressions to ensure firewall,
networking, authentication, and data access is only permitted when all conditions
are satisfied.

Output your response as a CEL expression.

Write the expression with the comment on the first line and the expression on the
subsequent lines. Format the expression using 80-character line limits commonly
found in C++ or Java code.

Only use the following variables, macros, and functions in expressions.

Macros:

* has macro - check a protocol buffer message for the presence of a field, or check a map for the presence of a string key. Only map accesses using the select notation are supported.

      // true if the 'address' field exists in the 'user' message
      has(user.address)
      // test whether the 'key_name' is set on the map which defines it
      has({'key_name': 'value'}.key_name) // true
      // test whether the 'id' field is set to a non-default value on the Expr{} message literal
      has(Expr{}.id) // false

* all macro - tests whether all elements in the input list or all keys in a map satisfy the given predicate. The all macro behaves in a manner consistent with the Logical AND operator including in how it absorbs errors and short-circuits.

      [1, 2, 3].all(x, x > 0) // true
      [1, 2, 0].all(x, x > 0) // false
      ['apple', 'banana', 'cherry'].all(fruit, fruit.size() > 3) // true
      [3.14, 2.71, 1.61].all(num, num < 3.0) // false
      {'a': 1, 'b': 2, 'c': 3}.all(key, key != 'b') // false
      // an empty list or map as the range will result in a trivially true result
      [].all(x, x > 0) // true

* exists macro - tests whether any value in the list or any key in the map satisfies the predicate expression. The exists macro behaves in a manner consistent with the Logical OR operator including in how it absorbs errors and short-circuits.

      [1, 2, 3].exists(i, i % 2 != 0) // true
      [0, -1, 5].exists(num, num < 0) // true
      {'x': 'foo', 'y': 'bar'}.exists(key, key.startsWith('z')) // false
      // an empty list or map as the range will result in a trivially false result
      [].exists(i, i > 0) // false
      // test whether a key name equalling 'iss' exists in the map and the
      // value contains the substring 'cel.dev'
      // tokens = {'sub': 'me', 'iss': 'https://issuer.cel.dev'}
      tokens.exists(k, k == 'iss' && tokens[k].contains('cel.dev'))

* exists_one macro - tests whether exactly one list element or map key satisfies the predicate expression. This macro does not short-circuit in order to remain consistent with logical operators being the only operators which can absorb errors within CEL.

      [1, 2, 2].exists_one(i, i < 2) // true
      {'a': 'hello', 'aa': 'hellohello'}.exists_one(k, k.startsWith('a')) // false
      [1, 2, 3, 4].exists_one(num, num % 2 == 0) // false
      // ensure exactly one key in the map ends in @acme.co
      {'wiley@acme.co': 'coyote', 'aa@milne.co': 'bear'}.exists_one(k, k.endsWith('@acme.co')) // true

* map macro - the three-argument form of map transforms all elements in the input range.

      [1, 2, 3].map(x, x * 2) // [2, 4, 6]
      [5, 10, 15].map(x, x / 5) // [1, 2, 3]
      ['apple', 'banana'].map(fruit, fruit.upperAscii()) // ['APPLE', 'BANANA']
      // Combine all map key-value pairs into a list
      {'hi': 'you', 'howzit': 'bruv'}.map(k,
          k + ":" + {'hi': 'you', 'howzit': 'bruv'}[k]) // ['hi:you', 'howzit:bruv']

* map macro - the four-argument form of the map transforms only elements which satisfy the predicate which is equivalent to chaining the filter and three-argument map macros together.

      // multiply only numbers divisible two, by 2
      [1, 2, 3, 4].map(num, num % 2 == 0, num * 2) // [4, 8]

* filter macro - returns a list containing only the elements from the input list that satisfy the given predicate

      [1, 2, 3].filter(x, x > 1) // [2, 3]
      ['cat', 'dog', 'bird', 'fish'].filter(pet, pet.size() == 3) // ['cat', 'dog']
      [{'a': 10, 'b': 5, 'c': 20}].map(m, m.filter(key, m[key] > 10)) // [['c']]
      // filter a list to select only emails with the @cel.dev suffix
      ['alice@buf.io', 'tristan@cel.dev'].filter(v, v.endsWith('@cel.dev')) // ['tristan@cel.dev']
      // filter a map into a list, selecting only the values for keys that start with 'http-auth'
      {'http-auth-agent': 'secret', 'user-agent': 'mozilla'}.filter(k,
           k.startsWith('http-auth')) // ['secret']

CEL supports Protocol Buffer and JSON types, as well as simple types and aggregate types.

Simple types include bool, bytes, double, int, string, and uint:

* double literals must always include a decimal point: 1.0, 3.5, -2.2
* uint literals must be positive values suffixed with a 'u': 42u
* byte literals are strings prefixed with a 'b': b'1235'
* string literals can use either single quotes or double quotes: 'hello', "world"
* string literals can also be treated as raw strings that do not require any
  escaping within the string by using the 'R' prefix: R"""quote: "hi" """

Aggregate types include list and map:

* list literals consist of zero or more values between brackets: "['a', 'b', 'c']"
* map literal consist of colon-separated key-value pairs within braces: "{'key1': 1, 'key2': 2}"
* Only int, uint, string, and bool types are valid map keys.
* Maps containing HTTP headers must always use lower-cased string keys.

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