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Constructing JSONata expressions to redact fields

To define a field for redaction or removal when using the Redaction policy with the DataPower® API Gateway, you supply a JSONata expression that defines the path to the field that you want to redact or remove.

JSONata support in API Connect

API Connect supports v2.0 of the JSONata specification, with the following limitations:

  • If you use a JSONata expression to extract or redact fields, soft linked copies of the field are also affected by the Extract or Redaction policy, even if the fields exist in different locations.
  • API Connect does not support higher order JSONata functions (functions that process other functions).
  • If a JSONata function supported by API Connect calls a higher order function as an argument, that argument is not supported (due to the lack of support for higher order functions).
  • The following JSONata v2.0 functions are not supported:
    • $eval()
    • $sift()
    • $each()
    • $error()
    • $assert()
    • $fromMillis() is supported with the following restrictions:
      • The $fromMillis() parameter supports numbers in the range -5364662400000 - 2903299199000.
        • A value less than -5364662400000 uses -5364662400000. In other words, reports the timestamp as 1800-01-01T00:00:00Z.
        • A value greater than 2903299199000 uses 2903299199000. In other words, reports the timestamp as 2261-12-31T23:59:59Z.
  • $now() is supported with the following restrictions:
    • The following component specifiers are not supported:
      • W = Week in year
      • w = Week in month
      • X = ISO week-numbering year
      • x = ISO week-numbering month
    • Representing numbers as words are not supported, so the following presentation modifiers are not supported:
      • W = Uppercase word (for example: [YW] => TWO THOUSAND AND TWENTY-FOUR)
      • w = Lowercase word (for example: [Yw] => two thousand and twenty-four)
      • Ww = Title case word (for example: [YWw] => Two Thousand and Twenty-Four)
    • Error messages are generic.

Table 1 lists the functional extensions that you can use with standard JSONata notation. Each extension corresponds to a part of the API context.

Table 1. Functional extensions to JSONata
Extension Variable Description
$apiCtx() Generic access to an API context The $apiCtx() extension gives generic access to an API context.
  • Sample transform field in an extract action:
    "$apiCtx().request.uri"
  • Sample condition of a case in a switch action:
    "$apiCtx().request.path = '/simple/apictx-function'"
$header(name) message.headers.name Message header
$httpVerb() request.verb HTTP method of the request
$operationID() api.operation.id ID of the operation
$operationPath() api.operation.path Path of the operation
$queryParameter('name')
  • request.parameters.name.locations

    The supported keyword is query.

  • request.parameters.name.values
 Searches for the index of query in request.parameters.name.locations and returns request.parameters.name.values[index], where [index] is the value for query in locations. Parameter values are not URL decoded.
$statusCode() message.status.code Status code
$storageType([arg]) variable.body

You can specify any variable in the API context. When no variable is specified, the default variable message.body is used.

 Storage type of the message. The supported values are binary, empty, graphql, json, stream, or xml.
$urlParameter('name')
  • request.parameters.name.locations

    The supported keywords are path and query

  • request.parameters.name.values
 Searches for the index of path and query in request.parameters.name.locations and returns a single array that contains both path and query values from request.parameters.name.values. When the URL contains both path and query parameter values, the array includes the path values first followed by the query values. The values of each parameter type are added in the order that they are received. Parameter values are URL decoded.
For example, the following URL contains both path and query parameter values.
http://example.com/petstore/cats/adopt?breed=Sphynx&breed=Siamese
The $urlParameter('breed') URL returns the following array of values.
[cats, adopt, Sphynx, Siamese]

In this example, the URL includes an API path that is configured as /petstore/{breed}/{breed}, where breed is configured to be a path parameter of the API path. As a result, cats and adopt are included in the output.
$xpath(path, xpathExpression) You can specify any writable variable in the API context. The xpathExpression must be a literal string. Allows use of XPath expressions. The following example specifies all price elements in the source.
$xpath($, '//price')

Table 2 lists the functional extensions that you can use with GraphQL APIs.

Table 2. Functional extensions to JSONata for GraphQL
Extension Variable Description
$gqlActiveOperation([graphql_message]) message.body Gets the active operation found in the specified GraphQL message. The operationName must be the same as the name of the active operation.
$gqlAlias(graphql_field_node) message.body Gets the alias of a GraphQL field node.
$gqlFragments([graphql_message]) message.body Gets the fragments found in the specified GraphQL message.
$gqlName([graphql_node]) message.body Gets the node name. For operations, the node name is the operationName. For fields, fragment definitions, arguments, and other elements, the node name is the name of the element. By default, the operationName of message.body is retrieved.
$gqlOperations([graphql_message]) message.body Gets the operations found in the specified GraphQL message.
$gqlType([graphql_node]) message.body The operation type of the active operation is retrieved for Query, Mutation, and Subscription query types.
In addition to the functional extensions, you can use the following operators:
  • You can use the & (concatenation) navigation operator.

You can use the following JSONata numeric operators:

  • + (addition)
  • - (subtraction)
  • * (multiplication)
  • / (division)
  • % (modulo)

You can use the following JSONata comparison operators for number values or strings:

  • =
  • !=
  • <
  • >
  • <=
  • >=
You can also use the following operators and expressions.
  • Parentheses to convert a sequence into an array, specify operator precedence, or compute complex expressions on a context value.
  • Array ranges and predicate expressions.
  • Single asterisk (*) and double asterisk (**) wildcard characters.
The following elements of a GraphQL query can be exposed in JSONata notation using the syntax shown.
  • query

    The entire GraphQL query including operations and fragments.

  • operationName

    For an anonymous operation, operationName can be empty.

  • ~fragmentSpreadName
  • on~typeCondition
  • ~~fragmentDefinitionName

You can define the path using either of the following options:

Using a JSONata expression

The path specified by the JSONata expression is relative to any value specified for the root property of the Redaction policy. If the root property has no value or is absent, begin the expression with the absolute content path. If the root property has a value then you can either begin the expression with $ to use the root path directly, or you can provide a sub-path relative to the root path.

Note: If you use a JSONata expression to redact fields and soft linked copies of a field exist in different locations, the Redaction policy can cause content from all of the linked fields to be redacted.

JSONata expressions can be used with content that is in either JSON or XML format.

Example 1
If the root property of the Redaction policy has no value or is absent, use the following expression to redact or remove all occurrences of the price field in the request and response data:
message.body.**.price
Example 2
If the root property of the Redaction policy has the value log.request_body, use the following expression to redact or remove all occurrences of the price field, specifically within an item element, in the logged request payload:
$.item.price
Example 3
If the root property of the Redaction policy has the value log, use the following expression to redact or remove all occurrences of the price field in the logged response payload:
response_body.**.price

The ** descendant wildcard traverses all descendants at all hierarchical levels.

Using the $xpath() JSONata extension

The $xpath() function has the following format:
$xpath(content_path, xpath_expression)
where:
  • content_path is the path to the content that contains the field that you want to redact or remove.
  • xpath_expression is the XPath expression that defines the field that you want to redact or remove.

The content_path is relative to any value specified for the root property of the Redaction policy. If the root property has no value or is absent, provide the absolute content path. If the root property has a value then you can either provide the value $ for the content_path parameter to use the root path directly, or you can provide a sub-path relative to the root path.

The $xpath() function can be used only with content that is in XML format.

Example 1
If the root property of the Redaction policy has no value or is absent, use the following expression to redact or remove all occurrences of the price field in the request and response data:
$xpath(message.body, '//price')
Example 2
If the root property of the Redaction policy has the value log.request_body, use the following expression to redact or remove all occurrences of the price field, specifically within an item element, in the logged request payload:
$xpath($, 'item/price')
Example 3
If the root property of the Redaction policy has the value log, use the following expression to redact or remove all occurrences of the price field in the logged response payload:
$xpath(response_body, '//price')

The // expression in the second parameter selects all occurrences anywhere in the content.