CDNI Processing Stages Metadata

3.2.2.1. MI.RequestTransform

The MI.RequestTransform object contains metadata for transforming the HTTP request for a specific StageRules object. The transformation can be the modification of any request header and/or the modification of the URI. Modifications are applied such that downstream processing stages receive the modified HTTP request as their input.¶

Property: header-transform¶

• Description: A HeaderTransform object specifying HTTP request headers to add, replace, or delete.¶

• Type: HeaderTransform object¶

• Mandatory-to-Specify: No¶

Property: uri¶

• Description: A replacement value for the HTTP request.¶

• Type: String. Either a literal (static string) or an expression using MEL [SVTA2031] to dynamically construct a URI value from elements of the HTTP request and/or response.¶

• Mandatory-to-Specify: No¶

Property: uri-is-expression¶

• Description: A flag to signal whether the URI is a static string literal or a MEL expression that needs to be dynamically evaluated.¶

• Type: Boolean¶

• Mandatory-to-Specify: No. The default is "False", indicating that the URI is a string literal and does not need to be evaluated.¶

The following is an example of a RequestTransform object illustrating a dynamically constructed URI rewrite:¶

{
  "generic-metadata-type": "MI.RequestTransform",
  "generic-metadata-value": {
    "header-transform": {},
    "uri": "req.uri.path",
    "uri-is-expression": true
  }
}

3.2.2.2. MI.ResponseTransform

The MI.ResponseTransform object contains metadata for transforming the HTTP response for a StageRules match. The transformation can be the modification of any response header, HTTP response status code, or the generation of a synthetic response. Modifications are applied such that downstream processing stages receive the modified HTTP response as their input.¶

Property: header-transform¶

• Description: A HeaderTransform object specifying HTTP response headers to add, replace, or delete.¶

• Type: HeaderTransform object¶

• Mandatory-to-Specify: No¶

Property: response-status¶

• Description: A replacement value for the HTTP response status code.¶

• Type: Integer. Either a static integer or an expression using MEL [SVTA2031] that evaluates to an integer to dynamically generate an HTTP status code based on elements of the HTTP request and/or response. Expressions that do not evaluate to an integer shall be considered invalid and result in no override of origin-provided response status.¶

• Mandatory-to-Specify: No¶

Property: status-is-expression¶

• Description: A flag to signal whether the response-status is a static integer or a MEL expression that needs to be dynamically evaluated to generate an HTTP response status code.¶

• Type: Boolean¶

• Mandatory-to-Specify: No. The default is "False", indicating that the response-status is a static integer and does not need to be evaluated.¶

Property: synthetic¶

• Description: The specification of a complete replacement of any HTTP response that may have been generated in an earlier processing stage with a synthetic response. Use of this property to specify a synthetic response would override any response transformations or status codes specified by other properties.¶

• Type: SyntheticResponse object¶

• Mandatory-to-Specify: No¶

The following is an example of a ResponseTransform object, illustrating a dynamically constructed header value that uses the metadata expression language [SVTA2031] to concatenate the user agent and host header, and forces a 403 HTTP response status code:¶

{
  "generic-metadata-type": "MI.ResponseTransform",
  "generic-metadata-value": {
    "header-transform": {
      "add": [
        {
          "name": "X-custom-response-header",
          "value": "req.h.user-agent . '-' . req.h.host",
          "value-is-expressions": true
        }
      ]
    },
    "response-status": "403"
  }
}

3.2.2.3. MI.SyntheticResponse

The MI.SyntheticResponse object allows for the specification of a synthetic response to be generated in response to the HTTP request being processed. The synthetic response can contain a set of response headers, a status code, and a response body, and is a complete replacement for any HTTP response elements generated in an earlier processing stage. Note that MI.SyntheticResponse is handled as a terminating object (see MI.StageRules (Section 3.2)) in that processing is terminated upon execution.¶

A dynamically generated Content-Length HTTP response header is generated based on the length of the generated response body.¶

Property: headers¶

• Description: An array of HTTP header objects that specifies the full set of headers to be applied to the synthetic response.¶

• Type: Array of HTTP header objects¶

• Mandatory-to-Specify: No, although it would be unusual to not specify minimal standard response headers, such as Content-Type.¶

Property: response-status¶

• Description: The HTTP response status code.¶

• Type: Either a static integer or a string containing an expression that evaluates to an integer using MEL [SVTA2031] to dynamically generate an HTTP status code based on elements of the upstream HTTP request and/or response. Expressions that do not evaluate to an integer shall be considered invalid and result in a 500 status for the synthetic response.¶

• Mandatory-to-Specify: Yes¶

Property: status-is-expression¶

• Description: The flag to signal whether the response-status is a static integer or a MEL expression [SVTA2031] that needs to be dynamically evaluated to generate an HTTP response status code.¶

• Type: Boolean¶

• Mandatory-to-Specify: No. The default is "False", indicating that the response-status is a static integer and does not need to be evaluated.¶

Property: body¶

• Description: The body for the synthetic HTTP response. The response body can either be static or dynamically constructed from a rich expression.¶

• Type: String. Either a literal (static string) or an expression using MEL [SVTA2031] to dynamically construct a response body from elements of the HTTP request and/or response.¶

• Mandatory-to-Specify: No. If absent, an empty HTTP response with a zero-value Content-Length header is generated.¶

Property: body-is-expression¶

• Description: A flag to signal whether the synthetic response body is a static string literal or a MEL expression [SVTA2031] that needs to be dynamically evaluated.¶

• Type: Boolean¶

• Mandatory-to-Specify: No. The default is "False", indicating that the body is a string literal and does not need to be evaluated.¶

The following is an example of a SyntheticResponse object illustrating a dynamically constructed response body that uses the expression language to combine the request URI with static text and forces a 405 HTTP response status code:¶

{
  "generic-metadata-type": "MI.SyntheticResponse",
  "generic-metadata-value": {
    "headers": [
      {
        "name": "content-type",
        "value": "text/plain"
      },
      {
        "name": "X-custom-response-header",
        "value": "some static value"
      }
    ],
    "response-status": 405,
    "response-body":
      "'Sorry, Access to resource ' . req.uri . ' not allowed'",
    "body-is-expression": true
  }
}

3.2.2.4. MI.HeaderTransform

The MI.HeaderTransform object specifies how HTTP requests and response headers can be transformed. Headers can be deleted, replaced, or added to an HTTP request or response, with the processing occurring in this order: DELETE, REPLACE, ADD.¶

Property: delete¶

• Description: A list of names of HTTP headers that MUST be deleted from the HTTP request or response. If a named header appears multiple times, all occurrences are deleted.¶

• Type: Array of strings, with each string naming an HTTP header to delete¶

• Mandatory-to-Specify: No¶

Property: replace¶

• Description: A list of HTTP headers (name/value pairs) that MUST be added to the HTTP request or response, replacing any previous headers with the same name.¶

• Type: Array of HTTPHeader objects containing header name/value pairs¶

• Mandatory-to-Specify: No¶

Property: add¶

• Description: A list of HTTP headers (name/value pairs) that MUST be added to the HTTP request or response. Note that any existing headers in the request or response with the same names of those added are not affected, resulting in multiple headers with the same name.¶

• Type: Array of HTTPHeader objects containing header name/value pairs¶

• Mandatory-to-Specify: No¶

The following is an example of a HeaderTransform object illustrating the addition of two customer headers, the replacement of any previously provided Accept-Encoding header, and the removal of any previously provided Authorization or Accept-Language headers:¶

{
  "generic-metadata-type": "MI.HeaderTransform",
  "generic-metadata-value": {
    "add": [
      {
        "name": "X-custom-header1",
        "value": "header-value 1"
      },
      {
        "name": "X-custom-header2",
        "value": "header-value 2"
      }
    ],
    "replace": [
      {
        "name": "Accept-Encoding",
        "value": "gzip,deflate,br"
      }
    ],
    "delete": [
      "Authorization",
      "Accept-Language"
    ]
  }
}

3.2.2.5. MI.HTTPHeader

The MIHTTPHeader object contains a name/value pair for an HTTP header to add or replace in a request or response. The metadata expression language (MEL) [SVTA2031] can be used to dynamically generate response values.¶

Property: name¶

• Description: The name of the HTTP header.¶

• Type: String¶

• Mandatory-to-Specify: Yes¶

Property: value¶

• Description: The new value of the named HTTP header.¶

• Type: String. Either a static string or an expression using the MEL expression language [SVTA2031] to dynamically construct a header value from elements of the HTTP request and/or response.¶

• Mandatory-to-Specify: Yes¶

Property: value-is-expression¶

• Description: A flag to signal whether the value is a static string literal or a MEL expression [SVTA2031] that needs to be dynamically evaluated.¶

• Type: Boolean¶

• Mandatory-to-Specify: No. The default is "False", indicating that the value is a string literal and does not need to be evaluated.¶

The following is an example of an HTTPHeader illustrating a dynamically constructed header value that equals the session parameter from the query string:¶

{
  "generic-metadata-type": "MI.HTTPHeader",
  "generic-metadata-value": {
    "name": "X-custom-response-header",
    "value": "req.uri.query.session",
    "value-is-expression": true
  }
}