Amazon API Gateway
Developer Guide

Use a Mapping Template to Override an API's Request and Response Parameters and Status Codes

Standard API Gateway parameter and response code mapping templates allow you to map parameters one-to-one and map a family of integration response status codes (matched by a regular expression) to a single response status code. Mapping template overrides provides you with the flexibility to perform many-to-one parameter mappings; override parameters after standard API Gateway mappings have been applied; conditionally map parameters based on body content or other parameter values; programmatically create new parameters on the fly; and override status codes returned by your integration endpoint. Any type of request parameter, response header, or response status code may be overridden.

Following are example uses for a mapping template override:

  • To create a new header (or overwrite an existing header) as a concatenation of two parameters

  • To override the response code to a success or failure code based on the contents of the body

  • To conditionally remap a parameter based on its contents or the contents of some other parameter

  • To iterate over the contents of a json body and remap key value pairs to headers or query strings

To create a mapping template override, use one or more of the following $context variables in a mapping template:

Request Body Mapping Template Response Body Mapping Template
$context.requestOverride.header.header_name $context.responseOverride.header.header_name
$context.requestOverride.path.path_name $context.responseOverride.status
$context.requestOverride.querystring.querystring_name

Note

Mapping template overrides cannot be used with proxy integration endpoints, which lack data mappings. For more information about integration types, see Choose an API Gateway API Integration Type.

Important

Overrides are final. An override may only be applied to each parameter once. Trying to override the same parameter multiple times will result in 5XX responses from Amazon API Gateway. If you must override the same parameter multiple times throughout the template, we recommend creating a variable and applying the override at the end of the template. Note that the template is applied only after the entire template is parsed. See Tutorial: Override an API's Request Parameters and Headers with the API Gateway Console.

The following tutorials show how to create and test a mapping template override in the API Gateway console. These tutorials use the PetStore sample API as a starting point. Both tutorials assume that you have already created the the PetStore sample API.

Tutorial: Override an API's Response Status Code with the API Gateway Console

To retrieve a pet using the PetStore sample API, you use the API method request of GET /pets/{petId}, where {petId} is a path parameter that can take a number at run time.

In this tutorial, you'll override this GET method's response code by creating a mapping template that maps $context.responseOverride.status to 400 when an error condition is detected.

  1. Sign in to the API Gateway console at https://console.aws.amazon.com/apigateway.

  2. Under APIs, choose the PetStore API.

  3. In the Resources column, choose the GET method under /{petId}.

  4. In the Client box, choose Test.

  5. Type -1 for {petId} and choose Test.

    In the results, you'll notice two things:

    First, the Response Body indicates an out-of-range error:

    { "errors": [ { "key": "GetPetRequest.petId", "message": "The value is out of range." } ] }

    Second, the last line under Logs box ends with: Method completed with status: 200.

  6. Go back to Method Execution. Choose Integration Response, and then choose the arrow next to 200.

  7. In the Mapping Templates section, choose Add mapping template.

  8. For Content Type, type application/json, and then choose the check mark icon to save the choice.

  9. Copy the following code into the template area:

    #set($inputRoot = $input.path('$')) $input.json("$") #if($inputRoot.toString().contains("error")) #set($context.responseOverride.status = 400) #end
  10. Choose Save.

  11. Go back to Method Execution

  12. In the Client box, choose Test.

  13. Type -1 for {petId} and choose Test.

    In the results, the Response Body indicates an out-of-range error:

    { "errors": [ { "key": "GetPetRequest.petId", "message": "The value is out of range." } ] }

    However, the last line under Logs box now ends with: Method completed with status: 400.

Tutorial: Override an API's Request Parameters and Headers with the API Gateway Console

In this tutorial, you'll override the GET method's request header code by creating a mapping template that maps $context.requestOverride.header.header_name to a new header that combines two other headers.

  1. Sign in to the API Gateway console at https://console.aws.amazon.com/apigateway.

  2. Under APIs, choose the PetStore API.

  3. In the Resources column, choose the GET method under /pets.

  4. Choose Method Request.

  5. Create a parameter as follows:

    1. Expand HTTP Request Headers.

    2. Choose Add header.

    3. Under Name, type header1.

    4. Choose the check mark icon to save your choice.

    Repeat the process to create a second header called header2.

  6. Go back to Method Execution

  7. Choose Integration Request.

  8. Expand HTTP Headers. You'll see the two headers you created, header1 and header2, along with their default mappings (under Mapped from).

  9. Expand Mapping Templates.

  10. Choose Add mapping template.

  11. For Content Type, type application/json, and then choose the check mark icon to save the choice.

  12. A popup will appear that says, Note: This template can map headers and body.

    Choose Yes, secure this integration.

  13. Copy the following code into the template area:

    #set($header1Override = "foo") #set($header3Value = "$input.params('header1')$input.params('header2')") $input.json("$") #set($context.requestOverride.header.header3 = $header3Value) #set($context.requestOverride.header.header1 = $header1Override)
  14. Choose Save.

  15. Go back to Method Execution

  16. In the Client box, choose Test.

  17. Under Headers for {pets}, copy the following code:

    header1:header1Val header2:header2Val
  18. Choose Test.

    In the Logs, you should see an entry that includes this text:

    Endpoint request headers: {header3=header1Valheader2Val, header2=header2Val, x-amzn-apigateway-api-id=<api-id>, header1=foo, Accept=application/json

Examples: Override an API's Request Parameters and Headers with the API Gateway CLI

The following CLI example shows how to use the put-integration command to override a response code:

aws apigateway put-integration --rest-api-id <API_ID> --resource-id <PATH_TO_RESOURCE_ID> --http-method <METHOD> --type <INTEGRATION_TYPE> --request-templates <REQUEST_TEMPLATE_MAP>

where <REQUEST_TEMPLATE_MAP> is a map from content type to a string of the template to apply. The structure of that map is as follows:

Content_type1=template_string,Content_type2=template_string

or, in JSON syntax:

{"content_type1": "template_string" ...}

The following example shows how to use the put-integration-response command to override an API's response code:

aws apigateway put-integration-response --rest-api-id <API_ID> --resource-id <PATH_TO_RESOURCE_ID> --http-method <METHOD> --status-code <STATUS_CODE> --response-templates <RESPONSE_TEMPLATE_MAP>

where <RESPONSE_TEMPLATE_MAP> has the same format as <REQUEST_TEMPLATE_MAP> above.

Example: Override an API's Request Parameters and Headers Using the SDK for JavaScript

The following example shows how to use the put-integration command to override a response code:

Request:

var params = { httpMethod: 'STRING_VALUE', /* required */ resourceId: 'STRING_VALUE', /* required */ restApiId: 'STRING_VALUE', /* required */ type: HTTP | AWS | MOCK | HTTP_PROXY | AWS_PROXY, /* required */ requestTemplates: { '<Content_type>': 'TEMPLATE_STRING', /* '<String>': ... */ }, }; apigateway.putIntegration(params, function(err, data) { if (err) console.log(err, err.stack); // an error occurred else console.log(data); // successful response });

Response:

var params = { httpMethod: 'STRING_VALUE', /* required */ resourceId: 'STRING_VALUE', /* required */ restApiId: 'STRING_VALUE', /* required */ statusCode: 'STRING_VALUE', /* required */ responseTemplates: { '<Content_type>': 'TEMPLATE_STRING', /* '<String>': ... */ }, }; apigateway.putIntegrationResponse(params, function(err, data) { if (err) console.log(err, err.stack); // an error occurred else console.log(data); // successful response });