Working with binary media types for REST APIs - Amazon API Gateway
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Working with binary media types for REST APIs

In API Gateway, the API request and response have a text or binary payload. A text payload is a UTF-8-encoded JSON string. A binary payload is anything other than a text payload. The binary payload can be, for example, a JPEG file, a GZip file, or an XML file. The API configuration required to support binary media depends on whether your API uses proxy or non-proxy integrations.

Amazon Lambda proxy integrations

To handle binary payloads for Amazon Lambda proxy integrations, you must base64-encode your function's response. You must also configure the binaryMediaTypes for your API. Your API's binaryMediaTypes configuration is a list of content types that your API treats as binary data. Example binary media types include image/png or application/octet-stream. You can use the wildcard character (*) to cover multiple media types. For example, */* includes all content types.

For example code, see Return binary media from a Lambda proxy integration.

Non-proxy integrations

To handle binary payloads for non-proxy integrations, you add the media types to the binaryMediaTypes list of the RestApi resource. Your API's binaryMediaTypes configuration is a list of content types that your API treats as binary data. Alternatively, you can set the contentHandling properties on the Integration and the IntegrationResponse resources. The contentHandling value can be CONVERT_TO_BINARY, CONVERT_TO_TEXT, or undefined.

Depending on the contentHandling value, and whether the Content-Type header of the response or the Accept header of the incoming request matches an entry in the binaryMediaTypes list, API Gateway can encode the raw binary bytes as a base64-encoded string, decode a base64-encoded string back to its raw bytes, or pass the body through without modification.

You must configure the API as follows to support binary payloads for your API in API Gateway:

  • Add the desired binary media types to the binaryMediaTypes list on the RestApi resource. If this property and the contentHandling property are not defined, the payloads are handled as UTF-8 encoded JSON strings.

  • Address the contentHandling property of the Integration resource.

    • To have the request payload converted from a base64-encoded string to its binary blob, set the property to CONVERT_TO_BINARY.

    • To have the request payload converted from a binary blob to a base64-encoded string, set the property to CONVERT_TO_TEXT.

    • To pass the payload through without modification, leave the property undefined. To pass a binary payload through without modification, you must also ensure that the Content-Type matches one of the binaryMediaTypes entries, and that passthrough behaviors are enabled for the API.

  • Set the contentHandling property of the IntegrationResponse resource. The contentHandling property, Accept header in client requests, and your API's binaryMediaTypes combined determine how API Gateway handles content type conversions. For details, see Content type conversions in API Gateway.

Important

When a request contains multiple media types in its Accept header, API Gateway honors only the first Accept media type. If you can't control the order of the Accept media types and the media type of your binary content isn't the first in the list, add the first Accept media type in the binaryMediaTypes list of your API. API Gateway handles all content types in this list as binary.

For example, to send a JPEG file using an <img> element in a browser, the browser might send Accept:image/webp,image/*,*/*;q=0.8 in a request. By adding image/webp to the binaryMediaTypes list, the endpoint receives the JPEG file as binary.

For detailed information about how API Gateway handles the text and binary payloads, see Content type conversions in API Gateway.