Content Handler

The ContentHandler is a middleware handler designed to manage the Content-Type header in HTTP responses. It ensures that a valid content type is always set, either by reflecting the request’s Content-Type or by applying a configured default.

Introduction

In some scenarios, backend services or handlers might not explicitly set the Content-Type header in their responses. This can lead to clients misinterpreting the response body. The ContentHandler solves this by:

1. Checking if the request has a Content-Type header. If so, it uses that same value for the response Content-Type.
2. If the request does not have a Content-Type, it sets the response Content-Type to a configured default value (usually application/json).

This is particularly useful when working with clients that expect specific content types or when enforcing a default format for your API.

Configuration

The handler is configured via the content.yml file.

Example content.yml

# Content middleware configuration
enabled: true
# The default content type to be used in the response if request content type is missing
contentType: application/json

Usage

To use the ContentHandler, you need to register it in your handler.yml configuration file and add it to the middleware chain.

handler.yml

handlers:
  - com.networknt.content.ContentHandler@content
  # ... other handlers

chains:
  default:
    - content
    # ... other handlers

Logic

The handleRequest method performs the following logic:

1. Check Request Header: It checks if the Content-Type header exists in the incoming request.
2. Reflect Context Type: If the request has a Content-Type, the handler sets the response Content-Type to match the request’s Content-Type.
3. Apply Default: If the request header is missing, the handler sets the response Content-Type to the value specified in contentType from the configuration (defaulting to application/json).
4. Next Handler: Finally, it passes control to the next handler in the chain.

if (exchange.getRequestHeaders().contains(Headers.CONTENT_TYPE)) {
    exchange.getResponseHeaders().put(Headers.CONTENT_TYPE, exchange.getRequestHeaders().get(Headers.CONTENT_TYPE).element());
} else {
    exchange.getResponseHeaders().put(Headers.CONTENT_TYPE, config.getContentType());
}
Handler.next(exchange, next);