ContentConfiguration

ContentConfiguration.global.use(encoder: JSONEncoder(), for: .json)

Each coder is registered to a specific HTTPMediaType. When decoding content from HTTP messages, the HTTPMediaType will be specified by the message itself. When encoding content from HTTP messages, the HTTPMediaType should be specified (HTTTMediaType/json is usually the assumed default).

try res.content.encode("hello", as: .plainText)
print(res.mediaType) // .plainText
print(res.body.string) // "hello"

Most often, these configured coders are used to encode and decode types conforming to Content. See the Content protocol for more information.