预计阅读时间： 4 分钟
DoubleReceive feature provides the ability to invoke
ApplicationCall.receive several times with no
RequestAlreadyConsumedException exception. This usually makes sense when a feature is consuming a request body
so a handler is unable to receive it again.
This feature is experimental including all options and behaviour. It is not guaranteed to work the same way in future releases.
Table of contents:
DoubleReceive feature into the ApplicationCall
After that you can receive from a call multiple times and every invocation may return the same instance.
val first = call.receiveText() val theSame = call.receiveText()
Not every content could be received twice. For example, a stream or a channel can’t be received twice unless
receiveEntireContent option is enabled.
Types that could be always received twice with this feature are:
Parameters and all types provided by ContentNegotiation feature (for example, objects deserialized from JSON payloads).
Receiving different types from the same call is not guaranteed to work without
receiveEntireContent but may work in some specific cases. For example, receiving a text after receiving a byte array always works.
receiveEntireContent is enabled, then receiving different types should always work. Also double receive of a channel or stream works as well. However,
receive executes the whole receive pipeline from the beginning so all content transformations and converters are executed every time that may be slower than with the option disabled.
|receiveEntireContent||same type||different type||channel|
|disabled||cached same instance||generally no||no|
If a custom content transformation is installed (for example, by intercepting receive pipeline), then a transformed value couldn’t be re-received without
receiveEntireContent option by default. However it is possible to mark a transformed value object as reusable by specifying
val converted = .... // convert somehow from a request payload proceedWith(ApplicationReceiveRequest(receive.typeInfo, converted, reusableValue = true))
receiveEntireContentWhen enabled, for every request the whole content will be received and stored as a byte array. This is useful when completely different types need to be received. You also can receive streams and channels. Note that enabling this causes the whole receive pipeline to be executed for every further receive pipeline.