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Data Encoding for Request and Reply Payloads

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The request, batch request, and reply messages of the Ice protocol carry the parameters, return value, or user exception of an operation in an encapsulation. This page describes the contents of these encapsulations.

The params encapsulation of a request holds the in-parameters of the operation:

  1. The required in-parameters, in order of declaration.
  2. The optional in-parameters that have a value, sorted by tag in ascending order.

No end marker follows the optional in-parameters: the end of the encapsulation marks their end. If the operation has no in-parameters, the encapsulation is empty.

The encapsulation has the encoding version of the proxy that sends the request.

A reply with status Ok or UserException carries an encapsulation with the encoding version of the request's params encapsulation.

For reply status Ok, the encapsulation holds the out-parameters and the return value of the operation:

  1. The required out-parameters, in order of declaration.
  2. The required return value, if any.
  3. The optional out-parameters and the optional return value that have a value, sorted by tag in ascending order.

No end marker follows the optional values: the end of the encapsulation marks their end. If the operation has a void return type and no out-parameters, the encapsulation is empty.

The optional parameters example shows a request payload and an Ok reply payload byte by byte.

For reply status UserException, the encapsulation holds the user exception, marshaled as described in Data Encoding for Exceptions.

Optional values require encoding version 1.1. With version 1.0, the payload holds the required parameters and the required return value only.