Jolie defines two types of operations:

  • one-way operations, which receive a message;
  • request-response operations, which reply or receive a message and send back a response.

Thus an interface is a collection of operation types, a list of One-Way and Request-Response operation declarations.

The basic declaration of an interface lists all the names of its operations, grouped by type:

interface identifier {
        ow_name1( t1 ),
        ow_name2( t2 ),
        ow_nameN( tN )
        rr_name1( tk1 )( tk2 ),
        rr_name2( tk3 )( tk4 ),
        rr_nameN( tkN )( tkN+1 )

The syntax presented above includes the types of the messages of each operation. One-way operations require only one message type, whilst request-responses define both request (left argument) and response (right argument) types.

As an example, let us declare the interface SumInterface:

interface SumInterface {
        sum( SumRequest )( int )

SumInterface defines a request-response operation sum. SumInterface is the same used in the declaration of SumInput and SumServ, shown at the end of ports subsection.

The type declarations of both request and response messages are explained further in the data types subsection below.

Declarations of Faults: the statement throws

The operations of type RequestResponse can reply with a fault instead of the response message. In such a case, we need to specify into the interface declaration that a request-response operation can raise a fault. In order to do that it is sufficient to list the faults after the usage of the statement throws as it is shown here in the complete syntax:

interface IfaceName {
        Op1( ReqType1 )( ResType1 ) throws ErrX( MsgTypeX ) ... ErrY( MsgTypeY )
        OpN( ReqTypeN )( ResTypeN ) throws ErrW( MsgTypeW ) ... ErrZ( MsgTypeZ )

where ErrX, ErrY, ErrW, ..., ErrZ are the fault names and MsgTypeX, ..., MsgTypeZ are the types of the messages. Examples of its usage can be found in Section Fault Handling.