9.Connection-Invitations-With-Attachment.md

9. Connection Invitations with Attachment

In the previous documents we went through how to establish a Connection which doesn't contain an attached message and after that perform some actions (like accepting credentials, sharing proofs, answering questions) using the connection established before.

An Aries Out-of-Band Invitation provides the ability to combine Connection Invitation and the following protocol message (Proof Request/ Credential Offer / Question) into a single message so that from the user's perspective it looks like a single interaction.

Note that Connection Invitation MUST be of Aries Out-Of-Band type.

In the document you can find all possible cases of how Out-Of-Band Invitation may look and a short overview of the steps that need to be taken depending on the invitation format.

In this document we will explain how to handle Out-Of-Band Invitation containing an additional protocol message as an attachment.

0. Edit application objects

We need to extend a previously defined application object for Proof Request, Credential Offer, Question with an invitation field where we will put an original Invitation.

{
    ... // previously defined fields 
    
    "invitation" - string // original invitation was received as JSON string
}

1. Analyze Invitation attachment

1. Extract the message attached to the invitation:

   iOS

   [appDelegate.sdkApi extractAttachedMessage:invite
      completion:^(NSError *error, NSString *attachedMessage) {
      // ...
   }];

   Android

   String invitationAttachedMessage = UtilsApi.vcxExtractAttachedMessage(invite).get();

2. Determine the type of the attached message:

   • Credential Offer - the value of @type field must end with issue-credential/1.0/offer-credential

   • Proof Request - the value of @type field must end with /present-proof/1.0/request-presentation

   • Question - the value of @type field must end with committedanswer/1.0/question

3. Create corresponding application object:

   • Credential Offer
     • Create SDK Credential state object as described in the Credential document here.
   • Proof Request
     • extract message attached to Proof Request in order to get the actual list of requested attributes and predicates.
     • Create SDK Proof state object as described in the Proofs document here.
     • Retrive credentials that can be used for proving as described in the Proof document here.
   • Question

2.1 Accept Invitation which contains at least one value in handshake_protocols

The existence of at least one handshake_protocols in the invitation means that connection must be established first and after that attached protocol must be executed using this connection.

1. Create SDK Connection state object as described in the Connections document here.

2. Check whether connection has been already established as described in the Connections document here.

3. Establish a new connection or Reuse existing one:

   3.1. Establish a new connection:

   • Follow the steps 4. Accept connection invitation ---> 7. Serialize Connection object and store in the application storage as described here.
     
     

   3.2. Reuse existing connection:

   • Follow the same steps described in the Connections document here.

4. Start protocol related to the attached message when the connection established or reused

• Credential Offer - Follow the steps 3. Accept Credential Offer -> 6. Serialize Credential object and store in the application storage. as described in the Credentials document here.

• Proof Request - Follow the steps 4. Share Proof as described in the Proofs document here.

• Question - Follow the steps 3. Answer on received Question as described in the Structured Messages document here.

2.2 Accept Invitation without handshake_protocols

The absence of at handshake_protocols in the invitation means that connection establishing can be omitted and receiver can just respond directly to the endpoint defined in the services field of the invitation. It implies single step interaction: Invitee sends message to Inviter.

1. Create SDK Connection state object as described in the Connections document here.

   NOTE: Connection is considered as established at this step for this type of invitation.

2. Start protocol related to the attached message

• Credential Offer - cannot be used for this invitation format.

• Proof Request - Follow the steps 4. Share Proof as described in the Proofs document here.

• Question - Follow the steps 3. Answer on received Question as described in the Structured Messages document here.

Next Step

Now your application is able to answer questions. Congratulations your application now supports base functionality! If you wish you can read about some advanced techniques.