message: VCX connection protocol acknowledgment
diff: @@ -24,7 +24,7 @@ use error::prelude::*;
  pub struct DidExchangeSM {
  source_id: String,
  agent_info: AgentInfo,
  - state: ActorDidExchangeState
  + state: ActorDidExchangeState,
  }
  #[derive(Debug, Clone, Serialize, Deserialize)]
  @@ -83,14 +83,14 @@ pub struct RequestedState {
  pub struct RespondedState {
  response: SignedResponse,
  did_doc: DidDoc,
  - prev_agent_info: AgentInfo
  + prev_agent_info: AgentInfo,
  }
  #[derive(Debug, Clone, Serialize, Deserialize)]
  pub struct CompleteState {
  did_doc: DidDoc,
  pending_messages: HashMap<MessageId, String>,
  - protocols: Option<Vec<ProtocolDescriptor>>
  + protocols: Option<Vec<ProtocolDescriptor>>,
  }
  impl From<(NullState, Invitation)> for InvitedState {
  @@ -204,11 +204,17 @@ impl RequestedState {
  return Err(VcxError::from_msg(VcxErrorKind::InvalidJson, format!("Cannot handle Response: thread id does not match: {:?}", response.thread)));
  }
  - if response.please_ack.is_some() {
  - // TODO: else send Ping ???
  - let ack = Ack::create().set_thread_id(&response.thread.thid.clone().unwrap_or_default());
  - agent_info.send_message(&ack.to_a2a_message(), &response.connection.did_doc)?;
  - }
  + let message = if response.please_ack.is_some() {
  + Ack::create()
  + .set_thread_id(&response.thread.thid.clone().unwrap_or_default())
  + .to_a2a_message()
  + } else {
  + Ping::create()
  + .set_thread_id(response.thread.thid.clone().unwrap_or_default())
  + .to_a2a_message()
  + };
  +
  + agent_info.send_message(&message, &response.connection.did_doc)?;
  Ok(response)
  }
  @@ -308,7 +314,7 @@ impl DidExchangeSM {
  DidExchangeSM {
  source_id: source_id.to_string(),
  state: ActorDidExchangeState::Invitee(DidExchangeState::Null(NullState {})),
  - agent_info: AgentInfo::default()
  + agent_info: AgentInfo::default(),
  }
  }
  }
  @@ -667,7 +673,7 @@ impl DidExchangeSM {
  #[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
  pub enum Actor {
  Inviter,
  - Invitee
  + Invitee,
  }
  #[cfg(test)]
  