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# Algorand Specifications

Each incoming message ∗M∗M is deferred to the correct _message handler_ MHt(∗M) given its protocol tag (tt).

The message handler then processes the message and decides on a ForwardingPolicy (see the [definition](https://specs.algorand.co/network/non-normative/network-nn-notation#messages-incoming-and-outgoing) of this data type for further details).

A message handler MHt(∗M) contains the logic for handling incoming messages.

The following is the list of registered message handlers defined in the reference implementation, ordered by tag:

- `AV` for Agreement Vote:
  - [Handler’s implementation starting point](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/agreement/gossip/network.go#L99).
  - [Handler’s registration](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/agreement/gossip/network.go#L89).
- `MI` for Message of Interest:
  - [Context](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/network/wsPeer.go#L633).
  - [Handler’s implementation](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/network/wsPeer.go#L714).
- `MS` for Message Digest Skip:
  - [Context](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/network/wsPeer.go#L669).
  - [Handler’s implementation](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/network/wsPeer.go#L760).
- `NP` for Net Priority Response:
  - [Handler’s implementation](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/network/netprio.go#L35).
  - [Handler’s registration](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/network/wsNetwork.go#L710).
- `NI` for Network ID Verification:
  - [Handler’s implementation](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/network/netidentity.go#L405).
  - [Handler’s registration](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/network/wsNetwork.go#L702).
- `PP` for Proposal Payload:
  - [Handler’s implementation](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/agreement/gossip/network.go#L103).
  - [Handler’s registration](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/agreement/gossip/network.go#L89).
- `SP` for State Proof Signature:
  - [Handler’s implementation](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/stateproof/builder.go#L312).
  - [Handler’s registration](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/stateproof/worker.go#L116).
- `TS` for Topic Message Response:
  - [Hardcoded implementation](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/network/wsPeer.go#L641).
- `TX` for Transaction:
  - [Handler’s implementation](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/data/txHandler.go#L735).
  - [Handler’s registration](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/data/txHandler.go#L262).
- `UE` for Unicast Catchup Request:
  - [Handler’s implementation](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/rpcs/blockService.go#L293).
  - [Handler’s registration](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/rpcs/blockService.go#L169).
- `VB` for Vote Bundle:
  - [Handler’s implementation](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/agreement/gossip/network.go#L110).
  - [Handler’s registration](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/agreement/gossip/network.go#L89).
- Unrecognized Tag case (a special tag value to account for transmission errors or adversarial behavior):
  - [Context](https://github.com/algorand/go-algorand/blob/0bc3d7e4750db8f98c5dd66f3377147532021c62/network/wsPeer.go#L679).

In general, after a preliminary validation and a series of computations, the produced output is an _outgoing message_ M∗M∗.

Internally, MHt(∗M) routes data to the corresponding component of the node (e.g., “Agreement” for protocol messages, “Transaction Pool” for transactions, etc.).

> Refer to the normative section of each node component to see how these messages are processed and their impact on the node’s overarching state.

> Important
>
> **IMPLEMENTATION:**
>
> In the reference implementation, a single entry point callback `Notify()` is used to monitor an outgoing connection whenever a message is received. This function then sends the message metadata to the appropriate processing stage of the `PerformanceMonitor`.
>
> Usage in [Relay Network](https://github.com/algorand/go-algorand/blob/7e562c35b02289ca95114b4b3a20a7dc2df79018/network/wsPeer.go#L626).
>
> Usage in [P2P Network](https://github.com/algorand/go-algorand/blob/7e562c35b02289ca95114b4b3a20a7dc2df79018/network/p2p/p2p.go#L187).