Merge pull request #3075 from ethDreamer/gossip_bls_to_execution_change

Capella: Add Gossip Topic bls_to_execution_change

specs/capella/p2p-interface.md

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+# Capella -- Networking
+
+This document contains the networking specification for Capella.
+
+The specification of these changes continues in the same format as the network specifications of previous upgrades, and assumes them as pre-requisite.
+
+## Table of contents
+
+<!-- TOC -->
+<!-- START doctoc generated TOC please keep comment here to allow auto update -->
+<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
+
+- [Modifications in Capella](#modifications-in-capella)
+  - [The gossip domain: gossipsub](#the-gossip-domain-gossipsub)
+    - [Topics and messages](#topics-and-messages)
+      - [Global topics](#global-topics)
+        - [`beacon_block`](#beacon_block)
+        - [`bls_to_execution_change`](#bls_to_execution_change)
+    - [Transitioning the gossip](#transitioning-the-gossip)
+  - [The Req/Resp domain](#the-reqresp-domain)
+    - [Messages](#messages)
+      - [BeaconBlocksByRange v2](#beaconblocksbyrange-v2)
+      - [BeaconBlocksByRoot v2](#beaconblocksbyroot-v2)
+
+<!-- END doctoc generated TOC please keep comment here to allow auto update -->
+<!-- /TOC -->
+
+
+# Modifications in Capella
+
+## The gossip domain: gossipsub
+
+A new topic is added to support the gossip of withdrawal credential change messages. And an existing topic is upgraded for updated types in Capella.
+
+### Topics and messages
+
+Topics follow the same specification as in prior upgrades. All existing topics remain stable except the beacon block topic which is updated with the modified type.
+
+The new topics along with the type of the `data` field of a gossipsub message are given in this table:
+
+| Name | Message Type |
+| - | - |
+| `beacon_block` | `SignedBeaconBlock` (modified) |
+| `bls_to_execution_change` | `SignedBLSToExecutionChange` |
+
+Note that the `ForkDigestValue` path segment of the topic separates the old and the new `beacon_block` topics.
+
+#### Global topics
+
+Capella changes the type of the global beacon block topic and adds one global topic to propagate withdrawal credential change messages to all potential proposers of beacon blocks.
+
+##### `beacon_block`
+
+The *type* of the payload of this topic changes to the (modified) `SignedBeaconBlock` found in Capella.
+Specifically, this type changes with the addition of `bls_to_execution_changes` to the inner `BeaconBlockBody`.
+See Capella [state transition document](./beacon-chain.md#beaconblockbody) for further details.
+
+##### `bls_to_execution_change`
+
+This topic is used to propagate signed bls to execution change messages to be included in future blocks.
+
+The following validations MUST pass before forwarding the `signed_bls_to_execution_change` on the network:
+
+- _[IGNORE]_ The `signed_bls_to_execution_change` is the first valid signed bls to execution change received
+  for the validator with index `signed_bls_to_execution_change.message.validator_index`.
+- _[REJECT]_ All of the conditions within `process_bls_to_execution_change` pass validation.
+
+### Transitioning the gossip
+
+See gossip transition details found in the [Altair document](../altair/p2p-interface.md#transitioning-the-gossip) for
+details on how to handle transitioning gossip topics for Capella.
+
+## The Req/Resp domain
+
+### Messages
+
+#### BeaconBlocksByRange v2
+
+**Protocol ID:** `/eth2/beacon_chain/req/beacon_blocks_by_range/2/`
+
+The Capella fork-digest is introduced to the `context` enum to specify Capella block type.
+
+Per `context = compute_fork_digest(fork_version, genesis_validators_root)`:
+
+[0]: # (eth2spec: skip)
+
+| `fork_version`           | Chunk SSZ type             |
+| ------------------------ | -------------------------- |
+| `GENESIS_FORK_VERSION`   | `phase0.SignedBeaconBlock` |
+| `ALTAIR_FORK_VERSION`    | `altair.SignedBeaconBlock` |
+| `BELLATRIX_FORK_VERSION` | `bellatrix.SignedBeaconBlock` |
+| `CAPELLA_FORK_VERSION`   | `capella.SignedBeaconBlock` |
+
+#### BeaconBlocksByRoot v2
+
+**Protocol ID:** `/eth2/beacon_chain/req/beacon_blocks_by_root/2/`
+
+The Capella fork-digest is introduced to the `context` enum to specify Capella block type.
+
+Per `context = compute_fork_digest(fork_version, genesis_validators_root)`:
+
+[1]: # (eth2spec: skip)
+
+| `fork_version`           | Chunk SSZ type             |
+| ------------------------ | -------------------------- |
+| `GENESIS_FORK_VERSION`   | `phase0.SignedBeaconBlock` |
+| `ALTAIR_FORK_VERSION`    | `altair.SignedBeaconBlock` |
+| `BELLATRIX_FORK_VERSION` | `bellatrix.SignedBeaconBlock` |
+| `CAPELLA_FORK_VERSION`   | `capella.SignedBeaconBlock` |
+