support connecting to peers without bellatrix (#4011)

* support connecting to peers without bellatrix

Make discovery fork ID aware of scheduled Bellatrix fork to enable
connections to peers that don't have Bellatrix scheduled yet.
Without this, has peering issues with peers on older SW version.

* expand tests with compatibility checks

* more exhaustive compatibility checks

AllTests-mainnet.md

@@ -126,6 +126,11 @@ OK: 4/4 Fail: 0/4 Skip: 0/4
 + Missing Authorization header [Beacon Node] [Preset: mainnet]                               OK
 ```
 OK: 5/5 Fail: 0/5 Skip: 0/5
+## Discovery fork ID
+```diff
++ Expected fork IDs                                                                          OK
+```
+OK: 1/1 Fail: 0/1 Skip: 0/1
 ## Diverging hardforks
 ```diff
 + Non-tail block in common                                                                   OK
@@ -590,4 +595,4 @@ OK: 1/1 Fail: 0/1 Skip: 0/1
 OK: 9/9 Fail: 0/9 Skip: 0/9
 
 ---TOTAL---
-OK: 331/336 Fail: 0/336 Skip: 5/336
+OK: 332/337 Fail: 0/337 Skip: 5/337

beacon_chain/spec/network.nim

@@ -123,10 +123,10 @@ func getENRForkID*(cfg: RuntimeConfig,
     next_fork_epoch: cfg.nextForkEpochAtEpoch(epoch))
 
 func getDiscoveryForkID*(cfg: RuntimeConfig,
-                   epoch: Epoch,
+                         epoch: Epoch,
-                   genesis_validators_root: Eth2Digest): ENRForkID =
+                         genesis_validators_root: Eth2Digest): ENRForkID =
-  # Until 1 epoch from fork, returns pre-fork value
+  # Until 1 epoch from fork, return pre-fork value.
-  if epoch + 1 >= cfg.ALTAIR_FORK_EPOCH:
+  if cfg.nextForkEpochAtEpoch(epoch) - epoch <= 1:
     getENRForkID(cfg, epoch, genesis_validators_root)
   else:
     let

tests/test_discovery.nim

@@ -1,10 +1,16 @@
+# beacon_chain
+# Copyright (c) 2021-2022 Status Research & Development GmbH
+# Licensed and distributed under either of
+#   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
+#   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
+# at your option. This file may not be copied, modified, or distributed except according to those terms.
+
 {.used.}
 
 import
   testutils/unittests,
   chronos, stew/shims/net, eth/keys, eth/p2p/discoveryv5/enr,
-  ../beacon_chain/spec/datatypes/base,
+  ../beacon_chain/spec/[forks, network],
-  ../beacon_chain/spec/network,
   ../beacon_chain/networking/[eth2_network, eth2_discovery],
   ./testutil
 
@@ -201,3 +207,117 @@ suite "Fork id compatibility test":
         fork_digest: ForkDigest([byte 0, 1, 2, 3]),
         next_fork_version: Version([byte 0, 0, 0, 0]),
         next_fork_epoch: Epoch(2)))
+
+suite "Discovery fork ID":
+  test "Expected fork IDs":
+    let genesis_validators_root = ZERO_HASH
+    var cfg = defaultRuntimeConfig
+    cfg.ALTAIR_FORK_EPOCH = 5.Epoch
+    cfg.BELLATRIX_FORK_EPOCH = 10.Epoch
+
+    let
+      # Phase 0
+      phase0ForkId = block:
+        let
+          current_fork_version = cfg.GENESIS_FORK_VERSION
+          next_fork_version = current_fork_version
+          fork_digest = compute_fork_digest(
+            current_fork_version, genesis_validators_root)
+          forkId = ENRForkID(
+            fork_digest: fork_digest,
+            next_fork_version: next_fork_version,
+            next_fork_epoch: FAR_FUTURE_EPOCH)
+        for epoch in GENESIS_EPOCH ..< cfg.ALTAIR_FORK_EPOCH - 1:
+          check cfg.getDiscoveryForkID(epoch, genesis_validators_root) == forkId
+        forkId
+
+      # Altair should become visible 1 epoch before the fork
+      phase0AltairForkId = block:
+        let
+          current_fork_version = cfg.GENESIS_FORK_VERSION
+          next_fork_version = cfg.ALTAIR_FORK_VERSION
+          fork_digest = compute_fork_digest(
+            current_fork_version, genesis_validators_root)
+          forkId = ENRForkID(
+            fork_digest: fork_digest,
+            next_fork_version: next_fork_version,
+            next_fork_epoch: cfg.ALTAIR_FORK_EPOCH)
+        for epoch in cfg.ALTAIR_FORK_EPOCH - 1 ..< cfg.ALTAIR_FORK_EPOCH:
+          check cfg.getDiscoveryForkID(epoch, genesis_validators_root) == forkId
+        forkId
+
+      # Altair
+      altairForkId = block:
+        let
+          current_fork_version = cfg.ALTAIR_FORK_VERSION
+          next_fork_version = current_fork_version
+          fork_digest = compute_fork_digest(
+            current_fork_version, genesis_validators_root)
+          forkId = ENRForkID(
+            fork_digest: fork_digest,
+            next_fork_version: next_fork_version,
+            next_fork_epoch: FAR_FUTURE_EPOCH)
+        for epoch in cfg.ALTAIR_FORK_EPOCH ..< cfg.BELLATRIX_FORK_EPOCH - 1:
+          check cfg.getDiscoveryForkID(epoch, genesis_validators_root) == forkId
+        forkId
+
+      # Bellatrix should become visible 1 epoch before the fork
+      altairBellatrixForkId = block:
+        let
+          current_fork_version = cfg.ALTAIR_FORK_VERSION
+          next_fork_version = cfg.BELLATRIX_FORK_VERSION
+          fork_digest = compute_fork_digest(
+            current_fork_version, genesis_validators_root)
+          forkId = ENRForkID(
+            fork_digest: fork_digest,
+            next_fork_version: next_fork_version,
+            next_fork_epoch: cfg.BELLATRIX_FORK_EPOCH)
+        for epoch in cfg.BELLATRIX_FORK_EPOCH - 1 ..< cfg.BELLATRIX_FORK_EPOCH:
+          check cfg.getDiscoveryForkID(epoch, genesis_validators_root) == forkId
+        forkId
+
+      # Bellatrix
+      bellatrixForkId = block:
+        let
+          current_fork_version = cfg.BELLATRIX_FORK_VERSION
+          next_fork_version = current_fork_version
+          fork_digest = compute_fork_digest(
+            current_fork_version, genesis_validators_root)
+          forkId = ENRForkID(
+            fork_digest: fork_digest,
+            next_fork_version: next_fork_version,
+            next_fork_epoch: FAR_FUTURE_EPOCH)
+        for epoch in cfg.BELLATRIX_FORK_EPOCH ..< cfg.BELLATRIX_FORK_EPOCH + 5:
+          check cfg.getDiscoveryForkID(epoch, genesis_validators_root) == forkId
+        forkId
+
+    check:  # isCompatibleForkId(ourForkId, peerForkId)
+      isCompatibleForkId(phase0ForkId, phase0ForkId)
+      isCompatibleForkId(phase0ForkId, phase0AltairForkId)
+      not isCompatibleForkId(phase0ForkId, altairForkId)
+      not isCompatibleForkId(phase0ForkId, altairBellatrixForkId)
+      not isCompatibleForkId(phase0ForkId, bellatrixForkId)
+
+      not isCompatibleForkId(phase0AltairForkId, phase0ForkId)  # fork -1 epoch
+      isCompatibleForkId(phase0AltairForkId, phase0AltairForkId)
+      not isCompatibleForkId(phase0AltairForkId, altairForkId)
+      not isCompatibleForkId(phase0AltairForkId, altairBellatrixForkId)
+      not isCompatibleForkId(phase0AltairForkId, bellatrixForkId)
+
+      not isCompatibleForkId(altairForkId, phase0ForkId)
+      not isCompatibleForkId(altairForkId, phase0AltairForkId)
+      isCompatibleForkId(altairForkId, altairForkId)
+      isCompatibleForkId(altairForkId, altairBellatrixForkId)
+      not isCompatibleForkId(altairForkId, bellatrixForkId)
+
+      not isCompatibleForkId(altairBellatrixForkId, phase0ForkId)
+      not isCompatibleForkId(altairBellatrixForkId, phase0AltairForkId)
+      not isCompatibleForkId(altairBellatrixForkId, altairForkId)  # fork -1 ep
+      isCompatibleForkId(altairBellatrixForkId, altairBellatrixForkId)
+      not isCompatibleForkId(altairBellatrixForkId, bellatrixForkId)
+
+      not isCompatibleForkId(bellatrixForkId, phase0ForkId)
+      not isCompatibleForkId(bellatrixForkId, phase0AltairForkId)
+      not isCompatibleForkId(bellatrixForkId, altairForkId)
+      not isCompatibleForkId(bellatrixForkId, altairBellatrixForkId)
+      isCompatibleForkId(bellatrixForkId, bellatrixForkId)