Merge bitcoin#20138: net: Assume that SetCommonVersion is called at most once per peer

fa0f415 net: Assume that SetCommonVersion is called at most once per peer (MarcoFalke)

Pull request description:

  This restores the check removed in bitcoin#17785 (comment)

  Instead of using `error`, which was used previously, it uses a newly introduced `Assume()`. `error` had several issues:
  * It logs unconditionally to the debug log
  * It doesn't abort the program when the error is hit in tests

ACKs for top commit:
  practicalswift:
    cr ACK fa0f415: patch looks correct
  jnewbery:
    utACK fa0f415

Tree-SHA512: cd7424a9485775e8c7093b725f8f52a90d47485185e79bac80f7810e450d0b3fda608d8805e9239094929f7bad2dca3fe772fb78ae606c2399d15405521e136b

Author: MarcoFalke

src/net.h

@@ -29,14 +29,15 @@
 #include <uint256.h>
 #include <util/system.h>
 #include <consensus/params.h>
+#include <util/check.h>
 
 #include <atomic>
+#include <condition_variable>
 #include <cstdint>
 #include <deque>
 #include <map>
-#include <thread>
 #include <memory>
-#include <condition_variable>
+#include <thread>
 #include <optional>
 #include <queue>
 
@@ -1417,6 +1418,7 @@ class CNode
 
     void SetCommonVersion(int greatest_common_version)
     {
+        Assume(m_greatest_common_version == INIT_PROTO_VERSION);
         m_greatest_common_version = greatest_common_version;
     }
     int GetCommonVersion() const

src/test/fuzz/net.cpp

@@ -31,6 +31,7 @@ FUZZ_TARGET_INIT(net, initialize_net)
 
     CNode node{ConsumeNode(fuzzed_data_provider)};
     SetMockTime(ConsumeTime(fuzzed_data_provider));
+    node.SetCommonVersion(fuzzed_data_provider.ConsumeIntegral<int>());
     while (fuzzed_data_provider.ConsumeBool()) {
         CallOneOf(
             fuzzed_data_provider,
@@ -42,9 +43,6 @@ FUZZ_TARGET_INIT(net, initialize_net)
             [&] {
                 node.MaybeSetAddrName(fuzzed_data_provider.ConsumeRandomLengthString(32));
             },
-            [&] {
-                node.SetCommonVersion(fuzzed_data_provider.ConsumeIntegral<int>());
-            },
             [&] {
                 const std::vector<bool> asmap = ConsumeRandomLengthBitVector(fuzzed_data_provider);
                 if (!SanityCheckASMap(asmap)) {