node: don't throw bad_optional_access on a snapshot network mismatch #36568

pull Ravan002 wants to merge 1 commits into bitcoin:master from Ravan002:snapshot-network-custom-signet changing 2 files +17 −1

Ravan002 commented at 7:52 PM on October 18, 2026: none
When a snapshot's network magic doesn't match the node's, SnapshotMetadata::Unserialize builds an error message with the names of both networks. The node's name comes from GetNetworkForMagic(m_network_magic).value(), which is empty on a custom signet because its magic is derived from the challenge and is not one of the built-in ones. loadtxoutset with a snapshot made for another network then fails with bad_optional_access instead of the message.

The node side now falls back to "custom signet", the only case where the lookup can be empty.
```
before: Unable to parse metadata: bad_optional_access
after:  Unable to parse metadata: The network of the snapshot (main) does not match the network of this node (custom signet).
```
New unit test snapshot_metadata_network_mismatch_custom_signet fails on master with std::bad_optional_access. validation_chainstatemanager_tests and feature_assumeutxo.py pass.

node: don't throw bad_optional_access on a snapshot network mismatch

SnapshotMetadata::Unserialize looked up the name of the node's network
with node_network.value(). On a custom signet the magic matches no
built-in network, so loading a snapshot made for another network threw
std::bad_optional_access instead of the intended message.

6e8ccff446

DrahtBot commented at 7:17 AM on October 19, 2026: contributor


The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.



External sites
- Code coverage & benchmarks: https://corecheck.dev/bitcoin/bitcoin/pulls/36568
- Ralph review <img src=https://review.fish.foo/assets/bitcoin/bitcoin/36568.png alt="Ralph review status"> https://git.fish.foo/bitcoin/bitcoin/pulls/36568#author-ralph


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Approach ACK Husteem

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Husteem commented at 11:42 AM on October 19, 2026: none

Concept ACK / Approach ACK

Verified the failure on master prior to this patch and confirmed the new test passes with this fix.

Empirical Reproduction on master Before this patch, running loadtxoutset on a custom signet node against a mainnet snapshot threw an uncaught std::bad_optional_access out of GetNetworkForMagic(m_network_magic).value().

Because loadtxoutset in src/rpc/blockchain.cpp specifically catches const std::ios_base::failure&, std::bad_optional_access bypassed the deserialization error handler and bubbled up to CRPCTable::execute as a generic RPC_MISC_ERROR ("std::bad_optional_access") rather than the intended RPC_DESERIALIZATION_ERROR.

While the fix and the new unit test resolve this issue. I left one small wording suggestion inline.

Type	Reviewers
Approach ACK	Husteem

in src/node/utxo_snapshot.h:97 in 6e8ccff446

  92 | @@ -93,7 +93,8 @@ class SnapshotMetadata
  93 |              if (metadata_network) {
  94 |                  std::string network_string{ChainTypeToString(metadata_network.value())};
  95 |                  auto node_network{GetNetworkForMagic(m_network_magic)};
  96 | -                std::string node_network_string{ChainTypeToString(node_network.value())};
  97 | +                // a custom signet has a magic that matches no built-in network
  98 | +                std::string node_network_string{node_network ? ChainTypeToString(*node_network) : "custom signet"};

fjahr commented at 8:50 AM on October 20, 2026:

It should just be unknown since we don't know if it's really a custom signet we are dealing with here. The comment also isn't needed.

fjahr commented at 8:52 AM on October 20, 2026: contributor

Concept ~0

Pretty minor edge case but improving the error message doesn't hurt.
maflcko commented at 9:06 AM on October 20, 2026: member

Closing for now due to controversy.
maflcko closed this on Oct 20, 2026

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node: don't throw bad_optional_access on a snapshot network mismatch #36568

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