Compatibility issues when upgrading bitcoind backend (v22 → v28+)

[pragmaxim]

Summary

When upgrading the bitcoind backend to a modern version (v22 → v28+), several RPC response format changes can cause Blockbook to break or behave incorrectly. This issue tracks the known problems and their remediation.

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1. 🔴 warnings field is now an array (Core ≥ v25.0) — must merge PR #1633

Bitcoin Core 25.0 changed the "warnings" field of getblockchaininfo and getnetworkinfo from a single string to a JSON array of strings. Without a fix, GetChainInfo() fails at startup with:

cannot unmarshal array into Go struct field .result.warnings of type string

Fix: #1633 introduces a custom coreWarnings type that accepts either wire shape. This PR must be merged before upgrading to Core ≥ 25.0.

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2. 🟡 getmempoolentry top-level fee fields deprecated (Core ≥ v23.0)

Bitcoin Core 23.0 deprecated the top-level fee, modifiedfee, ancestorfees, and descendantfees fields in getmempoolentry (and related RPCs) in favour of a nested fees object. The deprecated fields are still returned behind -deprecatedrpc=fees, but may be removed in a future release.

Blockbooks ResGetMempoolEntry (in bchain/coins/btc/bitcoinrpc.go) currently reads only the top-level fields:

Fee            common.JSONNumber `json:"fee"`
ModifiedFee    common.JSONNumber `json:"modifiedfee"`
DescendantFees uint32            `json:"descendantfees"`
AncestorFees   uint32            `json:"ancestorfees"`

If Core eventually drops the deprecated compat flag, these will silently return zero values (or fail to unmarshal), corrupting mempool tracking and fee estimation.

Suggested fix: Add a custom UnmarshalJSON or switch to reading the fees nested object and convert from BTC-denominated values back to satoshis.

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3. 🟡 DescendantFees / AncestorFees typed as uint32 — overflow risk

In bchain/coins/btc/bitcoinrpc.go, these fields are typed as uint32:

DescendantFees uint32 `json:"descendantfees"`
AncestorFees   uint32 `json:"ancestorfees"`

Bitcoin Core returns them as CAmount (int64, denominated in satoshis). The uint32 maximum is ~4.29 billion satoshis (~42.9 BTC). A sufficiently large mempool descendant tree (more likely with Cores package relay introduced in v26.0 and TRUC transactions in v27.0+) can exceed this threshold, causing silent truncation or a JSON unmarshal error.

Suggested fix: Change the types to common.JSONNumber (matching how Fee and ModifiedFee are already handled) and convert to satoshis via the existing helper.

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Affected coins

• Bitcoin and all coins that reuse bchain/coins/btc/ RPC types (Litecoin, Bitcoin Cash, eCash, Dash, Dogecoin, Firo, etc.)
• Zcash partially — it reuses ResGetNetworkInfo from the btc package.
• Decred has its own independent RPC implementation and is not affected by items 2 or 3.