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feat(eth-rpc): implement eth_baseFee, returning next block base fee #11522

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feat(eth-rpc): implement eth_baseFee, returning next block base fee #11522

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46 changes: 46 additions & 0 deletions src/Nethermind/Nethermind.JsonRpc.Test/Modules/Eth/EthRpcModuleTests.GasPrice.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,52 @@ public async Task<string> Eth_blobBaseFee_ShouldGiveCorrectResult(ulong? excessB
return await ctx.Test.TestEthRpc("eth_blobBaseFee");
}

[TestCaseSource(nameof(GetBaseFeeTestCases))]
public async Task<string> Eth_baseFee_ShouldGiveCorrectResult(UInt256 baseFeePerGas, long gasLimit, long gasUsed, bool londonEnabled)
{
ISpecProvider specProvider = londonEnabled
? new TestSpecProvider(London.Instance)
: GetSpecProviderWithEip1559EnabledAs(false);
using Context ctx = await Context.Create(specProvider);
Block[] blocks = [
Build.A.Block.WithNumber(0).WithBaseFeePerGas(baseFeePerGas).WithGasLimit(gasLimit).WithGasUsed(gasUsed).TestObject,
];
BlockTree blockTree = Build.A.BlockTree(blocks[0]).WithBlocks(blocks).TestObject;
ctx.Test = await TestRpcBlockchain.ForTest(SealEngineType.NethDev).WithBlockFinder(blockTree).Build(specProvider);

return await ctx.Test.TestEthRpc("eth_baseFee");
}

public static IEnumerable<TestCaseData> GetBaseFeeTestCases
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@claude claude Bot May 8, 2026

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Low — missing null-head test case

All four test cases supply a non-empty block tree, so the if (head is null) guard in the implementation is never exercised. Consider adding:

yield return new TestCaseData(UInt256.Zero, 0L, 0L, false)
{
    TestName = "Empty blockchain returns null",
    ExpectedResult = NullResult
};

with a corresponding ctx.Test built from an empty block tree (or simply leaving the default block tree with no explicit head). The guard is correct — this is just an untested branch.

{
get
{
static string Success(UInt256 result) => $"{{\"jsonrpc\":\"2.0\",\"result\":\"{result.ToHexString(true)}\",\"id\":67}}";
const string NullResult = "{\"jsonrpc\":\"2.0\",\"result\":null,\"id\":67}";

yield return new TestCaseData(UInt256.Zero, 30_000_000L, 0L, false)
{
TestName = "Pre-London block returns null",
ExpectedResult = NullResult
};
yield return new TestCaseData((UInt256)1_000_000_000, 30_000_000L, 15_000_000L, true)
{
TestName = "Block at gas target returns same base fee",
ExpectedResult = Success(1_000_000_000)
};
yield return new TestCaseData((UInt256)1_000_000_000, 30_000_000L, 30_000_000L, true)
{
TestName = "Block over gas target increases base fee by 12.5%",
ExpectedResult = Success(1_125_000_000)
};
yield return new TestCaseData((UInt256)1_000_000_000, 30_000_000L, 0L, true)
{
TestName = "Block under gas target decreases base fee by 12.5%",
ExpectedResult = Success(875_000_000)
};
}
}

[TestCase(true, "0x3")] //Gas Prices: 1,2,3,3,4,5 | Max Index: 5 | 60th Percentile: 5 * (3/5) = 3 | Result: 3 (0x3)
[TestCase(false, "0x2")] //Gas Prices: 0,1,1,2,2,3 | Max Index: 5 | 60th Percentile: 5 * (3/5) = 3 | Result: 2 (0x2)
public async Task Eth_gasPrice_BlocksAvailableLessThanBlocksToCheckWith1559Tx_ShouldGiveCorrectResult(bool eip1559Enabled, string expected)
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17 changes: 17 additions & 0 deletions src/Nethermind/Nethermind.JsonRpc/Modules/Eth/EthRpcModule.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -121,6 +121,23 @@ public ResultWrapper<string> eth_protocolVersion()
return ResultWrapper<UInt256?>.Success(feePerBlobGas);
}

public ResultWrapper<UInt256?> eth_baseFee()
{
BlockHeader? head = _blockFinder.Head?.Header;
if (head is null)
{
return ResultWrapper<UInt256?>.Success(null);
}

IEip1559Spec specFor1559 = _specProvider.GetSpecFor1559(head.Number + 1);
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svlachakis marked this conversation as resolved.
if (!specFor1559.IsEip1559Enabled)
{
return ResultWrapper<UInt256?>.Success(null);
}

return ResultWrapper<UInt256?>.Success(BaseFeeCalculator.Calculate(head, specFor1559));
}

public ResultWrapper<UInt256?> eth_maxPriorityFeePerGas()
{
UInt256 gasPriceWithBaseFee = _gasPriceOracle.GetMaxPriorityGasFeeEstimate();
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6 changes: 6 additions & 0 deletions src/Nethermind/Nethermind.JsonRpc/Modules/Eth/IEthRpcModule.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,12 @@ public interface IEthRpcModule : IRpcModule
ExampleResponse = "0x1")]
ResultWrapper<UInt256?> eth_blobBaseFee();

[JsonRpcMethod(IsImplemented = true,
Description = "Returns the base fee of the next block in wei",
IsSharable = true,
ExampleResponse = "0x3b9aca00")]
ResultWrapper<UInt256?> eth_baseFee();

[JsonRpcMethod(IsImplemented = false,
Description = "Returns accounts",
IsSharable = true,
Expand Down