Add block timestamp to `eth_getTransactionByHash`

[bogdan]

Rationale

eth_getTransactionByHash returns the transaction together with blockHash and blockNumber once it is mined, but it does not include the block timestamp.

As a result, clients must issue an additional RPC call (eth_getBlockByHash or eth_getBlockByNumber) to retrieve the timestamp, even though this information is already known by the node at that point.

This extra round-trip significantly increases latency and RPC load for a very common access pattern.

Use-cases include:

• Wallets displaying transaction history with timestamps
• NFT marketplaces and indexers tracking transfers
• Block explorers and analytics tools
• Mobile or high-latency clients where minimizing RPC calls is important

Including the timestamp directly would improve performance, simplify client code, and reduce unnecessary RPC traffic.

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Implementation

A possible implementation would be to add an optional field to the eth_getTransactionByHash response, for example:

"blockTimestamp": "0x6565f1a0"

• Present only for mined transactions
• null or omitted for pending transactions
• Encoded in the same hex format as block timestamps in eth_getBlockBy*

This change would be fully backward-compatible, as it only adds a new field.

Orignally from ethereum/go-ethereum#33491

[fjl]

There are no objections from Geth to adding this.

[canepat]

No objections from Erigon.

[jflo]

none from Besu either.