Add mechanism to get blockhash's last valid slot (solana-labs#10239)

automerge

src/apps/jsonrpc-api.md

@@ -27,6 +27,7 @@ To interact with a Solana node inside a JavaScript application, use the [solana-
 * [getEpochSchedule](jsonrpc-api.md#getepochschedule)
 * [getFeeCalculatorForBlockhash](jsonrpc-api.md#getfeecalculatorforblockhash)
 * [getFeeRateGovernor](jsonrpc-api.md#getfeerategovernor)
+* [getFees](jsonrpc-api.md#getfees)
 * [getFirstAvailableBlock](jsonrpc-api.md#getfirstavailableblock)
 * [getGenesisHash](jsonrpc-api.md#getgenesishash)
 * [getIdentity](jsonrpc-api.md#getidentity)
@@ -538,6 +539,34 @@ curl -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","id":1, "m
 {"jsonrpc":"2.0","result":{"context":{"slot":54},"value":{"feeRateGovernor":{"burnPercent":50,"maxLamportsPerSignature":100000,"minLamportsPerSignature":5000,"targetLamportsPerSignature":10000,"targetSignaturesPerSlot":20000}}},"id":1}
 ```
 
+### getFees
+
+Returns a recent block hash from the ledger, a fee schedule that can be used to
+compute the cost of submitting a transaction using it, and the last slot in
+which the blockhash will be valid.
+
+#### Parameters:
+
+* `<object>` - (optional) [Commitment](jsonrpc-api.md#configuring-state-commitment)
+
+#### Results:
+
+The result will be an RpcResponse JSON object with `value` set to a JSON object with the following fields:
+
+* `blockhash: <string>` - a Hash as base-58 encoded string
+* `feeCalculator: <object>` - FeeCalculator object, the fee schedule for this block hash
+* `lastValidSlot: <u64>` - last slot in which a blockhash will be valid
+
+#### Example:
+
+```bash
+// Request
+curl -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","id":1, "method":"getFees"}' http://localhost:8899
+
+// Result
+{"jsonrpc":"2.0","result":{"context":{"slot":1},"value":{"blockhash":"CSymwgTNX1j3E4qhKfJAUE41nBWEwXufoYryPbkde5RR","feeCalculator":{lamportsPerSignature":5000},"lastValidSlot":297}},"id":1}
+```
+
 ### getFirstAvailableBlock
 
 Returns the slot of the lowest confirmed block that has not been purged from the ledger
@@ -765,7 +794,7 @@ An RpcResponse containing a JSON object consisting of a string blockhash and Fee
 curl -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","id":1, "method":"getRecentBlockhash"}' http://localhost:8899
 
 // Result
-{"jsonrpc":"2.0","result":{"context":{"slot":1},"value":{"blockhash":"CSymwgTNX1j3E4qhKfJAUE41nBWEwXufoYryPbkde5RR","feeCalculator":{"burnPercent":50,"lamportsPerSignature":5000,"maxLamportsPerSignature":100000,"minLamportsPerSignature":5000,"targetLamportsPerSignature":10000,"targetSignaturesPerSlot":20000}}},"id":1}
+{"jsonrpc":"2.0","result":{"context":{"slot":1},"value":{"blockhash":"CSymwgTNX1j3E4qhKfJAUE41nBWEwXufoYryPbkde5RR","feeCalculator":{"lamportsPerSignature":5000}}},"id":1}
 ```
 
 ### getSignatureStatuses