Change how RPCs eth_call and eth_estimateGas handle "Pending" (#11127)

* Change how RPCs eth_call and eth_estimateGas handle "Pending"

Before this PR we would return a rather confusing error when calling `eth_call` and `eth_estimateGas` with `"Pending"`, e.g.:

```
{"jsonrpc":"2.0","error":{"code":-32000,"message":"This request is not supported because your node is running with state pruning. Run with --pruning=archive."},"id":"e237678f6648ed12ff05a74933d06d17"}
```

In reality what is going on is that users often use `"Pending"` when they really mean `"Latest"` (e.g. MyCrypto…) and when the block in question is not actually pending. This changes our behaviour for these two RPC calls to fall back to `"Latest"` when the query with `"Pending"` fails.
Note that we already behave this way for many other RPCs:

	- eth_call (after this PR)
	- eth_estimateGas (after this PR)
	- eth_getBalance
	- eth_getCode
	- eth_getStorageAt

Closes https://github.com/paritytech/parity-ethereum/issues/10096

* Fetch jsonrpc from git

* No real need to wait for new jsonrpc

* Add tests for calling eth_call/eth_estimateGas with "Pending"

* Fix a todo, add another

* Change client.latest_state to return the best header as well so we avoid potential data races and do less work

* Impl review suggestions

* Update rpc/src/v1/impls/eth.rs

Co-Authored-By: Niklas Adolfsson <niklasadolfsson1@gmail.com>

* Review grumbles

* update docs

rpc/src/v1/tests/helpers/miner_service.rs

@@ -93,8 +93,8 @@ impl StateClient for TestMinerService {
 	// State will not be used by test client anyway, since all methods that accept state are mocked
 	type State = TestState;
 
-	fn latest_state(&self) -> Self::State {
-		TestState
+	fn latest_state_and_header(&self) -> (Self::State, Header) {
+		(TestState, Header::default())
 	}
 
 	fn state_at(&self, _id: BlockId) -> Option<Self::State> {

rpc/src/v1/tests/mocked/eth.rs

@@ -663,6 +663,43 @@ fn rpc_eth_call_latest() {
 	assert_eq!(tester.io.handle_request_sync(request), Some(response.to_owned()));
 }
 
+#[test]
+fn rpc_eth_call_pending() {
+	let tester = EthTester::default();
+	tester.client.set_execution_result(Ok(Executed {
+		exception: None,
+		gas: U256::zero(),
+		gas_used: U256::from(0xff30),
+		refunded: U256::from(0x5),
+		cumulative_gas_used: U256::zero(),
+		logs: vec![],
+		contracts_created: vec![],
+		output: vec![0x12, 0x34, 0xff],
+		trace: vec![],
+		vm_trace: None,
+		state_diff: None,
+	}));
+
+	let request = r#"{
+		"jsonrpc": "2.0",
+		"method": "eth_call",
+		"params": [{
+			"from": "0xb60e8dd61c5d32be8058bb8eb970870f07233155",
+			"to": "0xd46e8dd67c5d32be8058bb8eb970870f07244567",
+			"gas": "0x76c0",
+			"gasPrice": "0x9184e72a000",
+			"value": "0x9184e72a",
+			"data": "0xd46e8dd67c5d32be8d46e8dd67c5d32be8058bb8eb970870f072445675058bb8eb970870f072445675"
+		},
+		"pending"],
+		"id": 1
+	}"#;
+	// Falls back to "Latest" and gives the same result.
+	let response = r#"{"jsonrpc":"2.0","result":"0x1234ff","id":1}"#;
+
+	assert_eq!(tester.io.handle_request_sync(request), Some(response.to_owned()));
+}
+
 #[test]
 fn rpc_eth_call() {
 	let tester = EthTester::default();
@@ -770,6 +807,43 @@ fn rpc_eth_estimate_gas() {
 	assert_eq!(tester.io.handle_request_sync(request), Some(response.to_owned()));
 }
 
+#[test]
+fn rpc_eth_estimate_gas_pending() {
+	let tester = EthTester::default();
+	tester.client.set_execution_result(Ok(Executed {
+		exception: None,
+		gas: U256::zero(),
+		gas_used: U256::from(0xff30),
+		refunded: U256::from(0x5),
+		cumulative_gas_used: U256::zero(),
+		logs: vec![],
+		contracts_created: vec![],
+		output: vec![0x12, 0x34, 0xff],
+		trace: vec![],
+		vm_trace: None,
+		state_diff: None,
+	}));
+
+	let request = r#"{
+		"jsonrpc": "2.0",
+		"method": "eth_estimateGas",
+		"params": [{
+			"from": "0xb60e8dd61c5d32be8058bb8eb970870f07233155",
+			"to": "0xd46e8dd67c5d32be8058bb8eb970870f07244567",
+			"gas": "0x76c0",
+			"gasPrice": "0x9184e72a000",
+			"value": "0x9184e72a",
+			"data": "0xd46e8dd67c5d32be8d46e8dd67c5d32be8058bb8eb970870f072445675058bb8eb970870f072445675"
+		},
+		"pending"],
+		"id": 1
+	}"#;
+	// Falls back to "Latest" so the result is the same
+	let response = r#"{"jsonrpc":"2.0","result":"0x5208","id":1}"#;
+
+	assert_eq!(tester.io.handle_request_sync(request), Some(response.to_owned()));
+}
+
 #[test]
 fn rpc_eth_estimate_gas_default_block() {
 	let tester = EthTester::default();