rpcclient: safe read and write to batch

[ynewmann]

This PR tries to make batchList concurrent-safe.

The Send() could panic at the line 1730 if c.removeRequest returned nil. It could return nil if we try to call Send() concurrently.

btcd/rpcclient/infrastructure.go

Lines 1708 to 1730 in 684d64a

	request := c.removeRequest(id)
	// If there's an error, we log it and continue to the next
	// request.
	fullResult, err := json.Marshal(resp.Result)
	if err != nil {
	log.Errorf("Unable to marshal result: %v for req=%v",
	err, request.id)
	continue
	}
	// If there's a response error, we send it back the request.
	var requestError error
	if resp.Error != nil {
	requestError = resp.Error
	}
	result := Response{
	result: fullResult,
	err: requestError,
	}
	request.responseChan <- &result

After the quick look I've noticed that there are places where the batchList is update unsafely. So, the simplest fix is just to add locks, but I'm afraid if it could break something else, because I'm not very familiar with the library.

[Roasbeef]

Approved CI.

[coveralls]

Pull Request Test Coverage Report for Build 12370739640

Details

• 0 of 24 (0.0%) changed or added relevant lines in 1 file are covered.
• 8 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.02%) to 57.259%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
rpcclient/infrastructure.go	0	24	0.0%

Files with Coverage Reduction	New Missed Lines	%
rpcclient/infrastructure.go	2	39.87%
peer/peer.go	6	74.16%

Totals
Change from base Build 12253655920:	-0.02%
Covered Lines:	29906
Relevant Lines:	52229

---

💛 - Coveralls

[guggero]

Thanks for the fix! Just two minor nits.

[ynewmann]

Thanks for the fix! Just two minor nits.

One more nit here b3d9947

[guggero]

Can you squash the commits into one please?
Then this is good to go.

[yyforyongyu]

Could you do a rebase on master? I'm trying to test it in lnd but the current branch doesn't include some recent fixes that were pushed to master.

[ynewmann]

Could you do a rebase on master? I'm trying to test it in lnd but the current branch doesn't include some recent fixes that were pushed to master.

done

[yyforyongyu]

LGTM 🚢