ethclient, mobile: add TransactionSender (#15127)

* core/types: make Signer derive address instead of public key

There are two reasons to do this now: The upcoming ethclient signer
doesn't know the public key, just the address. EIP 208 will introduce a
new signer which derives the 'entry point' address for transactions with
zero signature. The entry point has no public key.

Other changes to the interface ease the path make to moving signature
crypto out of core/types later.

* ethclient, mobile: add TransactionSender

The new method can get the right signer without any crypto, and without
knowledge of the signature scheme that was used when the transaction was
included.

1 files changed, 59 insertions, 0 deletions

diff --git a/ethclient/signer.go b/ethclient/signer.go
new file mode 100644
index 000000000..74a93f1e2
--- /dev/null
+++ b/ethclient/signer.go
@@ -0,0 +1,59 @@
+// Copyright 2017 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package ethclient
+
+import (
+	"errors"
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+)
+
+// senderFromServer is a types.Signer that remembers the sender address returned by the RPC
+// server. It is stored in the transaction's sender address cache to avoid an additional
+// request in TransactionSender.
+type senderFromServer struct {
+	addr      common.Address
+	blockhash common.Hash
+}
+
+var errNotCached = errors.New("sender not cached")
+
+func setSenderFromServer(tx *types.Transaction, addr common.Address, block common.Hash) {
+	// Use types.Sender for side-effect to store our signer into the cache.
+	types.Sender(&senderFromServer{addr, block}, tx)
+}
+
+func (s *senderFromServer) Equal(other types.Signer) bool {
+	os, ok := other.(*senderFromServer)
+	return ok && os.blockhash == s.blockhash
+}
+
+func (s *senderFromServer) Sender(tx *types.Transaction) (common.Address, error) {
+	if s.blockhash == (common.Hash{}) {
+		return common.Address{}, errNotCached
+	}
+	return s.addr, nil
+}
+
+func (s *senderFromServer) Hash(tx *types.Transaction) common.Hash {
+	panic("can't sign with senderFromServer")
+}
+func (s *senderFromServer) SignatureValues(tx *types.Transaction, sig []byte) (R, S, V *big.Int, err error) {
+	panic("can't sign with senderFromServer")
+}