accounts, eth, clique, signer: support for external signer API (#18079)

* accounts, eth, clique: implement external backend + move sighash calc to backend

* signer: implement account_Version on external API

* accounts/external: enable ipc, add copyright

* accounts, internal, signer: formatting

* node: go fmt

* flags: disallow --dev in combo with --externalsigner

* accounts: remove clique-specific signing method, replace with more generic

* accounts, consensus: formatting + fix error in tests

* signer/core: remove (test-) import cycle

* clique: remove unused import

* accounts: remove CliqueHash and avoid dependency on package crypto

* consensus/clique: unduplicate header encoding

2 files changed, 52 insertions, 38 deletions

diff --git a/consensus/clique/clique.go b/consensus/clique/clique.go
index c79c30cae..c0f78ce65 100644
--- a/consensus/clique/clique.go
+++ b/consensus/clique/clique.go
@@ -20,6 +20,7 @@ package clique
 import (
 	"bytes"
 	"errors"
+	"io"
 	"math/big"
 	"math/rand"
 	"sync"
@@ -136,40 +137,9 @@ var (
 	errRecentlySigned = errors.New("recently signed")
 )
 
-// SignerFn is a signer callback function to request a hash to be signed by a
+// SignerFn is a signer callback function to request a header to be signed by a
 // backing account.
-type SignerFn func(accounts.Account, []byte) ([]byte, error)
-
-// sigHash returns the hash which is used as input for the proof-of-authority
-// signing. It is the hash of the entire header apart from the 65 byte signature
-// contained at the end of the extra data.
-//
-// Note, the method requires the extra data to be at least 65 bytes, otherwise it
-// panics. This is done to avoid accidentally using both forms (signature present
-// or not), which could be abused to produce different hashes for the same header.
-func sigHash(header *types.Header) (hash common.Hash) {
-	hasher := sha3.NewLegacyKeccak256()
-
-	rlp.Encode(hasher, []interface{}{
-		header.ParentHash,
-		header.UncleHash,
-		header.Coinbase,
-		header.Root,
-		header.TxHash,
-		header.ReceiptHash,
-		header.Bloom,
-		header.Difficulty,
-		header.Number,
-		header.GasLimit,
-		header.GasUsed,
-		header.Time,
-		header.Extra[:len(header.Extra)-65], // Yes, this will panic if extra is too short
-		header.MixDigest,
-		header.Nonce,
-	})
-	hasher.Sum(hash[:0])
-	return hash
-}
+type SignerFn func(accounts.Account, string, []byte) ([]byte, error)
 
 // ecrecover extracts the Ethereum account address from a signed header.
 func ecrecover(header *types.Header, sigcache *lru.ARCCache) (common.Address, error) {
@@ -185,7 +155,7 @@ func ecrecover(header *types.Header, sigcache *lru.ARCCache) (common.Address, er
 	signature := header.Extra[len(header.Extra)-extraSeal:]
 
 	// Recover the public key and the Ethereum address
-	pubkey, err := crypto.Ecrecover(sigHash(header).Bytes(), signature)
+	pubkey, err := crypto.Ecrecover(SealHash(header).Bytes(), signature)
 	if err != nil {
 		return common.Address{}, err
 	}
@@ -646,7 +616,7 @@ func (c *Clique) Seal(chain consensus.ChainReader, block *types.Block, results c
 		log.Trace("Out-of-turn signing requested", "wiggle", common.PrettyDuration(wiggle))
 	}
 	// Sign all the things!
-	sighash, err := signFn(accounts.Account{Address: signer}, sigHash(header).Bytes())
+	sighash, err := signFn(accounts.Account{Address: signer}, "application/x-clique-header", CliqueRLP(header))
 	if err != nil {
 		return err
 	}
@@ -663,7 +633,7 @@ func (c *Clique) Seal(chain consensus.ChainReader, block *types.Block, results c
 		select {
 		case results <- block.WithSeal(header):
 		default:
-			log.Warn("Sealing result is not read by miner", "sealhash", c.SealHash(header))
+			log.Warn("Sealing result is not read by miner", "sealhash", SealHash(header))
 		}
 	}()
 
@@ -693,7 +663,7 @@ func CalcDifficulty(snap *Snapshot, signer common.Address) *big.Int {
 
 // SealHash returns the hash of a block prior to it being sealed.
 func (c *Clique) SealHash(header *types.Header) common.Hash {
-	return sigHash(header)
+	return SealHash(header)
 }
 
 // Close implements consensus.Engine. It's a noop for clique as there are no background threads.
@@ -711,3 +681,47 @@ func (c *Clique) APIs(chain consensus.ChainReader) []rpc.API {
 		Public:    false,
 	}}
 }
+
+// SealHash returns the hash of a block prior to it being sealed.
+func SealHash(header *types.Header) (hash common.Hash) {
+	hasher := sha3.NewLegacyKeccak256()
+	encodeSigHeader(hasher, header)
+	hasher.Sum(hash[:0])
+	return hash
+}
+
+// CliqueRLP returns the rlp bytes which needs to be signed for the proof-of-authority
+// sealing. The RLP to sign consists of the entire header apart from the 65 byte signature
+// contained at the end of the extra data.
+//
+// Note, the method requires the extra data to be at least 65 bytes, otherwise it
+// panics. This is done to avoid accidentally using both forms (signature present
+// or not), which could be abused to produce different hashes for the same header.
+func CliqueRLP(header *types.Header) []byte {
+	b := new(bytes.Buffer)
+	encodeSigHeader(b, header)
+	return b.Bytes()
+}
+
+func encodeSigHeader(w io.Writer, header *types.Header) {
+	err := rlp.Encode(w, []interface{}{
+		header.ParentHash,
+		header.UncleHash,
+		header.Coinbase,
+		header.Root,
+		header.TxHash,
+		header.ReceiptHash,
+		header.Bloom,
+		header.Difficulty,
+		header.Number,
+		header.GasLimit,
+		header.GasUsed,
+		header.Time,
+		header.Extra[:len(header.Extra)-65], // Yes, this will panic if extra is too short
+		header.MixDigest,
+		header.Nonce,
+	})
+	if err != nil {
+		panic("can't encode: " + err.Error())
+	}
+}
diff --git a/consensus/clique/snapshot_test.go b/consensus/clique/snapshot_test.go
index 41dae1426..b920312a8 100644
--- a/consensus/clique/snapshot_test.go
+++ b/consensus/clique/snapshot_test.go
@@ -80,7 +80,7 @@ func (ap *testerAccountPool) sign(header *types.Header, signer string) {
 		ap.accounts[signer], _ = crypto.GenerateKey()
 	}
 	// Sign the header and embed the signature in extra data
-	sig, _ := crypto.Sign(sigHash(header).Bytes(), ap.accounts[signer])
+	sig, _ := crypto.Sign(SealHash(header).Bytes(), ap.accounts[signer])
 	copy(header.Extra[len(header.Extra)-extraSeal:], sig)
 }