[lbry] blockchain, wire: verify blockheaders using LBRY PoW

blockchain/validate.go

@@ -324,7 +324,7 @@ func checkProofOfWork(header *wire.BlockHeader, powLimit *big.Int, flags Behavio
 	// to avoid proof of work checks is set.
 	if flags&BFNoPoWCheck != BFNoPoWCheck {
 		// The block hash must be less than the claimed target.
-		hash := header.BlockHash()
+		hash := header.BlockPoWHash()
 		hashNum := HashToBig(&hash)
 		if hashNum.Cmp(target) > 0 {
 			str := fmt.Sprintf("block hash of %064x is higher than "+

wire/blockheader.go

@@ -59,6 +59,18 @@ func (h *BlockHeader) BlockHash() chainhash.Hash {
 	return chainhash.DoubleHashH(buf.Bytes())
 }
 
+// BlockPoWHash computes the block identifier hash for the given block header.
+func (h *BlockHeader) BlockPoWHash() chainhash.Hash {
+	// Encode the header and double sha256 everything prior to the number of
+	// transactions.  Ignore the error returns since there is no way the
+	// encode could fail except being out of memory which would cause a
+	// run-time panic.
+	buf := bytes.NewBuffer(make([]byte, 0, MaxBlockHeaderPayload))
+	_ = writeBlockHeader(buf, 0, h)
+
+	return chainhash.LbryPoWHashH(buf.Bytes())
+}
+
 // BtcDecode decodes r using the bitcoin protocol encoding into the receiver.
 // This is part of the Message interface implementation.
 // See Deserialize for decoding block headers stored to disk, such as in a