ethdb/remotedb, cmd: add support for remote (readonly) databases (#24836)

* ethdb/remotedb, cmd: add support for remote (readonly) databases

* ethdb/remotedb: minor changes

* ethdb/remotedb: close the conn

* cmd, ethdb: add rpc accessor for ancient data

* internal/ethapi: license

* ethdb/remotedb: linter fixes

internal/ethapi/api.go

@@ -1959,15 +1959,6 @@ func (api *PrivateDebugAPI) SetHead(number hexutil.Uint64) {
 	api.b.SetHead(uint64(number))
 }
 
-// DbGet returns the raw value of a key stored in the database.
-func (api *PrivateDebugAPI) DbGet(key string) (hexutil.Bytes, error) {
-	blob, err := common.ParseHexOrString(key)
-	if err != nil {
-		return nil, err
-	}
-	return api.b.ChainDb().Get(blob)
-}
-
 // PublicNetAPI offers network related RPC methods
 type PublicNetAPI struct {
 	net            *p2p.Server

internal/ethapi/dbapi.go

@@ -0,0 +1,43 @@
+// Copyright 2022 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 ethapi
+
+import (
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/hexutil"
+)
+
+// DbGet returns the raw value of a key stored in the database.
+func (api *PrivateDebugAPI) DbGet(key string) (hexutil.Bytes, error) {
+	blob, err := common.ParseHexOrString(key)
+	if err != nil {
+		return nil, err
+	}
+	return api.b.ChainDb().Get(blob)
+}
+
+// DbAncient retrieves an ancient binary blob from the append-only immutable files.
+// It is a mapping to the `AncientReaderOp.Ancient` method
+func (api *PrivateDebugAPI) DbAncient(kind string, number uint64) (hexutil.Bytes, error) {
+	return api.b.ChainDb().Ancient(kind, number)
+}
+
+// DbAncients returns the ancient item numbers in the ancient store.
+// It is a mapping to the `AncientReaderOp.Ancients` method
+func (api *PrivateDebugAPI) DbAncients() (uint64, error) {
+	return api.b.ChainDb().Ancients()
+}