all: add read-only option to database (#22407)

* all: add read-only option to database

* all: fixes tests

* cmd/geth: migrate flags

* cmd/geth: fix the compact

* cmd/geth: fix the format

* cmd/geth: fix log

* cmd: add chain-readonly

* core: add readonly notion to freezer

* core/rawdb: add log

* core/rawdb: fix freezer close

* cmd: fix

* cmd, core: construct db

* core: update tests

core/rawdb/accessors_chain.go

@@ -825,3 +825,29 @@ func FindCommonAncestor(db ethdb.Reader, a, b *types.Header) *types.Header {
 	}
 	return a
 }
+
+// ReadHeadHeader returns the current canonical head header.
+func ReadHeadHeader(db ethdb.Reader) *types.Header {
+	headHeaderHash := ReadHeadHeaderHash(db)
+	if headHeaderHash == (common.Hash{}) {
+		return nil
+	}
+	headHeaderNumber := ReadHeaderNumber(db, headHeaderHash)
+	if headHeaderNumber == nil {
+		return nil
+	}
+	return ReadHeader(db, headHeaderHash, *headHeaderNumber)
+}
+
+// ReadHeadHeader returns the current canonical head block.
+func ReadHeadBlock(db ethdb.Reader) *types.Block {
+	headBlockHash := ReadHeadBlockHash(db)
+	if headBlockHash == (common.Hash{}) {
+		return nil
+	}
+	headBlockNumber := ReadHeaderNumber(db, headBlockHash)
+	if headBlockNumber == nil {
+		return nil
+	}
+	return ReadBlock(db, headBlockHash, *headBlockNumber)
+}