How can I get the key of blockindex

Question

According to this post: What are the keys used in the blockchain levelDB (ie what are the key:value pairs)?

One type of the keys in leveldb of bitcoin is formed in the following way

'b' + 32-byte block hash

I wrote the following code in go but I got "not found".

genesisBlockHash := "000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f"
hashBytes, _ := hex.DecodeString(genesisBlockHash)
keyBytes := append([]byte("b"), hashBytes...)
data, err := db.Get(keyBytes, nil)

Where did I do wrong? How can I add 'b' to the hash?

---

Tried a simple case:

'R' -> 1-byte boolean ('1' if true): whether we're in the process of reindexing.

Go code

data, err := db.Get([]byte("R"), nil)

But I still got "not found". Why...

---

Tried file.

'f' + 4-byte file number -> file information record.

I could get some data. I think the following code should retrieve the "blk00000.dat" block file information, right?

readFile(db, []byte{0, 0, 0, 0})

func readFile(db *leveldb.DB, file []byte) {
    data, err := db.Get(append([]byte("f"), file...), nil)
    if err != nil {
        log.Println(err)
        os.Exit(1)
    }
    // read data
}

Answer 1

Where did I do wrong? How can I add 'b' to the hash?

The block hashes need to be byteswapped. Instead of 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f, you should have 6fe28c0ab6f1b372c1a6a246ae63f74f931e8365e15a089c68d6190000000000.

But I still got "not found". Why...

This key-value pair is not always present.

I could get some data. I think the following code should retrieve the "blk00000.dat" block file information, right?

Yes.