Query a Block Header

Preparing data

As a prerequisite, we use all data used in the provenance example (see [here]), including transactions from the [Prepare data] section.

Block header query

The first query provided by the ledger API is a block header query. The block header contains all cryptographic-related data used for all blockchain properties of the BCDB. For more information, see [Block Header Data]. The result of this query is used both to validate TxReceipt and ledger connectivity. To access it, use /ledger/block/{blocknum} GET query.

In this example, we query the ledger for the block 5 header.

Sign JSON serialized query

bin/signer -data '{"user_id":"alice","block_number":5}' -privatekey=deployment/sample/crypto/alice/alice.key

Signature

MEQCIEpt+TSeA6keDsecrim2EajdVtoeo1cgq9NN/WXEJ5HWAiB5ijMeZZ5y16CCzjXfIpqqnLCANGslD8nZ+0pTVwDrdA==

Submit query

curl \
     -H "Content-Type: application/json" \
     -H "UserID: alice" \
     -H "Signature: MEQCIEpt+TSeA6keDsecrim2EajdVtoeo1cgq9NN/WXEJ5HWAiB5ijMeZZ5y16CCzjXfIpqqnLCANGslD8nZ+0pTVwDrdA==" \
     -X GET http://127.0.0.1:6001/ledger/block/5 | jq .

Output

{
  "response": {
    "header": {
      "node_id": "bdb-node-1"
    },
    "block_header": {
      "base_header": {
        "number": 5,
        "previous_base_header_hash": "NqyVWNBl/XmWLM7PkK8NbI0qrwFmYvGHSTc03vj/zus=",
        "last_committed_block_hash": "nDNWHZPrlG3JVq6eLcuHPaS1iEZkBkemV7IleIVx6Jc=",
        "last_committed_block_num": 4
      },
      "skipchain_hashes": [
        "nDNWHZPrlG3JVq6eLcuHPaS1iEZkBkemV7IleIVx6Jc=",
        "wZmtCr8rJp/NGsEDjySSfHhi7Omr2Yw/d8rUaetrzLE=",
        "tl3PgPL/E52yhCWG1vLGk/bJXRqhw3rDxSXZzvMcuWo="
      ],
      "tx_merkle_tree_root_hash": "UXXqKu/I2Vr0Ma5cV9Hfun4Xo5285ZwdV9jcKspTnJo=",
      "state_merkle_tree_root_hash": "ksPp+NOrYLi909AYgrmrmGN1DKuez8ItpRJeLFpWy9g=",
      "validation_info": [
        {}
      ]
    }
  },
  "signature": "MEUCIQDMER7sTBmOQNHRV6/GON4OjrsKhE6Di5ok181JpwLFvgIgIQA+DHIr6x+GJe8dnF0FLgzXJ+29H9sZHZE46fVg5HQ="
}

As you can see, the block header contains 3 hashes in the skipchain_hashes section (blocks 4, 3, 1), the previous block hash previous_base_header_hash (block 4), the roots of the tx Merkle tree tx_merkle_tree_root_hash and the state Merkle-Patricia trie state_merkle_tree_root_hash.