Parsing json data with serde

The transaction data for a particular txid from a bitcoin node will look similar to the following,

{
  "txid": "00000a2d1a9e29116b539b85b6e893213b1ed95a08b7526a8d59a4b088fc6571",
  "version": 1,
  "locktime": 0,
  "vin": [
    {
      "txid": "2e4843d552ca9487efd9e69c0359f05375b7de5449eb49510d17a25bb5b15ec0",
      "vout": 1,
      "prevout": {
        "scriptpubkey": "512065fd3d423ea46a70505248db989e7302bfbbdd64ee4193dd9a59f69894f0de48",
        "scriptpubkey_asm": "OP_PUSHNUM_1 OP_PUSHBYTES_32 65fd3d423ea46a70505248db989e7302bfbbdd64ee4193dd9a59f69894f0de48",
        "scriptpubkey_type": "v1_p2tr",
        "scriptpubkey_address": "bc1pvh7n6s375348q5zjfrde38nnq2lmhhtyaeqe8hv6t8mf398smeyqnug47s",
        "value": 13413
      },
      "scriptsig": "",
      "scriptsig_asm": "",
      "witness": [
        "29783b151d376d5178451ce14f62b091059021680bff36aec2814e33ecacf130e8aa92d6da23f35be7a8c2245b8f910261d4e6a5169f79d6ff7a3f412981f486"
      ],
      "is_coinbase": false,
      "sequence": 1610616404
    }
  ],
  "vout": [
    {
      "scriptpubkey": "51204b918d31f22461021ed54e354ac9dcbbe94b98edcfd3615b76c068b08222a87f",
      "scriptpubkey_asm": "OP_PUSHNUM_1 OP_PUSHBYTES_32 4b918d31f22461021ed54e354ac9dcbbe94b98edcfd3615b76c068b08222a87f",
      "scriptpubkey_type": "v1_p2tr",
      "scriptpubkey_address": "bc1pfwgc6v0jy3ssy8k4fc654jwuh055hx8delfkzkmkcp5tpq3z4pls7tx8q3",
      "value": 2908
    },
    {
      "scriptpubkey": "512065fd3d423ea46a70505248db989e7302bfbbdd64ee4193dd9a59f69894f0de48",
      "scriptpubkey_asm": "OP_PUSHNUM_1 OP_PUSHBYTES_32 65fd3d423ea46a70505248db989e7302bfbbdd64ee4193dd9a59f69894f0de48",
      "scriptpubkey_type": "v1_p2tr",
      "scriptpubkey_address": "bc1pvh7n6s375348q5zjfrde38nnq2lmhhtyaeqe8hv6t8mf398smeyqnug47s",
      "value": 8503
    }
  ],
  "size": 205,
  "weight": 616,
  "fee": 2002,
  "status": {
    "confirmed": true,
    "block_height": 834552,
    "block_hash": "00000000000000000001dd0468a70c94f619251d286585cff57aeb4bd9ede330",
    "block_time": 1710355598
  },
  "hex": "01000000000101c05eb1b55ba2170d5149eb4954deb77553f059039ce6d9ef8794ca52d543482e0100000000540e0060025c0b0000000000002251204b918d31f22461021ed54e354ac9dcbbe94b98edcfd3615b76c068b08222a87f372100000000000022512065fd3d423ea46a70505248db989e7302bfbbdd64ee4193dd9a59f69894f0de48014029783b151d376d5178451ce14f62b091059021680bff36aec2814e33ecacf130e8aa92d6da23f35be7a8c2245b8f910261d4e6a5169f79d6ff7a3f412981f48600000000"
}

We observe that String, boolean and integer are the primitive types which are being used. The entire object could be named as a Transaction type and the complex fields can be given their own types as shown here.

Deserialize trait

serde crate provides macros to derive implementation of Deserialize trait for a struct type T if all the fields of the struct implement Deserialize trait. You can notice that we have done exactly that for all the defined types.

Selective parsing

We don't have to specify all the keys in the json, some of the keys could be ignored if we don't need that information. Note that in the example scriptpubkey_asm key in the json is ignored in the struct definition of Vout.

serde and serde_json

serde is a protocol agnostic crate which defines the generic traits like Serialize, Deserialize, the associated macros for derivation and more. serde_json has features and functionalities necessary to work with json strings. So in a typical project we will be using both the crates together. Review the main function, imports and the Cargo.toml file.

Missing Field error

Try removing one of the fields from the example json string and run the demo cargo project. The assertion at the end should fail. Change the type of the specific field in the rust to an Option<T>, whatever that specific T was, then it should pass.

Further reading

serde tutorial by Shaan