How to correctly unpack "packed_trx" from transaction?

Question

Hello Dear EOSIO Community,

I have following transaction on mainnet that I want to unpack. I get its data using curl:

curl https://api.tokenika.io/v1/history/get_transaction -d'{"id": "474157059f407274020d9c498c3a02b07bce36a3229838677de8947efe153ed0"}'
[...]
"packed_trx":"4936395b23cae0baad75000000000100a6823403ea3055000000572d3ccdcd0180a92206baa920cd00000000a8ed32322b80a92206baa920cdc0d52406baa920cd102700000000000004454f53000000000a756e7061636b206d652100"
[...]
"trx":{
  "expiration":"2018-07-01T20:15:05",
  "ref_block_num":51747,
  "ref_block_prefix":1974319840,
  "max_net_usage_words":0,
  "max_cpu_usage_ms":0,
  "delay_sec":0,
  "context_free_actions":[],
  "actions":[
    {
      "account":"eosio.token",
      "name":"transfer",
      "authorization":[{
        "actor":"tokenika4eos",
        "permission":"active"
      }],
[...]

I try to unpack packed_trx using struct defined in transaction.hpp

time_point_sec         expiration;   ///< the time at which a transaction expires
uint16_t               ref_block_num       = 0U; ///< specifies a block num in the last 2^16 blocks.
uint32_t               ref_block_prefix    = 0UL; ///< specifies the lower 32 bits of the blockid at get_ref_blocknum
fc::unsigned_int       max_net_usage_words = 0UL; /// upper limit on total network bandwidth (in 8 byte words) billed for this transaction
uint8_t                max_cpu_usage_ms    = 0; /// upper limit on the total CPU time billed for this transaction
fc::unsigned_int delay_sec = 0UL;

After few source code checks, I've found that both time_point_sec and fc::unsigned_int should be uint32.

So I try to read first field of that struct, expiration. I read first 8 characters from packed_trx string (32 input bits/8 bits per byte = 4 bytes, *2 hex numbers per byte = 8 hex numbers) that's 4936395b and cast that to integer using little-endian format getting 1530476105 at the end, which is Unix timestamp date 07/01/2018 @ 8:15pm (UTC) which is cool because it matches my expiration date from transaction.

When I repeat whole process to rest of the data, I get:

expiration = 1530476105
ref_block_num = 51747
ref_block_prefix = 1974319840
max_net_usage_words = 0
max_cpu_usage_ms = 1
delay_sec = 880977408

This would be really nice, but it isn't true since this transaction is defined to have all three values max_net_usage_words, max_cpu_usage_ms, delay_sec set to 0.

Is there anything obvious that I'm doing wrong? How to correctly unpack "packed_trx" from transaction?

Answer 1

An unsigned_int is stored locally as uint32_t, but it is serialized as varuint32.

See for example: https://github.com/EOSIO/eos/blob/master/contracts/eosiolib/varint.hpp and there's something similar in https://github.com/EOSIO/fc/blob/9a0ed1f85e38adc6ace8c944b5f5f725f4829ba2/include/fc/io/varint.hpp which is the packing lib.

Answer 2

Okay, way simpler,

//rpc/api stuff see here https://github.com/EOSIO/eosjs
const api = new Api({ rpc, signatureProvider, textDecoder: new TextDecoder(), textEncoder: new TextEncoder() });

const info = await rpc.get_table_rows({
        code: "eosio.msig",
        index_position: 1,
        json: true,
        limit: 1,
        lower_bound: proposal.proposal_name,
        reverse: false,
        scope: proposal.proposer,
        show_payer: false,
        table: "proposal"
    });
    console.log(info.rows[0])
    const resss = api.deserializeTransaction(hexToUint8Array(info.rows[0].packed_transaction));
    console.log(resss)

deserializeTransaction

{
  proposal_name: 'dappgovernorb',
  packed_transaction: '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',
  earliest_exec_time: '2021-03-24T11:13:53.000'
}

To:

{
  expiration: '2021-03-25T11:03:19.000',
  ref_block_num: 0,
  ref_block_prefix: 0,
  max_net_usage_words: 0,
  max_cpu_usage_ms: 0,
  delay_sec: 0,
  context_free_actions: [],
  actions: [
    {
      account: 'eosio',
      name: 'updateauth',
      authorization: [Array],
      data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
    }
  ],
  transaction_extensions: []
}