3

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?

2

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.

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