Beem-0.19.54: Serialization of transactions in the appbase format

Project Information

• Repository: https://github.com/holgern/beem
• Project Name: Beem
• Publisher: @holger80

A GitHub issue wasn created and a fix could be provided. Holger merged the fix into beem-0.19.55.

Expected behavior

Beem's Signed_Transaction class should be able to handle transaction data as retrieved from the blockchain and should be able to calculate the transaction signer's pubkey from the signature. This should work for appbase and non-appbase nodes.This functionality is, among others, used in the beempy verify command.

Actual behavior

The actual problem only showed over time. Initially, an exception was discovered when loading an appbase-transaction with beneficiaries with the Signed_Transaction class. The same could be reproduced with beempy verify. Later on, it was observed that the beempy verify command additionally gives empty results whenever asset amounts in the appbase-format are contained in the operations.

How to reproduce

The following snippet was used to reproduce the problem with the exception:

from beem import Steem
from beem.nodelist import NodeList
from beem.blockchain import Blockchain
from beembase.signedtransactions import Signed_Transaction

s = Steem(node=NodeList().get_nodes(appbase=True, normal=False))
b = Blockchain(steem_instance=s)
for block in b.blocks(start=25304468, stop=25304468):
    for trx in block.transactions:
        try:
            st = Signed_Transaction(trx.copy())
        except Exception:
            print(trx)
            raise

The same problem could then be reproduced with beempy verify:

$ beempy set nodes https://api.steemit.com
$ beempy verify --trx 3 25304468
[...]
  File "/usr/local/lib/python3.6/site-packages/beembase/objects.py", line 268, in __init__
    raise Exception("Unknown CommentOptionExtension")
Exception: Unknown CommentOptionExtension

In that context, it turned out that transactions with amounts give empty results:

$ beempy verify --trx 5 25304468
+-----+------------+---------+
| trx | Signer key | Account |
+-----+------------+---------+
| 5   | []         | []      |
+-----+------------+---------+

Fix

https://github.com/holgern/beem/pull/77

The problem was with the serialization of the transactions. An appbase beneficiary extension has the following format:

'extensions': [{
  'type': 'comment_payout_beneficiaries', 
  'value': {
    'beneficiaries': [
      {'account': 'steempress', 'weight': 1500}
    ]
}]

The same data from a non-appbase node looks like this:

'extensions': [[
  0, [{'account': 'steempress', 'weight': 1500}]
    ]
}]

Beem was expecting only the non-appbase format and serialized the type/value keys instead of their values in the appbase-case. By adding a check for the appbase format and extracting the values behind the keys, beem could serialize the transaction without raising an exception. However, the recovery of the transaction signer still gave emtpy results due to the serialization of appbase amounts contained in the same operation.

While beem correctly identified the appbase-format for amounts, it serialized the NAI number instead of the asset symbol. By implementing a look-up of the symbol from the NAI via the list of known chains, this could be fixed as well.

With both changes in place, the transaction with the beneficiaries can be loaded and the signer key can be extracted:

# beempy set nodes https://api.steemit.com
# beempy verify --trx 3 25304468
+-----+-------------------------------------------------------+--------------+
| trx | Signer key                                            | Account      |
+-----+-------------------------------------------------------+--------------+
| 3   | STM8UsiAQE3nCAjs719SJ3cBTJzH8KQ5jwAemcrn6DVVCphQvjH2j | buffalo-goku |
+-----+-------------------------------------------------------+--------------+

One aspect that needs to be further investigated is the behavior with custom chain parameters provided via the Steem() constructor. Those are not contained in the static known chain list and may, therefore, fail to resolve asset symbols correctly.

GitHub Account

https://github.com/crokkon