# debug_node : what-if test tool¶

## Introduction¶

The debug_node is a tool to allow developers to run many interesting sorts of “what-if” tests using state from a production blockchain. Like “what happens if I produce enough blocks for the next hardfork time to arrive?” or “what would happen if this account (which I don’t have a private key for) did this transaction?”

## Setup¶

Be sure you’ve built the right build targets:

$make get_dev_key debug_node cli_wallet witness_node  Use the get_dev_key utility to generate a keypair: $ programs/genesis_util/get_dev_key "" nathan


Obtain a copy of the blockchain in block_db directory: $programs/witness_node/witness_node –data-dir data/mydatadir # … wait for chain to sync ^C$ cp -Rp data/mydatadir/blockchain/database/block_num_to_block ./block_db

Set up a new datadir with the following :ref: config.ini settings:

# setup API endpoint
rpc-endpoint = 127.0.0.1:8090
# setting this to empty effectively disables the p2p network
seed-nodes = []
# set apiaccess.json so we can set up


Then set up data/debug_datadir/api-access.json to allow access to the debug API like this:

{
"permission_map" :
[
[
"bytemaster",
{
"allowed_apis" : ["database_api", "network_broadcast_api", "history_api", "network_node_api", "debug_api"]
}
],
[
"*",
{
}
]
]
}


See Accessing Restricted API’s for more detail on the api-access.json format.

Once that is set up, run debug_node against your newly prepared datadir:

programs/debug_node/debug_node --data-dir data/debug_datadir


Run cli_wallet to connect to the debug_node port, using the username and password to access the new debug_api (and also a different wallet file):

programs/cli_wallet/cli_wallet -s 127.0.0.1:8090 -w debug.wallet -u bytemaster -p supersecret


### Example usage¶

dbg_push_blocks block_db 20000


Note, when pushing a very large number of blocks sometimes cli_wallet hangs and you must Ctrl+C and restart it (leaving the debug_node running).

Generate (fake) blocks with our own private key:

dbg_generate_blocks 5KQwrPbwdL6PhXujxW37FSSQZ1JiwsST4cqQzDeyXtP79zkvFD3 1000


Update angel account to be controlled by our own private key and generate a (fake) transfer:

dbg_update_object {"_action":"update", "id":"1.2.1090", "active":{"weight_threshold":1,"key_auths":[["BTS6MRyAjQq8ud7hVNYcfnVPJqcVpscN5So8BhtHuGYqET5GDW5CV",1]]}}
import_key angel 5KQwrPbwdL6PhXujxW37FSSQZ1JiwsST4cqQzDeyXtP79zkvFD3
transfer angel init0 999999 BTS "" true


## How it works¶

The commands work by creating diff(s) from the main chain that are applied to the local chain at specified block height(s). It lets you easily check out “what-if” scenarios in a fantasy debug toy world forked from the real chain, e.g. “if we take all of the blocks until today, then generate a bunch more until a hardfork time in the future arrives, does the chain stay up? Can I do transactions X, Y, and Z in the wallet after the hardfork?” Anyone connecting to this node sees the same fantasy world, so you can e.g. make changes with the cli_wallet and see them exist in other cli_wallet instances (or GUI wallets or API scripts).

## Limitations¶

The main limitations are:

• No export format for the diffs, so you can’t really [1] connect multiple debug_node to each other.
• Once faked block(s) or tx(s) have been produced on your chain, you can’t really [1] stream blocks or tx’s from the main network to your chain.

[1] It should theoretically be possible, but it’s non-trivial and totally untested.