Event Watching

Watch and decrypt SRC20 Transfer and Approval events

SRC20 tokens emit Transfer and Approval events with encrypted amounts. The event watching system polls for these events, decrypts them using your viewing key, and invokes callbacks with decoded data.

Factory Functions

Function	Description
watch_src20_events	Watch with automatic key fetching from Directory
watch_src20_events_with_key	Watch with an explicit viewing key

Both have async variants (async_watch_src20_events, async_watch_src20_events_with_key).

Watcher Classes

Class	Description
SRC20EventWatcher	Thread-based polling watcher (sync)
AsyncSRC20EventWatcher	Task-based polling watcher (async)

Example

import os
from seismic_web3 import PrivateKey, SEISMIC_TESTNET
from seismic_web3.src20 import watch_src20_events

pk = PrivateKey.from_hex_str(os.environ["PRIVATE_KEY"])
w3 = SEISMIC_TESTNET.wallet_client(pk)

watcher = watch_src20_events(
    w3,
    encryption=w3.seismic.encryption,
    private_key=pk,
    on_transfer=lambda log: print(f"Transfer: {log.decrypted_amount}"),
    on_approval=lambda log: print(f"Approval: {log.decrypted_amount}"),
)

# Later...
watcher.stop()

How It Works

1. Key hash — keccak256(viewing_key) is used to filter events by the 4th topic

2. Polling — eth_getLogs at a configurable interval (default 2s)

3. Decryption — AES-256-GCM with the viewing key (no AAD)

4. Callbacks — invoked with DecryptedTransferLog or DecryptedApprovalLog

See Also

• Types — Decrypted event data structures

• Intelligence Providers — Viewing key management