zhlink 0.1.14

Self-contained Python library for ZHCASH addresses, balances, ZHC sends, and USDZ gas-free sends.

ZHLink Python Library

zhlink is a self-contained Python library for ZHCASH.

The public API is intentionally small:

• create a new ZHC address;
• check ZHC + USDZ balance;
• send native ZHC from a private key;
• dry-run/read ZHCASH smart contracts with callcontract;
• send payable ZHCASH smart-contract calls from a private key;
• send ZHC, USDZ or any ZRC-20 token to many recipients from a JSON plan;
• send USDZ with admin-paid ZHC gas;
• optionally read extra ZRC-20 token balances.

The library is async-first for long-running wallet apps: WSS is used as the primary realtime signal and automatically falls back to HTTP/RPC polling when WSS is unavailable. Synchronous wrappers are still provided for simple scripts.

The raw transaction engine is bundled inside the package. Normal users only import zhlink.

Install

Recommended Python:

• Python 3.10 or newer is required.
• Python 3.10 and 3.11 are the safest choices for deployment.
• Python 3.12 should work.
• Python 3.9 and older are not supported.

Install With pip

Create a virtual environment and install from PyPI:

python3 -m venv .venv
. .venv/bin/activate
python -m pip install --upgrade pip
pip install zhlink

Install With uv

Into the current Python environment:

uv pip install zhlink

Inside a uv project with pyproject.toml:

uv add zhlink

Run a one-off script without manually creating a venv:

uv run --with zhlink python your_script.py

Install Directly From GitHub

Latest main branch:

pip install git+https://github.com/zerohourcash/zhlink.git

With uv:

uv pip install git+https://github.com/zerohourcash/zhlink.git

Inside a uv project:

uv add git+https://github.com/zerohourcash/zhlink.git

Install a fixed release tag:

pip install "git+https://github.com/zerohourcash/zhlink.git@v0.1.5"
uv pip install "git+https://github.com/zerohourcash/zhlink.git@v0.1.5"

Verify Install

python - <<'PY'
import zhlink

wallet = zhlink.create_address()
print(wallet.address)
print(zhlink.get_mass_send_template("usdz")["asset"])
PY

Install From Source

From this repository folder:

cd /root/wallet/zhlink
python3 -m venv .venv
. .venv/bin/activate
pip install -e .

For direct local use without installing:

cd /root/wallet/zhlink
export PYTHONPATH=/root/wallet/zhlink

Create Address

from zhlink import create_address

wallet = create_address()

print(wallet.address)
print(wallet.priv_key)

Private keys are generated locally. The library never sends private keys to ZeroScan or RPC.

Get Balance

By default get_balance returns ZHC and USDZ.

from zhlink import get_balance

balance = get_balance("Z...")

print(balance["zhc"])
print(balance.get("confirmed_zhc"))
print(balance.get("pending_zhc"))
print(balance["usdz"])

zhc is the visible balance. When ZeroScan exposes pending data, positive 0-confirmation change is included in zhc, while confirmed_zhc and pending_zhc are also returned separately. Sending still uses only confirmed spendable UTXO.

Extra ZRC-20 tokens can be requested when needed:

from zhlink import get_balance

balance = get_balance(
    "Z...",
    tokens={"EDS": "dc71958156a945d3071374521e1a7a42f5ba8038"},
)

print(balance["tokens"]["EDS"])

Cached Balance and WSS Updates

zhlink stores public balance snapshots in a small local SQLite cache. Private keys are never stored there.

from zhlink import force_refresh_balance, get_cached_balance

cached = get_cached_balance("Z...")
fresh = force_refresh_balance("Z...")  # throttled, default: once per 10 sec

For a Python wallet UI, use the async client and subscribe to address updates:

import asyncio
from zhlink import watch_balance

async def main():
    async for balance in watch_balance("Z..."):
        print(balance["address"], balance["zhc"], balance["usdz"])

asyncio.run(main())

For one-shot scripts, use the sync wrappers:

from zhlink import get_balance, send_zhc

print(get_balance("Z..."))

Realtime detection uses the best available channel:

1. one shared WSS connection from configured block_ws_urls;
2. ZeroScan /info polling if WSS is interrupted;
3. public RPC getblockcount fallback if ZeroScan is unavailable.

The default primary endpoint is:

wss://ws.zeroscan.st/ws

zhlink treats WSS as the primary realtime signal and multiplexes block and address subscriptions over one shared WebSocket hub per asyncio event loop. Subscribing 100 addresses does not create 100 sockets; it sends address subscriptions through the same connection and refreshes only addresses that receive realtime transaction events.

Address subscriptions have a default lifetime of one hour. Every getbalance call or balance subscription touch extends that lifetime. If an address is not requested again, zhlink sends unsubscribe for that address so long-running wallet processes do not keep stale subscriptions forever. For long-lived wallet sessions the TTL can be raised, for example to 12 hours:

from zhlink import ZHLinkConfig

config = ZHLinkConfig.public_network(
    address_subscription_ttl_seconds=12 * 60 * 60,
    ws_max_failures=3,
    ws_cooldown_seconds=60,
)

WSS is an accelerator, not a hard dependency. If all WSS endpoints fail several times, the WSS hub enters a short cooldown and the watcher keeps working through block polling, ZeroScan HTTP and public RPC fallback. When the cooldown expires, WSS reconnects automatically.

Normal get_balance() reads SQLite when the cached snapshot is still valid. Use force_refresh_balance() when the user explicitly presses refresh; the library will refuse to refresh the same address more often than once per force_refresh_seconds seconds.

UTXO snapshots are cached in the same SQLite file. If a ZeroScan endpoint hangs or RPC is temporarily unavailable, the library can still read the last known UTXO set and show useful wallet state. Real sends still use the normal safety pipeline: local UTXO reservation, dry-run when available, ZeroScan broadcast, then RPC broadcast fallback.

Watch a USDZ deposit and forward it gas-free

The example below creates a fresh USDZ receiving address, watches it through the shared WSS hub, and forwards the detected USDZ to the admin address with send_usdz_gas_free(). It is guarded by default so it cannot accidentally wait or send during smoke tests.

RUN_WATCH_EXAMPLE=1 \
RUN_REAL_SEND=1 \
ZHLINK_ADMIN_GAS_WIF="K-or-L-admin-gas-wif" \
ZHLINK_ADMIN_ADDRESS="ZGqDPGCds5CBRHLZZCnYWsYWYPF3i9NCvi" \
python examples/watch_deposit_and_forward_usdz.py

Without RUN_REAL_SEND=1, the example builds the gas-free transaction but does not broadcast it.

For a long-running receiver, create a new deposit address only when your application receives a new deposit request:

python examples/usdz_receiver_service.py new

The generated address is stored in .zhlink-usdz-receiver.sqlite3. Then run the receiver service. It watches already-created active addresses through one shared WSS hub and forwards received USDZ to the admin address:

RUN_USDZ_RECEIVER=1 \
RUN_REAL_SEND=1 \
ZHLINK_ADMIN_GAS_WIF="K-or-L-admin-gas-wif" \
python examples/usdz_receiver_service.py serve

The service does not pre-generate addresses. It only watches addresses that were created by explicit new requests. Receiver state is stored in .zhlink-usdz-receiver.sqlite3 by default.

Send ZHC

from zhlink import send_zhc

result = send_zhc(
    private_key_wif="L...",
    to_address="Z...",
    amount="1.25",
)

print(result)

The sender address is derived from the private key automatically.

If the previous transaction already used the only large UTXO and the visible balance now mostly comes from 0-confirmation change, send_zhc does not build a conflicting transaction. It returns:

{
    "status": "error",
    "action_required": "wait_next_block",
    "reason": "Wait for the next block before sending again. ...",
    "diagnostics": {...},
}

Handle this by waiting for the next ZHCASH block, then call send_zhc again. This prevents accidental double-spend attempts and confusing mempool errors.

Smart Contracts

Use call_contract before any contract transaction. It calls ZHCASH callcontract through configured public RPC endpoints and returns the raw execution result plus common fields.

from zhlink import call_contract

result = call_contract(
    contract_address="a48d0ee7365ce1add8e595de4d54344239f8ca28",
    data_hex="70a08231...",
    from_address="Z...",  # optional
    gas=1_000_000,
)

print(result["output"])

Use send_to_contract for a real payable contract call.

from zhlink import send_to_contract

result = send_to_contract(
    private_key_wif="L...",
    contract_address="...",
    data_hex="...",
    amount="0",        # ZHC sent to the contract, if needed
    gas=1_000_000,
)

print(result)

The sender address is derived locally. The function runs callcontract preflight, selects UTXO, signs locally, checks mempool when RPC is available, broadcasts through ZeroScan and falls back to RPC broadcast.

send_to_contract uses the same UTXO reservation rule as send_zhc: if the only suitable gas UTXO is already reserved by a pending local transaction, it returns action_required: "wait_next_block" instead of sending a broken contract transaction.

Mass Send

send_mass sends ZHC, USDZ or any ZRC-20 token to many recipients from a JSON plan.

Bundled templates are available directly from the package:

from zhlink import get_mass_send_template, write_mass_send_template

print(get_mass_send_template("usdz"))
write_mass_send_template("usdz", "mass_send.json")
write_mass_send_template("zhc", "mass_send_zhc.json")
write_mass_send_template("zrc20", "mass_send_zrc20.json")

{
  "asset": "USDZ",
  "token_contract": "a48d0ee7365ce1add8e595de4d54344239f8ca28",
  "token_decimals": 8,
  "gas": 1000000,
  "recipients": [
    {"address": "Z...", "amount": "0.1"},
    {"address": "Z...", "amount": "0.2"}
  ]
}

For native ZHC:

{
  "asset": "ZHC",
  "recipients": [
    {"address": "Z...", "amount": "1"}
  ]
}

Run an estimate first:

from zhlink import estimate_mass_send, load_mass_send_plan

plan = load_mass_send_plan("mass_send.json")
print(estimate_mass_send("L...", plan))

Then send:

from zhlink import send_mass

result = send_mass("L...", "mass_send.json")
print(result["sent_count"], result["failed_count"])

Mass-send UTXO rules:

1. One recipient uses one on-chain transaction.
2. The library never starts more transactions in one batch than confirmed UTXO currently available.
3. If there are too few UTXO and auto_prepare_utxos=True, the library splits the largest UTXO into up to 100 self-outputs.
4. Every prepared output must be at least 1 ZHC.
5. After a reorg/split, the library waits for the next block before mailing.
6. Between mailing batches it waits for the next block so change outputs become confirmed before being reused.

Manual preparation is also available:

from zhlink import prepare_mass_send_utxos

prepare_mass_send_utxos("L...", "mass_send.json", target_utxos=100)

Send USDZ Gas-Free

send_usdz_gas_free signs the USDZ transfer with the sender key and pays ZHC gas from the admin gas wallet.

from zhlink import send_usdz_gas_free

result = send_usdz_gas_free(
    sender_private_key_wif="L...",
    admin_private_key_wif="K...",
    to_address="Z...",
    amount="0.1",
)

print(result["broadcast"]["txid"])

The function does the required checks automatically:

1. derives sender/admin addresses from WIF keys;
2. checks sender USDZ balance;
3. runs callcontract dry-run;
4. loads admin gas UTXO from ZeroScan;
5. skips locally used gas UTXO;
6. builds and signs rawtx locally;
7. runs testmempoolaccept;
8. if one UTXO is rejected, tries another UTXO;
9. broadcasts through ZeroScan;
10. falls back to RPC sendrawtransaction.

For mass sends, prepare independent admin gas UTXO first. One gas-free transfer needs one spendable admin gas UTXO. The recommended ticket size is 0.5 ZHC.

from zhlink import admin_gas_wallet_info

info = admin_gas_wallet_info("K...")
print(info["suitable_gas_utxo_count"])
print(info["recommended_split_count"])

Custom RPC / ZeroScan

Defaults:

• ZeroScan API: https://ws.zeroscan.st, https://ws.zeroscan.io
• RPC: https://rpc.zeroscan.st
• USDZ contract: a48d0ee7365ce1add8e595de4d54344239f8ca28

Override them when needed:

from zhlink import ZHLinkConfig, get_balance

config = ZHLinkConfig.public_network(
    zeroscan_endpoints=("https://ws.zeroscan.st", "https://ws.zeroscan.io"),
    public_rpc_urls=("https://rpc.zeroscan.st", "https://my-node.example/rpc"),
)

print(get_balance("Z...", config=config))

Examples

Run examples one by one:

cd /root/wallet/zhlink
PYTHONPATH=. python3 examples/create_wallet.py
PYTHONPATH=. python3 examples/create_bip39_wallet.py
PYTHONPATH=. ZHLINK_ADDRESS="Z..." python3 examples/check_balance.py
PYTHONPATH=. python3 examples/send_to_contract.py
PYTHONPATH=. python3 examples/mass_send.py

Run all safe examples at once:

cd /root/wallet/zhlink
PYTHONPATH=. python3 examples/run_all_examples.py

Send examples are guarded by RUN_REAL_SEND=1 and will not broadcast by accident. Never commit real private keys.

Publishing

GitHub Actions workflow .github/workflows/python-publish.yml builds, tests, checks, and publishes the package to PyPI.

Release flow:

git tag v0.1.5
git push origin v0.1.5

The workflow uses PyPI Trusted Publishing, so the PyPI project must allow this GitHub repository/workflow as a trusted publisher.