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TradeFlow AI — Blockchain Anchoring Service (Phase 4, Step 4.2)
PRD §15 — Content hash anchoring on Polygon (Amoy testnet → PoS mainnet).
1. Compute SHA-256 content hash of submission payload
2. Build Merkle root from all document hashes
3. Call smart contract anchor(bytes32 merkleRoot, bytes32 contentHash)
4. Store tx_hash + IPFS CID to blockchain_records table
5. Return PolygonScan URL
Contract: TradeFlowAudit.sol (deployed on Amoy / Polygon PoS)
"""
from __future__ import annotations
import hashlib
import json
import time
from typing import Any
import structlog
from web3 import Web3
from web3.middleware import ExtraDataToPOAMiddleware
from ..config import settings
log = structlog.get_logger()
# ── TradeFlowAudit ABI (minimal — only anchor function) ──────────────────────
AUDIT_ABI = [
{
"inputs": [
{"internalType": "bytes32", "name": "merkleRoot", "type": "bytes32"},
{"internalType": "bytes32", "name": "contentHash", "type": "bytes32"},
{"internalType": "string", "name": "ipfsCid", "type": "string"},
],
"name": "anchor",
"outputs": [{"internalType": "uint256", "name": "recordId", "type": "uint256"}],
"stateMutability": "nonpayable",
"type": "function",
},
{
"anonymous": False,
"inputs": [
{"indexed": True, "name": "recordId", "type": "uint256"},
{"indexed": True, "name": "contentHash", "type": "bytes32"},
{"indexed": False, "name": "merkleRoot", "type": "bytes32"},
{"indexed": False, "name": "ipfsCid", "type": "string"},
{"indexed": False, "name": "timestamp", "type": "uint256"},
],
"name": "Anchored",
"type": "event",
},
]
def _sha256_bytes(data: str | bytes) -> bytes:
if isinstance(data, str):
data = data.encode()
return hashlib.sha256(data).digest()
def _compute_merkle_root(leaves: list[bytes]) -> bytes:
"""Simple binary Merkle tree implementation."""
if not leaves:
return b"\x00" * 32
if len(leaves) == 1:
return leaves[0]
# Pad to even number
if len(leaves) % 2 == 1:
leaves.append(leaves[-1])
parents = [
_sha256_bytes(leaves[i] + leaves[i + 1])
for i in range(0, len(leaves), 2)
]
return _compute_merkle_root(parents)
async def _upload_to_ipfs(content: dict) -> str:
"""Upload JSON metadata to IPFS via Pinata (JWT Bearer auth)."""
import httpx
if not settings.PINATA_JWT:
log.warning("Pinata not configured — skipping IPFS upload")
return ""
async with httpx.AsyncClient() as client:
resp = await client.post(
"https://api.pinata.cloud/pinning/pinJSONToIPFS",
json={"pinataContent": content, "pinataMetadata": {"name": "tradeflow-audit"}},
headers={
"Authorization": f"Bearer {settings.PINATA_JWT.get_secret_value()}",
},
timeout=30.0,
)
resp.raise_for_status()
cid = resp.json()["IpfsHash"]
log.info("IPFS upload successful", cid=cid)
return cid
class BlockchainService:
"""Anchors submission hashes to Polygon via TradeFlowAudit smart contract."""
def __init__(self) -> None:
self._w3: Web3 | None = None
def _get_web3(self) -> Web3:
if self._w3 is not None:
return self._w3
# POLYGON_RPC_URL is set per-environment in .env
# (Amoy testnet for dev/staging, PoS mainnet for production)
rpc_url = settings.POLYGON_RPC_URL
w3 = Web3(Web3.HTTPProvider(rpc_url))
# PoA middleware required for Polygon Amoy
w3.middleware_onion.inject(ExtraDataToPOAMiddleware, layer=0)
if not w3.is_connected():
raise ConnectionError(f"Cannot connect to Polygon RPC: {rpc_url}")
self._w3 = w3
return w3
def _fee_params(self, w3: Web3) -> dict[str, int]:
"""
Build EIP-1559 fee params with caps so Polygon gas spikes do not
silently turn an audit anchor into an expensive transaction.
"""
max_fee_cap = w3.to_wei(settings.POLYGON_MAX_FEE_GWEI, "gwei")
priority_cap = w3.to_wei(settings.POLYGON_MAX_PRIORITY_FEE_GWEI, "gwei")
try:
latest = w3.eth.get_block("latest")
base_fee = int(latest.get("baseFeePerGas") or w3.eth.gas_price)
priority_fee = min(int(getattr(w3.eth, "max_priority_fee", priority_cap)), priority_cap)
max_fee = min((base_fee * 2) + priority_fee, max_fee_cap)
if max_fee <= priority_fee:
max_fee = min(priority_fee * 2, max_fee_cap)
return {"maxFeePerGas": max_fee, "maxPriorityFeePerGas": priority_fee}
except Exception as exc:
fallback_gas_price = min(int(w3.eth.gas_price), max_fee_cap)
log.warning("Falling back to legacy gas price", error=str(exc), gas_price=fallback_gas_price)
return {"gasPrice": fallback_gas_price}
async def anchor(
self,
batch_id: str,
payload: dict,
document_hashes: list[str],
) -> dict[str, Any]:
"""
Anchor a submission to Polygon.
Returns: {tx_hash, block_number, content_hash, merkle_root, ipfs_cid, polygonscan_url}
"""
if not settings.ENABLE_BLOCKCHAIN:
log.info("Blockchain disabled — skipping anchor", batch_id=batch_id)
return {"tx_hash": None, "block_number": None, "ipfs_cid": None}
if not settings.CONTRACT_ADDRESS or not settings.OPERATOR_WALLET_PRIVATE_KEY:
log.warning("Blockchain not configured — skipping", batch_id=batch_id)
return {"tx_hash": None, "block_number": None, "ipfs_cid": None}
log.info("Anchoring to blockchain", batch_id=batch_id)
# ── Hashes ─────────────────────────────────────────────────
content_hash_bytes = _sha256_bytes(json.dumps(payload, sort_keys=True))
leaf_bytes = [bytes.fromhex(h) if len(h) == 64 else _sha256_bytes(h) for h in document_hashes]
merkle_root_bytes = _compute_merkle_root(leaf_bytes)
# ── IPFS upload ────────────────────────────────────────────
ipfs_cid = await _upload_to_ipfs({
"batch_id": batch_id,
"content_hash": content_hash_bytes.hex(),
"merkle_root": merkle_root_bytes.hex(),
"timestamp": int(time.time()),
})
# ── Contract call ──────────────────────────────────────────
try:
w3 = self._get_web3()
contract = w3.eth.contract(
address=Web3.to_checksum_address(settings.CONTRACT_ADDRESS),
abi=AUDIT_ABI,
)
account = w3.eth.account.from_key(
settings.OPERATOR_WALLET_PRIVATE_KEY.get_secret_value()
)
nonce = w3.eth.get_transaction_count(account.address)
tx_func = contract.functions.anchor(
merkle_root_bytes,
content_hash_bytes,
ipfs_cid,
)
tx_params = {
"from": account.address,
"nonce": nonce,
"gas": settings.POLYGON_ANCHOR_GAS_LIMIT,
**self._fee_params(w3),
}
try:
estimated_gas = tx_func.estimate_gas({"from": account.address})
tx_params["gas"] = min(int(estimated_gas * 1.2), settings.POLYGON_ANCHOR_GAS_LIMIT)
except Exception as exc:
log.warning("Gas estimation failed; using configured gas limit", error=str(exc))
tx = tx_func.build_transaction(tx_params)
signed = account.sign_transaction(tx)
tx_hash = w3.eth.send_raw_transaction(signed.raw_transaction)
receipt = w3.eth.wait_for_transaction_receipt(tx_hash, timeout=120)
block_num = receipt["blockNumber"]
explorer_base = (
"https://amoy.polygonscan.com"
if settings.ENVIRONMENT != "production"
else "https://polygonscan.com"
)
polygonscan_url = f"{explorer_base}/tx/{tx_hash.hex()}"
log.info(
"Blockchain anchor successful",
batch_id=batch_id,
tx_hash=tx_hash.hex(),
block=block_num,
)
return {
"tx_hash": tx_hash.hex(),
"block_number": block_num,
"content_hash": content_hash_bytes.hex(),
"merkle_root": merkle_root_bytes.hex(),
"ipfs_cid": ipfs_cid,
"polygonscan_url": polygonscan_url,
}
except Exception as exc:
log.error("Blockchain anchor failed", error=str(exc), batch_id=batch_id)
raise
# ── Singleton ────────────────────────────────────────────────────────────────
blockchain_service = BlockchainService()
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