attesto-go/anchors.go

package attesto

import (
	"bytes"
	"context"
	"encoding/hex"
	"encoding/json"
	"net/http"
	"strconv"
	"strings"
	"time"
)

// GetCommitmentSelector is the first 4 bytes of keccak256("getCommitment(string)"),
// fixed by the contract ABI (APSProvenance.abi.json); pinned so no keccak
// implementation is needed.
const GetCommitmentSelector = "a7b09e2a"

// EncodeGetCommitmentCall ABI-encodes getCommitment(string) calldata: selector,
// then the single dynamic string argument (offset word, length word, padded bytes).
func EncodeGetCommitmentCall(batchID string) string {
	raw := []byte(batchID)
	pad := (32 - len(raw)%32) % 32
	body := make([]byte, 0, 64+len(raw)+pad)
	offset := make([]byte, 32)
	offset[31] = 0x20
	length := make([]byte, 32)
	for i, v := 31, len(raw); v > 0; i, v = i-1, v>>8 {
		length[i] = byte(v & 0xff)
	}
	body = append(body, offset...)
	body = append(body, length...)
	body = append(body, raw...)
	body = append(body, make([]byte, pad)...)
	return "0x" + GetCommitmentSelector + hex.EncodeToString(body)
}

func stripHex(value string) string {
	return strings.TrimPrefix(strings.ToLower(strings.TrimSpace(value)), "0x")
}

func rpcCall(ctx context.Context, httpClient *http.Client, rpcURL, method string, params []any) (json.RawMessage, string) {
	payload, err := json.Marshal(map[string]any{
		"jsonrpc": "2.0", "id": 1, "method": method, "params": params,
	})
	if err != nil {
		return nil, "rpc " + method + " failed"
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, rpcURL, bytes.NewReader(payload))
	if err != nil {
		return nil, "rpc " + method + " failed"
	}
	req.Header.Set("Content-Type", "application/json")
	resp, err := httpClient.Do(req)
	if err != nil {
		return nil, "rpc " + method + " failed"
	}
	defer resp.Body.Close()
	var envelope struct {
		Result json.RawMessage `json:"result"`
		Error  json.RawMessage `json:"error"`
	}
	if resp.StatusCode != http.StatusOK || json.NewDecoder(resp.Body).Decode(&envelope) != nil {
		return nil, "rpc " + method + " failed"
	}
	if len(envelope.Error) > 0 && string(envelope.Error) != "null" {
		return nil, "rpc " + method + " failed"
	}
	if len(envelope.Result) == 0 {
		return nil, "rpc " + method + " failed"
	}
	return envelope.Result, ""
}

func anchorField(epoch map[string]any, keys ...string) (string, bool) {
	for _, key := range keys {
		if value, ok := epoch[key].(string); ok && value != "" {
			return value, true
		}
	}
	return "", false
}

// VerifyAnchorOnchain verifies an anchor epoch against the chain itself via raw
// JSON-RPC: one eth_call to getCommitment(batchId) comparing the on-chain merkle
// root with the anchor's merkle_root, plus one eth_getTransactionReceipt
// confirming the anchoring transaction succeeded in the expected block. The
// anchor object is accepted in snake_case or camelCase; the contract address is
// read from the epoch's hashed payload. rpcURL is customer-chosen — this
// function never talks to Attesto.
func VerifyAnchorOnchain(ctx context.Context, anchorEpoch map[string]any, rpcURL string, timeout time.Duration) VerifyReport {
	problems := make([]string, 0)

	payload, _ := anchorEpoch["payload"].(map[string]any)
	merkleRoot, okRoot := anchorField(anchorEpoch, "merkle_root", "merkleRoot")
	txHash, okTx := anchorField(anchorEpoch, "tx_hash", "txHash")
	batchID, okBatch := anchorField(anchorEpoch, "anchor_batch_id", "anchorBatchId")
	contractAddress, okAddr := anchorField(anchorEpoch, "contract_address", "contractAddress")
	if !okAddr && payload != nil {
		contractAddress, okAddr = anchorField(payload, "contract_address")
	}
	blockNumber := int64(-1)
	switch v := anchorEpoch["block_number"].(type) {
	case float64:
		blockNumber = int64(v)
	case int64:
		blockNumber = v
	default:
		switch v := anchorEpoch["blockNumber"].(type) {
		case float64:
			blockNumber = int64(v)
		case int64:
			blockNumber = v
		}
	}
	if !okRoot || !okTx || !okBatch || !okAddr || blockNumber < 0 {
		return VerifyReport{
			Kind: "anchor-onchain", OK: false,
			Problems: []string{"anchor epoch is missing required fields"},
		}
	}

	if timeout <= 0 {
		timeout = 15 * time.Second
	}
	httpClient := &http.Client{Timeout: timeout}

	callResult, problem := rpcCall(ctx, httpClient, rpcURL, "eth_call", []any{
		map[string]any{"to": contractAddress, "data": EncodeGetCommitmentCall(batchID)},
		"latest",
	})
	if problem != "" {
		problems = append(problems, problem)
	} else {
		var returned string
		if json.Unmarshal(callResult, &returned) != nil {
			problems = append(problems, "rpc eth_call failed")
		} else {
			// Return tuple is (bytes32 merkleRoot, uint32, string, uint64);
			// the root is the first 32-byte word.
			onchain := stripHex(returned)
			if len(onchain) < 64 || onchain[:64] != stripHex(merkleRoot) {
				problems = append(problems, "anchor merkle root mismatch")
			}
		}
	}

	receiptResult, problem := rpcCall(ctx, httpClient, rpcURL, "eth_getTransactionReceipt", []any{txHash})
	if problem != "" {
		problems = append(problems, problem)
	} else if string(receiptResult) == "null" {
		problems = append(problems, "anchor transaction not found")
	} else {
		var receipt struct {
			Status      string `json:"status"`
			BlockNumber string `json:"blockNumber"`
		}
		if json.Unmarshal(receiptResult, &receipt) != nil {
			problems = append(problems, "anchor transaction not found")
		} else {
			if receipt.Status != "0x1" {
				problems = append(problems, "anchor transaction failed")
			}
			mined, err := strconv.ParseInt(stripHex(receipt.BlockNumber), 16, 64)
			if err != nil || mined != blockNumber {
				problems = append(problems, "anchor transaction block mismatch")
			}
		}
	}

	return VerifyReport{Kind: "anchor-onchain", OK: len(problems) == 0, Problems: problems}
}