Seamless Blockchain API Development: Design Patterns and Testing Strategies

Decision‑makers: this field guide shows how to ship reliable, scalable blockchain APIs your product can trust. We translate fast‑moving protocol changes (EIP‑4844 blobs, ERC‑4337, EIP‑7702; Solana priority fees and SWQoS) into concrete patterns, test plans, and code you can put in CI today. (eips.ethereum.org)

Executive summary

Well‑architected blockchain APIs require consistency under reorgs, multi‑client quirks, fee market volatility, and new transaction types (blobs, user operations). The fastest path to “it just works” is a layered design: RPC gateway + read models + async eventing + rigorous fork/reorg/fee simulations in CI. (eips.ethereum.org)

1) Why blockchain API design is different

Finality and reorgs are normal: Ethereum JSON‑RPC lets you anchor reads to a specific block hash and require canonicality; use this everywhere you need consistency across multiple reads. Tags like latest/safe/finalized exist for different risk profiles. (eips.ethereum.org)
Client diversity matters: Geth, Nethermind, and Erigon expose the same core methods but differ in tracing/debug APIs, performance, and pruning defaults. Don’t assume parity for debug/trace. Lock down debug endpoints in production. (geth.ethereum.org)
Fee markets evolve: since London (EIP‑1559) transactions moved to maxFeePerGas/maxPriorityFeePerGas and added effectiveGasPrice and baseFeePerGas in receipts/blocks. Dencun (Mar 13, 2024) added blob transactions with an independent blob fee market, plus RPC surfaces like eth_blobBaseFee. Your API must understand both gas markets. (hackmd.io)
New transaction forms change integration points: ERC‑4337 introduced UserOperation flows via bundlers; EIP‑7702 (Set Code for EOAs) targets compatibility with 4337 and adds an authorization tuple to txs. Expect additional RPCs and simulation steps around validation. (eips.ethereum.org)
Non‑EVM ecosystems have their own levers: on Solana, you’ll estimate/attach priority fees per account set and can gain delivery advantages via Stake‑weighted QoS (SWQoS) peering. (solana.com)

2) API design patterns that survive mainnet

2.1 Read consistency: always pin state

Pattern: for multi‑call reads that must reflect one state, pass a block identifier object with blockHash to every eth_call/get* method; set requireCanonical for correctness under reorgs. Example payload:

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "eth_call",
  "params": [
    { "to": "0x…", "data": "0x…" },
    { "blockHash": "0xabc…", "requireCanonical": true }
  ]
}

This avoids drift across sequential reads. Build a helper so engineers never pass "latest" by mistake in consistency‑sensitive code paths. (eips.ethereum.org)

For batched front‑end dashboards, use Multicall3 on the chain to guarantee same‑block results and reduce round‑trips. Pair it with block number/timestamp in the return to detect staleness. (github.com)

2.2 Write paths: idempotency and replacement semantics

Idempotency anchor = nonce. Treat each business operation as “one nonce”. To resubmit under EIP‑1559, replace the pending tx using the same nonce and bump both maxPriorityFeePerGas and maxFeePerGas (≥10% is commonly required by nodes/mempools). Build a retry policy around this rule. (alchemy.com)
Internal API layer: add an Idempotency‑Key header mapped to a durable nonce reservation record; reject duplicate attempts that would violate sequential nonces. This prevents accidental double‑spend logic above the RPC layer.

2.3 Batching and connection hygiene

Use JSON‑RPC 2.0 batching to reduce HTTP round‑trips and amortize TLS/connection overhead. Implement batch chunking and response correlation by id; never rely on array order. (json-rpc.org)
Separate hot read paths (cached + subgraph/Firehose) from write paths (RPC). This is CQRS for web3: reads from an indexed model, writes via canonical nodes. (thegraph.com)

2.4 Eventing instead of polling

Replace address log polling with webhooks/streams. Providers like Alchemy can push mined/dropped transactions and address activity; this slashes RPC spend and reduces missed updates under reorg. Use retries and signature verification on webhook payloads. (alchemy.com)
For pending‑tx workflows, subscribe to provider‑specific pending streams (e.g., alchemy_pendingTransactions) and blend with your node’s mempool view for best coverage. (alchemy.com)

2.5 Observability from day one

Export client metrics: enable Geth’s Prometheus endpoint (–metrics, /debug/metrics/prometheus) and ingest into your observability stack; Nethermind ships with Prometheus/Grafana dashboards as well. Track p95 eth_call latency, error rates by method, and reorg‑induced rollbacks. (geth.ethereum.org)
Emit OpenTelemetry spans around external RPC and webhook processing so you can correlate an on‑chain write with the event that confirmed it. Prometheus now ingests OTLP HTTP natively; wire your OTel SDKs to Prom via the OTLP receiver. (prometheus.io)

3) Platform‑specific integration details that matter

3.1 Ethereum after Dencun (EIP‑4844)

Your API must recognize blob transactions (type 0x03) with fields like max_fee_per_blob_gas and blob_versioned_hashes; “blob gas” has its own base fee schedule, independent of normal gas. Add blob fee estimation (eth_blobBaseFee) alongside eth_feeHistory for standard gas. (eips.ethereum.org)
Fee strategy: when blobs are congested, your normal gas estimator won’t capture blob base fee dynamics—treat blob and normal gas as two knobs. Keep a separate surge policy and alerting for “blob capacity exhausted” conditions surfaced by your builder/relay telemetry. (ethresear.ch)

3.2 Account abstraction in practice (ERC‑4337 + EIP‑7702)

If you support smart accounts, add bundler RPCs: eth_sendUserOperation, eth_estimateUserOperationGas, eth_getUserOperationReceipt, eth_supportedEntryPoints. Simulate validation before enqueueing; failures must surface preVerificationGas/verificationGasLimit guidance to the client. (alchemy.com)
EIP‑7702 lets EOAs attach authorization tuples so they temporarily (or persistently per spec evolution) act like contracts; recent drafts target compatibility with 4337 EntryPoint v0.8, adding an optional eip7702Auth field to sendUserOperation. Audit flows that rely on msg.sender == tx.origin. (eips.ethereum.org)

Code: sending a UserOperation with gas estimation

[
  {
    "jsonrpc": "2.0",
    "id": 1,
    "method": "eth_estimateUserOperationGas",
    "params": [
      {
        "sender": "0xSender",
        "nonce": "0x0",
        "initCode": "0x",
        "callData": "0x…",
        "maxFeePerGas": "0x0",
        "maxPriorityFeePerGas": "0x0",
        "paymasterAndData": "0x"
      },
      "0xEntryPoint",
      "0x1" // chainId
    ]
  }
]

Then submit via eth_sendUserOperation with returned gas fields; include eip7702Auth only on networks that enabled 7702. (alchemy.com)

MEV protection: route wallet traffic through Flashbots Protect (private tx) or integrate MEV‑Share for orderflow rebates; your API gateway can transparently proxy eth_sendRawTransaction to a Protect RPC for frontrun‑sensitive flows. (github.com)

3.3 Solana production specifics

Priority fees: estimate with getRecentPrioritizationFees while passing all writable accounts used by your transaction—fee requirements are account‑set dependent. Combine with getFeeForMessage for base fees. (solana.com)
Stake‑weighted QoS (SWQoS): partner with staked validators or RPCs that peer with them; 80% of leader TPU capacity is reserved for staked peers by default. This dramatically improves success under load; configure rpc‑send‑transaction‑tpu‑peer. (solana.com)
Confirmations: expose commitment levels (processed/confirmed/finalized) as first‑class options in your API; don’t default to finalized for UX responsiveness. (solana.com)

4) Testing strategies your CI must include

4.1 Deterministic mainnet forking

Fork mainnet at a pinned block for deterministic tests; cache state to speed runs. Use Hardhat or Anvil with an archive RPC; snapshot/revert between tests. Pinning enables ~20× faster reruns. (hardhat.org)

Anvil methods to script chaos:

anvil_snapshot/anvil_revert to time‑travel.
anvil_setNextBlockBaseFeePerGas to simulate fee spikes.
anvil_impersonateAccount for protocol‑level flows.
anvil_mine and evm_setNextBlockTimestamp to script timing. (learnblockchain.cn)

4.2 Reorg and consistency tests

Given a business flow that does N reads and one write, run it twice: (a) using "latest" (expect occasional flakiness), (b) with EIP‑1898 blockHash pinning (expect stability). Fail the build if (a) and (b) produce different side‑effects—this catches latent “latest” usage leaking into core code. (eips.ethereum.org)
Add tests against safe/finalized tags to validate your confirmation policy toggles. (ethereum.org)

4.3 Fee‑market tests

EIP‑1559 replacement: simulate “replacement transaction underpriced” by attempting same‑nonce resubmission with insufficient tip; verify your policy bumps both maxPriorityFeePerGas and maxFeePerGas and that the UI shows “replaced” semantics. (alchemy.com)
Blob stress: when eth_blobBaseFee spikes, validate your fallback path (e.g., degrade to calldata when permissible or queue the operation). (docs.metamask.io)
External estimators: consider integrating Blocknative’s gas APIs to cross‑check next‑block inclusion predictions; use in canary regions first. (docs.blocknative.com)

4.4 Tracing and client‑compat tests

For any protocol integration, run the same debug_traceTransaction on Geth and Erigon, compare output structures, and store diffs to catch vendor‑specific assumptions. Only enable debug on private infra. (geth.ethereum.org)

4.5 ERC‑4337 validation suites

In CI, call eth_estimateUserOperationGas and simulateValidation pre‑bundle. Fail fast on validation reverts, and assert that your paymaster/signature logic sets correct validAfter/validUntil windows. (docs.erc4337.io)

4.6 Solana devnet tests

Test priority fee calculation using the exact account lists your instruction locks as writable. Verify success under SWQoS and non‑SWQoS routing to quantify benefits. Use getFeeForMessage to assert base fee deltas across blockhashes. (solana.com)

5) Reference implementation snippets

5.1 A resilient Ethereum RPC gateway (Node.js/TypeScript)

import pLimit from "p-limit";
import { request } from "undici";

const limit = pLimit(16); // cap concurrency per provider

type RpcReq = { id:number; jsonrpc:"2.0"; method:string; params:any[] };
type RpcRes = { id:number; jsonrpc:"2.0"; result?:any; error?:any };

// provider pool with health + method allowlists
const providers = [
  { url: process.env.RPC_A!, methods: new Set(["eth_call","eth_sendRawTransaction","eth_feeHistory","eth_blobBaseFee"]) },
  { url: process.env.RPC_B!, methods: new Set(["eth_call","eth_sendRawTransaction","eth_feeHistory"]) }
];

export async function rpcCall<T=any>(req: RpcReq): Promise<T> {
  const candidates = providers.filter(p => p.methods.has(req.method));
  let lastErr: any;
  for (const p of candidates) {
    try {
      const { body } = await limit(() => request(p.url, {
        method: "POST",
        headers: { "content-type":"application/json" },
        body: JSON.stringify(req)
      }));
      const res = await body.json() as RpcRes;
      if (res.error) throw Object.assign(new Error(res.error.message), { code: res.error.code });
      return res.result as T;
    } catch (e) { lastErr = e; /* mark p unhealthy, continue */ }
  }
  throw lastErr;
}

Notes: permit eth_blobBaseFee only where available; maintain per‑provider health and cut over on elevated error rates; batch where safe for reads. (docs.metamask.io)

5.2 Consistent reads using blockHash pinning

export async function consistentCall(to: string, data: string, blockHash: string) {
  return rpcCall({
    id: 1,
    jsonrpc: "2.0",
    method: "eth_call",
    params: [{ to, data }, { blockHash, requireCanonical: true }]
  });
}

Always pin follow‑up calls (storage, code, balances) to the same object. (eips.ethereum.org)

5.3 ERC‑4337: estimate and submit

// estimate
const est = await rpcCall({
  id: 1,
  jsonrpc: "2.0",
  method: "eth_estimateUserOperationGas",
  params: [ userOp, entryPoint, chainIdHex ]
});

// submit
userOp.preVerificationGas = est.preVerificationGas;
userOp.verificationGasLimit = est.verificationGasLimit;
userOp.callGasLimit = est.callGasLimit;

const uoHash = await rpcCall({
  id: 2,
  jsonrpc: "2.0",
  method: "eth_sendUserOperation",
  params: [ userOp, entryPoint ]
});

If the network supports 7702 and your flow upgrades EOAs, include eip7702Auth. (alchemy.com)

5.4 Solana: estimating priority fees correctly

// Identify all writable accounts in your Message
const accounts = ["CxELquR1gPP8wHe33gZ4QxqGB3sZ9RSwsJ2KshVewkFY", /* ... */];

const resp = await fetch(SOL_RPC, {
  method: "POST",
  headers: { "content-type":"application/json" },
  body: JSON.stringify({
    jsonrpc:"2.0", id:1, method:"getRecentPrioritizationFees", params:[accounts]
  })
}).then(r => r.json());

const priorityMicrolamports = Math.max(...resp.result.map((r:any)=>r.prioritizationFee));

Combine with getFeeForMessage to set the full fee. (solana.com)

6) Emerging best practices we’re adopting at 7Block Labs

Treat “read state” and “event state” as different products. For query performance and stability, move heavy reads off raw RPC and into subgraphs or Firehose/Substreams; keep a Prometheus‑backed health budget for your indexers. (thegraph.com)
Fee intelligence as a service: wrap eth_feeHistory, eth_blobBaseFee, and an external estimator (e.g., Blocknative) behind one internal endpoint; provide “next‑block,” “fast,” “economy” recommendations with confidence intervals. (anukul.js.org)
Multi‑client staging: every release gets smoke‑tested against Geth and Erigon (and Besu where relevant) with the same test vectors; block debug/trace in prod. (geth.ethereum.org)
Proactive 4337 validation: pre‑simulate every UserOperation, surface wallet‑readable failure reasons, and expose “why it failed” telemetry to support. (docs.erc4337.io)
Solana SWQoS contracts: for high‑stakes flows, ensure your RPC partner peers with staked validators and supports SWQoS; measure uplift vs. public RPC. (solana.com)

7) Decision checklist

Consistency
- All eth_call/get* reads accept a blockHash object (EIP‑1898) in your SDK.
- Multicall3 used for dashboards; responses include block metadata. (eips.ethereum.org)
Writes
- Nonce reservation + idempotency keys in your internal API.
- Replacement policy updates both maxPriorityFeePerGas and maxFeePerGas; alerts on underpriced replacements. (alchemy.com)
Fees
- Dual estimator for normal gas and blob gas; alert on blob congestion. (eips.ethereum.org)
4337
- Bundler endpoints present; simulateValidation gate enabled; 7702 paths guarded. (alchemy.com)
Solana
- Priority fees computed with account‑aware estimates; SWQoS routing in place. (solana.com)
Observability
- Geth/Nethermind Prometheus metrics; OpenTelemetry spans for RPC/webhooks. (geth.ethereum.org)
Testing
- Forked, pinned‑block CI; reorg tests; client‑compat diffs; 4337 validation tests; Solana devnet fee tests. (hardhat.org)

Appendix: method/name quick reference

Ethereum JSON‑RPC: EIP‑1474 (core), EIP‑1898 (blockHash parameter), EIP‑1193 (provider API), EIP‑1559 (fee model), eth_feeHistory, eth_blobBaseFee (blob fee), EIP‑4844 fields. (eips.ethereum.org)
ERC‑4337 Bundler: eth_estimateUserOperationGas, eth_sendUserOperation, eth_getUserOperationReceipt, eth_supportedEntryPoints. (alchemy.com)
EIP‑7702: Set Code for EOAs; forward‑compatible with account abstraction. (eips.ethereum.org)
Solana: getRecentPrioritizationFees, getFeeForMessage; SWQoS. (solana.com)

If you want us to review your API gateway or test plan, 7Block Labs can run a two‑week “production readiness” sprint: consistency audit, fee strategy, 4337 simulation gates, and Solana SWQoS routing—tailored to your stack and chain mix.