Reference: A DeFi Program + dApp

This reference build walks a minimal lending pool: deposit SOL, mint share tokens, withdraw with pro-rata accounting. It ties together Anchor 0.32.1, LiteSVM 0.6.x tests, and a Next.js dApp using @solana/kit 7.0.0 - the shape most DeFi teams ship.

Recipe

Quick-reference recipe card - copy-paste ready.

programs/lending/     Anchor program (deposit, withdraw, pause)
tests/litesvm/        Exploit replay + happy path
app/                  Next.js wallet + simulate + send
packages/idl/         Published IDL + codegen types

When to reach for this:

Greenfield DeFi protocol architecture
Onboarding full-stack Solana engineer
Audit scope document baseline
Comparing your layout to a known-good structure

Working Example

Program (Anchor 0.32.1 excerpt)

use anchor_lang::prelude::*;
 
declare_id!("Fg6PaFpoGXkYsidMpWTK6W2BeZ7FEfcYkg476zPFsLnS");
 
#[program]
pub mod lending {
    use super::*;
 
    pub fn deposit(ctx: Context<Deposit>, amount: u64) -> Result<()> {
        require!(!ctx.accounts.config.paused, LendingError::Paused);
        // transfer SOL to vault; mint shares to user_position
        Ok(())
    }
}
 
#[account]
pub struct PoolConfig {
    pub admin: Pubkey,
    pub paused: bool,
    pub total_shares: u64,
}

Client (TypeScript excerpt)

import { createSolanaRpc } from "@solana/kit";
import { buildDepositIx } from "@lending/idl-client";
 
const rpc = createSolanaRpc(process.env.NEXT_PUBLIC_RPC_URL!);
 
export async function deposit(amount: bigint, wallet: Wallet) {
  const ix = await buildDepositIx({ amount, user: wallet.publicKey });
  const sim = await rpc.simulateTransaction(await wallet.sign(ix), { sigVerify: true }).send();
  if (sim.value.err) throw new Error(JSON.stringify(sim.value.err));
  return wallet.send(ix);
}

Repo layout

lending-reference/
  programs/lending/src/lib.rs
  tests/litesvm/deposit_withdraw.rs
  app/src/app/pool/page.tsx
  packages/idl/lending.json
  docs/adr/0001-upgradeable-pool.md

What this demonstrates:

Pause guard on all mutating instructions
IDL package consumed by Next.js app
Simulation before user-facing send
ADR slot for upgrade policy

Deep Dive

Account Model

Account	Type	Purpose
`pool_config`	PDA	Admin, pause, totals
`vault`	PDA	Holds SOL lamports
`user_position`	PDA	Per-user shares

Release Train

anchor test + LiteSVM on PR
Devnet deploy on merge to main
Squads proposal for mainnet with verifiable hash
Frontend promote when IDL version matches

Gotchas

Client math duplicates on-chain - Share price drift exploits. Fix: Read totals from chain; display only.
Missing pause in withdraw - Attacker drains during incident. Fix: Central require!(!paused).
IDL not versioned - Client calls removed ix. Fix: Semver in packages/idl.
Public RPC on launch - Rate limit outage. Fix: Dedicated write RPC in production env.

Alternatives

Alternative	Use When	Don't Use When
Pinocchio for hot ix	CU proven bottleneck	First version
Separate client repo	Multiple consumers	Small team overhead
Immutable program	Fixed simple pool	Need post-audit fixes

FAQs

Why Anchor not Pinocchio here?

Velocity and audit familiarity outweigh CU savings until profiled.

Where Jupiter fit?

Separate CPI module; allowlist program ID in constants.

Indexer needed?

For history charts yes; MVP can poll PDAs via RPC.

Test validator role?

Manual debug; CI uses LiteSVM per manifest pins.

Mobile?

Add MWA path in app; same IDL client package.

Token shares SPL?

Yes - mint authority = pool PDA; see SPL token launch reference.

Upgrade policy?

Document in ADR; Squads 2-of-3 before mainnet TVL.

How small can this be?

This reference is teachable size; production adds oracles, liquidations, events.

Audit package?

Program + IDL + this architecture doc + threat model appendix.

Clone repo?

Use as template; replace program ID and regenerate keypairs per env.

Reference: An SPL Token Launch - share token mint
Before/After: Optimizing CU & Rent - scale path
Anchor Basics - framework fundamentals

Stack versions: This page was written for Agave 4.1.1, Solana CLI 3.0.10, Anchor 0.32.1, anchor-lang 0.32.1, Rust 1.91.1, @solana/kit 7.0.0, Surfpool 0.12.0, and LiteSVM 0.6.x.

Recipe

Quick-reference recipe card - copy-paste ready.

programs/lending/     Anchor program (deposit, withdraw, pause)
tests/litesvm/        Exploit replay + happy path
app/                  Next.js wallet + simulate + send
packages/idl/         Published IDL + codegen types

When to reach for this:

Greenfield DeFi protocol architecture
Onboarding full-stack Solana engineer
Audit scope document baseline
Comparing your layout to a known-good structure

Working Example

Program (Anchor 0.32.1 excerpt)

use anchor_lang::prelude::*;
 
declare_id!("Fg6PaFpoGXkYsidMpWTK6W2BeZ7FEfcYkg476zPFsLnS");
 
#[program]
pub mod lending {
    use super::*;
 
    pub fn deposit(ctx: Context<Deposit>, amount: u64) -> Result<()> {
        require!(!ctx.accounts.config.paused, LendingError::Paused);
        // transfer SOL to vault; mint shares to user_position
        Ok(())
    }
}
 
#[account]
pub struct PoolConfig {
    pub admin: Pubkey,
    pub paused: bool,
    pub total_shares: u64,
}

Client (TypeScript excerpt)

import { createSolanaRpc } from "@solana/kit";
import { buildDepositIx } from "@lending/idl-client";
 
const rpc = createSolanaRpc(process.env.NEXT_PUBLIC_RPC_URL!);
 
export async function deposit(amount: bigint, wallet: Wallet) {
  const ix = await buildDepositIx({ amount, user: wallet.publicKey });
  const sim = await rpc.simulateTransaction(await wallet.sign(ix), { sigVerify: true }).send();
  if (sim.value.err) throw new Error(JSON.stringify(sim.value.err));
  return wallet.send(ix);
}

Repo layout

lending-reference/
  programs/lending/src/lib.rs
  tests/litesvm/deposit_withdraw.rs
  app/src/app/pool/page.tsx
  packages/idl/lending.json
  docs/adr/0001-upgradeable-pool.md

What this demonstrates:

Pause guard on all mutating instructions
IDL package consumed by Next.js app
Simulation before user-facing send
ADR slot for upgrade policy

Deep Dive

Account Model

Account	Type	Purpose
`pool_config`	PDA	Admin, pause, totals
`vault`	PDA	Holds SOL lamports
`user_position`	PDA	Per-user shares

Release Train

anchor test + LiteSVM on PR
Devnet deploy on merge to main
Squads proposal for mainnet with verifiable hash
Frontend promote when IDL version matches

Gotchas

Client math duplicates on-chain - Share price drift exploits. Fix: Read totals from chain; display only.
Missing pause in withdraw - Attacker drains during incident. Fix: Central require!(!paused).
IDL not versioned - Client calls removed ix. Fix: Semver in packages/idl.
Public RPC on launch - Rate limit outage. Fix: Dedicated write RPC in production env.

Alternatives

Alternative	Use When	Don't Use When
Pinocchio for hot ix	CU proven bottleneck	First version
Separate client repo	Multiple consumers	Small team overhead
Immutable program	Fixed simple pool	Need post-audit fixes

FAQs

Why Anchor not Pinocchio here?

Velocity and audit familiarity outweigh CU savings until profiled.

Where Jupiter fit?

Separate CPI module; allowlist program ID in constants.

Indexer needed?

For history charts yes; MVP can poll PDAs via RPC.

Test validator role?

Manual debug; CI uses LiteSVM per manifest pins.

Mobile?

Add MWA path in app; same IDL client package.

Token shares SPL?

Yes - mint authority = pool PDA; see SPL token launch reference.

Upgrade policy?

Document in ADR; Squads 2-of-3 before mainnet TVL.

How small can this be?

This reference is teachable size; production adds oracles, liquidations, events.

Audit package?

Program + IDL + this architecture doc + threat model appendix.

Clone repo?

Use as template; replace program ID and regenerate keypairs per env.

Reference: An SPL Token Launch - share token mint
Before/After: Optimizing CU & Rent - scale path
Anchor Basics - framework fundamentals

Stack versions: This page was written for Agave 4.1.1, Solana CLI 3.0.10, Anchor 0.32.1, anchor-lang 0.32.1, Rust 1.91.1, @solana/kit 7.0.0, Surfpool 0.12.0, and LiteSVM 0.6.x.

Reference: A DeFi Program + dApp

Search Documentation

Reference: A DeFi Program + dApp