Centralize validation with a typed schema layer for request bodies and params

[mikewheeleer]

Refactor scattered validation into a typed schema layer

Description

Validation in src/index.ts is duplicated and ad-hoc: isAssetCode, parseAmount, the regex checks in the pair PATCH handlers, and the body checks in webhook/api-key/config handlers all repeat the same 400 invalid_request + requestId pattern by hand. This issue centralizes validation behind a small typed schema layer (e.g. zod) and a reusable validate() middleware.

Requirements and context

• Repository scope: StableRoute-Org/Stableroute-backend only.
• Add zod and create src/validation.ts (create file) with schemas for quote params, pair body, fee/min/max/liquidity patches, webhook body, api-key body, and config patch.
• Provide a validate(schema, source) middleware that emits the existing canonical { error: "invalid_request", message, requestId } body on failure.
• Preserve the exact BigInt amount semantics (no leading zero, positive) and the 1–12 char asset rule.
• Keep all current error messages semantically equivalent so tests asserting on message text still pass (adjust regexes if needed).

Suggested execution

• Fork the repo and create a branch
• git checkout -b refactor/validation-14-schema-layer
• Implement changes
  • Write code in: create src/validation.ts; refactor handlers in src/index.ts.
  • Write comprehensive tests in: create src/__tests__/validation.test.ts plus keep src/__tests__/index.test.ts green.
  • Add documentation: describe the validation layer in README.md.
  • Add TSDoc on each schema and the middleware.
  • Validate security: ensure array/param-pollution inputs are still rejected.
• Test and commit

Test and commit

• Run npm run build, npm run lint, and npm test.
• Cover edge cases: each schema's invalid inputs, including array-form params.
• Paste full npm test output in the PR.

Example commit message

refactor(validation): centralize request validation in a zod schema layer

Guidelines

• Minimum 95 percent test coverage for impacted code.
• Clear, reviewer-focused documentation.
• Timeframe: 96 hours.

Community & contribution rewards

• 💬 Join the StableRoute community on Discord for questions, reviews, and faster merges: https://discord.gg/37aCpusvx
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[GBOYEE]

Hi maintainers! I can work on this — centralizing the scattered validation into a typed zod schema layer is a clean refactor. I will create src/validation.ts with reusable schemas for all request bodies/params and a validate() middleware emitting the canonical error shape. All existing tests will stay green. PR incoming shortly.