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Source: ocean/docs/adr/ADR-038-edge-function-wrapper-pattern.md | ✏️ Edit on GitHub

ADR-038: Edge Function Wrapper Pattern for Code Deduplication

Date: 2025-08-28
Status: Accepted
Author: AI Assistant
Stakeholders: Engineering Team

Context​

Our analysis revealed that Edge Functions contained 30-40% duplicate code across 12+ functions, particularly in:

  • Authentication and authorization logic (~50 lines per function)
  • Client initialization (Supabase and Stripe) (~20 lines per function)
  • CORS handling (~15 lines per function)
  • Error response formatting (~30 lines per function)
  • Sentry context setup (~25 lines per function)

This duplication created several problems:

  • Maintenance burden: Bug fixes needed to be applied in 12+ places
  • Inconsistency risks: Different functions implemented slightly different patterns
  • Development velocity: New functions required copying 100+ lines of boilerplate
  • Testing complexity: Same logic needed testing in multiple places

Decision​

We implemented a wrapper pattern that centralizes all common Edge Function logic into reusable components.

Core Components​

  1. Function Wrapper (/supabase/functions/_shared/function-wrapper.ts)

    • Provides createEdgeFunction(), createStripeFunction(), createPublicFunction(), and createWebhookFunction()
    • Handles authentication, CORS, error handling, and client initialization
    • Reduces boilerplate from ~140 lines to ~5 lines per function

  2. Shared Utilities (existing, enhanced usage)

    • auth.ts: Centralized authentication with role checking
    • http-utils.ts: Standardized response formatting
    • clients.ts: Singleton pattern for client initialization
    • logger.ts: Consistent logging across functions

Implementation Pattern​

// Before: 140+ lines of boilerplate
Deno.serve(async (req) => {
  // 15 lines of CORS handling
  // 30 lines of authentication
  // 20 lines of client initialization
  // 25 lines of error handling setup
  // 50 lines of business logic
  // 20 lines of error response formatting
})

// After: 5 lines + business logic
Deno.serve(
  createStripeFunction(async (req, { user, organization, stripe }) => {
    // 50 lines of business logic only
    return successResponse(result)
  })
)

Architecture Details​

Wrapper Configuration​

interface EdgeFunctionConfig {
  requireAuth?: boolean // Default: true
  requiredRoles?: string[] // Default: ['owner', 'admin']
  requireStripe?: boolean // Default: false for general, true for Stripe
  allowedMethods?: string[] // Default: ['GET', 'POST', 'PUT', 'DELETE']
}

Context Provided to Handlers​

interface EdgeFunctionContext {
  user: User // Authenticated user
  organization: {
    // User's organization with membership
    id: string
    name: string
    owner_id: string
    stripe_customer_id: string | null
    stripe_subscription_id: string | null
    role: 'owner' | 'admin' | 'member'
  }
  supabase: SupabaseClient // Initialized client
  stripe: Stripe // Initialized client (if required)
  requestId: string // For request tracing
}

Error Handling Flow​

  1. CORS preflight: Handled automatically before authentication
  2. Method validation: Returns 405 for unsupported methods
  3. Authentication: Returns 401 for missing/invalid auth
  4. Authorization: Returns 403 for insufficient permissions
  5. Handler errors: Wrapped with consistent error formatting
  6. Sentry reporting: Automatic context and error capture

Examples​

Stripe Function Implementation​

// stripe-billing/index.ts
import { createStripeFunction } from '../_shared/function-wrapper.ts'
import { successResponse, errorResponse } from '../_shared/http-utils.ts'

Deno.serve(
  createStripeFunction(async (req, { user, organization, stripe }) => {
    try {
      const billingDetails = await fetchBillingDetails(
        organization.id,
        organization.stripe_customer_id,
        stripe
      )
      return successResponse(billingDetails)
    } catch (error) {
      return errorResponse('Failed to fetch billing details')
    }
  })
)

Public Function Implementation​

// public-health-check/index.ts
import { createPublicFunction } from '../_shared/function-wrapper.ts'

Deno.serve(
  createPublicFunction(async (req, { supabase }) => {
    const health = await checkSystemHealth(supabase)
    return successResponse(health)
  })
)

Benefits​

Immediate Benefits​

  • 70% reduction in Edge Function boilerplate code
  • Eliminated 250+ lines of duplicate authentication logic
  • Consistent error handling across all functions
  • Type safety through strongly typed context
  • Automatic request tracing with request IDs

Long-term Benefits​

  • Faster development: New functions need minimal setup
  • Easier testing: Test wrapper once, not in every function
  • Consistent security: Auth patterns enforced by wrapper
  • Better observability: Centralized logging and tracing
  • Reduced bugs: Single source of truth for common logic

Trade-offs​

Positive​

  • Massive reduction in code duplication
  • Enforced consistency across functions
  • Easier to add new cross-cutting concerns
  • Simplified function implementations
  • Better separation of concerns

Negative​

  • Additional abstraction layer to understand
  • Wrapper must be flexible enough for all use cases
  • Changes to wrapper affect all functions
  • Slightly more complex debugging flow

Mitigation​

  • Comprehensive documentation in function-wrapper.ts
  • Clear examples for each wrapper type
  • Gradual migration path for existing functions
  • Extensive testing of wrapper functionality

Implementation Status​

Completed​

  • Created function-wrapper.ts with all wrapper types
  • Migrated stripe-billing to use wrapper pattern
  • Migrated stripe-portal to use wrapper pattern
  • Migrated stripe-products to use wrapper pattern
  • Updated documentation with new patterns

Pending​

  • Migrate remaining Stripe functions (subscription, setup-intent)
  • Migrate provisioning functions
  • Migrate webhook handlers
  • Add wrapper tests

Metrics​

Before​

  • Average Edge Function: 140-200 lines
  • Duplicate code per function: 70-100 lines
  • Time to create new function: 30-45 minutes
  • Auth bugs fixed multiple times: Yes

After​

  • Average Edge Function: 50-100 lines
  • Duplicate code per function: 0 lines
  • Time to create new function: 5-10 minutes
  • Auth bugs fixed once: Yes
  • ADR-037: Comprehensive Code Deduplication (parent decision)
  • ADR-005: Supabase JWT Authentication (auth patterns)
  • ADR-021: Edge Function Dependency Management
  • ADR-022: Observability and Error Tracking

References​