Building API Middleware for FileMaker

Beginner

Create a middleware layer between clients and FileMaker that handles authentication, validation, logging, and error normalization.

What you'll learn

How to structure a middleware chain for FM API calls
How to implement request validation middleware
How to normalize FileMaker errors into human-readable messages
How to add structured logging to every FM operation

Middleware sits between the caller and FileMaker, intercepting every request and response. A well-designed middleware layer handles cross-cutting concerns -- logging, auth, validation, error translation -- in one place, so application code stays focused on business logic.

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Middleware chain pattern

A middleware chain is a list of functions, each of which receives the request context, does its work, and calls next() to pass control to the next middleware. The last in the chain makes the actual FM API call.

FileMaker Script

type Middleware = (ctx: FmContext, next: () => Promise<void>) => Promise<void>;

async function runChain(ctx: FmContext, middlewares: Middleware[]) {
  let idx = 0;
  const next = async () => {
    if (idx < middlewares.length) {
      await middlewares[idx++](ctx, next);
    }
  };
  await next();
}

// Usage
await runChain(ctx, [logMiddleware, authMiddleware, validateMiddleware, fmCallMiddleware]);

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