Core API Methods

Suvidha uses CtxRequest which extends the standard Express.js Request object with a context property, for accessing request-specific data added by middlewares.

/**
 * Extends the standard Express.js `Request` object with a `context` property.
 * This allows you to store and access request-specific data throughout the
 * request lifecycle, particularly useful for middleware communication and
 * data sharing between middleware and request handler.
 *
 * @template C The type of the context object. Defaults to an empty object `{}`.
 *
 * @extends Express.js Request object
 */
interface CtxRequest<C extends Context = {}, ...> extends Request<...> {
    context: C;
}

Suvidha(handlers: Handlers)

Main class for creating a new instance of Suvidha; requires a Handlers instance.

constructor(handlers: Handlers);

Handlers

Refer to Handlers for more details.

.body(schema: ZodType)

Purpose

Validates and types the request body using Zod schemas.

Parameters

schema: Zod schema definition.
Returns: Chainable Suvidha instance.

Example

suvidha().body(
    z.object({
        email: z.string().email(),
        password: z.string().min(8),
    }),
);

Behavior

Validates request body before handler execution.
Overrides default any type with schema inference.

.params(schema: ZodType)

Purpose

Validates and types URL path parameters.

Example

suvidha().params(
    z.object({
        userId: z.string().uuid(),
        postId: z.coerce.number(),
    }),
);

Access in Handler

handler((req) => {
    console.log(req.params.userId); // Type-safe string
});

.query(schema: ZodType)

Purpose

Validates and types query string parameters.

Example

suvidha().query(
    z.object({
        page: z.number().default(1),
        sort: z.enum(["asc", "desc"]),
    }),
);

Default Values

// If ?page=3 not provided
req.query.page; // 1 (from default)

.use(middleware)

Purpose

Builds request context through chainable middleware. Each call merges new properties into the context while preserving type safety. Any exceptions thrown will be handled by onErr handler.

Key Characteristics

Order-Sensitive: Middleware executes in the order of declaration.
Type Accumulation: Each middleware’s return type merges with previous context.
Immutable Context: Each middleware gets current context in Readonly wrapper to prevent mutations.
Early Termination: Middleware can end response with res.send().

Merging is the same as using the ... spread operator, new_ctx = { ...current_ctx, ...ctx }

Middleware Signature

type Middleware<Ctx> = (
    req: CtxRequest<CurrentContext>,
    res: Response,
) => Ctx | Promise<Ctx>;

Example

.use(async (req) => ({
  user: await authenticate(req)
}))
.use((req) => ({
  permissions: getPermissions(req.context.user)
}))

Type Safety

// In handler:
req.context.user; // AuthenticatedUser
req.context.permissions; // string[]

.handler(fn)

Purpose

Defines the final request handler with full type safety.

Signature

.handler(
  (req: CtxRequest, res: Response, next: NextFunction) => Reply
)

Parameters

req is express’ Request object with added context.
res is express’ Request object.
next is express’ NextFunction to call next middleware.

.next()

Acts as an Express.js middleware. It executes the configured Suvidha middleware functions (both validation via .body(), .query(), .params() and custom logic via .use()) in the order they are defined. After successful execution of these middlewares, .next() calls the next middleware in the Express.js chain using the express’ next() function.It’s like handler() but with request handler as express’ next() function.

Example

const bannedHosts = new Set(["malicious.example.com", "spam.org"]);

app.use(
    "/protected",
    suvidha()
        .use(async (req) => {
            const clientHost = req.hostname;
            if (bannedHosts.has(clientHost)) {
                throw Http.Forbidden.body({
                    message: `Host "${clientHost}" is banned.`,
                });
            }
            return {};
        })
        .query(z.object({ resourceId: z.string() }))
        .next(), // Proceed to the protected resource handler
    (req, res) => {
        // Access validated query parameter
        const resourceId = req.query.resourceId; // infered type: string
        res.json({ message: `Access granted to resource: ${resourceId}` });
    },
);

The execution order of middlewares is the same as the order of declaration.

app.get(
    "/reports",
    suvidha()
        .query(pageSchema)
        .use(middyA)
        .use(middyB)
        .params(IdSchema)
        .handler((req) => {
            // Business logic
        }),
);

Execution order is query -> middyA -> middyB -> params -> handler.

Usage

Data Validation

Validate the request body using Zod schemas.

const userSchema = z.object({
    username: z.string().min(3),
    email: z.string().email(),
    age: z.number().min(13),
});

app.post(
    "/users",
    suvidha()
        .body(userSchema)
        .handler(async (req) => {
            const newUser = req.body; // type of newUser: z.infer<typeof UserSchema>
            // Execute business logic
        }),
);

Writing Middlewares

middlewares take CtxRequest and Response as input arguments and return Context | Promise<Context>.

// Middleware expects { user: User } in the context.
// specify the constraint in type signature, that way
// Suvidha will ensure that middleware is called
// only when expected context data is available.
type ExpectedContext = { user: User };

const middleware = (req: CtxRequest<ExpectedContext>, res: Response) => {
    // business logic
    return {
        // return context that will be merged with the current context
    };
};

works
doesn't work

app.get(
    "/reports",
    suvidha()
        .use(() => ({ user: authenticate() })) // { auth: Auth }
        .use(middleware) // { user: User }
        .handler((req) => {
            // Business logic
        }),
);

app.get(
    "/reports",
    suvidha()
        .use(middleware) // error: middleware expects { user: User } in context
        .use(() => ({ user: authenticate() })) // { auth: Auth }
        .handler((req) => {
            // Business logic
        }),
);

TypeScript will throw an error because middleware expects { user: User } in context, but the context is {} because the authenticate middleware has not been called yet.

typescript error [2345]

Property 'user' is missing in type '{}' but required in type 'ExpectedContext'.

By specifying the constraint in type signature, we can build type-safe context through ordered middlewares - TypeScript enforces dependency sequence:

app.get(
    "/reports",
    suvidha()
        .use(() => ({ auth: getAuth() })) // { auth: Auth }
        .use((req) => ({
            // Requires previous auth
            user: getUser(req.context.auth), // + { user: User }
        }))
        .use(async (req) => ({
            // Requires user
            report: await fetchReport(req.context.user), // + { report: Report }
        }))
        .handler((req) => req.context.report), // Final: auth + user + report
);

Reorder middlewares → Type error ← Context dependencies broken.

Loosely Coupled Business Logic

Handles responses using onComplete and onErr when using Suvidha with Handlers. This separates your core business logic from framework-specific response methods, keeping your code cleaner by delegating response handling to the handlers.

const UserSchema = z.object({
    username: z.string().min(3),
    email: z.string().email(),
});

type UserDTO = z.infer<typeof UserSchema>;

// Keep your business logic clean and loosely coupled
const requestHandler = (user: UserDTO, role: string) => {
    // Execute business logic
    return {
        id: "67619c28758da37270b925a8",
    };
};

app.post(
    "/users",
    suvidha()
        .use(authenticate)
        .use(roleCheck)
        .body(UserSchema)
        .handler(async (req) => {
            const newUser = req.body;
            const { role } = req.context.user;
            return requestHandler(newUser, role); // Execute business logic
        }),
);

Suvidha as data validation middleware

To use Suvidha solely as data validation middleware with TypeScript inference, implement onSchemaErr method.

// Customize the error response
class CustomHandlers implements Handlers {
    onSchemaErr(_: ZodError, conn: Conn) {
        const fmt = {
            success: false,
            error: "VALIDATION_FAILURE",
        };
        conn.res.status(400).json(fmt);
    }

    onErr(): Promise<void> | void {
        throw new Error("Method not implemented.");
    }

    onComplete(): Promise<void> | void {
        throw new Error("Method not implemented.");
    }

    onPostResponse(): Promise<void> | void {
        throw new Error("Method not implemented.");
    }
}

const userSchema = z.object({
    username: z.string().min(3),
    email: z.string().email(),
});

const verifyBody = <T extends z.ZodTypeAny>(schema: T) =>
    suvidha().body(schema).next();

app.post("/users", verifyBody(userSchema), (req, res) => {
    // type of req.body: z.infer<typeof userSchema>
    const { email, username } = req.body;
    res.send({ email, username });
});

DRY Suvidha

If you have common middlewares across multiple routes, you can create a Suvidha instance and reuse it.

import { Suvidha, DefaultHandlers, Http } from "suvidha";

declare function authenticate(req: Request): Promise<{ role: string }>;

const suvidha = () => Suvidha.create(new DefaultHandlers());

// instance with middlewares for authentication
const auth = () =>
    suvidha().use(async (req) => {
        const user = await authenticate(req).catch((_) => {
            throw new Http.Unauthorized();
        });
        return { user };
    });

// instance with middlewares for admin authorization
const adminAuth = () =>
    // Reuse auth middleware
    auth().use((req) => {
        if (req.context.user.role !== "admin") {
            throw new Http.Forbidden();
        }
        return {};
    });

// Admin protected user creation endpoint
app.post(
    "/users",
    adminAuth()
        .body(userSchema)
        .handler(async (req) => {
            // Business logic
        }),
);

// Anyone authenticated user can access reports
app.get(
    "/reports",
    auth()
        .query(pageSchema)
        .handler(async (req) => {
            // Business logic
        }),
);

Adopting Suvidha in Existing Projects

Suvidha’s CtxRequest extends the standard Request object by adding a context property. Existing handlers that accept Request will also work with CtxRequest. The context can be accessed using CtxRequest.

declare function identity(req: Request): Promise<User>;

const BookSchema = z.object({
    title: z.string().min(3),
    author: z.string().min(3),
});

type Book = z.infer<typeof BookSchema>;
type User = { id: string; name: string };

function validateBody(req: Request, res: Response, zodSchema: ZodType<any>) {
    try {
        req.body = zodSchema.parse(req.body);
        next();
    } catch (err) {
        return void res.status(400).send("Bad Request");
    }
}

const authenticate = async (
    req: Request,
    res: Response,
    next: NextFunction,
) => {
    try {
        (req as any).user = await identity(req);
        next();
    } catch (_) {
        return void res.status(401).json({ error: "Unauthorized" });
    }
};

async function createBookHandler(
    req: Request<any, any, Book>,
    res: Response,
): Promise<void> {
    const user = (req as any).user as User;
    const book = req.body;
    // Business logic ...
}

app.post(
    "/books",
    authenticate,
    (req, res) => validateBody(req, res, BookSchema),
    createBookHandler,
);

Get Started

Usage

Reference

API

Core API Methods

Purpose

Parameters

Example

Behavior

Purpose

Example

Access in Handler

Purpose

Example

Default Values

Purpose

Middleware Signature

Example

Type Safety

Purpose

Signature

Parameters

Example

Usage

Data Validation

Writing Middlewares

Loosely Coupled Business Logic

Suvidha as data validation middleware

DRY Suvidha

Adopting Suvidha in Existing Projects

Get Started

Usage

Reference

​Core API Methods

​Purpose

​Parameters

​Example

​Behavior

​Purpose

​Example

​Access in Handler

​Purpose

​Example

​Default Values

​Purpose

​Middleware Signature

​Example

​Type Safety

​Purpose

​Signature

​Parameters

​Example

​Usage

​Data Validation

​Writing Middlewares

​Loosely Coupled Business Logic

​Suvidha as data validation middleware

​DRY Suvidha

​Adopting Suvidha in Existing Projects

Core API Methods

Purpose

Parameters

Example

Behavior

Purpose

Example

Access in Handler

Purpose

Example

Default Values

Purpose

Middleware Signature

Example

Type Safety

Purpose

Signature

Parameters

Example

Usage

Data Validation

Writing Middlewares

Loosely Coupled Business Logic

Suvidha as data validation middleware

DRY Suvidha

Adopting Suvidha in Existing Projects