Add support to validate req headers

Author: sergioalvz

src/index.ts

@@ -2,7 +2,7 @@ import { Schema } from "joi";
 import { NextApiHandler, NextApiRequest, NextApiResponse } from "next";
 import { NextHandler, RequestHandler } from "next-connect";
 
-export type ValidableRequestFields = Pick<NextApiRequest, "query" | "body">;
+export type ValidableRequestFields = Pick<NextApiRequest, "body" | "headers" | "query">;
 
 export type ValidationSchemas = {
   [K in keyof ValidableRequestFields]?: Schema;
@@ -22,7 +22,7 @@ export default function withJoi(config?: Configuration): ValidationFunction {
 
   return (schemas, handler) => {
     return (req: NextApiRequest, res: NextApiResponse, next?: NextHandler) => {
-      const fields: (keyof ValidableRequestFields)[] = ["body", "query"];
+      const fields: (keyof ValidableRequestFields)[] = ["body", "headers", "query"];
 
       const hasValidationErrors = fields.some((field) => {
         const schema = schemas[field];

tests/index.spec.ts

@@ -114,6 +114,45 @@ function buildSuite({ handlerBuilder, title }: BuildSuiteOptions): void {
       });
     });
 
+    describe("handling headers validation", () => {
+      const schema = Joi.object({
+        "accept-language": Joi.string().valid("en", "es").required(),
+      });
+
+      it("returns a 400 by default if unknown headers are not ignored", async () => {
+        const handler = handlerBuilder(validate, { headers: schema }, postANewUser);
+
+        const response = await server.inject(handler, {
+          headers: { "accept-language": "en" },
+          method: "post",
+        });
+
+        expect(response.status).toBe(400);
+      });
+
+      it("returns a 200 response if the validation passes", async () => {
+        const handler = handlerBuilder(validate, { headers: schema.unknown() }, postANewUser);
+
+        const response = await server.inject(handler, {
+          headers: { "accept-language": "en" },
+          method: "post",
+        });
+
+        expect(response.status).toBe(200);
+      });
+
+      it("returns a 400 response if the validation doesn't pass", async () => {
+        const handler = handlerBuilder(validate, { headers: schema.unknown() }, postANewUser);
+
+        const response = await server.inject(handler, {
+          headers: { "accept-language": "pt" },
+          method: "post",
+        });
+
+        expect(response.status).toBe(400);
+      });
+    });
+
     describe("working with custom error handling", () => {
       const body = Joi.object({ name: Joi.string().required() });