ability to return multiple content types / bodies

Counterfact will use the one that best matches the request's accept header.

If there are no matches it will return a 406 error.

.changeset/modern-ducks-taste.md

@@ -0,0 +1,5 @@
+---
+"counterfact": minor
+---
+
+ability to respond with multiple content types, return the best match for the request's accept header

.eslintrc.cjs

@@ -83,6 +83,7 @@ module.exports = {
 
         "no-magic-numbers": ["off"],
         "id-length": ["off"],
+        "max-lines": "off",
       },
     },
 

docs/usage.md

@@ -6,8 +6,6 @@ These features do not depend on TypeScript or the code generator. In order to ge
 
 ## Hello World
 
-[ Depends on #https://github.com/pmcelhaney/counterfact/issues/132 and https://github.com/pmcelhaney/counterfact/issues/128 ]
-
 To get started, create a directory called `paths` and under that a file called `hello.js`.
 
 ```js
@@ -426,7 +424,7 @@ The `GET()` and `POST()` functions are now simplified. The business logic has be
 
 ## Multiple Content Types
 
-Sometimes an endpoint can return a response body with one of multiple content types. Which one is sent depends on which ones the client reports in its `Accepts:` header.
+Sometimes an endpoint can return a response body with one of multiple content types. It returns the best match per the client's `Accept:` header.
 
 ```js
 export function GET({ path, query }) {
@@ -439,20 +437,20 @@ export function GET({ path, query }) {
       "X-Unit": query.unit,
     },
 
-    contentType: [
-      [
-        "application/json",
-        {
+    content: [
+      {
+        type: "application/json",
+        body: {
           city: path.city,
           temperature: context.getTemperature(path.city, query.unit),
         },
-      ],
-      [
-        "text/plain",
-        `It is ${context.getTemperature(path.city, query.unit)} in ${
+      },
+      {
+        type: "text/plain",
+        body: `It is ${context.getTemperature(path.city, query.unit)} in ${
           path.city
         }.`,
-      ],
+      },
     ],
   };
 }

package.json

@@ -53,6 +53,7 @@
     "supertest": "6.2.4"
   },
   "dependencies": {
+    "@hapi/accept": "^6.0.0",
     "@types/json-schema": "^7.0.11",
     "chokidar": "^3.5.3",
     "fs-extra": "^10.1.0",

src/dispatcher.js

@@ -1,3 +1,5 @@
+import Accept from "@hapi/accept";
+
 import { Tools } from "./tools.js";
 
 export class Dispatcher {
@@ -8,7 +10,7 @@ export class Dispatcher {
   }
 
   request({ method, path, headers, body, query }) {
-    return this.wrapResponse(
+    const normalizedResponse = this.normalizeResponse(
       this.registry.endpoint(
         method,
         path
@@ -19,11 +21,22 @@ export class Dispatcher {
         body,
         query,
         headers,
-      })
+      }),
+      headers?.accept ?? "*/*"
     );
+
+    if (
+      !Accept.mediaTypes(headers?.accept ?? "*/*").some((type) =>
+        this.isMediaType(normalizedResponse.contentType, type)
+      )
+    ) {
+      return { status: 406, body: Accept.mediaTypes(headers?.accept ?? "*/*") };
+    }
+
+    return normalizedResponse;
   }
 
-  wrapResponse(response) {
+  normalizeResponse(response, acceptHeader) {
     if (typeof response === "string") {
       return {
         status: 200,
@@ -33,6 +46,66 @@ export class Dispatcher {
       };
     }
 
+    if (response.content) {
+      const content = this.selectContent(acceptHeader, response.content);
+
+      if (!content) {
+        return {
+          status: 406,
+        };
+      }
+
+      const normalizedResponse = {
+        ...response,
+        contentType: content.type,
+        body: content.body,
+        content: undefined,
+      };
+
+      delete normalizedResponse.content;
+
+      return normalizedResponse;
+    }
+
     return response;
   }
+
+  selectContent(acceptHeader, content) {
+    const preferredMediaTypes = Accept.mediaTypes(acceptHeader);
+
+    for (const mediaType of preferredMediaTypes) {
+      const contentItem = content.find((item) =>
+        this.isMediaType(item.type, mediaType)
+      );
+
+      if (contentItem) {
+        return contentItem;
+      }
+    }
+
+    return {
+      type: preferredMediaTypes,
+      body: "no match",
+    };
+  }
+
+  isMediaType(type, pattern) {
+    if (pattern === "*/*") {
+      return true;
+    }
+
+    const [baseType, subType] = type.split("/");
+
+    const [patternType, patternSubType] = pattern.split("/");
+
+    if (baseType === patternType) {
+      return subType === patternSubType || patternSubType === "*";
+    }
+
+    if (subType === patternSubType) {
+      return baseType === patternType || patternType === "*";
+    }
+
+    return false;
+  }
 }

test/dispatcher.test.js

@@ -45,6 +45,114 @@ describe("a dispatcher", () => {
     });
   });
 
+  it("finds the best content item for an accept header", () => {
+    const dispatcher = new Dispatcher();
+
+    const html = dispatcher.selectContent("text/html", [
+      {
+        type: "text/plain",
+        body: "hello",
+      },
+      {
+        type: "text/html",
+        body: "<h1>hello</h1>",
+      },
+    ]);
+
+    expect(html.type).toBe("text/html");
+  });
+
+  it("returns HTTP 406 if it can't return content matching the accept header", async () => {
+    const registry = new Registry();
+
+    registry.add("/hello", {
+      GET() {
+        return {
+          status: 200,
+          contentType: "text/plain",
+          body: "I am not JSON",
+        };
+      },
+    });
+
+    const dispatcher = new Dispatcher(registry);
+    const response = await dispatcher.request({
+      method: "GET",
+      path: "/hello",
+
+      headers: {
+        accept: "application/json",
+      },
+    });
+
+    expect(response.status).toBe(406);
+  });
+
+  it.each([
+    ["text/html", ["text/html"], "text/html"],
+    ["text/plain", ["text/html", "text/plain"], "text/plain"],
+    ["text/*", ["text/html", "text/plain"], "text/html"],
+    ["*/json", ["text/html", "application/json"], "application/json"],
+    [
+      "*/html;q=0.1,*/json;q=0.2",
+      ["text/html", "application/json"],
+      "application/json",
+    ],
+  ])(
+    'given accept header "%s" and content types: %s, select %s',
+    (acceptHeader, types, expected) => {
+      const dispatcher = new Dispatcher();
+
+      const content = types.map((type) => ({ type }));
+
+      expect(dispatcher.selectContent(acceptHeader, content).type).toBe(
+        expected
+      );
+    }
+  );
+
+  it("selects the best content item matching the Accepts header", async () => {
+    const registry = new Registry();
+
+    registry.add("/hello", {
+      GET() {
+        return {
+          status: 200,
+
+          headers: {},
+
+          content: [
+            {
+              type: "text/plain",
+              body: "Hello, world!",
+            },
+            {
+              type: "text/html",
+              body: "<h1>Hello, world!</h1>",
+            },
+          ],
+        };
+      },
+    });
+
+    const dispatcher = new Dispatcher(registry);
+    const html = await dispatcher.request({
+      method: "GET",
+      path: "/hello",
+
+      headers: {
+        accept: "text/html",
+      },
+    });
+
+    expect(html).toStrictEqual({
+      status: 200,
+      headers: {},
+      contentType: "text/html",
+      body: "<h1>Hello, world!</h1>",
+    });
+  });
+
   it("passes the request body", async () => {
     const registry = new Registry();
 
@@ -212,7 +320,7 @@ describe("a dispatcher", () => {
   });
 });
 
-describe("given a in invalid path", () => {
+describe("given an invalid path", () => {
   it("returns a 404 when the route is not found", () => {
     const registry = new Registry();
 

yarn.lock

@@ -642,6 +642,26 @@
     minimatch "^3.1.2"
     strip-json-comments "^3.1.1"
 
+"@hapi/accept@^6.0.0":
+  version "6.0.0"
+  resolved "https://registry.yarnpkg.com/@hapi/accept/-/accept-6.0.0.tgz#360d6a12c7597489b19ad7830b41e3c38fe8c8c4"
+  integrity sha512-aG/Ml4kSBWCVmWvR8N8ULRuB385D8K/3OI7lquZQruH11eM7sHR5Nha30BbDzijJHtyV7Vwc6MlMwNfwb70ISg==
+  dependencies:
+    "@hapi/boom" "^10.0.0"
+    "@hapi/hoek" "^10.0.0"
+
+"@hapi/boom@^10.0.0":
+  version "10.0.0"
+  resolved "https://registry.yarnpkg.com/@hapi/boom/-/boom-10.0.0.tgz#3624831d0a26b3378423b246f50eacea16e04a08"
+  integrity sha512-1YVs9tLHhypBqqinKQRqh7FUERIolarQApO37OWkzD+z6y6USi871Sv746zBPKcIOBuI6g6y4FrwX87mmJ90Gg==
+  dependencies:
+    "@hapi/hoek" "10.x.x"
+
+"@hapi/hoek@10.x.x", "@hapi/hoek@^10.0.0":
+  version "10.0.1"
+  resolved "https://registry.yarnpkg.com/@hapi/hoek/-/hoek-10.0.1.tgz#ee9da297fabc557e1c040a0f44ee89c266ccc306"
+  integrity sha512-CvlW7jmOhWzuqOqiJQ3rQVLMcREh0eel4IBnxDx2FAcK8g7qoJRQK4L1CPBASoCY6y8e6zuCy3f2g+HWdkzcMw==
+
 "@html-eslint/eslint-plugin@^0.13.2":
   version "0.13.2"
   resolved "https://registry.yarnpkg.com/@html-eslint/eslint-plugin/-/eslint-plugin-0.13.2.tgz#5e7e6242b912c740467266671026e06019325249"