11 files changed, 1368 insertions, 166 deletions

diff --git a/tests/js/db.js b/tests/js/db.js
deleted file mode 100644
index c99dd1b..0000000
--- a/tests/js/db.js
+++ /dev/null
@@ -1,16 +0,0 @@
-const { runTests } = require("../runner.js");
-const { init } = require("../../src/db.js");
-
-
-const test_init = t => {
-	t.start("init()");
-	t.test("FIXME", () => {
-		// init();
-	});
-};
-
-const tests = [
-	test_init,
-];
-
-runTests(tests);
diff --git a/tests/js/db.mjs b/tests/js/db.mjs
new file mode 100644
index 0000000..e4a8a51
--- /dev/null
+++ b/tests/js/db.mjs
@@ -0,0 +1,15 @@
+import { runTests } from "../runner.mjs";
+import { init }     from "../../src/db.mjs";
+
+
+const test_init = t => {
+	t.start("init()");
+	t.test("FIXME", () => {
+		// init();
+	});
+};
+
+
+await runTests([
+	test_init,
+]);
diff --git a/tests/js/escape.mjs b/tests/js/escape.mjs
new file mode 100644
index 0000000..2cad16a
--- /dev/null
+++ b/tests/js/escape.mjs
@@ -0,0 +1,62 @@
+import assert from "node:assert/strict";
+import { runTests } from "../runner.mjs";
+import { escape } from "../../src/escape.mjs";
+
+const test_escape = t => {
+	t.start("escape()");
+
+	t.test("numbers", () => {
+		assert.equal(escape(0),  "0");
+		assert.equal(escape(42), "42");
+		assert.equal(escape(-1), "-1");
+	});
+
+	t.test("object", () => {
+		assert.equal(escape({}),         "[object Object]");
+		assert.equal(escape({ k: "v" }), "[object Object]");
+	});
+
+	t.test("string with special chars", () => {
+		assert.strictEqual(escape(`"`),        """);
+		assert.strictEqual(escape(`"bar`),     ""bar");
+		assert.strictEqual(escape(`foo"`),     "foo"");
+		assert.strictEqual(escape(`foo"bar`),  "foo"bar");
+		assert.strictEqual(escape(`foo""bar`), "foo""bar");
+
+		assert.strictEqual(escape("&"),        "&");
+		assert.strictEqual(escape("&bar"),     "&bar");
+		assert.strictEqual(escape("foo&"),     "foo&");
+		assert.strictEqual(escape("foo&bar"),  "foo&bar");
+		assert.strictEqual(escape("foo&&bar"), "foo&&bar");
+
+		assert.strictEqual(escape("'"),        "'");
+		assert.strictEqual(escape("'bar"),     "'bar");
+		assert.strictEqual(escape("foo'"),     "foo'");
+		assert.strictEqual(escape("foo'bar"),  "foo'bar");
+		assert.strictEqual(escape("foo''bar"), "foo''bar");
+
+		assert.strictEqual(escape("<"),        "&lt;");
+		assert.strictEqual(escape("<bar"),     "&lt;bar");
+		assert.strictEqual(escape("foo<"),     "foo&lt;");
+		assert.strictEqual(escape("foo<bar"),  "foo&lt;bar");
+		assert.strictEqual(escape("foo<<bar"), "foo&lt;&lt;bar");
+
+		assert.strictEqual(escape(">"),        "&gt;");
+		assert.strictEqual(escape(">bar"),     "&gt;bar");
+		assert.strictEqual(escape("foo>"),     "foo&gt;");
+		assert.strictEqual(escape("foo>bar"),  "foo&gt;bar");
+		assert.strictEqual(escape("foo>>bar"), "foo&gt;&gt;bar");
+	});
+
+	t.test("the combination of all special characters", () => {
+		assert.strictEqual(	
+			escape(`foo, "bar", 'baz' & <quux>`),
+			"foo, &quot;bar&quot;, &#39;baz&#39; &amp; &lt;quux&gt;",
+		);
+	});
+};
+
+
+await runTests([
+	test_escape,
+]);
diff --git a/tests/js/hero.mjs b/tests/js/hero.mjs
new file mode 100644
index 0000000..09e6e54
--- /dev/null
+++ b/tests/js/hero.mjs
@@ -0,0 +1,1050 @@
+import assert from "node:assert/strict";
+import { runTests } from "../runner.mjs";
+import { assocIn } from "../../src/utils.mjs";
+import {
+	normalizeSegments,
+	pathToSegments,
+	hasPathParams,
+	addRoute,
+	buildRoutes,
+	findStaticHandler,
+	firstParamMatch,
+	findDynamicHandler,
+	findHandler,
+	extractQueryParams,
+	handleRequest,
+	makeRequestListener,
+	interceptorsFn,
+	chainInterceptors,
+	wrapHandler,
+} from "../../src/hero.mjs";
+
+
+const test_normalizeSegments = t => {
+	t.start("normalizeSegments()");
+
+	t.test("unchanged when already normalized", () => {
+		assert.deepEqual(normalizeSegments([""]), [""]);
+	});
+
+	t.test("empty terminator added when missing", () => {
+		assert.deepEqual(normalizeSegments([]), [""]);
+		assert.deepEqual(normalizeSegments([" "]), [" ", ""]);
+		assert.deepEqual(normalizeSegments(["_"]), ["_", ""]);
+		assert.deepEqual(normalizeSegments(["a"]), ["a", ""]);
+		assert.deepEqual(normalizeSegments([":a"]), [":a", ""]);
+		assert.deepEqual(normalizeSegments(["path"]), ["path", ""]);
+	});
+};
+
+const test_pathToSegments = t => {
+	t.start("pathToSegments()");
+
+	t.test("simple paths", () => {
+		assert.deepEqual(pathToSegments("/"), [ "" ]);
+		assert.deepEqual(pathToSegments("/simple"), ["simple", ""]);
+		assert.deepEqual(pathToSegments("/simple/route"), ["simple", "route", ""]);
+
+		assert.deepEqual(pathToSegments("/api/user/:id"),      ["api", "user", ":id", ""]);
+		assert.deepEqual(pathToSegments("/api/user/:id/info"), ["api", "user", ":id", "info", ""]);
+	});
+
+	t.test("extra separators", () => {
+		assert.deepEqual(pathToSegments("/api/health/"),     ["api", "health", ""]);
+		assert.deepEqual(pathToSegments("/api///health"),    ["api", "health", ""]);
+		assert.deepEqual(pathToSegments("//api///health//"), ["api", "health", ""]);
+	});
+};
+
+const test_hasPathParams = t => {
+	t.start("hasPathParam()");
+
+	t.test("has it", () => {
+		assert(hasPathParams(["some", ":path", ""]));
+		assert(hasPathParams(["path", ":params", ""]));
+		assert(hasPathParams(["api", "user", ":id", "info", ""]));
+	});
+
+	t.test("doesn't have it", () => {
+		assert(!hasPathParams([]));
+		assert(!hasPathParams([ "" ]));
+		assert(!hasPathParams(["some", "path", ""]));
+		assert(!hasPathParams(["s:o:m:e:", "p::ath:::"]));
+		assert(!hasPathParams([" :"]));
+	});
+};
+
+const test_addRoute = t => {
+	t.start("addRoute()");
+
+	const fn1 = () => {};
+
+	t.test("daily usage examples", () => {
+		assert.deepEqual(
+			addRoute({}, "GET", "/home", fn1),
+			{ static: { GET: { home: { "": fn1 }}}},
+		);
+
+		assert.deepEqual(
+			addRoute({}, ["PUT", "POST", "PATCH"], "/api/user", fn1),
+			{
+				static: {
+					PUT:   { api: { user: { "": fn1 }}},
+					POST:  { api: { user: { "": fn1 }}},
+					PATCH: { api: { user: { "": fn1 }}},
+				},
+			},
+		);
+
+		assert.deepEqual(
+			addRoute({}, "*", "/settings", fn1),
+			{
+				static: {
+					GET:     { settings: { "": fn1 }},
+					HEAD:    { settings: { "": fn1 }},
+					POST:    { settings: { "": fn1 }},
+					PUT:     { settings: { "": fn1 }},
+					PATCH:   { settings: { "": fn1 }},
+					DELETE:  { settings: { "": fn1 }},
+					OPTIONS: { settings: { "": fn1 }},
+				},
+			},
+		);
+
+		assert.deepEqual(
+			addRoute({}, "GET", "/", fn1),
+			{ static: { GET: { "": fn1 }}},
+		);
+
+		assert.deepEqual(
+			addRoute({}, "GET", "/api/user/:id", fn1),
+			{ dynamic: { GET: { api: { user: { ":id": { "": fn1 }}}}}},
+		);
+
+		assert.deepEqual(
+			addRoute({}, ["PUT", "PATCH"], "/api/org/:orgid/member/:memberid", fn1),
+			{
+				dynamic: {
+					PUT:   { api: { org: { ":orgid": { member: { ":memberid": { "": fn1 }}}}}},
+					PATCH: { api: { org: { ":orgid": { member: { ":memberid": { "": fn1 }}}}}},
+				},
+			},
+		);
+	});
+
+	t.test("bad method", () => {
+		assert.throws(
+			() => addRoute({}, "VERB", "/path", fn1),
+			assert.AssertionError,
+		);
+	});
+
+	t.test("empty methods array", () => {
+		assert.deepEqual(addRoute({}, [], "", fn1), {});
+	});
+
+	t.test("subpaths", () => {
+		const fn1 = () => {};
+		const fn2 = () => {};
+
+		const t1 = addRoute({}, "GET", "/home",         fn1);
+		const t2 = addRoute(t1, "GET", "/home/details", fn2);
+		assert.deepEqual(
+			t2,
+			{
+				static: {
+					GET: {
+						home: {
+							"": fn1,
+							details: {
+								"": fn2,
+							},
+						},
+					},
+				},
+			},
+		);
+	});
+};
+
+const test_buildRoutes = t => {
+	t.start("buildRoutes()");
+
+	t.test("empty values", () => {
+		assert.deepEqual(buildRoutes([]), {});
+	});
+
+	t.test("overwrites", () => {
+		const fn1 = () => {};
+		const fn2 = () => {};
+
+		const r1 = [ [ "GET", "/", fn1 ] ];
+		const r2 = [ [ "GET", "/", fn2 ] ];
+
+		assert.deepEqual(
+			buildRoutes(r1),
+			{
+				static: {
+					GET: {
+						"": fn1,
+					},
+				},
+			},
+		);
+
+		assert.deepEqual(
+			buildRoutes(r2),
+			{
+				static: {
+					GET: {
+						"": fn2,
+					},
+				},
+			},
+		);
+
+		assert.deepEqual(
+			buildRoutes(r1.concat(r2)),
+			buildRoutes(r2),
+		);
+
+		assert.deepEqual(
+			buildRoutes(r2.concat(r1)),
+			buildRoutes(r1),
+		);
+	});
+
+	t.test("multiple routes built", () => {
+		const fn1 = () => {};
+		const fn2 = () => {};
+		const fn3 = () => {};
+		const fn4 = () => {};
+		const fn5 = () => {};
+
+		const routes = [
+			[ "GET",  "/",         fn1 ],
+			[ "GET",  "/home",     fn2 ],
+			[ "GET",  "/user",     fn3 ],
+			[ "POST", "/user",     fn4 ],
+			[ "GET",  "/user/:id", fn5 ],
+		];
+
+		assert.deepEqual(
+			buildRoutes(routes),
+			{
+				static: {
+					GET: {
+						"": fn1,
+						home: {
+							"": fn2,
+						},
+						user: {
+							"": fn3,
+						},
+					},
+					POST: {
+						user: {
+							"": fn4,
+						},
+					},
+				},
+				dynamic: {
+					GET: {
+						user: {
+							":id": {
+								"": fn5,
+							}
+						}
+					}
+				},
+			},
+		);
+	});
+};
+
+const test_findStaticHandler = t => {
+	t.start("findStaticHandler()");
+
+	t.test("multiple accesses to the same table", () => {
+		const fn1 = () => {};
+		const fn2 = () => {};
+		const fn3 = () => {};
+
+		const table = {
+			static: {
+				GET: {
+					api: {
+						home: { "": fn1 },
+						settings: { "": fn2 },
+					},
+				},
+				POST: {
+					api: {
+						settings: { "": fn3 },
+					},
+				},
+			},
+		};
+
+		assert.deepEqual(
+			findStaticHandler(table, "GET", [ "api", "home", "" ]),
+			{ handlerFn: fn1, params: {} },
+		);
+		assert.deepEqual(
+			findStaticHandler(table, "PUT", [ "api", "home", "" ]),
+			null,
+		);
+
+		assert.deepEqual(
+			findStaticHandler(table, "GET", [ "api", "settings", "" ]),
+			{ handlerFn: fn2, params: {} },
+		);
+		assert.deepEqual(
+			findStaticHandler(table, "POST", [ "api", "settings", "" ]),
+			{ handlerFn: fn3, params: {} },
+		);
+		assert.deepEqual(
+			findStaticHandler(table, "PUT", [ "api", "settings", "" ]),
+			null,
+		);
+
+		assert.deepEqual(
+			findStaticHandler(table, "GET", [ "api", "profile", "" ]),
+			null,
+		);
+
+		assert.deepEqual(
+			findStaticHandler({}, "GET", [ "api", "profile", "" ]),
+			null,
+		);
+	});
+};
+
+const test_firstParamMatch = t => {
+	t.start("firstParamMatch()");
+
+	const params = {};
+	const fn1 = () => {};
+	const fn2 = () => {};
+
+	t.test("we BACKTRACK when searching down routes", () => {
+		const segments = [ "path", "split", "match", "" ];
+
+		const tree = {
+			path: {
+				split: {
+					MISMATCH: {
+						"": fn1,
+					},
+				},
+				":param": {
+					match: {
+						"": fn2,
+					},
+				},
+			},
+		};
+
+		assert.deepEqual(
+			firstParamMatch(tree, segments, params),
+			{ handlerFn: fn2, params: { param: "split" }},
+		);
+	});
+
+	t.test("ambiguous route prefers params at the end", () => {
+		const segments = [ "path", "param1", "param2", "" ];
+
+		const tree1 = {
+			path: {
+				":shallower": {
+					param2: {
+						"": fn2,
+					},
+				},
+			},
+		};
+
+		const tree2 = assocIn(tree1, [ "path", "param1", ":deeper", "" ], fn1);
+
+		assert.deepEqual(
+			firstParamMatch(tree1, segments, params),
+			{ handlerFn: fn2, params: { shallower: "param1" }},
+		);
+
+		assert.deepEqual(
+			firstParamMatch(tree2, segments, params),
+			{ handlerFn: fn1, params: { deeper: "param2" }},
+		);
+	});
+
+	t.test("when 2 params are possible, we pick the first alphabetically", () => {
+		const segments = [ "user", "someId", "" ];
+
+		const tree1 = {
+			user: {
+				":bbb": {
+					"": fn2,
+				},
+			},
+		};
+
+		const tree2 = assocIn(tree1, ["user", ":aaa", ""], fn1);
+
+		assert.deepEqual(
+			firstParamMatch(tree1, segments, params),
+			{ handlerFn: fn2, params: { bbb: "someId" }},
+		);
+
+		assert.deepEqual(
+			firstParamMatch(tree2, segments, params),
+			{ handlerFn: fn1, params: { aaa: "someId" }},
+		);
+	});
+};
+
+const test_findDynamicHandler = t => {
+	t.start("findDynamicHandler()");
+
+	t.test("daily usage cases", () => {
+		const fn1 = () => {};
+		const fn2 = () => {};
+
+		const table = {
+			dynamic: {
+				GET: {
+					users: {
+						"by-id": {
+							":id": { "": fn1 },
+						},
+					},
+				},
+				PUT: {
+					user: {
+						":user-id": {
+							info: { "": fn2 },
+						},
+					},
+				},
+			},
+		};
+
+		assert.deepEqual(
+			findDynamicHandler(table, "GET", [ "users", "by-id", "123", "" ]),
+			{ handlerFn: fn1, params: { "id": "123" }},
+		);
+
+		assert.deepEqual(
+			findDynamicHandler({}, "GET", [ "users", "by-id", "123", "" ]),
+			null,
+		);
+
+		assert.deepEqual(
+			findDynamicHandler({ dynamic: { GET: { "": fn1 }}}, "GET", [ "users", "by-id", "123", "" ]),
+			null,
+		);
+
+		assert.deepEqual(
+			findDynamicHandler(table, "PUT", [ "user", "deadbeef", "info", "" ]),
+			{ handlerFn: fn2, params: { "user-id": "deadbeef" }},
+		);
+	});
+};
+
+const test_findHandler = t => {
+	t.start("findHandler()");
+
+	t.test("mix of static and dynamic routes", () => {
+		const static1  = () => {};
+		const static2  = () => {};
+		const static3  = () => {};
+		const dynamic1 = () => {};
+		const dynamic2 = () => {};
+		const dynamic3 = () => {};
+		const dynamic4 = () => {};
+
+		const table = {
+			static: {
+				GET: {
+					user: {
+						"": static1,
+					},
+					pages: {
+						"": static2,
+						home: {
+							"": static3,
+						},
+					},
+				},
+			},
+			dynamic: {
+				GET: {
+					user: {
+						":id": {
+							"": dynamic1,
+						},
+					},
+				},
+				PUT: {
+					user: {
+						":id": {
+							"": dynamic2,
+							"info": {
+								"": dynamic3,
+							},
+							"preferences": {
+								"": dynamic4,
+							},
+						},
+					},
+				},
+			},
+		};
+
+		assert.deepEqual(
+			findHandler(table, "GET", "/"),
+			null,
+		);
+
+		assert.deepEqual(
+			findHandler(table, "GET", "/user/"),
+			{ handlerFn: static1, params: {} },
+		);
+
+		assert.deepEqual(
+			findHandler(table, "GET", "/pages"),
+			{ handlerFn: static2, params: {} },
+		);
+		assert.deepEqual(
+			findHandler(table, "GET", "/pages/home/"),
+			{ handlerFn: static3, params: {} },
+		);
+
+		assert.deepEqual(
+			findHandler(table, "GET", "/user/some-id"),
+			{ handlerFn: dynamic1, params: { id: "some-id" }},
+		);
+		assert.deepEqual(
+			findHandler(table, "GET", "/user/other-id/info"),
+			null,
+		);
+
+		assert.deepEqual(
+			findHandler(table, "PUT", "/user/other-id/info"),
+			{ handlerFn: dynamic3, params: { id: "other-id" }},
+		);
+		assert.deepEqual(
+			findHandler(table, "PUT", "/user/another-id/preferences"),
+			{ handlerFn: dynamic4, params: { id: "another-id" }},
+		);
+		assert.deepEqual(
+			findHandler(table, "POST", "/user/another-id/preferences"),
+			null,
+		);
+	});
+};
+
+const test_extractQueryParams = t => {
+	t.start("extractQueryParams()");
+
+	t.test("empty values", () => {
+		assert.deepEqual(extractQueryParams(),          {});
+		assert.deepEqual(extractQueryParams(null),      {});
+		assert.deepEqual(extractQueryParams(undefined), {});
+	});
+
+	t.test("we get a flat key-value strings", () => {
+		assert.deepEqual(
+			extractQueryParams("a[]=1&b=text&c=___"),
+			{
+				"a[]": "1",
+				b: "text",
+				c: "___",
+			},
+		);
+	});
+
+	t.test("duplicate values are suppressed, deterministically", () => {
+		assert.deepEqual(extractQueryParams("a=1&a=2&a=3"), { a: "3" });
+		assert.deepEqual(extractQueryParams("a=1&b=2&a=3"), { a: "3", b: "2" });
+	});
+};
+
+const test_handleRequest = t => {
+	t.start("handleRequest()");
+
+	const fn = req => req;
+
+	t.test("request without params", async () => {
+		const table = {
+			static: {
+				GET: {
+					"": fn,
+				},
+			},
+		};
+
+		assert.deepEqual(
+			await handleRequest(table, "GET", "/?q=1"),
+			{
+				params: {
+					path: {},
+					query: {
+						q: "1",
+					},
+				},
+				method: "GET",
+				path: "/",
+				handler: fn,
+			},
+		);
+	});
+
+	t.test("request with params", async () => {
+		const table = {
+			dynamic: {
+				PUT: {
+					api: {
+						user: {
+							":userId": {
+								"": fn,
+							},
+						},
+					},
+				},
+			},
+		};
+
+		assert.deepEqual(
+			await handleRequest(table, "PUT", "/api/user/2222"),
+			{
+				params: {
+					path: {
+						userId: "2222",
+					},
+					query: {},
+				},
+				method: "PUT",
+				path: "/api/user/2222",
+				handler: fn,
+			},
+		);
+	});
+
+	t.test("missing route", async () => {
+		assert.deepEqual(
+			await handleRequest({}, "GET", "/"),
+			{
+				status: 404,
+				body: "Not Found",
+			},
+		);
+	});
+};
+
+const test_makeRequestListener = t => {
+	t.start("makeRequestListener()");
+
+	t.test("straightforward body execution", async () => {
+		const fn = _ => ({
+			status:  "test status",
+			body:    "test body",
+			headers: "test headers",
+		});
+		const routes = [[ "GET", "/route1", fn ]];
+		const requestListener = makeRequestListener(buildRoutes(routes));
+		const req = {
+			method: "GET",
+			url:    "/route1",
+		};
+
+		const heads  = [];
+		const bodies = [];
+		const res = {
+			writeHead: (status, headers) => heads.push({ status, headers }),
+			end: body => bodies.push(body),
+		};
+		await requestListener(req, res);
+
+		assert.deepEqual(
+			heads,
+			[{
+				status:  "test status",
+				headers: "test headers",
+			}],
+		);
+		assert.deepEqual(
+			bodies,
+			[ "test body" ],
+		);
+	});
+
+	t.test("we break if handleRequest() throws an error", async () => {
+		const fn = _ => { throw new Error("handler error"); };
+		const routes = [[ "GET", "/route2", fn ]];
+		const requestListener = makeRequestListener(buildRoutes(routes));
+		const req = {
+			method: "GET",
+			url:    "/route2",
+		};
+
+		const heads  = [];
+		const bodies = [];
+		const res = {
+			writeHead: (status, headers) => heads.push({ status, headers }),
+			end: body => bodies.push(body),
+		};
+
+		await assert.rejects(
+			async () => await requestListener(req, res),
+			{ message: "handler error" },
+		);
+
+		assert.deepEqual(heads,  []);
+		assert.deepEqual(bodies, []);
+	});
+};
+
+const test_interceptorsFn = t => {
+	const next = x => x;
+
+	{
+		t.start("interceptorsFn().requestId()");
+
+		let i = 0;
+		const uuidFn = () => `${i++}`;
+
+		t.test("we add an id to whatever we receive", () => {
+			assert.deepEqual(
+				interceptorsFn({uuidFn}).requestId({}, next),
+				{
+					id: "0",
+				},
+			);
+			assert.deepEqual(
+				interceptorsFn({uuidFn}).requestId({ a: "existing data" }, next),
+				{
+					a: "existing data",
+					id: "1",
+				},
+			);
+		});
+
+		t.test(`we overwrite the "id" if it already exists`, async () => {
+			assert.deepEqual(
+				interceptorsFn({uuidFn}).requestId({ id: "before" }, next),
+				{
+					id: "2",
+				},
+			);
+		});
+	}
+
+	{
+		t.start("interceptorsFn().logged()");
+
+		t.test("we log before and after next()", async () => {
+			const contents = [];
+			const logger = x => contents.push(x);
+			const status = 201;
+			const req = {
+				id: "an ID",
+				url: "a URL",
+				method: "a method",
+			};
+
+			assert.deepEqual(
+				await interceptorsFn({logger}).logged(req, _ => ({ status })),
+				{ status },
+			);
+			assert.deepEqual(
+				contents,
+				[
+					{ ...req, type: "in-request"  },
+					{ id: req.id, status, type: "in-response" },
+				],
+			);
+		});
+	}
+
+	{
+		t.start("interceptorsFn().contentType()");
+
+		t.test("empty values", async () => {
+			assert.deepEqual(
+				await interceptorsFn().contentType({}, next),
+				{
+					body: "",
+					headers: {
+						"Content-Type": "application/json",
+						"Content-Length": 0,
+					},
+				},
+			);
+
+			assert.deepEqual(
+				await interceptorsFn().contentType({ body: "" }, next),
+				{
+					body: "",
+					headers: {
+						"Content-Type": "text/html",
+						"Content-Length": 0,
+					},
+				},
+			);
+		});
+
+		t.test("body values", async () => {
+			assert.deepEqual(
+				await interceptorsFn().contentType({ body: { a: 1 }}, next),
+				{
+					body: `{"a":1}`,
+					headers: {
+						"Content-Type": "application/json",
+						"Content-Length": 7,
+					},
+				},
+			);
+
+			assert.deepEqual(
+				await interceptorsFn().contentType({ body: "<br />" }, next),
+				{
+					body: "<br />",
+					headers: {
+						"Content-Type": "text/html",
+						"Content-Length": 6,
+					},
+				},
+			);
+		});
+
+		t.test("header values preference", async () => {
+			assert.deepEqual(
+				await interceptorsFn().contentType({
+					body: "",
+					headers: {
+						"Content-Type": "we have preference",
+						"Content-Length": "and so do we",
+					},
+				}, next),
+				{
+					body: "",
+					headers: {
+						"Content-Type": "we have preference",
+						"Content-Length": "and so do we",
+					},
+				}
+			);
+		});
+
+		t.test("headers get propagated", async () => {
+			assert.deepEqual(
+				await interceptorsFn().contentType({
+					body: "",
+					headers: {
+						"My": "Header",
+					},
+				}, next),
+				{
+					body: "",
+					headers: {
+						"My": "Header",
+						"Content-Type": "text/html",
+						"Content-Length": 0,
+					},
+				},
+			);
+		});
+	}
+
+	{
+		t.start("interceptorsFn().serverError()");
+
+		t.test("no-op when no error occurs", async () => {
+			assert.deepEqual(
+				await interceptorsFn().serverError({ status: 1 }, next),
+				{ status: 1 },
+			);
+		});
+
+		t.test(`an error is thrown if "status" is missing`, async () => {
+			const contents = [];
+			const logger = x => contents.push(x);
+			assert.deepEqual(
+				await interceptorsFn({ logger }).serverError({ id: 123 }, next),
+				{
+					status: 500,
+					body: "Internal Server Error",
+				},
+			);
+			assert.deepEqual(
+				contents,
+				[{
+					id: 123,
+					type: "server-error-interceptor",
+					message: `Missing "status"`,
+				}],
+			);
+		});
+
+		t.test("we turn a handler error into a 500 response", async () => {
+			const contents = [];
+			const logger = x => contents.push(x);
+			assert.deepEqual(
+				await interceptorsFn({ logger }).serverError(
+					{ id: "some ID" },
+					_ => { throw new Error("My test error message"); },
+				),
+				{
+					status: 500,
+					body: "Internal Server Error",
+				},
+			);
+			assert.deepEqual(
+				contents,
+				[{
+					id: "some ID",
+					type: "server-error-interceptor",
+					message: "My test error message",
+				}],
+			);
+		});
+	}
+};
+
+const test_chainInterceptors = t => {
+	t.start("chainInterceptors()");
+
+	t.test("empty values", () => {
+		assert.equal(chainInterceptors([])("req"), "req");
+	});
+
+	t.test("the order of interceptors matter", () => {
+		const a = [];
+
+		const i1 = (req, next) => {
+			a.push("i1");
+			return next(req);
+		};
+		const i2 = (req, next) => {
+			a.push("i2");
+			return next(req);
+		};
+
+		assert.equal(chainInterceptors([i1, i2])("req"), "req");
+		assert.deepEqual(a, ["i1", "i2"]);
+		assert.equal(chainInterceptors([i2, i1])("req"), "req");
+		assert.deepEqual(a, ["i1", "i2", "i2", "i1"]);
+	});
+
+	t.test("with ordering, interceptors implicitly depend on each other", () => {
+		const i1 = (req, next) => next({ ...req, id: 1 });
+		const i2 = (req, next) => next({ ...req, id: req.id + 1 });
+
+		assert.deepEqual(
+			chainInterceptors([i1, i2])({}),
+			{ id: 2 },
+		);
+
+		assert.deepEqual(
+			chainInterceptors([i2])({}),
+			{ id: NaN },
+		);
+
+		assert.deepEqual(
+			chainInterceptors([i2, i1])({}),
+			{ id: 1 },
+		);
+	});
+
+	t.test("we can chain async interceptors", async () => {
+		const i1 = async (req, next) => await next({ ...req, i1: true });
+		const i2 = async (req, next) => await next({ ...req, i2: true });
+
+		assert.deepEqual(
+			await chainInterceptors([i1, i2])({}),
+			{
+				i1: true,
+				i2: true,
+			},
+		);
+	});
+};
+
+const test_wrapHandler = t => {
+	t.start("wrapHandler()");
+
+	t.test("a handler with chained interceptors change its behaviour", async () => {
+		let i = 0;
+		const uuidFn = () => `${i++}`;
+
+		const contents = [];
+		const logger = x => contents.push(x);
+
+		const interceptors = interceptorsFn({uuidFn, logger});
+
+		const fn = async _ => await { status: 1, body: { a: 1 }};
+		const wrappedFn = wrapHandler(fn, [
+			interceptors.requestId,
+			interceptors.logged,
+			interceptors.contentType,
+		]);
+
+		const req = {
+			url:    "URL",
+			method: "METHOD",
+		};
+
+		assert.deepEqual(
+			await fn(req),
+			{ status: 1, body: { a: 1 }},
+		);
+		assert.deepEqual(contents, []);
+
+		assert.deepEqual(
+			await wrappedFn(req),
+			{
+				status: 1,
+				body: `{"a":1}`,
+				headers: {
+					"Content-Type": "application/json",
+					"Content-Length": 7,
+				},
+			},
+		);
+		assert.deepEqual(
+			contents,
+			[
+				{
+					id:     "0",
+					url:    "URL",
+					method: "METHOD",
+					type:   "in-request",
+				},
+				{
+					id:    "0",
+					status: 1,
+					type:   "in-response",
+				},
+			],
+		);
+	});
+};
+
+
+await runTests([
+	test_normalizeSegments,
+	test_pathToSegments,
+	test_hasPathParams,
+	test_addRoute,
+	test_buildRoutes,
+	test_findStaticHandler,
+	test_firstParamMatch,
+	test_findDynamicHandler,
+	test_findHandler,
+	test_extractQueryParams,
+	test_handleRequest,
+	test_makeRequestListener,
+	test_interceptorsFn,
+	test_chainInterceptors,
+	test_wrapHandler,
+]);
diff --git a/tests/js/ircd.js b/tests/js/ircd.js
deleted file mode 100644
index 08bb6dc..0000000
--- a/tests/js/ircd.js
+++ /dev/null
@@ -1,7 +0,0 @@
-const { runTests } = require("../runner.js");
-const { } = require("../../src/ircd.js");
-
-const tests = [
-];
-
-runTests(tests);
diff --git a/tests/js/ircd.mjs b/tests/js/ircd.mjs
new file mode 100644
index 0000000..e5eda66
--- /dev/null
+++ b/tests/js/ircd.mjs
@@ -0,0 +1,7 @@
+import { runTests } from "../runner.mjs";
+import { } from "../../src/ircd.mjs";
+
+
+
+await runTests([
+]);
diff --git a/tests/js/utils.js b/tests/js/utils.js
deleted file mode 100644
index 670d89a..0000000
--- a/tests/js/utils.js
+++ /dev/null
@@ -1,130 +0,0 @@
-const assert = require("node:assert");
-
-const { runTests } = require("../runner.js");
-const { eq, keys } = require("../../src/utils.js");
-
-const test_eq = t => {
-	t.start("eq()");
-	t.test("scalar values equality", () => {
-		assert(eq(0, 0));
-		assert(eq(100, 100));
-		assert(eq(1.5, 1.5));
-		assert(eq(-9, -9));
-
-		assert(!eq(0, 1));
-		assert(!eq(100, 99));
-		assert(!eq(1.5, 1.4));
-		assert(!eq(-9, 9));
-
-
-		assert(eq(null, null));
-		assert(eq(undefined, undefined));
-		assert(eq("", ""));
-		assert(eq("a string", "a string"));
-
-		assert(!eq(null, undefined));
-		assert(!eq(undefined, 0));
-		assert(!eq("", "0"));
-		assert(!eq("a string", "another string"));
-
-
-		assert(eq(true, true));
-		assert(eq(false, false));
-
-		assert(!eq(true, false));
-
-
-		assert(eq(1n, 1n));
-		assert(eq(99999999999999n, 99999999999999n));
-	});
-
-	t.test("array equality", () => {
-		assert(eq([], []));
-
-
-		assert(eq([0, 1, 2], [0, 1, 2]));
-		assert(eq([0, 1, 2], new Array(0, 1, 2)));
-
-		assert(!eq([0, 1, 2], [0, 1]));
-		assert(!eq([0, 1], new Array(0, 1, 2)));
-
-
-		assert(eq([undefined], [undefined]));
-		assert(eq([null, 0, "", true], [null, 0, "", true]));
-
-
-		assert(eq([[[[0]]]], [[[[0]]]]));
-
-		assert(!eq([[[[0]]]], [0]));
-	});
-
-	t.test("object equality", () => {
-		assert(eq({}, {}));
-		assert(eq({ a: 1 }, { a: 1 }));
-
-		assert(!eq({ a: 1, b: undefined }, { a: 1 }));
-
-
-		assert(eq(
-			{ a: 1, b: { c: { d: "e" } } },
-			{ a: 1, b: { c: { d: "e" } } },
-		));
-
-		class C {}
-		// ... FIXME: finish
-	});
-
-	t.test("mixed values", () => {
-		assert(eq(
-			{a: ["", 1, 2, 3, [{ b: { c: [ "d", "e" ]}}]]},
-			{a: ["", 1, 2, 3, [{ b: { c: [ "d", "e" ]}}]]},
-		));
-
-		assert(!eq(null, {}));
-
-		assert(!eq([], {}));
-	});
-};
-
-const test_keys = t => {
-	t.start("keys()");
-	t.test("happy paths", () => {
-		assert.deepEqual(
-			{ a: 1, b: 2 },
-			keys(["a", "b"], { a: 1, b: 2, c: 3 }),
-		);
-	});
-
-	t.test("stress scenarios", () => {
-		assert.deepEqual(
-			{},
-			keys([], {}),
-			"empty selection of empty object",
-		);
-
-		assert.deepEqual(
-			{},
-			keys([], {a: 1}),
-			"empty selection of non-empty object",
-		);
-
-		assert.deepEqual(
-			{},
-			keys(["a"], {}),
-			"non-empty selection of empty object",
-		);
-
-		assert.deepEqual(
-			{ a: undefined, b: null },
-			keys(["a", "b", "c"], { a: undefined, b: null }),
-			"falsy values",
-		);
-	});
-};
-
-const tests = [
-	test_eq,
-	test_keys,
-];
-
-runTests(tests);
diff --git a/tests/js/utils.mjs b/tests/js/utils.mjs
new file mode 100644
index 0000000..1875ce5
--- /dev/null
+++ b/tests/js/utils.mjs
@@ -0,0 +1,225 @@
+import assert from "node:assert/strict";
+
+import { runTests } from "../runner.mjs";
+import {
+	eq,
+	keys,
+	assocIn,
+	getIn,
+	first,
+	log,
+} from "../../src/utils.mjs";
+
+const test_eq = t => {
+	t.start("eq()");
+	t.test("scalar values equality", () => {
+		assert(eq(0, 0));
+		assert(eq(100, 100));
+		assert(eq(1.5, 1.5));
+		assert(eq(-9, -9));
+
+		assert(!eq(0, 1));
+		assert(!eq(100, 99));
+		assert(!eq(1.5, 1.4));
+		assert(!eq(-9, 9));
+
+
+		assert(eq(null, null));
+		assert(eq(undefined, undefined));
+		assert(eq("", ""));
+		assert(eq("a string", "a string"));
+
+		assert(!eq(null, undefined));
+		assert(!eq(undefined, 0));
+		assert(!eq("", "0"));
+		assert(!eq("a string", "another string"));
+
+
+		assert(eq(true, true));
+		assert(eq(false, false));
+
+		assert(!eq(true, false));
+
+
+		assert(eq(1n, 1n));
+		assert(eq(99999999999999n, 99999999999999n));
+	});
+
+	t.test("array equality", () => {
+		assert(eq([], []));
+
+
+		assert(eq([0, 1, 2], [0, 1, 2]));
+		assert(eq([0, 1, 2], new Array(0, 1, 2)));
+
+		assert(!eq([0, 1, 2], [0, 1]));
+		assert(!eq([0, 1], new Array(0, 1, 2)));
+
+
+		assert(eq([undefined], [undefined]));
+		assert(eq([null, 0, "", true], [null, 0, "", true]));
+
+
+		assert(eq([[[[0]]]], [[[[0]]]]));
+
+		assert(!eq([[[[0]]]], [0]));
+	});
+
+	t.test("object equality", () => {
+		assert(eq({}, {}));
+		assert(eq({ a: 1 }, { a: 1 }));
+
+		assert(!eq({ a: 1, b: undefined }, { a: 1 }));
+
+
+		assert(eq(
+			{ a: 1, b: { c: { d: "e" } } },
+			{ a: 1, b: { c: { d: "e" } } },
+		));
+	});
+
+	t.test("mixed values", () => {
+		assert(eq(
+			{a: ["", 1, 2, 3, [{ b: { c: [ "d", "e" ]}}]]},
+			{a: ["", 1, 2, 3, [{ b: { c: [ "d", "e" ]}}]]},
+		));
+
+		assert(!eq(null, {}));
+
+		assert(!eq([], {}));
+	});
+};
+
+const test_keys = t => {
+	t.start("keys()");
+	t.test("happy paths", () => {
+		assert.deepEqual(
+			{ a: 1, b: 2 },
+			keys(["a", "b"], { a: 1, b: 2, c: 3 }),
+		);
+	});
+
+	t.test("stress scenarios", () => {
+		assert.deepEqual(
+			{},
+			keys([], {}),
+			"empty selection of empty object",
+		);
+
+		assert.deepEqual(
+			{},
+			keys([], {a: 1}),
+			"empty selection of non-empty object",
+		);
+
+		assert.deepEqual(
+			{},
+			keys(["a"], {}),
+			"non-empty selection of empty object",
+		);
+
+		assert.deepEqual(
+			{ a: undefined, b: null },
+			keys(["a", "b", "c"], { a: undefined, b: null }),
+			"falsy values",
+		);
+	});
+};
+
+const test_assocIn = t => {
+	t.start("assocIn()");
+
+	t.test("empty values", () => {
+		assert.deepEqual(assocIn({}, [], null), {});
+		assert.deepEqual(assocIn({ k: "v" }, [], null), { k: "v" });
+	});
+
+	t.test("adding values", () => {
+		assert.deepEqual(assocIn({}, ["k"], "v"), { k: "v" });
+		assert.deepEqual(assocIn({}, ["k1", "k2"], "v"), { k1: { k2: "v" }});
+		assert.deepEqual(assocIn({}, ["k1", "k2", "k3"], "v"), { k1: { k2: { k3: "v" }}});
+		assert.deepEqual(assocIn({ k: "v" }, ["k1", "k2"], "v"), { k: "v",  k1: { k2: "v" }});
+	});
+
+	t.test("replacing values", () => {
+		assert.deepEqual(
+			assocIn(
+				{ k1: { k2: { k3: "before" }}},
+				["k1", "k2", "k3"],
+				"after"
+			),
+			{ k1: { k2: { k3: "after" }}}
+		);
+	});
+};
+
+const test_getIn = t => {
+	t.start("getIn()");
+
+	t.test("empty values", () => {
+		assert.deepEqual(getIn({}, []), {});
+		assert.deepEqual(getIn({ k: "v" }, []), { k: "v" });
+	});
+
+	t.test("missing values", () => {
+		assert.deepEqual(getIn({}, ["a", "b", "c"]), undefined);
+		assert.deepEqual(getIn({ a: {}}, ["a", "b", "c"]), undefined);
+		assert.deepEqual(getIn({ a: { b: {}}}, ["a", "b", "c"]), undefined);
+		assert.deepEqual(getIn({ a: { b: {}, c: {}}}, ["a", "b", "c"]), undefined);
+	});
+
+	t.test("nested valeues", () => {
+		assert.deepEqual(getIn({ a: { b: { c: { d: "e" }}}}, ["a", "b", "c", "d"]), "e");
+	});
+};
+
+const test_first = t => {
+	t.start("first()");
+
+	t.test("empty values", () => {
+		assert.equal(first([], () => {}), null);
+	});
+
+	t.test("when function doesn't transform, it behaves similarly to [].find()", () => {
+		const arr1 = [ 0, null, undefined, "", 1, 2 ];
+		assert.equal(first(arr1, x => x), 1);
+		assert.equal(arr1.find(x => x),   1);
+
+		const arr2 = [ 0, null, undefined, "", false ];
+		assert.equal(first(arr2, x => x), null);
+		assert.equal(arr2.find(x => x),   undefined);
+	});
+
+	t.test("when it does transform, we return the transformed value", () => {
+		const arr = [ 1, 3, 5, 6 ];
+
+		assert.equal(
+			first(arr, x => x % 2 === 0 && "a brand new value"),
+			"a brand new value",
+		);
+	});
+};
+
+const test_log = t => {
+	t.start("log()");
+
+        t.test("we can log data", () => {
+		log({ a: 1, type: "log-test" });
+	});
+
+	t.test("we can't log unserializable things", () => {
+		const obj = { self: null };
+		obj.self = obj;
+		assert.throws(() => log(obj), TypeError);
+	});
+};
+
+
+await runTests([
+	test_eq,
+	test_keys,
+	test_assocIn,
+	test_getIn,
+	test_first,
+	test_log,
+]);
diff --git a/tests/js/web.js b/tests/js/web.js
deleted file mode 100644
index 6562433..0000000
--- a/tests/js/web.js
+++ /dev/null
@@ -1,7 +0,0 @@
-const { runTests } = require("../runner.js");
-const { } = require("../../src/web.js");
-
-const tests = [
-];
-
-runTests(tests);
diff --git a/tests/js/web.mjs b/tests/js/web.mjs
new file mode 100644
index 0000000..00cce70
--- /dev/null
+++ b/tests/js/web.mjs
@@ -0,0 +1,7 @@
+import { runTests } from "../runner.mjs";
+import { } from "../../src/web.mjs";
+
+
+
+await runTests([
+]);
diff --git a/tests/runner.js b/tests/runner.mjs
index 4772a28..79bda8c 100644
--- a/tests/runner.js
+++ b/tests/runner.mjs
@@ -1,4 +1,4 @@
-const { eq } = require("../src/utils.js");
+import { eq } from "../src/utils.mjs";
 
 class AssertionError extends Error {}
 
@@ -25,12 +25,8 @@ const t = {
 	},
 };
 
-const runTests = async tests => {
+export const runTests = async tests => {
 	for (const testFn of tests) {
 		await testFn(t);
 	}
 };
-
-module.exports = {
-	runTests,
-};