src/hero.mjs: Add makeLineEmitter()

2 files changed, 100 insertions, 0 deletions

diff --git a/src/hero.mjs b/src/hero.mjs
index 6b6fa77..8cbbe36 100644
--- a/src/hero.mjs
+++ b/src/hero.mjs
@@ -338,6 +338,25 @@ export const rmIf = path => {
 export const mkfifo = path =>
 	child_process.execFileSync("mkfifo", [path]);
 
+export const makeLineEmitter = fn => {
+	let data = "";
+	return chunk => {
+		const segments = chunk.split("\n");
+		assert.ok(segments.length > 0);
+
+		if (segments.length === 1) {
+			data += segments[0];
+			return;
+		}
+
+		[
+			data + u.first(segments),
+			...u.butlast(u.rest(segments)),
+		].forEach(fn);
+		data = u.last(segments);
+	};
+};
+
 export const buildRoutes = (routes, globalInterceptors = []) =>
 	routes.reduce(
 		(acc, [methods, path, handlerFn, interceptors = []]) =>
diff --git a/tests/js/hero.mjs b/tests/js/hero.mjs
index ebb2c27..1debdc5 100644
--- a/tests/js/hero.mjs
+++ b/tests/js/hero.mjs
@@ -32,6 +32,7 @@ import {
 	lineHandlerFn,
 	rmIf,
 	mkfifo,
+	makeLineEmitter,
 	buildRoutes,
 	promisifyServer,
 	buildServer,
@@ -1289,6 +1290,85 @@ const test_mkfifo = async t => {
 	});
 };
 
+const test_makeLineEmitter = async t => {
+	t.start("makeLineEmitter()");
+
+	await t.test("noop when we only get empty strings", async () => {
+		const entries = [];
+		const record  = x => entries.push(x);
+		const emitter = makeLineEmitter(record);
+
+		emitter("");
+		emitter("");
+		emitter("");
+		emitter("");
+		emitter("");
+
+		assert.deepEqual(entries, []);
+	});
+
+	await t.test("empty strings when we only get newlines", async () => {
+		const entries = [];
+		const record  = x => entries.push(x);
+		const emitter = makeLineEmitter(record);
+
+		emitter("\n\n\n");
+		emitter("\n\n");
+		emitter("\n");
+
+		assert.deepEqual(entries, [ "", "", "", "", "", "" ]);
+	});
+
+	await t.test("noop also if we never get a newline", async () => {
+		const entries = [];
+		const record  = x => entries.push(x);
+		const emitter = makeLineEmitter(record);
+
+		emitter(" ");
+		emitter("some string");
+		emitter("     ");
+		emitter("a lot of text");
+		assert.deepEqual(entries, []);
+
+		emitter("\n");
+		assert.deepEqual(entries, [ " some string     a lot of text" ]);
+	});
+
+	await t.test("if a newline always comes, we always emit", async () => {
+		const entries = [];
+		const record  = x => entries.push(x);
+		const emitter = makeLineEmitter(record);
+
+		emitter("first\n");
+		emitter("second\n");
+		emitter("third\n");
+
+		assert.deepEqual(entries, [ "first", "second", "third" ]);
+	});
+
+	await t.test("lines can acummulate accross multiple writes", async () => {
+		const entries = [];
+		const record  = x => entries.push(x);
+		const emitter = makeLineEmitter(record);
+
+		emitter("fir");
+		emitter("s");
+		emitter("t\ns");
+		emitter("econd\nthir");
+		emitter("d");
+		emitter("\n");
+		emitter("fourth\nfifth\nsixth");
+
+		assert.deepEqual(entries, [
+			"first",
+			"second",
+			"third",
+			"fourth",
+			"fifth",
+		]);
+	});
+};
+
 const test_buildRoutes = async t => {
 	t.start("buildRoutes()");
 
@@ -1523,6 +1603,7 @@ await runner.runTests([
 	test_buildRoutes,
 	test_rmIf,
 	test_mkfifo,
+	test_makeLineEmitter,
 	test_promisifyServer,
 	test_buildServer,
 ]);