test: createUTF8Stream

Author: effigies

src/files/streams.test.ts

@@ -0,0 +1,45 @@
+import { assert, assertEquals } from '@std/assert'
+import { createUTF8Stream, UnicodeDecodeError } from './streams.ts'
+
+function streamFromUint8Array(arr: Uint8Array): ReadableStream<Uint8Array> {
+  return new ReadableStream({
+    start(controller) {
+      controller.enqueue(arr)
+      controller.close()
+    },
+  })
+}
+
+Deno.test('createUTF8Stream', async (t) => {
+  await t.step('should return a TransformStream with UTF8StreamTransformer', () => {
+    const stream = createUTF8Stream()
+    assertEquals(stream instanceof TransformStream, true)
+  })
+
+  await t.step('should correctly transform UTF-8 input', async () => {
+    const rawstream = streamFromUint8Array(new TextEncoder().encode('Hello, world!'))
+    const reader = rawstream.pipeThrough(createUTF8Stream()).getReader()
+    const { value } = await reader.read()
+    assertEquals(value, 'Hello, world!')
+
+    await reader.cancel()
+  })
+
+  await t.step('should throw UnicodeDecodeError for UTF-16 input', async () => {
+    const rawStream = streamFromUint8Array(new Uint8Array([0xFF, 0xFE, 0x00, 0x00]))
+
+    let reader
+    try {
+      // The exception can't be localized to either of the following lines
+      // but is raised before the second returns
+      reader = rawStream.pipeThrough(createUTF8Stream()).getReader()
+      const { value } = await reader.read()
+      assert(false, 'Expected UnicodeDecodeError, got ' + value)
+    } catch (e: any) {
+      assertEquals(e instanceof UnicodeDecodeError, true)
+      assertEquals(e?.message, 'This file appears to be UTF-16')
+    } finally {
+      if (reader) await reader.cancel
+    }
+  })
+})