서버, 클라이언트, 서비스 워커 공용 코드를 lib/shared로 분리하고 브라우저 전용 모듈을 lib/client로 재구성

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/unit/range.test.ts

@@ -1,7 +1,13 @@
 import { describe, expect, it } from "vitest";
-import { CHUNK_SIZE, ENCRYPTED_CHUNK_SIZE, ENCRYPTION_OVERHEAD } from "#lib/constants/index.js";
-import { getContentRangeHeader, parseRangeHeader } from "#lib/modules/http.js";
-import { getDecryptedSize, getEncryptedRange } from "../../src/service-worker/modules/crypto";
+import {
+  CHUNK_SIZE,
+  ENCRYPTED_CHUNK_SIZE,
+  ENCRYPTION_OVERHEAD,
+  getDecryptedSize,
+  getEncryptedRange,
+  getEncryptedSize,
+} from "#lib/shared/format/index.js";
+import { getContentRangeHeader, parseRangeHeader, resolveRange } from "#lib/shared/http.js";
 
 describe("parseRangeHeader", () => {
   it("parses byte ranges", () => {
@@ -9,6 +15,33 @@ describe("parseRangeHeader", () => {
     expect(parseRangeHeader("bytes=0-")).toEqual({ start: 0, end: undefined });
     expect(parseRangeHeader("bytes=10-20")).toEqual({ start: 10, end: 20 });
     expect(parseRangeHeader("bytes=10-20, 30-40")).toEqual({ start: 10, end: 20 });
+    expect(parseRangeHeader("bytes=-500")).toEqual({ suffixLength: 500 });
+  });
+
+  it("ignores invalid ranges", () => {
+    expect(parseRangeHeader("bytes=-")).toBeUndefined();
+    expect(parseRangeHeader("items=0-1")).toBeUndefined();
+  });
+});
+
+describe("resolveRange", () => {
+  it("resolves the whole content without a range", () => {
+    expect(resolveRange(undefined, 100)).toEqual({ start: 0, end: 99, total: 100 });
+  });
+
+  it("clamps the end to the content size", () => {
+    expect(resolveRange({ start: 10, end: 1000 }, 100)).toEqual({ start: 10, end: 99, total: 100 });
+    expect(resolveRange({ start: 10 }, 100)).toEqual({ start: 10, end: 99, total: 100 });
+  });
+
+  it("resolves suffix ranges", () => {
+    expect(resolveRange({ suffixLength: 10 }, 100)).toEqual({ start: 90, end: 99, total: 100 });
+    expect(resolveRange({ suffixLength: 1000 }, 100)).toEqual({ start: 0, end: 99, total: 100 });
+  });
+
+  it("rejects unsatisfiable ranges", () => {
+    expect(resolveRange({ start: 100 }, 100)).toBeNull();
+    expect(resolveRange({ start: 20, end: 10 }, 100)).toBeNull();
   });
 
   it("formats Content-Range", () => {
@@ -19,13 +52,13 @@ describe("parseRangeHeader", () => {
 });
 
 describe("encrypted chunk layout", () => {
-  const encryptedSizeOf = (size: number) =>
-    size + Math.ceil(size / CHUNK_SIZE) * ENCRYPTION_OVERHEAD;
-
   it.each([1, CHUNK_SIZE - 1, CHUNK_SIZE, CHUNK_SIZE + 1, 3 * CHUNK_SIZE + 12345])(
     "computes the decrypted size of %i bytes",
     (size) => {
-      expect(getDecryptedSize(encryptedSizeOf(size), false)).toBe(size);
+      expect(getEncryptedSize(size)).toBe(
+        size + Math.ceil(size / CHUNK_SIZE) * ENCRYPTION_OVERHEAD,
+      );
+      expect(getDecryptedSize(getEncryptedSize(size), false)).toBe(size);
     },
   );
 
@@ -35,7 +68,7 @@ describe("encrypted chunk layout", () => {
 
   it("maps a plaintext range to whole encrypted chunks", () => {
     const totalSize = 3 * CHUNK_SIZE + 100;
-    const totalEncryptedSize = encryptedSizeOf(totalSize);
+    const totalEncryptedSize = getEncryptedSize(totalSize);
 
     expect(getEncryptedRange(0, 10, totalEncryptedSize, false)).toEqual({
       firstChunkIndex: 0,