Initial import from garrytan/gstack@026751e (main snapshot via local relay)

Source: https://github.com/garrytan/gstack/commit/026751e

browse/test/server-sanitize-surrogates.test.ts

@@ -0,0 +1,129 @@
+import { describe, test, expect } from 'bun:test';
+import * as fs from 'fs';
+import * as path from 'path';
+
+// The sanitizer is module-private in server.ts. Rather than refactor it to a
+// separate module just for testing, we extract its source via a regex slice and
+// eval it in a fresh function scope. Keeps the production layout untouched.
+const SERVER_PATH = path.resolve(import.meta.dir, '..', 'src', 'server.ts');
+const SERVER_SRC = fs.readFileSync(SERVER_PATH, 'utf-8');
+
+const fnMatch = SERVER_SRC.match(
+  /function sanitizeLoneSurrogates\(str: string\): string \{[\s\S]*?\n\}/
+);
+if (!fnMatch) throw new Error('Could not locate sanitizeLoneSurrogates in server.ts');
+
+// Strip TS annotations so eval works under plain JS.
+const jsSrc = fnMatch[0].replace('(str: string): string', '(str)');
+const sanitizeLoneSurrogates = new Function(`${jsSrc}\nreturn sanitizeLoneSurrogates;`)() as (
+  s: string,
+) => string;
+
+describe('sanitizeLoneSurrogates — unit cases', () => {
+  test('passthrough ASCII', () => {
+    expect(sanitizeLoneSurrogates('hello')).toBe('hello');
+  });
+
+  test('passthrough empty string', () => {
+    expect(sanitizeLoneSurrogates('')).toBe('');
+  });
+
+  test('preserves valid surrogate pair (U+1F389 🎉)', () => {
+    expect(sanitizeLoneSurrogates('hi 🎉')).toBe('hi 🎉');
+  });
+
+  test('replaces lone high surrogate mid-string', () => {
+    expect(sanitizeLoneSurrogates('a\uD800b')).toBe('a<>b');
+  });
+
+  test('replaces lone low surrogate mid-string', () => {
+    expect(sanitizeLoneSurrogates('a\uDC00b')).toBe('a<>b');
+  });
+
+  test('replaces trailing lone high at end of string', () => {
+    expect(sanitizeLoneSurrogates('a\uD800')).toBe('a<>');
+  });
+
+  test('replaces leading lone low at start of string', () => {
+    expect(sanitizeLoneSurrogates('\uDC00b')).toBe('<27>b');
+  });
+
+  test('replaces two adjacent lone highs', () => {
+    expect(sanitizeLoneSurrogates('\uD800\uD800')).toBe('<27><>');
+  });
+
+  test('replaces two adjacent lone lows', () => {
+    expect(sanitizeLoneSurrogates('\uDC00\uDC00')).toBe('<27><>');
+  });
+
+  test('preserves valid pair followed by lone low', () => {
+    // 𐀀 = U+10000 = 𐀀, then a separate lone low.
+    const input = '𐀀\uDC00';
+    const output = sanitizeLoneSurrogates(input);
+    // Valid pair intact, trailing lone low replaced.
+    expect(output).toBe('𐀀<>');
+  });
+
+  test('preserves valid pair preceded by lone low', () => {
+    const input = '\uDC00𐀀';
+    const output = sanitizeLoneSurrogates(input);
+    expect(output).toBe('<27>𐀀');
+  });
+});
+
+describe('sanitizeLoneSurrogates — bug-repro (D5)', () => {
+  // Pin the regression intent: a future refactor that drops sanitization
+  // must fail this test even if happy-path tests still pass.
+  test('unsanitized lone surrogate causes UTF-8 encode to substitute, sanitized version is stable', () => {
+    const badPayload = 'page content\uD800more content';
+
+    // Buffer.from(str, 'utf-8') silently substitutes invalid sequences with
+    // EF BF BD (U+FFFD). Round-trip is therefore lossy for lone surrogates.
+    const roundTrippedRaw = Buffer.from(badPayload, 'utf-8').toString('utf-8');
+    expect(roundTrippedRaw).not.toBe(badPayload); // proves the bug exists pre-sanitize
+
+    // After sanitization the round-trip is stable.
+    const sanitized = sanitizeLoneSurrogates(badPayload);
+    const roundTrippedSanitized = Buffer.from(sanitized, 'utf-8').toString('utf-8');
+    expect(roundTrippedSanitized).toBe(sanitized);
+  });
+
+  test('JSON.parse(JSON.stringify(...)) round-trip is stable after sanitization', () => {
+    // Anthropic's API path wraps the response body in a tool_result JSON
+    // object. JSON.stringify CAN encode a lone surrogate (escapes it), but
+    // some downstream consumers reject the resulting body.
+    const badPayload = 'before\uD800after';
+    const sanitized = sanitizeLoneSurrogates(badPayload);
+    const wrapped = JSON.stringify({ content: sanitized });
+    const reparsed = JSON.parse(wrapped) as { content: string };
+    // .toBe(sanitized) already proves the surrogate was replaced; the
+    // additional explicit check below documents the specific code points.
+    expect(reparsed.content).toBe(sanitized);
+    expect(reparsed.content.charCodeAt(6)).toBe(0xfffd); // <20> not \uD800
+  });
+});
+
+describe('sanitizeLoneSurrogates — wiring invariants', () => {
+  test('server.ts wraps every command result through handleCommandInternal', () => {
+    // The architectural choice is to wrap once at handleCommandInternal so
+    // both single-command HTTP and the batch loop inherit. If a future
+    // refactor moves sanitization back to handleCommand only, this test
+    // fails by detecting the missing wrapper.
+    expect(SERVER_SRC).toContain('async function handleCommandInternalImpl(');
+    expect(SERVER_SRC).toContain('result: sanitizeLoneSurrogates(cr.result)');
+  });
+
+  test('SSE activity feed sanitizes outbound frames via sanitizeReplacer', () => {
+    // Replacer must run DURING stringify; post-stringify regex is ineffective
+    // because JSON.stringify converts \uD800 → "\\ud800" before our regex sees it.
+    expect(SERVER_SRC).toContain('JSON.stringify(entry, sanitizeReplacer)');
+  });
+
+  test('SSE inspector stream sanitizes outbound frames via sanitizeReplacer', () => {
+    expect(SERVER_SRC).toContain('JSON.stringify(event, sanitizeReplacer)');
+  });
+
+  test('sanitizeReplacer is a function defined in server.ts', () => {
+    expect(SERVER_SRC).toContain('function sanitizeReplacer(');
+  });
+});