Speed up SimpleHTTPRequestHandler.list_directory() by using os.scandir()

SimpleHTTPRequestHandler.list_directory() calls os.listdir() and then, for every entry, os.path.isdir() (a stat) and os.path.islink() (an lstat) — two stat-family syscalls per entry. This is wasted work on any filesystem and dominates listing time for large directories; on network filesystems like NFS, where each call is a round-trip, it becomes severe.

os.scandir() returns the entry type from the directory read itself (POSIX d_type / NFS READDIRPLUS), eliminating the per-entry stats in the common case. CPython already did this migration for os.walk(), glob, and pathlib.Path.iterdir() (gh-117727); http.server was missed.

Benchmark

Directory with 1000 files + 1000 dirs (plus a few symlinks):

• stat-family syscalls (strace): 4088 → 88 (the 88 is constant interpreter startup; the per-entry loop drops from ~2 syscalls to ~0)
• local filesystem wall-clock: ~10× faster
• emulating NFS by injecting per-stat latency: the listing goes from seconds to ~2 ms

Worst case — a mount that returns DT_UNKNOWN — falls back to one cached lstat per entry, which is still fewer calls than today and never worse.

The change is behavior-preserving: DirEntry.is_dir()/is_symlink() match os.path.isdir/os.path.islink semantics (follow-symlinks behavior and return-False-on-error), verified across real dirs/files, symlink-to-dir, symlink-to-file, and broken symlinks. The existing test_httpservers suite passes unchanged.

I have a patch ready and will open a PR.

This issue was prepared with AI assistance (Claude Code); the analysis and benchmarks were reviewed by me.

Linked PRs

• gh-151789

Bắt đầu từ SimpleHTTPRequestHandler.list_directory() và kiểm tra test suite test_httpservers hiện có. So sánh các kiểm tra mục thư mục với hành vi của os.scandir(), bao gồm symlink và các trường hợp fallback, sau đó chạy các bài kiểm tra HTTP server; công việc được hoàn tất khi hành vi vẫn không thay đổi đồng thời số lần gọi stat trên mỗi mục được giảm xuống. Một pull request được liên kết đã bao quát công việc này.