gzip: cannot create file if mtime > `2106-02-07T06:28:15`

Bug report

Bug description:

We had a VM where ntp went very wonky and ended up thinking it was the year 2141!
Trying to write a gzip file with the system clock greater than 2106-02-07T06:28:15 results in a struct error because we tried to cram a 64-bit int into a 32 bit field (which won't work).

I wouldn't expect the gzip module to explode in this case, I'd expect it to set the MTIME to 0.
RFC 1952 (if that's at all relevant these days) states

MTIME = 0 means no time stamp is available

MWE

Only tested this on macOS on 3.13.2, but from a cursory glance, the mtime handling hasn't changed in over a decade.

>>> import gzip
>>> gzip.GzipFile("/dev/null", "w", mtime=2**32+1)
Traceback (most recent call last):
  File "<python-input-3>", line 1, in <module>
    gzip.GzipFile("/dev/null", "w", mtime=2**32+1)
    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/gzip.py", line 237, in __init__
    self._write_gzip_header(compresslevel)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/gzip.py", line 281, in _write_gzip_header
    write32u(self.fileobj, int(mtime))
    ~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/gzip.py", line 77, in write32u
    output.write(struct.pack("<L", value))
                 ~~~~~~~~~~~^^^^^^^^^^^^^
struct.error: 'L' format requires 0 <= number <= 4294967295

Proposed Patch

I'd naïvely fix it with this patch

diff --git a/Lib/gzip.py b/Lib/gzip.py
index c00f51858de..29345de4659 100644
--- a/Lib/gzip.py
+++ b/Lib/gzip.py
@@ -297,6 +297,8 @@ def _write_gzip_header(self, compresslevel):
         mtime = self._write_mtime
         if mtime is None:
             mtime = time.time()
+        if mtime > 4294967295:
+            mtime = 0
         write32u(self.fileobj, int(mtime))
         if compresslevel == _COMPRESS_LEVEL_BEST:
             xfl = b'\002'

CPython versions tested on:

3.13

Operating systems tested on:

macOS

Linked PRs

• gh-134278
• gh-150221
• gh-151828

從 Lib/gzip.py 中的 _write_gzip_header 開始，使用超出 32 位範圍的 mtime 重現所提供的 GzipFile 範例。在開始工作之前檢查連結的 PRs，因為它們表明此問題可能已經獲得處理。完成的標準是 gzip 檔案建立時將 MTIME 設為 0，而不是引發 struct.error。