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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"gzip: cannot create file if mtime \u003e `2106-02-07T06:28:15`","articleBody":"# Bug report\n\n### Bug description:\n\nWe had a VM where ntp went very wonky and ended up thinking it was the year 2141!\nTrying 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).\n\nI wouldn't expect the gzip module to explode in this case, I'd expect it to set the `MTIME` to 0.\n[RFC 1952](https://datatracker.ietf.org/doc/html/rfc1952#page-7) (if that's at all relevant these days) states\n\u003e MTIME = 0 means no time stamp is available\n\n### MWE\nOnly tested this on macOS on 3.13.2, but from a cursory glance, the mtime handling hasn't changed in over a decade.\n```python\n\u003e\u003e\u003e import gzip\n\u003e\u003e\u003e gzip.GzipFile(\"/dev/null\", \"w\", mtime=2**32+1)\nTraceback (most recent call last):\n  File \"\u003cpython-input-3\u003e\", line 1, in \u003cmodule\u003e\n    gzip.GzipFile(\"/dev/null\", \"w\", mtime=2**32+1)\n    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/lib/python3.13/gzip.py\", line 237, in __init__\n    self._write_gzip_header(compresslevel)\n    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^\n  File \"/usr/local/lib/python3.13/gzip.py\", line 281, in _write_gzip_header\n    write32u(self.fileobj, int(mtime))\n    ~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/lib/python3.13/gzip.py\", line 77, in write32u\n    output.write(struct.pack(\"\u003cL\", value))\n                 ~~~~~~~~~~~^^^^^^^^^^^^^\nstruct.error: 'L' format requires 0 \u003c= number \u003c= 4294967295\n```\n\n### Proposed Patch\nI'd naïvely fix it with this patch\n```diff\ndiff --git a/Lib/gzip.py b/Lib/gzip.py\nindex c00f51858de..29345de4659 100644\n--- a/Lib/gzip.py\n+++ b/Lib/gzip.py\n@@ -297,6 +297,8 @@ def _write_gzip_header(self, compresslevel):\n         mtime = self._write_mtime\n         if mtime is None:\n             mtime = time.time()\n+        if mtime \u003e 4294967295:\n+            mtime = 0\n         write32u(self.fileobj, int(mtime))\n         if compresslevel == _COMPRESS_LEVEL_BEST:\n             xfl = b'\\002'\n```\n\n\n### CPython versions tested on:\n\n3.13\n\n### Operating systems tested on:\n\nmacOS\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-134278\n* gh-150221\n* gh-151828\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/huwcbjones","@type":"Person","name":"huwcbjones"},"datePublished":"2025-05-14T11:06:07.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":6},"url":"https://github.com/133998/cpython/issues/133998"}