Last-Modified time format is invalid, failed with unable to parse in any of the input formats

[wijetnga]

When I use "mc" client (minio) I get below error when I try to copy objects.

mincli: Unable to read from my-minio-alias/python-test-bucket/my-test-file.txt. Last-Modified time format is invalid, failed with unable to parse in any of the input formats: [Mon, 2 Jan 2006 15:04:05 GMT Mon, _2 Jan 2006 15:04:05 GMT Mon, _2 Jan 06 15:04:05 GMT].

I see "Last-Modified: Thu, 09 Oct 2025 17:10:35 GMT" when I use debug.

mc: HTTP/1.1 200 OK
Content-Length: 1493
Accept-Ranges: bytes
Connection: keep-alive
Content-Type: text/markdown
Date: Mon, 13 Oct 2025 16:18:16 GMT
Etag: "8c722fe82af282527f2d9d8c8f12ec95"
Last-Modified: Thu, 09 Oct 2025 17:10:35 GMT
Server: nginx/1.18.0 (Ubuntu)

Log:
time="2025-10-13T23:26:57Z" level=info msg=listening ip=0.0.0.0 port=4433 region=us-east-1
time="2025-10-13T23:26:57Z" level=warning msg="TLS is disabled"

I also changed "router.go" to use RFC1123Z. Still the same issue.

func parseRetentionTime(raw string) (time.Time, error) {
if raw == "" {
return time.Time{}, nil
}
return time.Parse(time.RFC1123Z, raw)
}

Any idea why?

[wijetnga]

Any one, please?

[ynsta]

This is not an s3proxy bug — the proxy passes Last-Modified through unchanged from the upstream backend. There is no code path in s3proxy that parses, formats, or rewrites this header on the response side, so changing parseRetentionTime (a request-side helper for retention dates) has no effect.

The header value you observed — Thu, 09 Oct 2025 17:10:35 GMT — is valid RFC1123. The issue is in the mc client:

input formats: [Mon, 2 Jan 2006 15:04:05 GMT Mon, _2 Jan 2006 15:04:05 GMT Mon, _2 Jan 06 15:04:05 GMT]

mc only accepts non-zero-padded (2) or space-padded (_2) days. The upstream backend (nginx in your trace) sends zero-padded (09), which is what canonical RFC1123 actually specifies. mc's parser is wrong: RFC 7231 §7.1.1.1 requires 09, not 9 or 9.

Recommended path: file the bug against mc (minio/mc) — they need to accept Mon, 02 Jan 2006 15:04:05 GMT as a valid input format. Or, if you control the backend, configure it to emit the space-padded form.

We could add a header-normalization layer to s3proxy to rewrite Last-Modified into a form mc tolerates, but that papers over a client bug and risks breaking other clients. Not planning to do it unless multiple non-mc clients hit the same parser.