Timestamps of zipped files are UTC

[svenyonson]

Summary

I zip a file from the iOS filesystem (log file). I then read that file as data and send it as an attachment in an email. When I receive the email, the zip file itself has the correct timestamp, but when I extract the zip, the enclosed file has a timestamp that equates to UTC (i.e. tomorrow for me, US Mountain time)

Steps to Reproduce

Create a file in iOS
Zip the file
Send the file
Extract the file
Observe the modification time of the file.

Expected Results

The timestamp of the extracted file should be in your timezone if originator and recipient are in the same timezone

Actual Results

The timezone is "tomorrow", 7 hours ahead, which is my UTC offset.

Regression & Version

Related Link

[svenyonson]

Code for above:

`

func onSendLogfile() {
    
    let sourceURL = Utils.LogFileUrl()
    let zipURL = Utils.ZipLogFileUrl()
    
    // Zip log file
    do {
        try FileManager().zipItem(at: sourceURL, to: zipURL);
        
        // Read entire file into a data object.
        let zipData = NSData(contentsOfFile: zipURL.path) as Data?
        if let zipData = zipData {
            mailData = ComposeMailData(subject: "This is a zipped log file",
               recipients: ["somebody@me.com"],
               message: "Please add additional information as needed to help us identify the issue.",
               attachments: [AttachmentData(data: zipData, mimeType: "application/zip", fileName: "arc.logz")])
        }
    }
    catch {
        
    }
    showMailView = true
}

`

[weichsel]

Hi,

Thanks for reporting this with a detailed example.

The ZIP format has very limited support for preserving date and time information of files. It doesn't offer a field to store time zone information so the archiving library can only assume that the stored timestamps are in the local time zone (or store that information elsewhere - e.g. in a separate file within the archive). (https://en.wikipedia.org/wiki/ZIP_(file_format)#Structure).
Some applications and frameworks store the "creation" time zone in an extra field, but there is no idiomatic way to store that information in an archive entry.

[svenyonson]

It looks like this has been addressed for other archivers?

https://trac.edgewall.org/ticket/11162

[weichsel]

Implementing the "Extended Timestamp Extra Field" would work for me. If you can provide a PR, I can review it and try to get it into an upcoming release.