Zip files fail to expand on OSX

[rschroll]

We've noticed that the zip files produced here fail to expand automatically when double-clicked on some Macs. The user gets a pop-up window saying, "Unable to expand '<file.zip>' into ''. (Error 2 - No such file or directory.)". However, the zip file will unpack just fine on the command line with unzip.

Most reports of this online are connected to too-large zip files (GBs) or corrupt files, but this happens with small files, and they open just fine on the command line. A couple of possibly-relevant issues:

• A ruby zip streamer ran into a problem with their streaming zip files, which was fixed by adjusting some headers in the zip file: Fix streamed files cannot be extacted by MacOS default unzip fringd/zipline#2. See also the reported issue: Streamed Zipfiles won't open with Mac OS X Finder/default-ZIP fringd/zipline#1.
• A JS zip library encountered this same error message (Zip Files Do Not Unzip on Mac OS gildas-lormeau/zip.js#6), and fixed it by tweaking headers as well: gildas-lormeau/zip.js@fb677d8.

I'm going to keep poking around here, but I wanted to document what I've found so far.

[rschroll]

I've found that Python produces different zip files depending on whether the output file handle is streaming (no seek method). It looks like OSX is happy with the non-streaming files, but can't deal with the streaming-produced ones.

The file out.zip was created with a standard file handle. It unzips just fine on OSX. In contrast, out-stream.zip was created with a file handle where seek was disabled. It doesn't unzip on OSX.