Downloaded Cask asset symlink creation can error due to length

[samford]

brew doctor output

Your system is ready to brew.

Verification

• I ran brew update twice and am still able to reproduce my issue.
• My "brew doctor output" above says Your system is ready to brew or a definitely unrelated Tier message.
• This issue's title and/or description do not reference a single formula e.g. brew install wget. If they do, open an issue at https://github.com/Homebrew/homebrew-core/issues/new/choose instead.

brew config output

HOMEBREW_VERSION: 4.6.10-63-geda9e78
ORIGIN: https://github.com/Homebrew/brew.git
HEAD: eda9e78529af3c96e40baaee98a3d7a556f9b707
Last commit: 29 minutes ago
Branch: main
Core tap HEAD: 9752b9d057e87bc43c238324442b467f0d8d58fe
Core tap last commit: 5 minutes ago
Core tap JSON: 08 Sep 14:22 UTC
Core cask tap origin: https://github.com/Homebrew/homebrew-cask.git
Core cask tap HEAD: 3c31d99b2ae19cc01c3faace308b261c1a1a0b67
Core cask tap last commit: 7 minutes ago
Core cask tap JSON: 08 Sep 14:25 UTC
HOMEBREW_PREFIX: /opt/homebrew
HOMEBREW_CASK_OPTS: []
HOMEBREW_DEVELOPER: set
HOMEBREW_GITHUB_API_TOKEN: set
HOMEBREW_LIVECHECK_AUTOBUMP: set
HOMEBREW_MAKE_JOBS: 14
HOMEBREW_NO_ENV_HINTS: set
HOMEBREW_NO_INSTALL_FROM_API: set
HOMEBREW_SORBET_RUNTIME: set
HOMEBREW_UPGRADE_GREEDY: set
Homebrew Ruby: 3.4.5 => /opt/homebrew/Library/Homebrew/vendor/portable-ruby/3.4.5/bin/ruby
CPU: 14-core 64-bit arm_brava
Clang: 17.0.0 build 1700
Git: 2.51.0 => /opt/homebrew/opt/git/bin/git
Curl: 8.7.1 => /usr/bin/curl
macOS: 26.0-arm64
CLT: 26.0.0.0.1.1756965055
Xcode: 26.0
Rosetta 2: false

For what it's worth, I do have Rosetta installed. I'm not sure why it's showing as false but it could have something to do with Tahoe.

What were you trying to do (and why)?

I opened a version bump PR for the qqmusic cask in homebrew/cask (Homebrew/homebrew-cask#225644) but brew audit fails because a symlink can't be created for the downloaded dmg file due to the symlink file name being too long.

What happened (include all command output)?

brew audit displays an error due to the symlink file name being too long:

$ brew audit --online --strict qqmusic
==> Downloading and extracting artifacts
==> Downloading https://c.y.qq.com/cgi-bin/file_redirect.fcg?bid=dldir&file=ecos
Already downloaded: /Users/user/Library/Caches/Homebrew/downloads/ab2ba3ac2e9004a8c536c2922f9d6982d845215106b7add72e8b2b0f3a5bb2ab--QQMusicMac10.7.1Build00.dmg
Warning: Removed Sorbet lines from backtrace!
audit for qqmusic: failed
 - exception while auditing qqmusic: File name too long @ rb_file_s_symlink - (../downloads/ab2ba3ac2e9004a8c536c2922f9d6982d845215106b7add72e8b2b0f3a5bb2ab--QQMusicMac10.7.1Build00.dmg, /Users/user/Library/Caches/Homebrew/Cask/file_redirect.fcg?bid=dldir&file=ecosfile%2Fmusic_clntupate%2Fmac%2Fother%2FQQMusicMac10.7.1Build00.dmg&sign=1-0cb9ee4c40e7447e2113cfdee2dc11c88487b0e31fe37cfe1c59e12c20956dce-689e9373--10.7.1,00,1-0cb9ee4c40e7447e2113cfdee2dc11c88487b0e31fe37cfe1c59e12c20956dce-689e9373.dmg)
qqmusic
  * exception while auditing qqmusic: File name too long @ rb_file_s_symlink - (../downloads/ab2ba3ac2e9004a8c536c2922f9d6982d845215106b7add72e8b2b0f3a5bb2ab--QQMusicMac10.7.1Build00.dmg, /Users/user/Library/Caches/Homebrew/Cask/file_redirect.fcg?bid=dldir&file=ecosfile%2Fmusic_clntupate%2Fmac%2Fother%2FQQMusicMac10.7.1Build00.dmg&sign=1-0cb9ee4c40e7447e2113cfdee2dc11c88487b0e31fe37cfe1c59e12c20956dce-689e9373--10.7.1,00,1-0cb9ee4c40e7447e2113cfdee2dc11c88487b0e31fe37cfe1c59e12c20956dce-689e9373.dmg)
Error: 1 problem in 1 cask detected.

This can also be replicated using brew fetch qqmusic (using the aforementioned cask PR branch) for a more isolated test.

What did you expect to happen?

brew audit --online --strict qqmusic should complete without any errors.

Step-by-step reproduction instructions (by running brew commands)

1. Check out the related homebrew/cask PR branch (https://github.com/Homebrew/homebrew-cask/tree/qqmusic-10.7.1).
2. Run brew fetch qqmusic or brew audit --online --strict qqmusic to observe the symlink error.

[samford]

I opened this issue as a way of having a discussion on how to resolve the aforementioned symlink file name length error, as I don't have any particular ideas on how to best resolve it and wanted to solicit ideas.

This issue isn't common but it's something that we have to address because it's blocking a version update for a cask that otherwise works and it may affect other casks in the near future. There are other related casks that will also have to be updated to include a sign query string parameter to be able to update to a newer version and they may run into this same issue.

[MikeMcQuaid]

• exception while auditing qqmusic: File name too long @ rb_file_s_symlink - (../downloads/ab2ba3ac2e9004a8c536c2922f9d6982d845215106b7add72e8b2b0f3a5bb2ab--QQMusicMac10.7.1Build00.dmg, /Users/user/Library/Caches/Homebrew/Cask/file_redirect.fcg?bid=dldir&file=ecosfile%2Fmusic_clntupate%2Fmac%2Fother%2FQQMusicMac10.7.1Build00.dmg&sign=1-0cb9ee4c40e7447e2113cfdee2dc11c88487b0e31fe37cfe1c59e12c20956dce-689e9373--10.7.1,00,1-0cb9ee4c40e7447e2113cfdee2dc11c88487b0e31fe37cfe1c59e12c20956dce-689e9373.dmg)

This seems like it should be, at most, ab2ba3ac2e9004a8c536c2922f9d6982d845215106b7add72e8b2b0f3a5bb2ab--QQMusicMac10.7.1Build00.dmg.

Doesn't make sense to me to have to store the entire URL in there with the same content repeated 2-3 times in the filename.

[samford]

I'm not sure if there's a reason behind why the symlink uses the cask url and version but maybe someone in @Homebrew/cask has some insight. That said, the duplicated text in the symlink is because the cask version is interpolated into the url.

[cho-m]

I guess it is a simple implementation to avoid conflicts with multiple versions and allowing symlink name to be easily constructed without any extra work.

In many cases, the url's basename would be the filename

brew/Library/Homebrew/downloadable.rb

Lines 160 to 161 in 47b7bf3

	def download_name
	@download_name ||= File.basename(determine_url.to_s).freeze

And symlink name would be reasonable

brew/Library/Homebrew/download_strategy.rb

Lines 315 to 316 in 47b7bf3

	ext = Pathname(parse_basename(url)).extname
	@symlink_location = T.let(@cache/Utils.safe_filename("#{name}--#{version}#{ext}"), T.nilable(Pathname))

---

Since we already compute parse_basename(url) above, it may be possible to use that to get a better alternative to #{name}. Probably need something better as formulae resource names don't work as well with this.

EDIT: May also be that casks need some extra work to fixup the name prior to creating the downloadable.

[cho-m]

Thinking over this some more, we may just want to override download_name in Cask::Download

Maybe cask.full_token.gsub("/", "--") which should then reduce symlink to

• qqmusic--10.7.1,00,1-0cb9ee4c40e7447e2113cfdee2dc11c88487b0e31fe37cfe1c59e12c20956dce-689e9373.dmg

Though this could make some file names longer, it at least avoids the worst case situation of just using URL.

From there, implementing old idea could help avoid the less useful parts of version:

• Introduce additional versioning information for casks #17077

[MikeMcQuaid]

Though this could make some file names longer, it at least avoids the worst case situation of just using URL.

Seems better to me 👍🏻. Alternatively, just take that strategy when the alternative generated version is over a certain length?