[BUG]: Dalli 5.0 compatibility - `uninitialized constant Dalli::Protocol::Binary`

[makimoto]

Tracer Version(s)

2.28.0

Ruby Version(s)

ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [arm64-darwin24]

Relevent Library and Version(s)

dalli 5.0.0

Bug Report

Dalli 5.0.0 removed the binary protocol entirely, including the Dalli::Protocol::Binary class. The dalli integration's dalli_class method references this class for dalli >= 3.0.0, which causes a NameError at instrumentation time
:

https://github.com/DataDog/dd-trace-rb/blob/v2.28.0/lib/datadog/tracing/contrib/dalli/integration.rb#L33-L38

def self.dalli_class
  if version >= DALLI_PROTOCOL_BINARY_VERSION
    ::Dalli::Protocol::Binary  # Removed in dalli 5.0.0
  else
    ::Dalli::Server
  end
end

Dalli 5.0.0 removed the binary protocol and SASL authentication in petergoldstein/dalli#1064 (merged 2026-02-06). It now only supports the meta protocol (Dalli::Protocol::Meta). S
ee: https://github.com/petergoldstein/dalli/blob/main/5.0-Upgrade.md

Suggested Fixes

There are two possible approaches:

1. Full support (preferred): Update dalli_class to target Dalli::Protocol::Meta for dalli >= 5.0.0, since it replaces Dalli::Protocol::Binary as the class that implements the request method. The Instrumentation module pr
   epends request, so this should work if the interface is compatible.

   DALLI_META_ONLY_VERSION = Gem::Version.new('5.0.0')
   
   def self.dalli_class
     if version >= DALLI_META_ONLY_VERSION
       ::Dalli::Protocol::Meta
     elsif version >= DALLI_PROTOCOL_BINARY_VERSION
       ::Dalli::Protocol::Binary
     else
       ::Dalli::Server
     end
   end

2. Quick fix: Add a MAXIMUM_VERSION to compatible? to exclude dalli 5.0+ until full support is implemented. This would cause the integration to gracefully skip instrumentation rather than raising a NameError.

   MINIMUM_VERSION = Gem::Version.new('2.0.0')
   MAXIMUM_VERSION = Gem::Version.new('5.0.0')
   
   def self.compatible?
     super && version >= MINIMUM_VERSION && version < MAXIMUM_VERSION
   end

Note: PR #5331 (automated dependency update) also bumps dalli to 5.0.0 in lockfiles and its CI is failing for the same reason.

Reproduction Code

# Gemfile
gem 'dalli', '~> 5.0.0'
gem 'datadog', '~> 2.28'

# reproduce.rb
require 'dalli'
require 'datadog'

puts "dalli version: #{Dalli::VERSION}"
puts "datadog version: #{Datadog::VERSION::STRING}"
puts "Dalli::Protocol::Binary defined? #{defined?(Dalli::Protocol::Binary) || 'no'}"

Datadog.configure do |c|
  c.tracing.instrument :dalli
end

$ bundle exec ruby reproduce.rb
dalli version: 5.0.0
datadog version: 2.28.0
Dalli::Protocol::Binary defined? no

E, [...] ERROR -- datadog: [datadog] (...) Failed to apply Datadog::Tracing::Contrib::Dalli::Patcher patch.
Cause: uninitialized constant Dalli::Protocol::Binary
Location: .../datadog-2.28.0/lib/datadog/tracing/contrib/dalli/integration.rb:35:in
'Datadog::Tracing::Contrib::Dalli::Integration.dalli_class'

Configuration Block

No response

Error Logs

With DD_TRACE_DEBUG=true:

E, [2026-02-13T15:03:23.811996 #37394] ERROR -- datadog: [datadog] (.../gems/datadog-2.28.0/lib/datadog/tracing/contrib/patcher.rb:54:in 'Datadog::Tracing::Contrib::Patcher::CommonMethods#on_patch_error') Failed to apply Datadog::Tracing::Contrib::Dalli::Patcher patch. Cause: uninitialized constant Dalli::Protocol::Binary Location: .../gems/datadog-2.28.0/lib/datadog/tracing/contrib/dalli/integration.rb:35:in 'Datadog::Tracing::Contrib::Dalli::Integration.dalli_class'

No other dalli-related debug output is produced. The error is logged once during initialization and dalli instrumentation is silently skipped.

Operating System

Darwin FV3FYM96WW 25.2.0 Darwin Kernel Version 25.2.0: Tue Nov 18 21:09:45 PST 2025; root:xnu-12377.61.12~1/RELEASE_ARM64_T6030 arm64

How does Datadog help you?

No response

[Strech]

Hey @makimoto 👋🏼

Thanks a lot for a very detailed issue. We are working on that now and I hope the fix will be on time for the next release.

[Strech]

@makimoto want to let you know that we have merged the fix #5435 and it will be released as a part of 2.30 version.

I will close the issue, but feel free to reopen it.

[makimoto]

Thank you, @Strech, for the update!
I just confirmed our systems are now working correctly with dalli 5.0.2 and dd-trace-rb 2.30.

[Strech]

@makimoto Great news! Once again thank you for reporting it 🤝