Duplicate key warning in Metrics#message - JSON 3.0 compatibility concern

[ikad]

Hello, thank you for maintaining this excellent gem. I've encountered an issue that I'd like to bring to your attention.

Issue Description

When using lambdakiq 2.3.0 with Ruby 3.4, I'm seeing warnings about duplicate keys in the hash returned by Lambdakiq::Metrics#message. While this currently only produces warnings, it may cause errors in the future when JSON 3.0 is released.

Warning Message

/path/to/gems/lambdakiq-2.3.0/lib/lambdakiq/metrics.rb:20: warning: detected duplicate key "JobName" in {...}.
This will raise an error in json 3.0 unless enabled via `allow_duplicate_key: true`

Root Cause Analysis

Looking at lib/lambdakiq/metrics.rb (around lines 105-109), I noticed that the message method merges data from two sources:

def message
  {
    '_aws': { ... }
  }.tap do |m|
    dimensions.each { |d| m.merge!(d) }  # Merges Symbol keys (e.g., JobName: "SampleJob")
    m.merge!(@properties)                 # Merges String keys (e.g., "JobName" => "SampleJob")
  end
end

The dimensions array contains hashes with Symbol keys (:JobName, :AppName, etc.), while @properties contains String keys ("JobName", "AppName", etc.). This results in duplicate keys in the final hash.

Suggested Fix

I believe converting the dimension keys to strings before merging would resolve this issue:

def message
  {
    '_aws': { ... }
  }.tap do |m|
    dimensions.each { |d| d.each { |key, value| m[key.to_s] = value } }
    m.merge!(@properties)
  end
end

Temporary Workaround

For now, I've implemented the following workaround in our application:

module Lambdakiq
  class Metrics
    private

    alias original_message message

    def message
      original_message.transform_keys(&:to_s)
    end
  end
end

Environment

• lambdakiq version: 2.3.0
• Ruby version: 3.4.0
• Rails version: 8.0.3

Request

Would you be open to accepting a pull request to fix this issue? I'd be happy to submit one if that would be helpful.

Thank you for your time and consideration.