41 lines
1.8 KiB
Ruby
41 lines
1.8 KiB
Ruby
class ClaimsController < ApplicationController
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before_action :require_authentication
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# Giveaway slots are a hard cap that has to hold under real concurrency,
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# not just in whichever request happens to run first: two visitors
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# racing the same "claim a slot" button must never both walk away
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# believing they won one of the last N copies. Post#with_lock
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# (Prism::Orm::Pessimistic, wired into every Model since session ~99)
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# holds Store's real cross-process file lock for this entire
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# reload-check-decide-write critical section, so a concurrent request -
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# even from a completely separate `Prism::Server` OS process sharing this
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# same database file, not just another thread of this one, see
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# blog_giveaway_demo.rb/blog_giveaway_worker.rb - blocks on its own
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# transaction until this one has already committed, instead of both
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# reading the same not-yet-updated claims_count and both deciding a slot
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# was still free.
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def create
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post = Post.find_by!(slug: params['post_id'])
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raise Prism::Orm::RecordNotFound unless post.giveaway?
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outcome = nil
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post.with_lock do |locked_post|
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if locked_post.giveaway_sold_out?
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outcome = :sold_out
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else
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claim = Claim.new(post_id: locked_post.id, user_id: current_user.id)
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# The only realistic validation failure left once
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# giveaway_sold_out? has already passed is the uniqueness scope -
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# the same visitor double-submitting the claim form (e.g. a
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# doubled-click, or hitting back and resubmitting).
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outcome = claim.save ? :claimed : :already_claimed
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end
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end
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flash[:notice] = t("claims.#{outcome}_notice")
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redirect url_for(:post, slug: post.to_param)
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rescue Prism::Orm::RecordNotFound
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respond_not_found(t('posts.not_found'))
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end
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end
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