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Sam RubyandClaude Opus 5.5
c8f74a0b0e
Every page parsed the importmap and joined each of its URLs against the request's base URL, about a millisecond of CPU a page, though the answer changes only with the importmap and the host. Keep the last answer, keyed by both. One entry, so a request with a made-up Host header can't grow it. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
70 lines
3.1 KiB
Ruby
70 lines
3.1 KiB
Ruby
# Allows the scripts the importmap helper emits and nothing else: the inline
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# importmap and its entry-point module by content hash, and the asset
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# directory its URLs point into. Not the whole origin, because uploads are
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# served from this origin too. The hashes change only when the importmap does
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# (a deploy), so cached HTML stays valid, unlike a per-request nonce.
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module InlineScriptHashes
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extend ActiveSupport::Concern
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ENTRY_POINT_SCRIPT = %(import "application")
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included do
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# With the policy turned off there's nothing to add to, so leave the
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# request without one rather than starting an empty policy
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content_security_policy if: -> { request.content_security_policy } do |policy|
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if sources = policy.directives["script-src"]
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importmap = Rails.application.importmap.to_json(resolver: helpers)
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policy.directives["script-src"] = (sources - [ "'self'" ]) | script_sources(importmap)
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policy.worker_src "#{request.host_with_port}#{service_worker_path(format: :js)}"
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end
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end
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end
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mattr_accessor :last_script_sources
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private
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# Parsing the importmap and resolving each of its URLs costs about a
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# millisecond a page, yet the answer changes only with the importmap and
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# the host the page is served from. Keep the last one: a single entry, so
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# a request with a made-up Host header can't grow it.
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def script_sources(importmap)
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key = [ importmap, request.base_url, request.host_with_port, config.relative_url_root ]
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cached_key, sources = InlineScriptHashes.last_script_sources
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if cached_key == key
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sources
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else
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(script_locations(importmap) | script_hashes(importmap, ENTRY_POINT_SCRIPT)).freeze.tap do |sources|
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InlineScriptHashes.last_script_sources = [ key, sources ].freeze
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end
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end
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end
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# The importmap is resolved by Rails' asset helpers, so its URLs already
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# carry any relative root and asset host, however the host is written:
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# with or without a scheme, protocol-relative, a %d set, or a proc. Each
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# is allowed up to its asset directory, the last one in its path, since an
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# asset host's own path may contain one too; a URL outside it is allowed
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# exactly.
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#
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# This origin's own sources leave out the scheme, so they match the page's
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# scheme even behind a proxy that terminates TLS without saying so.
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#
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# A path only limits the first request: browsers check just the origin
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# after a redirect. Nothing under the asset directory redirects.
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def script_locations(importmap)
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assets = File.join(config.relative_url_root.to_s, Rails.application.config.assets.prefix, "")
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JSON.parse(importmap)["imports"].values.map do |url|
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url = URI.join(request.base_url, url)
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origin = url.origin == request.base_url ? request.host_with_port : url.origin
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directory = url.path[0, url.path.rindex(assets) + assets.length] if url.path.include?(assets)
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"#{origin}#{directory || url.path}"
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end.uniq
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end
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def script_hashes(*scripts)
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scripts.map { |script| "'sha256-#{Digest::SHA256.base64digest(script)}'" }
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end
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end
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