Merge pull request #226 from prefab-cloud/cache-config-fetches

Cache config fetches

Author: jkebinger

lib/prefab-cloud-ruby.rb

@@ -55,3 +55,5 @@ module Prefab
 require 'prefab/murmer3'
 require 'prefab/javascript_stub'
 require 'prefab/semver'
+require 'prefab/fixed_size_hash'
+require 'prefab/caching_http_connection'

lib/prefab/caching_http_connection.rb

@@ -0,0 +1,95 @@
+# frozen_string_literal: true
+
+module Prefab
+  class CachingHttpConnection
+    CACHE_SIZE = 2.freeze
+    CacheEntry = Struct.new(:data, :etag, :expires_at)
+
+    class << self
+      def cache
+        @cache ||= FixedSizeHash.new(CACHE_SIZE)
+      end
+
+      def reset_cache!
+        @cache = FixedSizeHash.new(CACHE_SIZE)
+      end
+    end
+
+    def initialize(uri, api_key)
+      @connection = HttpConnection.new(uri, api_key)
+    end
+
+    def get(path)
+      now = Time.now.to_i
+      cache_key = "#{@connection.uri}#{path}"
+      cached = self.class.cache[cache_key]
+
+      # Check if we have a valid cached response
+      if cached&.data && cached.expires_at && now < cached.expires_at
+        return Faraday::Response.new(
+          status: 200,
+          body: cached.data,
+          response_headers: {
+            'ETag' => cached.etag,
+            'X-Cache' => 'HIT',
+            'X-Cache-Expires-At' => cached.expires_at.to_s
+          }
+        )
+      end
+
+      # Make request with conditional GET if we have an ETag
+      response = if cached&.etag
+                   @connection.get(path, { 'If-None-Match' => cached.etag })
+                 else
+                   @connection.get(path)
+                 end
+
+      # Handle 304 Not Modified
+      if response.status == 304 && cached&.data
+        return Faraday::Response.new(
+          status: 200,
+          body: cached.data,
+          response_headers: {
+            'ETag' => cached.etag,
+            'X-Cache' => 'HIT',
+            'X-Cache-Expires-At' => cached.expires_at.to_s
+          }
+        )
+      end
+
+      # Parse caching headers
+      cache_control = response.headers['Cache-Control'].to_s
+      etag = response.headers['ETag']
+
+      # Always add X-Cache header
+      response.headers['X-Cache'] = 'MISS'
+
+      # Don't cache if no-store is present
+      return response if cache_control.include?('no-store')
+
+      # Calculate expiration
+      max_age = cache_control.match(/max-age=(\d+)/)&.captures&.first&.to_i
+      expires_at = max_age ? now + max_age : nil
+
+      # Cache the response if we have caching headers
+      if etag || expires_at
+        self.class.cache[cache_key] = CacheEntry.new(
+          response.body,
+          etag,
+          expires_at
+        )
+      end
+
+      response
+    end
+
+    # Delegate other methods to the underlying connection
+    def post(path, body)
+      @connection.post(path, body)
+    end
+
+    def uri
+      @connection.uri
+    end
+  end
+end

lib/prefab/config_client.rb

@@ -118,7 +118,7 @@ def _get(key, properties)
     end
 
     def load_checkpoint
-      success = load_source_checkpoint
+      success = load_source_checkpoint(:start_at_id => @config_loader.highwater_mark)
       return if success
 
       success = load_cache
@@ -127,11 +127,10 @@ def load_checkpoint
       LOG.warn 'No success loading checkpoints'
     end
 
-    def load_source_checkpoint
+    def load_source_checkpoint(start_at_id: 0)
       @options.config_sources.each do |source|
-        conn = Prefab::HttpConnection.new("#{source}/api/v1/configs/0", @base_client.api_key)
+        conn = Prefab::CachingHttpConnection.new("#{source}/api/v1/configs/#{start_at_id}", @base_client.api_key)
         result = load_url(conn, :remote_api)
-
         return true if result
       end
 
@@ -146,18 +145,18 @@ def load_url(conn, source)
         cache_configs(configs)
         true
       else
-        LOG.info "Checkpoint #{source} failed to load. Response #{resp.status}"
+        LOG.info "Checkpoint #{source} [#{conn.uri}] failed to load. Response #{resp.status}"
         false
       end
     rescue Faraday::ConnectionFailed => e
       if !initialized?
-        LOG.warn "Connection Fail loading #{source} checkpoint."
+        LOG.warn "Connection Fail loading #{source} [#{conn.uri}] checkpoint."
       else
-        LOG.debug "Connection Fail loading #{source} checkpoint."
+        LOG.debug "Connection Fail loading #{source} [#{conn.uri}] checkpoint."
       end
       false
     rescue StandardError => e
-      LOG.warn "Unexpected #{source} problem loading checkpoint #{e} #{conn}"
+      LOG.warn "Unexpected #{source} [#{conn.uri}] problem loading checkpoint #{e} #{conn}"
       LOG.debug e.backtrace
       false
     end

lib/prefab/fixed_size_hash.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+module Prefab
+  class FixedSizeHash < Hash
+    def initialize(max_size)
+      @max_size = max_size
+      super()
+    end
+
+    def []=(key, value)
+      shift if size >= @max_size && !key?(key) # Only evict if adding a new key
+      super
+    end
+  end
+end

lib/prefab/http_connection.rb

@@ -9,13 +9,17 @@ class HttpConnection
       'X-PrefabCloud-Client-Version' => "prefab-cloud-ruby-#{Prefab::VERSION}"
     }.freeze
 
-    def initialize(api_root, api_key)
-      @api_root = api_root
+    def initialize(uri, api_key)
+      @uri = uri
       @api_key = api_key
     end
 
-    def get(path)
-      connection(PROTO_HEADERS).get(path)
+    def uri
+      @uri
+    end
+
+    def get(path, headers = {})
+      connection(PROTO_HEADERS.merge(headers)).get(path)
     end
 
     def post(path, body)
@@ -24,13 +28,13 @@ def post(path, body)
 
     def connection(headers = {})
       if Faraday::VERSION[0].to_i >= 2
-        Faraday.new(@api_root) do |conn|
+        Faraday.new(@uri) do |conn|
           conn.request :authorization, :basic, AUTH_USER, @api_key
 
           conn.headers.merge!(headers)
         end
       else
-        Faraday.new(@api_root) do |conn|
+        Faraday.new(@uri) do |conn|
           conn.request :basic_auth, AUTH_USER, @api_key
 
           conn.headers.merge!(headers)