5074: Improve discovery document caching in Ruby SDK.

[arvados.git] / sdk / ruby / lib / arvados / google_api_client.rb

diff --git a/sdk/ruby/lib/arvados/google_api_client.rb b/sdk/ruby/lib/arvados/google_api_client.rb
new file mode 100644 (file)
index 0000000..71a53f0
--- /dev/null
+++ b/sdk/ruby/lib/arvados/google_api_client.rb
@@ -0,0 +1,55 @@
+require 'google/api_client'
+require 'json'
+require 'tempfile'
+
+class Google::APIClient
+  def discovery_document(api, version)
+    api = api.to_s
+    discovery_uri = self.discovery_uri(api, version)
+    discovery_uri_hash = Digest::MD5.hexdigest(discovery_uri)
+    discovery_cache_path =
+      File.expand_path("~/.cache/arvados/discovery-#{discovery_uri_hash}.json")
+    @discovery_documents[discovery_uri_hash] ||=
+      disk_cached_discovery_document(discovery_cache_path) or
+      fetched_discovery_document(discovery_uri, discovery_cache_path)
+  end
+
+  private
+
+  def disk_cached_discovery_document(cache_path)
+    begin
+      if (Time.now - File.mtime(cache_path)) < 86400
+        open(cache_path) do |cache_file|
+          return JSON.load(cache_file)
+        end
+      end
+    rescue IOError, SystemCallError, JSON::JSONError
+      # Error reading the cache.  Act like it doesn't exist.
+    end
+    nil
+  end
+
+  def write_cached_discovery_document(cache_path, body)
+    cache_dir = File.dirname(cache_path)
+    cache_file = nil
+    begin
+      FileUtils.makedirs(cache_dir)
+      cache_file = Tempfile.new("discovery", cache_dir)
+      cache_file.write(body)
+      cache_file.flush
+      File.rename(cache_file.path, cache_path)
+    rescue IOError, SystemCallError
+      # Failure to write the cache is non-fatal.  Do nothing.
+    ensure
+      cache_file.close! unless cache_file.nil?
+    end
+  end
+
+  def fetched_discovery_document(uri, cache_path)
+    response = self.execute!(:http_method => :get,
+                             :uri => uri,
+                             :authenticated => false)
+    write_cached_discovery_document(cache_path, response.body)
+    JSON.load(response.body)
+  end
+end