add task for downloading benchmark data files

profile/driver_bench/rake/tasks.rake

@@ -2,7 +2,37 @@
 
 require_relative '../suite'
 
-desc 'Runs the DriverBench benchmark suite'
-task :driver_bench do
-  Mongo::DriverBench::Suite.run!
+task driver_bench: %i[ driver_bench:data driver_bench:run ]
+
+SPECS_REPO_URI = 'git@github.com:mongodb/specifications.git'
+SPECS_PATH = File.expand_path('../../../specifications', __dir__)
+DRIVER_BENCH_DATA = File.expand_path('../../data/driver_bench', __dir__)
+
+namespace :driver_bench do
+  desc 'Downloads the DriverBench data files, if necessary'
+  task :data do
+    if File.directory?('./profile/data/driver_bench')
+      puts 'DriverBench data files are already downloaded'
+      next
+    end
+
+    if File.directory?(SPECS_PATH)
+      puts 'specifications repo is already checked out'
+    else
+      sh 'git', 'clone', SPECS_REPO_URI
+    end
+
+    mkdir_p DRIVER_BENCH_DATA
+
+    Dir.glob(File.join(SPECS_PATH, 'source/benchmarking/data/*.tgz')) do |archive|
+      Dir.chdir(DRIVER_BENCH_DATA) do
+        sh 'tar', 'xzf', archive
+      end
+    end
+  end
+
+  desc 'Runs the DriverBench benchmark suite'
+  task :run do
+    Mongo::DriverBench::Suite.run!
+  end
 end