Correctly measure Redis nested array responses

lib/gitlab/instrumentation/redis_interceptor.rb

@@ -61,15 +61,14 @@ module Gitlab
         # 4. "Binary" string (i.e. may contain zero byte)
         # 5. Array of binary string
 
-        size = if result.is_a? Array
-                 # This count is an approximation that omits the Redis protocol overhead
-                 # of type prefixes, length prefixes and line endings.
-                 result.inject(0) { |sum, y| sum + y.to_s.bytesize }
-               else
-                 result.to_s.bytesize
-               end
-
-        instrumentation_class.increment_read_bytes(size)
+        if result.is_a? Array
+          # Redis can return nested arrays, e.g. from XRANGE or GEOPOS, so we use recursion here.
+          result.each { |x| measure_read_size(x) }
+        else
+          # This count is an approximation that omits the Redis protocol overhead
+          # of type prefixes, length prefixes and line endings.
+          instrumentation_class.increment_read_bytes(result.to_s.bytesize)
+        end
       end
 
       # That's required so it knows which GitLab Redis instance

spec/lib/gitlab/instrumentation/redis_interceptor_spec.rb

@@ -24,6 +24,9 @@ describe Gitlab::Instrumentation::RedisInterceptor, :clean_gitlab_redis_shared_s
 
       # Exercise counting of a bulk reply
       [[:set, 'foo', 'bar' * 100]] | [:get, 'foo'] | 3 + 3 | 3 * 100
+
+      # Nested array response: ['123456-89', ['foo', 'bar']]
+      [[:xadd, 'mystream', '123456-89', 'foo', 'bar']] | [:xrange, 'mystream', '-', '+'] | 6 + 8 + 1 + 1 | 9 + 3 + 3
     end
 
     with_them do