[nikhilchowdary]

Add x-goog-is-transaction routing header in Ruby SDK to differentiate transactional requests and non-transactional requests from firestore. Having a routing header for transactions helps in routing grpc requests at GFE.

[quartzmo]

@nikhilchowdary Thanks for this PR. I'll contact you separately to discuss prioritization.

[quartzmo]

What do you think about passing the transaction itself instead of the computed boolean? Each call site already has transaction (or transaction_opt in begin_transaction), so call_options could implement the logic in one place:

    def call_options parent: nil, token: nil, transaction: nil
      Gapic::CallOptions.new(**{
        metadata:   default_headers(parent, transaction: transaction),
        page_token: token
      }.compact)
    end

    def default_headers parent = nil, transaction: nil
      parent ||= database_path
      routing_val = CGI.escapeURIComponent parent
      {
        "x-goog-request-params" => "database=#{routing_val}",
        "x-goog-is-transaction" => (!transaction.nil?).to_s
      }
    end

Call sites then read call_options(parent: database_path, transaction: transaction), and begin_transaction passes transaction: transaction_opt. The headers stay exactly the same, so the tests shouldn't need changes.

[nikhilchowdary]

Thanks for the suggestion. I have made the changes.