Make nameservers test more robust

The Nameservers test (in GitHub Actions), fails ~25% of the time, almost
invariably ns-do-sg.sslip.io (I don't know whether it's Digital Ocean's
fault or the large distance between my GitHub Actions runner &
Singapore).

The failures are noisy, typically one day, and have led me to stop
checking the status of my nameservers, which defeats the purpose.

This commit attempts to reduce the failures by increasing both the
timeout and the retries. We are nothing if not persistent.

spec/check-dns_spec.rb

@@ -6,6 +6,7 @@
 # against a DNS server -- a simple shell script would have been
 # shorter and more understandable. We are using rspec merely to
 # practice using rspec.
+#
 def get_whois_nameservers(domain)
   whois_output = `whois #{domain}`
   soa = nil
@@ -22,6 +23,10 @@ sslip_version = '4.1.0'
 whois_nameservers = get_whois_nameservers(domain)
 
 describe domain do
+  # I don't want a spurious failure, esp. ns-do-sg.sslip.io
+   # default is 3 tries, 5 seconds timeout
+  let(:dig_args) { ['+tries=15', '+timeout=10'] }
+  let(:dig_cmd) { "dig #{dig_args.join(' ')}" }
   soa = nil
 
   context "when evaluating $DOMAIN (\"#{domain}\") environment variable" do
@@ -40,73 +45,73 @@ describe domain do
 
   whois_nameservers.each do |whois_nameserver|
     it "nameserver #{whois_nameserver}'s NS records include all whois nameservers #{whois_nameservers}, " +
-      "`dig @#{whois_nameserver} ns #{domain} +short`" do
-      dig_nameservers = `dig @#{whois_nameserver} ns #{domain} +short`.split(/\n+/)
+      "`dig ... @#{whois_nameserver} ns #{domain} +short`" do
+      dig_nameservers = `#{dig_cmd} @#{whois_nameserver} ns #{domain} +short`.split(/\n+/)
       expect(whois_nameservers - dig_nameservers).to be_empty
     end
 
     it "nameserver #{whois_nameserver}'s SOA record match" do
-      dig_soa = `dig @#{whois_nameserver} soa #{domain} +short`
+      dig_soa = `#{dig_cmd} @#{whois_nameserver} soa #{domain} +short`
       soa = soa || dig_soa
       expect(dig_soa).to eq(soa)
     end
 
     it "nameserver #{whois_nameserver}'s has an A record" do
-      expect(`dig @#{whois_nameserver} a #{domain} +short`.chomp).not_to eq('')
+      expect(`#{dig_cmd} @#{whois_nameserver} a #{domain} +short`.chomp).not_to eq('')
       expect($?.success?).to be true
     end
 
     it "nameserver #{whois_nameserver}'s has an AAAA record" do
-      expect(`dig @#{whois_nameserver} a #{domain} +short`.chomp).not_to eq('')
+      expect(`#{dig_cmd} @#{whois_nameserver} a #{domain} +short`.chomp).not_to eq('')
       expect($?.success?).to be true
     end
 
     a = [ rand(256), rand(256), rand(256), rand(256) ]
     it "resolves #{a.join(".")}.#{domain} to #{a.join(".")}" do
-      expect(`dig @#{whois_nameserver} #{a.join(".") + "." + domain} +short`.chomp).to  eq(a.join("."))
+      expect(`#{dig_cmd} @#{whois_nameserver} #{a.join(".") + "." + domain} +short`.chomp).to  eq(a.join("."))
     end
 
     a = [ rand(256), rand(256), rand(256), rand(256) ]
     it "resolves #{a.join("-")}.#{domain} to #{a.join(".")}" do
-      expect(`dig @#{whois_nameserver} #{a.join("-") + "." + domain} +short`.chomp).to  eq(a.join("."))
+      expect(`#{dig_cmd} @#{whois_nameserver} #{a.join("-") + "." + domain} +short`.chomp).to  eq(a.join("."))
     end
 
     a = [ rand(256), rand(256), rand(256), rand(256) ]
     b = [ ('a'..'z').to_a, ('0'..'9').to_a ].flatten.shuffle[0,8].join
     it "resolves #{b}.#{a.join("-")}.#{domain} to #{a.join(".")}" do
-      expect(`dig @#{whois_nameserver} #{b}.#{a.join("-") + "." + domain} +short`.chomp).to  eq(a.join("."))
+      expect(`#{dig_cmd} @#{whois_nameserver} #{b}.#{a.join("-") + "." + domain} +short`.chomp).to  eq(a.join("."))
     end
 
     a = [ rand(256), rand(256), rand(256), rand(256) ]
     b = [ ('a'..'z').to_a, ('0'..'9').to_a ].flatten.shuffle[0,8].join
     it "resolves #{a.join("-")}.#{b} to #{a.join(".")}" do
-      expect(`dig @#{whois_nameserver} #{a.join("-") + "." + b} +short`.chomp).to  eq(a.join("."))
+      expect(`#{dig_cmd} @#{whois_nameserver} #{a.join("-") + "." + b} +short`.chomp).to  eq(a.join("."))
     end
 
     # don't begin the hostname with a double-dash -- `dig` mistakes it for an argument
     it "resolves api.--.#{domain}' to eq ::)}" do
-      expect(`dig @#{whois_nameserver} AAAA api.--.#{domain} +short`.chomp).to eq("::")
+      expect(`#{dig_cmd} @#{whois_nameserver} AAAA api.--.#{domain} +short`.chomp).to eq("::")
     end
 
     it "resolves localhost.--1.#{domain}' to eq ::1)}" do
-      expect(`dig @#{whois_nameserver} AAAA localhost.api.--1.#{domain} +short`.chomp).to eq("::1")
+      expect(`#{dig_cmd} @#{whois_nameserver} AAAA localhost.api.--1.#{domain} +short`.chomp).to eq("::1")
     end
 
     it "resolves 2001-4860-4860--8888.#{domain}' to eq 2001:4860:4860::8888)}" do
-      expect(`dig @#{whois_nameserver} AAAA 2001-4860-4860--8888.#{domain} +short`.chomp).to eq("2001:4860:4860::8888")
+      expect(`#{dig_cmd} @#{whois_nameserver} AAAA 2001-4860-4860--8888.#{domain} +short`.chomp).to eq("2001:4860:4860::8888")
     end
 
     it "resolves 2601-646-100-69f0--24.#{domain}' to eq 2601:646:100:69f0::24)}" do
-      expect(`dig @#{whois_nameserver} AAAA 2601-646-100-69f0--24.#{domain} +short`.chomp).to eq("2601:646:100:69f0::24")
+      expect(`#{dig_cmd} @#{whois_nameserver} AAAA 2601-646-100-69f0--24.#{domain} +short`.chomp).to eq("2601:646:100:69f0::24")
     end
 
     it "gets the expected version number, #{sslip_version}" do
-      expect(`dig @#{whois_nameserver} TXT version.status.#{domain} +short`).to include(sslip_version)
+      expect(`#{dig_cmd} @#{whois_nameserver} TXT version.status.#{domain} +short`).to include(sslip_version)
     end
 
     it "gets the source (querier's) IP address" do
       # Look on my Regular Expressions, ye mighty, and despair!
-      expect(`dig @#{whois_nameserver} TXT ip.#{domain} +short`).to match(/^"(\d+\.\d+\.\d+\.\d+)|(([[:xdigit:]]*:){2,7}[[:xdigit:]]*)"$/)
+      expect(`#{dig_cmd} @#{whois_nameserver} TXT ip.#{domain} +short`).to match(/^"(\d+\.\d+\.\d+\.\d+)|(([[:xdigit:]]*:){2,7}[[:xdigit:]]*)"$/)
     end
 
     # check the website