Using multiple NTP servers (#6173)

* Small improvements to time estimation.

* Allow multiple NTP servers to be used.

* Removing boxing.

* Be nice.

* Be nicer.

* Update list of servers and add reference.

parity/cli/config.toml

@@ -78,7 +78,7 @@ disable_periodic = true
 jit = false
 
 [misc]
-ntp_server = "pool.ntp.org:123"
+ntp_servers = ["0.parity.pool.ntp.org:123"]
 logging = "own_tx=trace"
 log_file = "/var/log/parity.log"
 color = true

parity/cli/mod.rs

@@ -359,8 +359,8 @@ usage! {
 			or |c: &Config| otry!(c.vm).jit.clone(),
 
 		// -- Miscellaneous Options
-		flag_ntp_server: String = "none",
-			or |c: &Config| otry!(c.misc).ntp_server.clone(),
+		flag_ntp_servers: String = "0.parity.pool.ntp.org:123,1.parity.pool.ntp.org:123,2.parity.pool.ntp.org:123,3.parity.pool.ntp.org:123",
+			or |c: &Config| otry!(c.misc).ntp_servers.clone().map(|vec| vec.join(",")),
 		flag_logging: Option<String> = None,
 			or |c: &Config| otry!(c.misc).logging.clone().map(Some),
 		flag_log_file: Option<String> = None,
@@ -606,7 +606,7 @@ struct VM {
 
 #[derive(Default, Debug, PartialEq, Deserialize)]
 struct Misc {
-	ntp_server: Option<String>,
+	ntp_servers: Option<Vec<String>>,
 	logging: Option<String>,
 	log_file: Option<String>,
 	color: Option<bool>,
@@ -919,7 +919,7 @@ mod tests {
 			flag_dapps_apis_all: None,
 
 			// -- Miscellaneous Options
-			flag_ntp_server: "none".into(),
+			flag_ntp_servers: "0.parity.pool.ntp.org:123,1.parity.pool.ntp.org:123,2.parity.pool.ntp.org:123,3.parity.pool.ntp.org:123".into(),
 			flag_version: false,
 			flag_logging: Some("own_tx=trace".into()),
 			flag_log_file: Some("/var/log/parity.log".into()),
@@ -1098,7 +1098,7 @@ mod tests {
 				jit: Some(false),
 			}),
 			misc: Some(Misc {
-				ntp_server: Some("pool.ntp.org:123".into()),
+				ntp_servers: Some(vec!["0.parity.pool.ntp.org:123".into()]),
 				logging: Some("own_tx=trace".into()),
 				log_file: Some("/var/log/parity.log".into()),
 				color: Some(true),

parity/cli/usage.txt

@@ -78,7 +78,7 @@ Operating Options:
 
 Convenience Options:
 -c --config CONFIG                 Specify a configuration. CONFIG may be either a
-                                   configuration file or a preset: dev, insecure, dev-insecure, 
+                                   configuration file or a preset: dev, insecure, dev-insecure,
                                    mining, or non-standard-ports.
                                    (default: {flag_config}).
   --ports-shift SHIFT              Add SHIFT to all port numbers Parity is listening on.
@@ -483,8 +483,10 @@ Internal Options:
   --can-restart                    Executable will auto-restart if exiting with 69.
 
 Miscellaneous Options:
-  --ntp-server HOST                NTP server to provide current time (host:port). Used to verify node health.
-                                   (default: {flag_ntp_server})
+  --ntp-servers HOSTS              Comma separated list of NTP servers to provide current time (host:port).
+                                   Used to verify node health. Parity uses pool.ntp.org NTP servers,
+                                   consider joining the pool: http://www.pool.ntp.org/join.html
+                                   (default: {flag_ntp_servers})
   -l --logging LOGGING             Specify the logging level. Must conform to the same
                                    format as RUST_LOG. (default: {flag_logging:?})
   --log-file FILENAME              Specify a filename into which logging should be