Add support for DNS Seed (#940)

* Add support for DNS Seed
* Add port
* Add seed.grin-tech.org
* Remove duplicate IPs

grin/src/seed.rs

@@ -18,6 +18,7 @@
 
 use std::io::Read;
 use std::net::SocketAddr;
+use std::net::ToSocketAddrs;
 use std::str;
 use std::sync::{mpsc, Arc};
 use std::sync::atomic::{AtomicBool, Ordering};
@@ -31,6 +32,7 @@ use p2p;
 use util::LOGGER;
 
 const SEEDS_URL: &'static str = "http://grin-tech.org/seeds.txt";
+const DNS_SEEDS: &'static [&'static str] = &["seed.grin-tech.org", "seed.grin.lesceller.com"];
 
 pub fn connect_and_monitor(
 	p2p_server: Arc<p2p::Server>,
@@ -231,6 +233,32 @@ fn listen_for_addrs(
 	}
 }
 
+pub fn dns_seeds() -> Box<Fn() -> Vec<SocketAddr> + Send> {
+	Box::new(|| {
+		let mut addresses: Vec<SocketAddr> = vec![];
+		for dns_seed in DNS_SEEDS {
+			let temp_addresses = addresses.clone();
+			debug!(LOGGER, "Retrieving seed nodes from dns {}", dns_seed);
+			match (dns_seed.to_owned(), 0).to_socket_addrs() {
+				Ok(addrs) => addresses.append(
+					&mut (addrs
+						.map(|mut addr| {
+							addr.set_port(13414);
+							addr
+						})
+						.filter(|addr| !temp_addresses.contains(addr))
+						.collect()),
+				),
+				Err(e) => debug!(
+					LOGGER,
+					"Failed to resolve seed {:?} got error {:?}", dns_seed, e
+				),
+			}
+		}
+		addresses
+	})
+}
+
 /// Extract the list of seeds from a pre-defined text file available through
 /// http. Easy method until we have a set of DNS names we can rely on.
 pub fn web_seeds() -> Box<Fn() -> Vec<SocketAddr> + Send> {

grin/src/server.rs

@@ -168,6 +168,7 @@ impl Server {
 					seed::predefined_seeds(vec![])
 				}
 				Seeding::List => seed::predefined_seeds(config.seeds.as_mut().unwrap().clone()),
+				Seeding::DNSSeed => seed::dns_seeds(),
 				Seeding::WebStatic => seed::web_seeds(),
 				_ => unreachable!(),
 			};

grin/src/types.rs

@@ -111,6 +111,8 @@ pub enum Seeding {
 	List,
 	/// Automatically download a text file with a list of server addresses
 	WebStatic,
+	/// Automatically get a list of seeds from mutliple DNS
+	DNSSeed,
 	/// Mostly for tests, where connections are initiated programmatically
 	Programmatic,
 }