Change for interpretting min and max peers

* Only min specified -> Set min to that value and max to default
* Only max specified -> Set min and max to that value
* Both specified -> Set min the smallest value and max to the largest value

parity/cli/mod.rs

@@ -388,11 +388,11 @@ usage! {
 			"--port=[PORT]",
 			"Override the port on which the node should listen.",
 
-			ARG arg_min_peers: (u16) = 25u16, or |c: &Config| c.network.as_ref()?.min_peers.clone(),
+			ARG arg_min_peers: (Option<u16>) = None, or |c: &Config| c.network.as_ref()?.min_peers.clone(),
 			"--min-peers=[NUM]",
 			"Try to maintain at least NUM peers.",
 
-			ARG arg_max_peers: (u16) = 50u16, or |c: &Config| c.network.as_ref()?.max_peers.clone(),
+			ARG arg_max_peers: (Option<u16>) = None, or |c: &Config| c.network.as_ref()?.max_peers.clone(),
 			"--max-peers=[NUM]",
 			"Allow up to NUM peers.",
 
@@ -1470,8 +1470,8 @@ mod tests {
 			// -- Networking Options
 			flag_no_warp: false,
 			arg_port: 30303u16,
-			arg_min_peers: 25u16,
-			arg_max_peers: 50u16,
+			arg_min_peers: Some(25u16),
+			arg_max_peers: Some(50u16),
 			arg_max_pending_peers: 64u16,
 			arg_snapshot_peers: 0u16,
 			arg_allow_ips: "all".into(),

parity/configuration.rs

@@ -19,7 +19,7 @@ use std::io::Read;
 use std::net::SocketAddr;
 use std::path::{Path, PathBuf};
 use std::collections::BTreeMap;
-use std::cmp::max;
+use std::cmp::{min, max};
 use std::str::FromStr;
 use cli::{Args, ArgsError};
 use hash::keccak;
@@ -54,6 +54,9 @@ use account::{AccountCmd, NewAccount, ListAccounts, ImportAccounts, ImportFromGe
 use snapshot::{self, SnapshotCommand};
 use network::{IpFilter};
 
+const DEFAULT_MAX_PEERS: u16 = 50;
+const DEFAULT_MIN_PEERS: u16 = 25;
+
 #[derive(Debug, PartialEq)]
 pub enum Cmd {
 	Run(RunCmd),
@@ -455,8 +458,8 @@ impl Configuration {
 	}
 
 	fn max_peers(&self) -> u32 {
-		let peers = self.args.arg_max_peers as u32;
-		max(self.min_peers(), peers)
+		max(self.args.arg_max_peers.unwrap_or(DEFAULT_MAX_PEERS) as u32,
+			self.args.arg_min_peers.unwrap_or(DEFAULT_MIN_PEERS) as u32)
 	}
 
 	fn ip_filter(&self) -> Result<IpFilter, String> {
@@ -467,7 +470,19 @@ impl Configuration {
 	}
 
 	fn min_peers(&self) -> u32 {
-		self.args.arg_peers.unwrap_or(self.args.arg_min_peers) as u32
+		match (self.args.arg_max_peers, self.args.arg_min_peers) {
+			// Only `max peers``specified and respect that by configuring `min peers` that value
+			(Some(max), None) => max as u32,
+
+			// Only `min_peers` specified pick that value
+			(None, Some(min)) => min as u32,
+
+			// Both or none specified, pick the smallest value
+			(_, _) => {
+				min(self.args.arg_max_peers.unwrap_or(DEFAULT_MAX_PEERS) as u32,
+				    self.args.arg_min_peers.unwrap_or(DEFAULT_MIN_PEERS) as u32)
+			}
+		}
 	}
 
 	fn max_pending_peers(&self) -> u32 {