initial server group implementation

Not a full implementation of #142 yet: default server isn't handled as it needs to be refactored separately (#140).

config.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"log"
+	"math/rand"
 	"os"
 	"sync"
 	"time"
@@ -27,6 +28,7 @@ var loadConfigOnce sync.Once
 type Server struct {
 	Addr      string
 	MediaPool string
+	Groups    []string
 	Fallbacks []string
 
 	dynamic   bool
@@ -236,6 +238,32 @@ func (cnf Config) Pools() map[string]map[string]Server {
 	return pools
 }
 
+// RandomGroupServer returns the name of a random member of a server group
+// or the input string if it is a valid, existent server name.
+// It also returns a boolean indicating success.
+// The returned string is blank if there is a failure,
+// i.e. if the input string is neither a server nor a group.
+func (cnf Config) RandomGroupServer(search string) (string, bool) {
+	candidates := make([]string, 0)
+	for name, srv := range cnf.Servers {
+		if name == search {
+			return name, true
+		}
+
+		for _, grp := range srv.Groups {
+			if grp == search {
+				candidates = append(candidates, name)
+			}
+		}
+	}
+
+	if len(candidates) == 0 {
+		return "", false
+	}
+
+	return candidates[rand.Intn(len(candidates))], true
+}
+
 // FallbackServers returns a slice of server names that
 // a server can fall back to.
 func FallbackServers(server string) []string {

doc/config.md

@@ -117,6 +117,17 @@ See [media_pools.md](https://github.com/HimbeerserverDE/mt-multiserver-proxy/blo
 for more information.
 ```
 
+> `Server.Groups`
+```
+Type: []string
+Default: []string{}
+Description: The server groups this server is in. Group hopping and default server
+selection accept server groups on top of regular server names,
+randomly choosing one of its servers. If a server name and a group name
+are in conflict, the server name is preferred.
+This feature can be used to implement simple load balancing.
+```
+
 > `Server.Fallbacks`
 ```
 Type: []string

hop.go

@@ -15,7 +15,8 @@ var (
 )
 
 // Hop connects the ClientConn to the specified upstream server
-// or the first working fallback server, saving the player's last server.
+// or the first working fallback server, saving the player's last server
+// unless `ForceDefaultSrv` is enabled.
 // If all attempts fail the client is kicked.
 // At the moment the ClientConn is NOT fixed if an error occurs
 // so the player may have to reconnect.
@@ -49,6 +50,23 @@ func (cc *ClientConn) Hop(serverName string) (err error) {
 	return nil
 }
 
+// HopGroup connects the ClientConn to the specified server group
+// or the first working fallback server, saving the player's last server
+// unless `ForceDefaultSrv` is enabled.
+// See the documentation on `Server.Groups` in `doc/config.md`
+// for details on how a specific game server is selected from the group name.
+// If all attempts fail the client is kicked.
+// At the moment the ClientConn is NOT fixed if an error occurs
+// so the player may have to reconnect.
+func (cc *ClientConn) HopGroup(groupName string) error {
+	choice, ok := Conf().RandomGroupServer(groupName)
+	if !ok {
+		return ErrNoSuchServer
+	}
+
+	return cc.Hop(choice)
+}
+
 // HopRaw connects the ClientConn to the specified upstream server.
 // At the moment the ClientConn is NOT fixed if an error occurs
 // so the player may have to reconnect.

run.go

@@ -120,15 +120,14 @@ func runFunc() {
 
 			srvName, srv := conf.DefaultServerInfo()
 			lastSrv, err := authIface.LastSrv(cc.Name())
-			if err == nil && !Conf().ForceDefaultSrv && lastSrv != srvName {
-				for name, s := range conf.Servers {
-					if name == lastSrv {
-						srvName = name
-						srv = s
-
-						break
-					}
+			if err == nil && !conf.ForceDefaultSrv && lastSrv != srvName {
+				choice, ok := conf.RandomGroupServer(lastSrv)
+				if !ok {
+					cc.Log("<-", "inexistent previous server")
 				}
+
+				srvName = choice
+				srv, _ = conf.Servers[choice] // Existence already checked.
 			}
 
 			addr, err := net.ResolveUDPAddr("udp", srv.Addr)