Process dns-map entries in order

Allows for predictable dns name mapping; most specific should appear
first in the list.

README.md

@@ -112,7 +112,7 @@ ssh-key: |
 * **host-sig** - The expected signature of the remote server - sshproxy will check that the signature presented by the server matches this
 to prevent man-in-the-middle attacks.  If it's omitted, sshproxy will prompt on first connection and then save it in the configuraiton file
 * **dns-map** - A map of hostname patterns to map to an alternative IP address.  The patterns may include asterisk and period operators per 
-the Match function documented here https://golang.org/pkg/path/#Match
+the Match function documented here https://golang.org/pkg/path/#Match.  Order is important as the first matching pattern is selected.
 * **ssh-key** - The ssh key to use to connect to the SSH server.  Must not be encrypted with a passphrase.  **NOTE** Each line of the key
 file must be indented.
 

config.go

@@ -15,12 +15,12 @@ import (
 
 type config struct {
 	filename    string
-	ProxyListen string            `yaml:"proxy-listen"`
-	SSHHost     string            `yaml:"ssh-host"`
-	SSHUser     string            `yaml:"ssh-user"`
-	HostSig     string            `yaml:"host-sig,omitempty"`
-	DNSMap      map[string]string `yaml:"dns-map"`
-	SSHKey      string            `yaml:"ssh-key"`
+	ProxyListen string        `yaml:"proxy-listen"`
+	SSHHost     string        `yaml:"ssh-host"`
+	SSHUser     string        `yaml:"ssh-user"`
+	HostSig     string        `yaml:"host-sig,omitempty"`
+	DNSMap      yaml.MapSlice `yaml:"dns-map"`
+	SSHKey      string        `yaml:"ssh-key"`
 }
 
 func fileExists(filename string) bool {
@@ -70,7 +70,12 @@ func (cfg config) save() {
 
 func (cfg config) mapHost(name string) string {
 	host := strings.ToLower(name)
-	for k, v := range cfg.DNSMap {
+	for _, entry := range cfg.DNSMap {
+		k, kok := entry.Key.(string)
+		v, vok := entry.Value.(string)
+		if !kok || !vok {
+			log.Fatalf("Invalid entry in dns-map - keys and values must be strings key=%v value=%v", entry.Key, entry.Value)
+		}
 		matched, err := filepath.Match(k, host)
 		if err != nil {
 			log.Fatalf("map host error for entry=%s host=%s", k, host)