Enforce config fields, fail on unknown keys (#1051)

If/when users have a typo or misindentation in their config file, we
would have silently failed to assign the value and moved on.

With this change it'll error out, alerting user of the problem.

pkg/config/config.go

@@ -3,6 +3,7 @@ package config
 import (
 	"fmt"
 	"os"
+	"strings"
 	"time"
 
 	"github.com/mitchellh/go-homedir"
@@ -258,7 +259,9 @@ func NewConfig(confString string, c *cli.Context) (*Config, error) {
 		Keys: map[string]string{},
 	}
 	if confString != "" {
-		if err := yaml.Unmarshal([]byte(confString), conf); err != nil {
+		decoder := yaml.NewDecoder(strings.NewReader(confString))
+		decoder.KnownFields(true)
+		if err := decoder.Decode(conf); err != nil {
 			return nil, fmt.Errorf("could not parse config: %v", err)
 		}
 	}

pkg/config/config_test.go

@@ -22,3 +22,11 @@ func TestConfig_DefaultsKept(t *testing.T) {
 	require.Equal(t, true, conf.Room.AutoCreate)
 	require.Equal(t, uint32(10), conf.Room.EmptyTimeout)
 }
+
+func TestConfig_UnknownKeys(t *testing.T) {
+	const content = `unknown: 10
+room:
+  empty_timeout: 10`
+	_, err := NewConfig(content, nil)
+	require.Error(t, err)
+}