Avoid unknown fields on config

This will reduce headaches when adding the wrong fields to the config.

Signed-off-by: Antonio Navarro Perez <antnavper@gmail.com>

config/serialize/serialize.go

@@ -27,9 +27,14 @@ func ReadConfigFile(filename string, cfg interface{}) error {
 		return err
 	}
 	defer f.Close()
-	if err := json.NewDecoder(f).Decode(cfg); err != nil {
+
+	dec := json.NewDecoder(f)
+	dec.DisallowUnknownFields()
+
+	if err := dec.Decode(cfg); err != nil {
 		return fmt.Errorf("failure to decode config: %s", err)
 	}
+
 	return nil
 }
 
@@ -51,13 +56,10 @@ func WriteConfigFile(filename string, cfg interface{}) error {
 
 // encode configuration with JSON
 func encode(w io.Writer, value interface{}) error {
-	// need to prettyprint, hence MarshalIndent, instead of Encoder
-	buf, err := config.Marshal(value)
-	if err != nil {
-		return err
-	}
-	_, err = w.Write(buf)
-	return err
+	enc := json.NewEncoder(w)
+	enc.SetIndent("", "    ")
+
+	return enc.Encode(value)
 }
 
 // Load reads given file and returns the read config, or error.

config/serialize/serialize_test.go

@@ -35,3 +35,25 @@ func TestConfig(t *testing.T) {
 		}
 	}
 }
+
+func TestConfigUnknownField(t *testing.T) {
+	const filename = ".ipfsconfig"
+
+	badConfig := map[string]string{
+		"BadField": "Value",
+	}
+
+	err := WriteConfigFile(filename, badConfig)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = Load(filename)
+	if err == nil {
+		t.Fatal("load must fail")
+	}
+
+	if err.Error() != "failure to decode config: json: unknown field \"BadField\"" {
+		t.Fatal("unexpected error:", err)
+	}
+}