Error when unknown config parameters

support/config/main.go

@@ -3,6 +3,9 @@
 package config
 
 import (
+	"fmt"
+	"io/ioutil"
+
 	"github.com/BurntSushi/toml"
 	"github.com/asaskevich/govalidator"
 	"github.com/stellar/go/strkey"
@@ -18,11 +21,26 @@ type InvalidConfigError struct {
 // Read takes the TOML configuration file at `path`, parses it into `dest` and
 // then uses github.com/asaskevich/govalidator to validate the struct.
 func Read(path string, dest interface{}) error {
-	_, err := toml.DecodeFile(path, dest)
+	bs, err := ioutil.ReadFile(path)
+	if err != nil {
+		return err
+	}
+	return decode(string(bs), dest)
+}
+
+func decode(content string, dest interface{}) error {
+	metadata, err := toml.Decode(content, dest)
 	if err != nil {
 		return errors.Wrap(err, "decode-file failed")
 	}
 
+	// Undecoded keys correspond to keys in the TOML document
+	// that do not have a concrete type in config struct.
+	undecoded := metadata.Undecoded()
+	if len(undecoded) > 0 {
+		return errors.New("Unknown fields: " + fmt.Sprintf("%+v", undecoded))
+	}
+
 	valid, err := govalidator.ValidateStruct(dest)
 
 	if valid {

support/config/main_test.go

@@ -83,3 +83,42 @@ func TestSeedValidator(t *testing.T) {
 	_, ok = fields["WrongType"]
 	assert.True(t, ok, "WrongType is not an invalid field")
 }
+
+func TestUndecoded(t *testing.T) {
+	var val struct {
+		Test string `toml:"test" valid:"optional"`
+		TLS  struct {
+			CertificateFile string `toml:"certificate-file" valid:"optional"`
+			PrivateKeyFile  string `toml:"private-key-file" valid:"optional"`
+		} `valid:"optional"`
+	}
+
+	// Notice _ in certificate_file
+	toml := `test="abc"
+[tls]
+certificate_file="hello"
+private-key-file="world"`
+
+	err := decode(toml, &val)
+	require.Error(t, err)
+	assert.Equal(t, "Unknown fields: [tls.certificate_file]", err.Error())
+}
+
+func TestCorrect(t *testing.T) {
+	var val struct {
+		Test string `toml:"test" valid:"optional"`
+		TLS  struct {
+			CertificateFile string `toml:"certificate-file" valid:"optional"`
+			PrivateKeyFile  string `toml:"private-key-file" valid:"optional"`
+		} `valid:"optional"`
+	}
+
+	// Notice _ in certificate_file
+	toml := `test="abc"
+[tls]
+certificate-file="hello"
+private-key-file="world"`
+
+	err := decode(toml, &val)
+	require.NoError(t, err)
+}