add text transform support

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

file_test.go

@@ -0,0 +1,72 @@
+package file
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"io"
+	"os"
+	"testing"
+
+	"go.unistack.org/micro/v3/codec"
+	"go.unistack.org/micro/v3/config"
+)
+
+type jsoncodec struct{}
+
+func (*jsoncodec) Marshal(v interface{}, opts ...codec.Option) ([]byte, error) {
+	return json.Marshal(v)
+}
+
+func (*jsoncodec) Unmarshal(buf []byte, v interface{}, opts ...codec.Option) error {
+	return json.Unmarshal(buf, v)
+}
+
+func (*jsoncodec) ReadBody(r io.Reader, v interface{}) error {
+	return nil
+}
+
+func (*jsoncodec) ReadHeader(r io.Reader, m *codec.Message, t codec.MessageType) error {
+	return nil
+}
+
+func (*jsoncodec) String() string {
+	return "json"
+}
+
+func (*jsoncodec) Write(w io.Writer, m *codec.Message, v interface{}) error {
+	return nil
+}
+
+func TestLoadReplace(t *testing.T) {
+	type Config struct {
+		Key  string
+		Pass string
+	}
+	os.Setenv("PLACEHOLDER", "test")
+	cfg := &Config{}
+	ctx := context.TODO()
+	buf := bytes.NewReader([]byte(`{"key":"val","pass":"${PLACEHOLDER}"}`))
+	tr, err := NewEnvTransformer(`(?s)\$\{.*?\}`, 2, 1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	c := NewConfig(config.Codec(
+		&jsoncodec{}),
+		config.Struct(cfg),
+		Reader(buf),
+		Transformer(tr),
+	)
+
+	if err := c.Init(); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := c.Load(ctx); err != nil {
+		t.Fatal(err)
+	}
+
+	if cfg.Pass != "test" {
+		t.Fatalf("not works %#+v\n", cfg)
+	}
+}