helper/flag-kv: can parse JSON files

helper/flag-kv/flag_json.go

+package kvflag
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+)
+
+// FlagJSON is a flag.Value implementation for parsing user variables
+// from the command-line using JSON files.
+type FlagJSON map[string]string
+
+func (v *FlagJSON) String() string {
+	return ""
+}
+
+func (v *FlagJSON) Set(raw string) error {
+	f, err := os.Open(raw)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	if *v == nil {
+		*v = make(map[string]string)
+	}
+
+	if err := json.NewDecoder(f).Decode(v); err != nil {
+		return fmt.Errorf(
+			"Error reading variables in '%s': %s", raw, err)
+	}
+
+	return nil
+}

helper/flag-kv/flag_json_test.go

+package kvflag
+
+import (
+	"flag"
+	"path/filepath"
+	"reflect"
+	"testing"
+)
+
+func TestFlagJSON_impl(t *testing.T) {
+	var _ flag.Value = new(FlagJSON)
+}
+
+func TestFlagJSON(t *testing.T) {
+	cases := []struct {
+		Input   string
+		Initial map[string]string
+		Output  map[string]string
+		Error   bool
+	}{
+		{
+			"basic.json",
+			nil,
+			map[string]string{"key": "value"},
+			false,
+		},
+
+		{
+			"basic.json",
+			map[string]string{"foo": "bar"},
+			map[string]string{"foo": "bar", "key": "value"},
+			false,
+		},
+
+		{
+			"basic.json",
+			map[string]string{"key": "bar"},
+			map[string]string{"key": "value"},
+			false,
+		},
+	}
+
+	for _, tc := range cases {
+		f := new(FlagJSON)
+		if tc.Initial != nil {
+			f = (*FlagJSON)(&tc.Initial)
+		}
+
+		err := f.Set(filepath.Join("./test-fixtures", tc.Input))
+		if (err != nil) != tc.Error {
+			t.Fatalf("bad error. Input: %#v\n\n%s", tc.Input, err)
+		}
+
+		actual := map[string]string(*f)
+		if !reflect.DeepEqual(actual, tc.Output) {
+			t.Fatalf("bad: %#v", actual)
+		}
+	}
+}

helper/flag-kv/test-fixtures/basic.json

+{
+    "key": "value"
+}