impr: modular sandbox configs

internal/fileio/fileio.go

@@ -2,6 +2,7 @@
 package fileio
 
 import (
+	"encoding/json"
 	"io"
 	"os"
 	"path/filepath"
@@ -37,3 +38,17 @@ func CopyFiles(pattern string, dstDir string) error {
 
 	return nil
 }
+
+// ReadJson reads the file and decodes it from JSON.
+func ReadJson[T any](path string) (T, error) {
+	var obj T
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return obj, err
+	}
+	err = json.Unmarshal(data, &obj)
+	if err != nil {
+		return obj, err
+	}
+	return obj, err
+}

internal/fileio/fileio_test.go

@@ -3,6 +3,7 @@ package fileio
 import (
 	"os"
 	"path/filepath"
+	"reflect"
 	"testing"
 )
 
@@ -54,3 +55,30 @@ func TestCopyFiles(t *testing.T) {
 		t.Errorf("unexpected file content: got %q, want %q", data, expected)
 	}
 }
+
+func TestReadJson(t *testing.T) {
+	type Person struct{ Name string }
+
+	t.Run("valid", func(t *testing.T) {
+		got, err := ReadJson[Person](filepath.Join("testdata", "valid.json"))
+		if err != nil {
+			t.Fatalf("unexpected error %v", err)
+		}
+		want := Person{"alice"}
+		if !reflect.DeepEqual(got, want) {
+			t.Errorf("expected %v, got %v", want, got)
+		}
+	})
+	t.Run("invalid", func(t *testing.T) {
+		_, err := ReadJson[Person](filepath.Join("testdata", "invalid.json"))
+		if err == nil {
+			t.Fatal("expected error, got nil")
+		}
+	})
+	t.Run("does not exist", func(t *testing.T) {
+		_, err := ReadJson[Person](filepath.Join("testdata", "missing.json"))
+		if err == nil {
+			t.Fatal("expected error, got nil")
+		}
+	})
+}

internal/fileio/testdata/invalid.json

@@ -0,0 +1 @@
+name: alice

internal/fileio/testdata/valid.json

@@ -0,0 +1,3 @@
+{
+    "name": "alice"
+}