impr: support binary files

internal/engine/docker.go

@@ -139,7 +139,7 @@ func (e *Docker) writeFiles(dir string, files Files) error {
 			name = e.cmd.Entry
 		}
 		path := filepath.Join(dir, name)
-		err = os.WriteFile(path, []byte(content), 0444)
+		err = fileio.WriteFile(path, content, 0444)
 		return err == nil
 	})
 	return err

internal/fileio/fileio.go

@@ -2,10 +2,14 @@
 package fileio
 
 import (
+	"encoding/base64"
 	"encoding/json"
+	"errors"
 	"io"
+	"io/fs"
 	"os"
 	"path/filepath"
+	"strings"
 )
 
 // CopyFile copies all files matching the pattern
@@ -52,3 +56,25 @@ func ReadJson[T any](path string) (T, error) {
 	}
 	return obj, err
 }
+
+// WriteFile writes the file to disk.
+// The content can be text or binary (encoded as a data URL),
+// e.g. data:application/octet-stream;base64,MTIz
+func WriteFile(path, content string, perm fs.FileMode) (err error) {
+	var data []byte
+	if strings.HasPrefix(content, "data:") {
+		// data-url encoded file
+		_, encoded, found := strings.Cut(content, ",")
+		if !found {
+			return errors.New("invalid data-url encoding")
+		}
+		data, err = base64.StdEncoding.DecodeString(encoded)
+		if err != nil {
+			return err
+		}
+	} else {
+		// text file
+		data = []byte(content)
+	}
+	return os.WriteFile(path, data, perm)
+}

internal/fileio/fileio_test.go

@@ -82,3 +82,59 @@ func TestReadJson(t *testing.T) {
 		}
 	})
 }
+
+func TestWriteFile(t *testing.T) {
+	dir, err := os.MkdirTemp("", "files")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dir)
+
+	t.Run("text", func(t *testing.T) {
+		path := filepath.Join(dir, "data.txt")
+		err = WriteFile(path, "hello", 0444)
+		if err != nil {
+			t.Fatalf("expected nil err, got %v", err)
+		}
+		got, err := os.ReadFile(path)
+		if err != nil {
+			t.Fatalf("read file: expected nil err, got %v", err)
+		}
+		want := []byte("hello")
+		if !reflect.DeepEqual(got, want) {
+			t.Errorf("read file: expected %v, got %v", want, got)
+		}
+	})
+
+	t.Run("binary", func(t *testing.T) {
+		path := filepath.Join(dir, "data.bin")
+		err = WriteFile(path, "data:application/octet-stream;base64,MTIz", 0444)
+		if err != nil {
+			t.Fatalf("expected nil err, got %v", err)
+		}
+		got, err := os.ReadFile(path)
+		if err != nil {
+			t.Fatalf("read file: expected nil err, got %v", err)
+		}
+		want := []byte("123")
+		if !reflect.DeepEqual(got, want) {
+			t.Errorf("read file: expected %v, got %v", want, got)
+		}
+	})
+
+	t.Run("missing data-url separator", func(t *testing.T) {
+		path := filepath.Join(dir, "data.bin")
+		err = WriteFile(path, "data:application/octet-stream:MTIz", 0444)
+		if err == nil {
+			t.Fatal("expected error, got nil")
+		}
+	})
+
+	t.Run("invalid binary value", func(t *testing.T) {
+		path := filepath.Join(dir, "data.bin")
+		err = WriteFile(path, "data:application/octet-stream;base64,12345", 0444)
+		if err == nil {
+			t.Fatal("expected error, got nil")
+		}
+	})
+}