Create a readerValue for values that can implement the io.Reader interface

internal/builtins/html.go

@@ -1,9 +1,6 @@
 package builtins
 
 import (
-	"io"
-	"strings"
-
 	"github.com/PuerkitoBio/goquery"
 	"go.starlark.net/starlark"
 	"go.starlark.net/starlarkstruct"
@@ -24,21 +21,11 @@ var htmlModule = &starlarkstruct.Module{
 }
 
 func htmlParse(thread *starlark.Thread, fn *starlark.Builtin, args starlark.Tuple, kwargs []starlark.Tuple) (starlark.Value, error) {
-	var val starlark.Value
-	err := starlark.UnpackArgs("html.selection.find", args, kwargs, "from", &val)
+	var r readerValue
+	err := starlark.UnpackArgs("html.selection.find", args, kwargs, "from", &r)
 	if err != nil {
 		return nil, err
 	}
-
-	var r io.ReadCloser
-	switch val := val.(type) {
-	case starlark.String:
-		r = io.NopCloser(strings.NewReader(string(val)))
-	case starlark.Bytes:
-		r = io.NopCloser(strings.NewReader(string(val)))
-	case starlarkReader:
-		r = val
-	}
 	defer r.Close()
 
 	doc, err := goquery.NewDocumentFromReader(r)

internal/builtins/reader.go

@@ -3,7 +3,9 @@ package builtins
 import (
 	"bufio"
 	"encoding/json"
+	"errors"
 	"io"
+	"strings"
 
 	"github.com/vmihailenco/msgpack/v5"
 	"go.elara.ws/lure-updater/internal/convert"
@@ -213,3 +215,24 @@ func (sr starlarkReader) Close() error {
 	}
 	return nil
 }
+
+type readerValue struct {
+	io.ReadCloser
+}
+
+func (rv *readerValue) Unpack(v starlark.Value) error {
+	switch val := v.(type) {
+	case starlark.String:
+		rv.ReadCloser = io.NopCloser(strings.NewReader(string(val)))
+	case starlark.Bytes:
+		rv.ReadCloser = io.NopCloser(strings.NewReader(string(val)))
+	case starlarkReader:
+		rv.ReadCloser = val
+	}
+
+	if rv.ReadCloser == nil {
+		return errors.New("invalid type for reader")
+	}
+
+	return nil
+}