helpers.go

func (app *application) readJSONArray(w http.ResponseWriter, r *http.Request, dst any) error {
	return app.readJSON(w, r, dst, jsontext.KindBeginArray)
}

func (app *application) readJSONObject(w http.ResponseWriter, r *http.Request, dst any) error {
	return app.readJSON(w, r, dst, jsontext.KindBeginObject)
}

func (app *application) readJSON(w http.ResponseWriter, r *http.Request, dst any, expectedFirstToken jsontext.Kind) error {
	err := json.UnmarshalRead(r.Body, dst)
	if err != nil {
		var synErr *jsontext.SyntacticError
		var semErr *json.SemanticError

		switch {
		case errors.As(err, &synErr):
			return convertSyntacticErrorToBadRequest(synErr)

		case errors.As(err, &semErr) && isClientSemanticError(semErr, expectedFirstToken):
			return convertSemanticErrorToBadRequest(semErr)

		default:
			return err
		}
	}

	return nil
}

func isClientSemanticError(semErr *json.SemanticError, expectedFirstToken jsontext.Kind) bool {
	if semErr.Err != nil {
		msgs := []string{
			"ambiguous object member name",
			"cannot derive concrete type for nil interface with finite type set",
			"Go struct has no exported fields",
			"value must be passed as a non-nil pointer reference",
		}
		if slices.Contains(msgs, semErr.Err.Error()) {
			return false
		}
	}

	if semErr.JSONKind == 0 {
		return false
	}

	if semErr.ByteOffset == 0 && semErr.JSONKind != expectedFirstToken {
		return true
	}
	
	if semErr.ByteOffset > 0 {
		return true
	}
	
	return false
}