Simplify the native code by introducing GoPlugin

client/go/outline/electron/go_plugin.go

@@ -0,0 +1,128 @@
+// Copyright 2024 The Outline Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+/*
+#include <stdlib.h>  // for C.free
+
+// InvokeGoAPIResult is a struct used to pass result from Go to TypeScript boundary.
+typedef struct InvokeGoAPIResult_t
+{
+  // A string representing the result of the Go function call.
+	// This may be a raw string or a JSON string depending on the API call.
+	const char *Output;
+
+	// A string containing a JSON representation of any error that occurred during the
+	// Go function call, or NULL if no error occurred.
+	// This error can be parsed by the PlatformError in TypeScript.
+	const char *ErrorJson;
+} InvokeGoAPIResult;
+*/
+import "C"
+import (
+	"fmt"
+	"log/slog"
+	"os"
+	"unsafe"
+
+	"github.com/Jigsaw-Code/outline-apps/client/go/outline"
+	"github.com/Jigsaw-Code/outline-apps/client/go/outline/platerrors"
+)
+
+// API name constants
+const (
+	// FetchResourceAPI fetches a resource located at a given URL.
+	//
+	//  - Input: the URL string of the resource to fetch
+	//  - Output: the content in raw string of the fetched resource
+	FetchResourceAPI = "FetchResource"
+)
+
+// InvokeGoFunc is the unified entry point for TypeScript to invoke various Go functions.
+//
+// The input and output are all defined as string, but they may represent either a raw string,
+// or a JSON string depending on the API call.
+//
+// Check the API name constants comment for more details about the input and output format.
+//
+//export InvokeGoAPI
+func InvokeGoAPI(api *C.char, input *C.char) C.InvokeGoAPIResult {
+	apiName := C.GoString(api)
+	switch apiName {
+
+	case FetchResourceAPI:
+		res := outline.FetchResource(C.GoString(input))
+		return C.InvokeGoAPIResult{
+			Output:    newCGoString(res.Content),
+			ErrorJson: marshalCGoErrorJson(platerrors.ToPlatformError(res.Error)),
+		}
+
+	default:
+		err := &platerrors.PlatformError{
+			Code:    platerrors.IllegalConfig,
+			Message: fmt.Sprintf("unsupported Go API: %s", apiName),
+		}
+		return C.InvokeGoAPIResult{ErrorJson: marshalCGoErrorJson(err)}
+	}
+}
+
+// newCGoString allocates memory for a C string based on the given Go string.
+// It should be paired with [FreeCGoString] to avoid memory leaks.
+func newCGoString(s string) *C.char {
+	res := C.CString(s)
+	slog.Debug("malloc CGoString", "addr", res)
+	return res
+}
+
+// FreeCGoString releases the memory allocated by newCGoString.
+// It also accepts null.
+//
+//export FreeCGoString
+func FreeCGoString(s *C.char) {
+	slog.Debug("free CGoString", "addr", s)
+	C.free(unsafe.Pointer(s))
+}
+
+// marshalCGoErrorJson marshals a PlatformError to a C style JSON string.
+// It always succeeds with a non-empty string if e is not nil.
+func marshalCGoErrorJson(e *platerrors.PlatformError) *C.char {
+	if e == nil {
+		return nil
+	}
+	json, err := platerrors.MarshalJSONString(e)
+	if err != nil {
+		return newCGoString(fmt.Sprintf("%s, failed to retrieve details due to: %s", e.Code, err.Error()))
+	}
+	return newCGoString(json)
+}
+
+// init initializes the backend module.
+// It sets up a default logger based on the OUTLINE_DEBUG environment variable.
+func init() {
+	opts := slog.HandlerOptions{Level: slog.LevelInfo}
+
+	dbg := os.Getenv("OUTLINE_DEBUG")
+	if dbg != "" && dbg != "false" {
+		dbg = "true"
+		opts.Level = slog.LevelDebug
+	} else {
+		dbg = "false"
+	}
+
+	logger := slog.New(slog.NewTextHandler(os.Stderr, &opts))
+	slog.SetDefault(logger)
+
+	slog.Info("Backend module initialized", "debug", dbg)
+}