feat(GODT-2373): introducing bridgelib Go dynamic library in bridge-gui.

pkg/bridgelib/bridgelib.go

@@ -0,0 +1,108 @@
+// Copyright (c) 2023 Proton AG
+//
+// This file is part of Proton Mail Bridge.
+//
+// Proton Mail Bridge is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Proton Mail Bridge is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Proton Mail Bridge. If not, see <https://www.gnu.org/licenses/>.
+
+package main
+
+// bridgelib export bridge go code as a C library. [More info](https://pkg.go.dev/cmd/go#hdr-Build_modes).
+// on Windows bridge-gui is built using the MSVC compiler with cannot link against mingw static library,
+// As a consequence, the library should be built as a C shared library (.dll/.so/.dylib depending on the platform):
+//
+// macOS:   go build -buildmode=c-shared -o bridgelib.dylib bridgelib.go
+// Linux:   go build -buildmode=c-shared -o bridgelib.so bridgelib.go
+// Windows: go build -buildmode=c-shared -o bridgelib.dll bridgelib.go
+//
+// In addition to the library file, the header will export a C header file container the relevant type declarations.
+//
+// Requirements to export a go library
+//
+// - The package name must be main, and as a consequence, must contain a main() function.
+// - The package must import "C"
+// - Functions to be exported must be annotated with the cgo //export comment.
+//
+// Heap allocated data such as go string needs to be released. On macOS and linux, the caller of the library function can call free/delete,
+// but it crashes on Windows because of the VC++/MinGW incompatibility. As a consequence, the caller is responsible for freeing the memory
+// using the DeleteCString function.
+
+//#include <stdlib.h>
+import "C"
+import (
+	"path/filepath"
+	"runtime"
+	"sync"
+	"unsafe"
+
+	"github.com/ProtonMail/proton-bridge/v3/internal/constants"
+	"github.com/ProtonMail/proton-bridge/v3/internal/locations"
+)
+
+// main is empty but required.
+func main() {
+}
+
+var locs *locations.DefaultProvider //nolint:gochecknoglobals
+var locsMutex sync.Mutex            //nolint:gochecknoglobals
+
+// GoOS returns the value of runtime.GOOS.
+//
+//export GoOS
+func GoOS() *C.char {
+	return C.CString(runtime.GOOS)
+}
+
+// UserCacheDir returns the path of the user's cache directory.
+//
+//export UserCacheDir
+func UserCacheDir() *C.char {
+	return withLocationProvider(func(loc *locations.DefaultProvider) string { return loc.UserCache() })
+}
+
+// UserConfigDir returns the path of the user's config directory.
+//
+//export UserConfigDir
+func UserConfigDir() *C.char {
+	return withLocationProvider(func(loc *locations.DefaultProvider) string { return loc.UserConfig() })
+}
+
+// UserDataDir returns the path of the user's data directory.
+//
+//export UserDataDir
+func UserDataDir() *C.char {
+	return withLocationProvider(func(loc *locations.DefaultProvider) string { return loc.UserData() })
+}
+
+// DeleteCString deletes a C-style string allocated by one of the library calls.
+//
+//export DeleteCString
+func DeleteCString(cStr *C.char) {
+	if cStr != nil {
+		C.free(unsafe.Pointer(cStr))
+	}
+}
+
+func withLocationProvider(fn func(provider *locations.DefaultProvider) string) *C.char {
+	locsMutex.Lock()
+	defer locsMutex.Unlock()
+
+	if locs == nil {
+		var err error
+		if locs, err = locations.NewDefaultProvider(filepath.Join(constants.VendorName, constants.ConfigName)); err != nil {
+			return nil
+		}
+	}
+
+	return C.CString(fn(locs))
+}