Share JNI file descriptor helper code
Move JNI File descriptor code from NetworkStack into a common native
static library.
Bug: 158749603
Test: atest NetworkStaticLibTests / treehugger
Change-Id: I3d14587ee8e8590b727736d7d2e29cba687e5514
diff --git a/staticlibs/native/netjniutils/netjniutils.cpp b/staticlibs/native/netjniutils/netjniutils.cpp
new file mode 100644
index 0000000..8ed72b0
--- /dev/null
+++ b/staticlibs/native/netjniutils/netjniutils.cpp
@@ -0,0 +1,104 @@
+// Copyright (C) 2020 The Android Open Source Project
+//
+// 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.
+
+#define LOG_TAG "netjniutils"
+
+#include "netjniutils/netjniutils.h"
+
+#include <dlfcn.h>
+#include <stdbool.h>
+#include <string.h>
+#include <sys/system_properties.h>
+
+#include <android/api-level.h>
+#include <android/log.h>
+
+namespace android {
+namespace netjniutils {
+
+namespace {
+
+bool IsAtLeastS() {
+ // TODO(b/158749603#comment19): move to android::modules::sdklevel::IsAtLeastS().
+ int api_level = android_get_device_api_level();
+
+ // Guarded check for branches that do not have __ANDROID_API_S__.
+#ifdef __ANDROID_API_S__
+ if (api_level >= __ANDROID_API_S__) {
+ return true;
+ }
+#endif
+
+ if (api_level < __ANDROID_API_R__) {
+ return false;
+ }
+
+ // Device looks like R or above, check codename as it could be (S or above).
+ static constexpr const char* kCodenameProperty = "ro.build.version.codename";
+ char codename[PROP_VALUE_MAX] = { 0 };
+ return (__system_property_get(kCodenameProperty, codename) > 0 &&
+ codename[0] >= 'S' && codename[1] == '\0');
+}
+
+int GetNativeFileDescriptorWithoutNdk(JNIEnv* env, jobject javaFd) {
+ // Prior to Android S, we need to find the descriptor field in the FileDescriptor class. The
+ // symbol name has been stable in libcore, but is a private implementation detail.
+ // Older libnativehelper_compat_c++ versions had a jniGetFdFromFileDescriptor method, but this
+ // was removed in S to replace it with the NDK API in libnativehelper.
+ // The code is copied here instead. This code can be removed once R is not supported anymore.
+ static const jfieldID descriptorFieldID = [env]() -> jfieldID {
+ jclass cls = env->FindClass("java/io/FileDescriptor");
+ jfieldID fieldID = env->GetFieldID(cls, "descriptor", "I");
+ env->DeleteLocalRef(cls);
+ if (fieldID == nullptr) {
+ __android_log_print(ANDROID_LOG_FATAL, LOG_TAG, "Failed to get descriptor field.");
+ }
+ return fieldID;
+ }();
+
+ return javaFd != nullptr ? env->GetIntField(javaFd, descriptorFieldID) : -1;
+}
+
+int GetNativeFileDescriptorWithNdk(JNIEnv* env, jobject javaFd) {
+ // Since Android S, there is an NDK API to get a file descriptor present in libnativehelper.so.
+ // libnativehelper is loaded into all processes by the zygote since the zygote uses it
+ // to load the Android Runtime and is also a public library (because of the NDK API).
+ typedef int (*ndkGetFD_t)(JNIEnv*, jobject);
+ static const ndkGetFD_t ndkGetFD = []() -> ndkGetFD_t {
+ void* handle = dlopen("libnativehelper.so", RTLD_NOLOAD | RTLD_NODELETE);
+ auto ndkGetFD = reinterpret_cast<ndkGetFD_t>(dlsym(handle, "AFileDescriptor_getFD"));
+ if (ndkGetFD == nullptr) {
+ __android_log_print(ANDROID_LOG_FATAL, LOG_TAG,
+ "Failed to dlsym(AFileDescriptor_getFD): %s", dlerror());
+ dlclose(handle);
+ }
+ return ndkGetFD;
+ }();
+
+ return javaFd != nullptr ? ndkGetFD(env, javaFd) : -1;
+}
+
+} // namespace
+
+int GetNativeFileDescriptor(JNIEnv* env, jobject javaFd) {
+ static const bool preferNdkFileDescriptorApi = []() -> bool { return IsAtLeastS(); }();
+ if (preferNdkFileDescriptorApi) {
+ return GetNativeFileDescriptorWithNdk(env, javaFd);
+ } else {
+ return GetNativeFileDescriptorWithoutNdk(env, javaFd);
+ }
+}
+
+} // namespace netjniutils
+} // namespace android