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// 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 <android-modules-utils/sdk_level.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 {
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 android::modules::sdklevel::IsAtLeastS(); }();
if (preferNdkFileDescriptorApi) {
return GetNativeFileDescriptorWithNdk(env, javaFd);
} else {
return GetNativeFileDescriptorWithoutNdk(env, javaFd);
}
}
} // namespace netjniutils
} // namespace android
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