Chromium浏览器的网络库是一个功能非常强大的网络库，它支持的网络协议非常多，除了常见的HTTP/1.1，它还支持HTTP/2，QUIC等比较新的协议。这里我们尝试将Chromium net网络库移植到Android平台，在我们的Android应用中跑起来。
移植Chromium net网络库有两种方式，一是将Chromium net网络库及其依赖的所有其它库编译为动态链接库，将这些so导入我们的Android应用，然后提取Chromium net网络库导出的头文件并导入我们的Android应用，我们自己编写JNI代码进而让Chromium net跑起来；二是利用Cronet。Cronet是对Chromium net网络库的封装，它为我们提供方便的Java接口。编译Cronet时，会将Cronet的JNI代码，Chromium net库及其依赖的所有其它库编译为一个单独的so，并将各个库的Java接口编译为jar包，我们可以将这些jar文件和so文件导入我们的Android应用，并调用Java接口。
这里我们会介绍这两种方式。
编译Chromium net模块
下载Chromium代码
首先要做的是下载完整的Chromium代码，这可以参考 Chromium Android编译指南 完成。然后执行（假设当前目录是chromium代码库的根目录）命令：
$ gclient runhooks
$ cd src
$ ./build/install-build-deps.sh
$ ./build/install-build-deps-android.sh这些命令帮我们下载构建Chromium所需的工具链。
对构建进行配置
构建之前需要对构建进行配置。编辑out/Default/args.gn文件，参照 Chromium Android编译指南 的说明，输入如下内容：
target_os = "android"
target_cpu = "arm" # (default)
is_debug = false # (default)
# Other args you may want to set:
is_component_build = true
is_clang = false
symbol_level = 1 # Faster build with fewer symbols. -g1 rather than -g2
enable_incremental_javac = false # Much faster; experimental
android_ndk_root = "~/dev_tools/Android/android-ndk-r10e"
android_sdk_root = "~/dev_tools/Android/sdk"
android_sdk_build_tools_version = "23.0.2"
disable_file_support = true
disable_ftp_support = true
enable_websockets = false
use_platform_icu_alternatives = true关键点主要有如下几个：
is_component_build被置为ture。Chromium文档 (gn args --list out/Default/输出) 中对这个配置项的说明如下：
is_component_build Default = false
//build/config/BUILDCONFIG.gn:162
Component build. Setting to true compiles targets declared as "components"
as shared libraries loaded dynamically. This speeds up development time.
When false, components will be linked statically.将这个配置项置为true，会使以components声明的targets被编译为动态链接库，否则它们将会被编译为静态库。这里我们需要将net等模块编译为动态链接库，因而将该配置项置为true。
is_debug被置为false，表示编译非Debug版。在这种情况下，enable_incremental_javac同样要被置为false。否则在执行gn gen out/Default生成 .ninja 文件时会报出如下的error：
ERROR at //build/config/android/config.gni:136:3: Assertion failed.
assert(!(enable_incremental_javac && !is_java_debug))
^-----
See //build/config/compiler/compiler.gni:5:1: whence it was imported.
import("//build/config/android/config.gni")
^-----------------------------------------
See //BUILD.gn:11:1: whence it was imported.
import("//build/config/compiler/compiler.gni")
^--------------------------------------------- 配置android_ndk_root为标准NDK的路径，即直接从Google开发者站点下载的NDK包。这个配置指示构建系统，在编译时使用标准NDK工具链，而不是Chromium代码库中的NDK工具链。这主要是因为Chromium代码库中的NDK工具链与标准NDK工具链之间的差异，会导致我们在JNI代码中调用Chromium net函数时，出现诡异的链接诶问题。
NDK版本的选择也要注意。Chromium使用的默认NDK相关信息 (gn args --list out/Default/输出) 如下：
android_ndk_major_version Default = "10"
//build/config/android/config.gni:65
android_ndk_root Default = "//third_party/android_tools/ndk"
//build/config/android/config.gni:66
android_ndk_version Default = "r10e"
//build/config/android/config.gni:67可见默认的NDK版本是r10e的。因而我们也选用r10e版的标准NDK。
-
is_clang选项被置为了false。Chromium文档 (gn args --list out/Default/输出) 中对这个配置项的说明如下：
is_clang Default = false
//build/config/BUILDCONFIG.gn:141
Set to true when compiling with the Clang compiler. Typically this is used
to configure warnings.这个配置项用于指定是否要用Clang编译器。
disable_file_support、disable_ftp_support和enable_websockets分别被置为true、true和false。这几个设置主要是为裁剪需要。我们要禁掉chromium net对这几种协议的支持，以减小最终编译出来的so文件的大小。use_platform_icu_alternatives被置为true。这个配置也是为了减小最终的so文件的总大小。ICU相关的几个so文件总和接近2M，通过将use_platform_icu_alternatives置为true，指示不使用Chromium代码库中的ICU。
保存out/Default/args.gn文件退出，执行如下命令：
$ gn gen out/Default产生ninja构建所需的 .ninja 文件。
编译Chromium net
输入如下命令编译net模块：
$ ninja -C out/Default net这个命令会编译net模块，及其依赖的所有模块，包括base，crypto，boringssl，protobuf，url等。看一下我们编译的成果：
$ ls -alh out/Default/ | grep so$
-rwxrwxr-x 1 chrome chrome 967K 11月 11 15:34 libbase.cr.so
-rwxrwxr-x 1 chrome chrome 785K 11月 11 15:34 libboringssl.cr.so
-rwxrwxr-x 1 chrome chrome 50K 11月 11 15:34 libcrcrypto.cr.so
-rwxrwxr-x 1 chrome chrome 3.3M 11月 11 15:36 libnet.cr.so
-rwxrwxr-x 1 chrome chrome 90K 11月 11 15:34 libprefs.cr.so
-rwxrwxr-x 1 chrome chrome 154K 11月 11 15:34 libprotobuf_lite.cr.so
-rwxrwxr-x 1 chrome chrome 70K 11月 11 15:36 liburl.cr.so总共7个共享库文件，总大小5.4M。
使用Chromium net
将Chromium net导入Android应用
在我们工程的app模块的jni目录下为chromium创建文件夹app/src/main/jni/third_party/chromium/libs和app/src/main/jni/third_party/chromium/include，分别用于存放我们编译出来的共享库和net等模块导出的头文件及这些头文件include的其它头文件。
这里我们将编译出来的所有so文件拷贝到app/src/main/jni/third_party/chromium/libs/armeabi和app/src/main/jni/third_party/chromium/libs/armeabi-v7a目录下：
cp out/Default/*.so ~/MyApplication/app/src/main/jni/third_party/chromium/libs/armeabi/
cp out/Default/*.so ~/MyApplication/app/src/main/jni/third_party/chromium/libs/armeabi-v7a/提取导出头文件
为了使用net模块提供的API，不可避免地要将net导出的头文件引入我们的项目。要做到这些，需要从chromium工程提取net导出的头文件。不像许多其它的C/C++项目，源代码文件、私有头文件及导出头文件存放的位置被很好地做了区隔，chromium各个模块的头文件和源代码文件都是放在一起的。这给我们提取导出头文件的工作带来了一点麻烦。
好在有gn工具。gn工具提供的desc命令（参考 GN的使用 - GN工具 一文）的输出有如下这样两段：
$ gn desc out/Default/ net
Target //net:net
Type: shared_library
Toolchain: //build/toolchain/android:arm
......
sources
//net/base/address_family.cc
//net/base/address_family.h
......
public
[All headers listed in the sources are public.]我们可以据此编写脚本提取net模块的头文件。
我们可以为脚本传入[chromium代码库的src目录路径]，[输出目录的路径]，[模块名]，及[保存头文件的目标目录路径]作为参数，以提取头文件，[保存头文件的目标目录路径]参数缺失时默认使用当前目录，如：
$ cd /media/data/MyProjects/MyApplication/app/src/main/jni/third_party/chromium/include
$ chromium_mod_headers_extracter.py ~/data/chromium_android/src out/Default net
$ chromium_mod_headers_extracter.py ~/data/chromium_android/src out/Default base
$ chromium_mod_headers_extracter.py ~/data/chromium_android/src out/Default url利用我们的脚本，提取net、base和url这三个模块导出的头文件。
这里一并将该脚本的完整内容贴出来供大家参考：
#!/usr/bin/env python
import os
import shutil
import sys
def print_usage_and_exit():
print sys.argv[0] + " [chromium_src_root]" + "[out_dir]" + " [target_name]" + " [targetroot]"
exit(1)
def copy_file(src_file_path, target_file_path):
if os.path.exists(target_file_path):
return
if not os.path.exists(src_file_path):
return
target_dir_path = os.path.dirname(target_file_path)
if not os.path.exists(target_dir_path):
os.makedirs(target_dir_path)
shutil.copy(src_file_path, target_dir_path)
def copy_all_files(source_dir, all_files, target_dir):
for one_file in all_files:
source_path = source_dir + os.path.sep + one_file
target_path = target_dir + os.path.sep + one_file
copy_file(source_path, target_path)
if __name__ == "__main__":
if len(sys.argv) < 4 or len(sys.argv) > 5:
print_usage_and_exit()
chromium_src_root = sys.argv[1]
out_dir = sys.argv[2]
target_name = sys.argv[3]
target_root_path = "."
if len(sys.argv) == 5:
target_root_path = sys.argv[4]
target_root_path = os.path.abspath(target_root_path)
os.chdir(chromium_src_root)
cmd = "gn desc " + out_dir + " " + target_name
outputs = os.popen(cmd).readlines()
source_start = False
all_headers = []
public_start = False
public_headers = []
for output_line in outputs:
output_line = output_line.strip()
if output_line.startswith("sources"):
source_start = True
continue
elif source_start and len(output_line) == 0:
source_start = False
continue
elif source_start and output_line.endswith(".h"):
output_line = output_line[1:]
all_headers.append(output_line)
elif output_line == "public":
public_start = True
continue
elif public_start and len(output_line) == 0:
public_start = False
continue
elif public_start:
public_headers.append(output_line)
if len(public_headers) == 1:
public_headers = all_headers
if len(public_headers) > 1:
copy_all_files(chromium_src_root, public_headers, target_dir=target_root_path)此外，前面的提取过程会遗漏一些必须的头文件。主要是如下几个：
base/callback_forward.h
base/message_loop/timer_slack.h
base/files/file.h
net/cert/cert_status_flags_list.h
net/cert/cert_type.h
net/base/privacy_mode.h
net/websockets/websocket_event_interface.h
net/quic/quic_alarm_factory.h对于这些文件，我们直接从chromium的代码库拷贝到我们的工程中对应的位置即可。
我们还需要引入chromium的build配置头文件build/build_config.h。直接将chromium代码库中的对应文件拷贝过来，放到对应的位置。
将app/src/main/jni/third_party/chromium/include/base/gtest_prod_util.h文件中对testing/gtest/include/gtest/gtest_prod.h的include注释掉，同时修改FRIEND_TEST_ALL_PREFIXES宏的定义为：
#if 0
#define FRIEND_TEST_ALL_PREFIXES(test_case_name, test_name) \
FRIEND_TEST(test_case_name, test_name); \
FRIEND_TEST(test_case_name, DISABLED_##test_name); \
FRIEND_TEST(test_case_name, FLAKY_##test_name)
#else
#define FRIEND_TEST_ALL_PREFIXES(test_case_name, test_name)
#endif这样就可以注释掉类定义中专门为gtest插入的代码。
Chromium net的简单使用
参照chromium/src/net/tools/get_server_time/get_server_time.cc的代码，来编写简单的demo程序。
首先是JNI的Java层代码：
package com.example.hanpfei0306.myapplication;
public class NetUtils {
static {
System.loadLibrary("neteasenet");
}
private static native void nativeSendRequest(String url);
public static void sendRequest(String url) {
nativeSendRequest(url);
}
}然后是JNI的native实现，app/src/main/jni/src/NetJni.cpp：
//
// Created by hanpfei0306 on 16-8-4.
//
#include <stdio.h>
#include <net/base/network_delegate_impl.h>
#include "jni.h"
#include "base/at_exit.h"
#include "base/json/json_writer.h"
#include "base/message_loop/message_loop.h"
#include "base/memory/ptr_util.h"
#include "base/run_loop.h"
#include "base/values.h"
#include "net/http/http_response_headers.h"
#include "net/proxy/proxy_config_service_fixed.h"
#include "net/url_request/url_fetcher.h"
#include "net/url_request/url_fetcher_delegate.h"
#include "net/url_request/url_request_context.h"
#include "net/url_request/url_request_context_builder.h"
#include "net/url_request/url_request_context_getter.h"
#include "net/url_request/url_request.h"
#include "JNIHelper.h"
#define TAG "NetUtils"
// Simply quits the current message loop when finished. Used to make
// URLFetcher synchronous.
class QuitDelegate : public net::URLFetcherDelegate {
public:
QuitDelegate() {}
~QuitDelegate() override {}
// net::URLFetcherDelegate implementation.
void OnURLFetchComplete(const net::URLFetcher* source) override {
LOGE("OnURLFetchComplete");
base::MessageLoop::current()->QuitWhenIdle();
int responseCode = source->GetResponseCode();
const net::URLRequestStatus status = source->GetStatus();
if (status.status() != net::URLRequestStatus::SUCCESS) {
LOGW("Request failed with error code: %s", net::ErrorToString(status.error()).c_str());
return;
}
const net::HttpResponseHeaders* const headers = source->GetResponseHeaders();
if (!headers) {
LOGW("Response does not have any headers");
return;
}
size_t iter = 0;
std::string header_name;
std::string date_header;
while (headers->EnumerateHeaderLines(&iter, &header_name, &date_header)) {
LOGW("Got %s header: %s\n", header_name.c_str(), date_header.c_str());
}
std::string responseStr;
if(!source->GetResponseAsString(&responseStr)) {
LOGW("Get response as string failed!");
}
LOGI("Content len = %lld, response code = %d, response = %s",
source->GetReceivedResponseContentLength(),
source->GetResponseCode(),
responseStr.c_str());
}
void OnURLFetchDownloadProgress(const net::URLFetcher* source,
int64_t current,
int64_t total) override {
LOGE("OnURLFetchDownloadProgress");
}
void OnURLFetchUploadProgress(const net::URLFetcher* source,
int64_t current,
int64_t total) override {
LOGE("OnURLFetchUploadProgress");
}
private:
DISALLOW_COPY_AND_ASSIGN(QuitDelegate);
};
// NetLog::ThreadSafeObserver implementation that simply prints events
// to the logs.
class PrintingLogObserver : public net::NetLog::ThreadSafeObserver {
public:
PrintingLogObserver() {}
~PrintingLogObserver() override {
// This is guaranteed to be safe as this program is single threaded.
net_log()->DeprecatedRemoveObserver(this);
}
// NetLog::ThreadSafeObserver implementation:
void OnAddEntry(const net::NetLog::Entry& entry) override {
// The log level of the entry is unknown, so just assume it maps
// to VLOG(1).
const char* const source_type = net::NetLog::SourceTypeToString(entry.source().type);
const char* const event_type = net::NetLog::EventTypeToString(entry.type());
const char* const event_phase = net::NetLog::EventPhaseToString(entry.phase());
std::unique_ptr<base::Value> params(entry.ParametersToValue());
std::string params_str;
if (params.get()) {
base::JSONWriter::Write(*params, ¶ms_str);
params_str.insert(0, ": ");
}
#ifdef DEBUG_ALL
LOGI("source_type = %s (id = %u): entry_type = %s : event_phase = %s params_str = %s",
source_type, entry.source().id, event_type, event_phase, params_str.c_str());
#endif
}
private:
DISALLOW_COPY_AND_ASSIGN(PrintingLogObserver);
};
// Builds a URLRequestContext assuming there's only a single loop.
static std::unique_ptr<net::URLRequestContext> BuildURLRequestContext(net::NetLog *net_log) {
net::URLRequestContextBuilder builder;
builder.set_net_log(net_log);
//#if defined(OS_LINUX)
// On Linux, use a fixed ProxyConfigService, since the default one
// depends on glib.
//
// TODO(akalin): Remove this once http://crbug.com/146421 is fixed.
builder.set_proxy_config_service(
base::WrapUnique(new net::ProxyConfigServiceFixed(net::ProxyConfig())));
//#endif
std::unique_ptr<net::URLRequestContext> context(builder.Build());
context->set_net_log(net_log);
return context;
}
static void NetUtils_nativeSendRequest(JNIEnv* env, jclass, jstring javaUrl) {
const char* native_url = env->GetStringUTFChars(javaUrl, NULL);
LOGW("Url: %s", native_url);
base::AtExitManager exit_manager;
LOGW("Url: %s", native_url);
GURL url(native_url);
if (!url.is_valid() || (url.scheme() != "http" && url.scheme() != "https")) {
LOGW("Not valid url: %s", native_url);
return;
}
LOGW("Url: %s", native_url);
base::MessageLoopForIO main_loop;
QuitDelegate delegate;
std::unique_ptr<net::URLFetcher> fetcher =
net::URLFetcher::Create(url, net::URLFetcher::GET, &delegate);
net::NetLog *net_log = nullptr;
#ifdef DEBUG_ALL
net_log = new net::NetLog;
PrintingLogObserver printing_log_observer;
net_log->DeprecatedAddObserver(&printing_log_observer,
net::NetLogCaptureMode::IncludeSocketBytes());
#endif
std::unique_ptr<net::URLRequestContext> url_request_context(BuildURLRequestContext(net_log));
fetcher->SetRequestContext(
// Since there's only a single thread, there's no need to worry
// about when the URLRequestContext gets created.
// The URLFetcher will take a reference on the object, and hence
// implicitly take ownership.
new net::TrivialURLRequestContextGetter(url_request_context.get(),
main_loop.task_runner()));
fetcher->Start();
// |delegate| quits |main_loop| when the request is done.
main_loop.Run();
env->ReleaseStringUTFChars(javaUrl, native_url);
}
int jniRegisterNativeMethods(JNIEnv* env, const char *classPathName, JNINativeMethod *nativeMethods, jint nMethods) {
jclass clazz;
clazz = env->FindClass(classPathName);
if (clazz == NULL) {
return JNI_FALSE;
}
if (env->RegisterNatives(clazz, nativeMethods, nMethods) < 0) {
return JNI_FALSE;
}
return JNI_TRUE;
}
static JNINativeMethod gNetUtilsMethods[] = {
NATIVE_METHOD(NetUtils, nativeSendRequest, "(Ljava/lang/String;)V"),
};
void register_com_netease_volleydemo_NetUtils(JNIEnv* env) {
jniRegisterNativeMethods(env, "com/example/hanpfei0306/myapplication/NetUtils",
gNetUtilsMethods, NELEM(gNetUtilsMethods));
}
// DalvikVM calls this on startup, so we can statically register all our native methods.
jint JNI_OnLoad(JavaVM* vm, void*) {
JNIEnv* env;
if (vm->GetEnv(reinterpret_cast<void**>(&env), JNI_VERSION_1_6) != JNI_OK) {
LOGE("JavaVM::GetEnv() failed");
abort();
}
register_com_netease_volleydemo_NetUtils(env);
return JNI_VERSION_1_6;
}这个文件里，在nativeSendRequest()函数中调用chromium net执行网络请求，获取响应，并打印出响应的headers及content。
配置Gradle
要在Android Studio中使用JNI，还需要对Gralde做一些配置文。这里需要对MyApplication/build.gradle、MyApplication/gradle/wrapper/gradle-wrapper.properties，和MyApplication/app/build.gradle这几个文件做修改。
修改MyApplication/build.gradle文件，最终的内容为：
// Top-level build file where you can add configuration options common to all sub-projects/modules.
buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle-experimental:0.7.0'
// NOTE: Do not place your application dependencies here; they belong
// in the individual module build.gradle files
}
}
allprojects {
repositories {
jcenter()
}
}
task clean(type: Delete) {
delete rootProject.buildDir
}在这个文件中配置gradle插件的版本为gradle-experimental:0.7.0。
修改MyApplication/gradle/wrapper/gradle-wrapper.properties文件，最终的内容为：
#Mon Dec 28 10:00:20 PST 2015
distributionBase=GRADLE_USER_HOME
distributionPath=wrapper/dists
zipStoreBase=GRADLE_USER_HOME
zipStorePath=wrapper/dists
distributionUrl=https\://services.gradle.org/distributions/gradle-2.10-all.zip在这个文件中配置gradle的版本。
修改MyApplication/app/build.gradle文件，最终的内容为：
apply plugin: 'com.android.model.application'
model {
repositories {
libs(PrebuiltLibraries) {
chromium_net {
headers.srcDir "src/main/jni/third_party/chromium/include"
binaries.withType(SharedLibraryBinary) {
sharedLibraryFile = file("src/main/jni/third_party/chromium/libs/${targetPlatform.getName()}/libnet.cr.so")
}
}
chromium_base {
headers.srcDir "src/main/jni/third_party/chromium/include"
binaries.withType(SharedLibraryBinary) {
sharedLibraryFile = file("src/main/jni/third_party/chromium/libs/${targetPlatform.getName()}/libbase.cr.so")
}
}
chromium_url {
headers.srcDir "src/main/jni/third_party/chromium/include"
binaries.withType(SharedLibraryBinary) {
sharedLibraryFile = file("src/main/jni/third_party/chromium/libs/${targetPlatform.getName()}/liburl.cr.so")
}
}
}
}
android {
compileSdkVersion 23
buildToolsVersion "23.0.3"
defaultConfig {
applicationId "com.example.hanpfei0306.myapplication"
minSdkVersion.apiLevel 19
targetSdkVersion.apiLevel 21
versionCode 1
versionName "1.0"
}
ndk {
moduleName "neteasenet"
toolchain "clang"
CFlags.addAll(['-I' + file('src/main/jni/third_party/chromium/include/'),])
cppFlags.addAll(["-std=gnu++11", ])
cppFlags.addAll(["-DV8_DEPRECATION_WARNINGS",
"-DENABLE_NOTIFICATIONS",
"-DENABLE_BROWSER_CDMS",
"-DENABLE_PRINTING=1",
"-DENABLE_BASIC_PRINTING=1",
"-DENABLE_SPELLCHECK=1",
"-DUSE_BROWSER_SPELLCHECKER=1",
"-DUSE_OPENSSL_CERTS=1",
"-DNO_TCMALLOC",
"-DUSE_EXTERNAL_POPUP_MENU=1",
"-DDISABLE_NACL",
"-DENABLE_SUPERVISED_USERS=1",
"-DCHROMIUM_BUILD",
"-D_FILE_OFFSET_BITS=64",
"-DANDROID",
"-DHAVE_SYS_UIO_H",
"-D__STDC_CONSTANT_MACROS",
"-D__STDC_FORMAT_MACROS",
"-D_FORTIFY_SOURCE=2",
"-DCOMPONENT_BUILD",
"-D__GNU_SOURCE=1",
"-D_DEBUG",
"-DDYNAMIC_ANNOTATIONS_ENABLED=1",
"-DWTF_USE_DYNAMIC_ANNOTATIONS=1",
"-DDLOPEN_KERBEROS",
"-DNET_IMPLEMENTATION",
"-DUSE_KERBEROS",
"-DENABLE_BUILT_IN_DNS",
"-DPOSIX_AVOID_MMAP",
"-DENABLE_WEBSOCKETS",
"-DGOOGLE_PROTOBUF_NO_RTTI",
"-DGOOGLE_PROTOBUF_NO_STATIC_INITIALIZER",
"-DHAVE_PTHREAD",
"-DPROTOBUF_USE_DLLS",
"-DBORINGSSL_SHARED_LIBRARY",
"-DU_USING_ICU_NAMESPACE=0",
"-DU_ENABLE_DYLOAD=0",
])
cppFlags.addAll(['-I' + file('src/main/jni/third_party/chromium/include'), ])
ldLibs.add("android")
ldLibs.add("log")
ldLibs.add("z")
stl "c++_shared"
}
sources {
main {
java {
source {
srcDir "src/main/java"
}
}
jni {
source {
srcDirs = ["src/main/jni",]
}
dependencies {
library 'chromium_base' linkage 'shared'
library 'chromium_url' linkage 'shared'
library 'chromium_net' linkage 'shared'
}
}
jniLibs {
source {
srcDirs =["src/main/jni/third_party/chromium/libs",]
}
}
}
}
buildTypes {
debug {
ndk {
abiFilters.add("armeabi")
abiFilters.add("armeabi-v7a")
}
}
release {
minifyEnabled false
proguardFiles.add(file("proguard-rules.pro"))
ndk {
abiFilters.add("armeabi")
abiFilters.add("armeabi-v7a")
}
}
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
testCompile 'junit:junit:4.12'
compile 'com.android.support:appcompat-v7:23.4.0'
}关键点主要有如下这些：
- 为net、base和url这几个模块创建PrebuiltLibraries libs元素，并正确的设置对这些模块的依赖。
- 配置stl为"c++_shared"。
- cppFlags的"-std=gnu++11"选项必不可少。
- buildType下的debug和release，需要给它们ndk的abiFilters添加我们想要支持的ABI，而不是留空，以防止Android Studio为我们编译我们不打算支持的ABI的so，而出现找不到文件的问题。
- CFlags和cppFlags中除了配置头文件搜索路径的那两行之外，其它的内容，主要是从chromium的构建环境中提取的。方法为：
$ gn desc out/Default/ net
Target //net:net
Type: shared_library
Toolchain: //build/toolchain/android:arm
......
cflags
-fno-strict-aliasing
--param=ssp-buffer-size=4
-fstack-protector
-funwind-tables
-fPIC
-pipe
-ffunction-sections
-fno-short-enums
-finline-limit=64
-march=armv7-a
-mfloat-abi=softfp
-mthumb
-mthumb-interwork
-mtune=generic-armv7-a
-fno-tree-sra
-fno-caller-saves
-mfpu=neon
-Wall
-Werror
-Wno-psabi
-Wno-unused-local-typedefs
-Wno-maybe-uninitialized
-Wno-missing-field-initializers
-Wno-unused-parameter
-Os
-fomit-frame-pointer
-fno-ident
-fdata-sections
-ffunction-sections
-g1
--sysroot=../../../../../../../~/dev_tools/Android/android-ndk-r12b/platforms/android-16/arch-arm
-fvisibility=hidden
cflags_cc
-fno-threadsafe-statics
-fvisibility-inlines-hidden
-std=gnu++11
-Wno-narrowing
-fno-rtti
-isystem../../../../../../../~/dev_tools/Android/android-ndk-r12b/sources/cxx-stl/llvm-libc++/libcxx/include
-isystem../../../../../../../~/dev_tools/Android/android-ndk-r12b/sources/cxx-stl/llvm-libc++abi/libcxxabi/include
-isystem../../../../../../../~/dev_tools/Android/android-ndk-r12b/sources/android/support/include
-fno-exceptions
......
defines
V8_DEPRECATION_WARNINGS
ENABLE_NOTIFICATIONS
ENABLE_BROWSER_CDMS
ENABLE_PRINTING=1
ENABLE_BASIC_PRINTING=1
ENABLE_SPELLCHECK=1
USE_BROWSER_SPELLCHECKER=1
USE_OPENSSL_CERTS=1
NO_TCMALLOC
USE_EXTERNAL_POPUP_MENU=1
ENABLE_WEBRTC=1
DISABLE_NACL
ENABLE_SUPERVISED_USERS=1
VIDEO_HOLE=1
SAFE_BROWSING_DB_REMOTE
CHROMIUM_BUILD
ENABLE_MEDIA_ROUTER=1
ENABLE_WEBVR
FIELDTRIAL_TESTING_ENABLED
_FILE_OFFSET_BITS=64
ANDROID
HAVE_SYS_UIO_H
ANDROID_NDK_VERSION=r10e
__STDC_CONSTANT_MACROS
__STDC_FORMAT_MACROS
_FORTIFY_SOURCE=2
COMPONENT_BUILD
__GNU_SOURCE=1
NDEBUG
NVALGRIND
DYNAMIC_ANNOTATIONS_ENABLED=0
DLOPEN_KERBEROS
NET_IMPLEMENTATION
USE_KERBEROS
ENABLE_BUILT_IN_DNS
POSIX_AVOID_MMAP
ENABLE_WEBSOCKETS
GOOGLE_PROTOBUF_NO_RTTI
GOOGLE_PROTOBUF_NO_STATIC_INITIALIZER
HAVE_PTHREAD
PROTOBUF_USE_DLLS
BORINGSSL_SHARED_LIBRARY
U_USING_ICU_NAMESPACE=0
U_ENABLE_DYLOAD=0
U_NOEXCEPT=
ICU_UTIL_DATA_IMPL=ICU_UTIL_DATA_FILE
......
libs
c++_shared
~/dev_tools/Android/android-ndk-r12b/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/lib/gcc/arm-linux-androideabi/4.9/libgcc.a
c
atomic
dl
m
log
unwind
lib_dirs
~/dev_tools/Android/android-ndk-r12b/sources/cxx-stl/llvm-libc++/libs/armeabi-v7a/主要是build.gradle的cppFlags添加的那些宏定义，它们来自defines。如果这些配置，在编译chromium net so的环境，和构建我们的工程的环境之间存在差异，则很可能会导致运行期一些莫名奇妙的问题，比如意外的缓冲区溢出之类的。
Cronet移植
如我们前面提到的，Chromium已经有提供一个称为cronet的模块，封装chromium net，提供Java接口。使用这个模块将大大简化我们的移植工作。构建cronet所需步骤主要有：
- 基于前面看到的配置文件
out/Default/args.gn，编辑该文件将is_component_build配置选项置为false。 - 执行如下命令：
$ gn gen out/Default产生ninja构建所需的 .ninja 文件。
- 执行如下命令生成cronet so文件：
$ ninja -C out/Default/ cronet并将产生的libcronet.so文件导入我们的应用中。我们的应用的build.gradle将如下面这样：
apply plugin: 'com.android.model.library'
model {
android {
compileSdkVersion 16
buildToolsVersion "21.1.2"
defaultConfig {
minSdkVersion.apiLevel 15
targetSdkVersion.apiLevel 19
versionCode 1
versionName "1.0"
}
sources {
main {
jniLibs {
source {
srcDirs =["src/main/jni/jniLibs/",]
}
}
}
}
buildTypes {
debug {
ndk {
abiFilters.add("armeabi")
abiFilters.add("armeabi-v7a")
}
}
release {
minifyEnabled false
proguardFiles.add(file("proguard-rules.pro"))
ndk {
abiFilters.add("armeabi")
abiFilters.add("armeabi-v7a")
}
}
}
}
}
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile 'com.android.support:support-annotations:20.0.0'
testCompile 'junit:junit:4.12'
}- 执行如下命令生成cronet Java层代码的jar包：
$ ninja -C out/Default/ cronet_java这将在out/Default/lib.java/的子目录下产生出多个jar文件，cronet_java.jar，cronet_api.jar，url_java.jar，base_java.jar，net_java.jar。将这些jar文件全部导入我们的应用中。
- 调用cronet提供的Java接口执行网络请求：
package com.netease.netlib;
import android.content.Context;
import org.chromium.net.CronetEngine;
import org.chromium.net.UploadDataProviders;
import org.chromium.net.UrlRequest;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
/**
* Created by hanpfei0306 on 16-8-15.
*/
public class CronetUtils {
private static final String TAG = "CronetUtils";
private static CronetUtils sInstance;
private CronetEngine mCronetEngine;
private Executor mExecutor = Executors.newCachedThreadPool();
private CronetUtils() {
}
public static synchronized CronetUtils getsInstance() {
if (sInstance == null) {
sInstance = new CronetUtils();
}
return sInstance;
}
public synchronized void init(Context context) {
if (mCronetEngine == null) {
CronetEngine.Builder builder = new CronetEngine.Builder(context);
builder.
enableHttpCache(CronetEngine.Builder.HTTP_CACHE_IN_MEMORY,
100 * 1024)
.enableHttp2(true)
.enableQuic(true)
.enableSDCH(true)
.setLibraryName("cronet");
mCronetEngine = builder.build();
}
}
public void getHtml(String url, UrlRequest.Callback callback) {
startWithURL(url, callback);
}
private void startWithURL(String url, UrlRequest.Callback callback) {
startWithURL(url, callback, null);
}
private void startWithURL(String url, UrlRequest.Callback callback, String postData) {
UrlRequest.Builder builder = new UrlRequest.Builder(url, callback, mExecutor, mCronetEngine);
applyPostDataToUrlRequestBuilder(builder, mExecutor, postData);
builder.build().start();
}
private void applyPostDataToUrlRequestBuilder(
UrlRequest.Builder builder, Executor executor, String postData) {
if (postData != null && postData.length() > 0) {
builder.setHttpMethod("POST");
builder.addHeader("Content-Type", "application/x-www-form-urlencoded");
builder.setUploadDataProvider(
UploadDataProviders.create(postData.getBytes()), executor);
}
}
}我们有专门将Chromium net及其依赖的模块，还有构建工具链，从Chromium的代码库中抽离出来，形成一个单独的repo，放在git上。有兴趣的朋友可以拿来玩一下。
Done。
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