在計算機網(wǎng)絡(luò)中，代理服務(wù)器 扮演著發(fā)起請求的客戶端與服務(wù)器之間的中間人的角色。客戶端連接到代理服務(wù)器，請求一些服務(wù)，比如文件，網(wǎng)頁，或其它可以從服務(wù)器獲得的資源，代理服務(wù)器以簡化和控制復(fù)雜度的形式獲取請求的響應(yīng)。代理被發(fā)明以為分布式系統(tǒng)添加結(jié)構(gòu)和封裝。

在我們做移動端開發(fā)時，代理常常可以作為我們網(wǎng)絡(luò)調(diào)試的利器。然而我們設(shè)置的代理究竟是如何對網(wǎng)絡(luò)訪問的整個過程產(chǎn)生影響的呢？本文將嘗試回答這個問題。

系統(tǒng)靜態(tài)代理服務(wù)器信息的解析

一個HTTP請求的執(zhí)行過程，大體為：

連接準(zhǔn)備。

建立TCP連接。

如果是HTTPS的話，完成SSL/TLS的握手。

如果是HTTP2的話，在SSL/TLS握手完成之后，執(zhí)行HTTP2的協(xié)商。

發(fā)送請求。

獲取響應(yīng)。

結(jié)束請求，關(guān)閉連接。

與代理相關(guān)的處理，主要發(fā)生在上面的連接準(zhǔn)備與連接建立階段，這主要包括解析系統(tǒng)中保存的靜態(tài)代理服務(wù)器設(shè)置信息，以及以特有的方式建立與代理之間的連接。

Chromium net在 HttpStreamFactoryImpl::Job::DoLoop(int result) 中執(zhí)行解析代理信息、建立連接、處理TLS握手/HTTP2握手/QUIC握手，并創(chuàng)建Stream的過程：

int HttpStreamFactoryImpl::Job::DoLoop(int result) {DCHECK_NE(next_state_, STATE_NONE);int rv = result;do {State state = next_state_;next_state_ = STATE_NONE;switch (state) {case STATE_START:DCHECK_EQ(OK, rv);rv = DoStart();break;case STATE_RESOLVE_PROXY:DCHECK_EQ(OK, rv);rv = DoResolveProxy();break;case STATE_RESOLVE_PROXY_COMPLETE:rv = DoResolveProxyComplete(rv);break;case STATE_WAIT:DCHECK_EQ(OK, rv);rv = DoWait();break;case STATE_WAIT_COMPLETE:rv = DoWaitComplete(rv);break;case STATE_INIT_CONNECTION:DCHECK_EQ(OK, rv);rv = DoInitConnection();break;case STATE_INIT_CONNECTION_COMPLETE:rv = DoInitConnectionComplete(rv);break;case STATE_WAITING_USER_ACTION:rv = DoWaitingUserAction(rv);break;case STATE_RESTART_TUNNEL_AUTH:DCHECK_EQ(OK, rv);rv = DoRestartTunnelAuth();break;case STATE_RESTART_TUNNEL_AUTH_COMPLETE:rv = DoRestartTunnelAuthComplete(rv);break;

具體到系統(tǒng)靜態(tài)代理服務(wù)器設(shè)置信息的解析，

int HttpStreamFactoryImpl::Job::DoResolveProxy() {DCHECK(!pac_request_);DCHECK(session_);next_state_ = STATE_RESOLVE_PROXY_COMPLETE;if (request_info_.load_flags & LOAD_BYPASS_PROXY) {proxy_info_.UseDirect();return OK;}// TODO(rch): remove this code since Alt-Svc seems to prohibit it.GURL url_for_proxy = origin_url_;// For SPDY via Alt-Svc, set |alternative_service_url_| to// https://<alternative host>:<alternative port>/...// so the proxy resolution works with the actual destination, and so// that the correct socket pool is used.if (IsSpdyAlternative()) {// TODO(rch): Figure out how to make QUIC iteract with PAC// scripts. By not re-writing the URL, we will query the PAC script// for the proxy to use to reach the original URL via TCP. But// the alternate request will be going via UDP to a different port.GURL::Replacements replacements;// new_port needs to be in scope here because GURL::Replacements references// the memory contained by it directly.const std::string new_port = base::UintToString(alternative_service_.port);replacements.SetSchemeStr("https");replacements.SetPortStr(new_port);url_for_proxy = url_for_proxy.ReplaceComponents(replacements);}return session_->proxy_service()->ResolveProxy(url_for_proxy, request_info_.method, &proxy_info_, io_callback_,&pac_request_, session_->params().proxy_delegate, net_log_); }int HttpStreamFactoryImpl::Job::DoResolveProxyComplete(int result) {pac_request_ = NULL;if (result == OK) {// Remove unsupported proxies from the list.int supported_proxies =ProxyServer::SCHEME_DIRECT | ProxyServer::SCHEME_HTTP |ProxyServer::SCHEME_HTTPS | ProxyServer::SCHEME_SOCKS4 |ProxyServer::SCHEME_SOCKS5;if (session_->params().enable_quic)supported_proxies |= ProxyServer::SCHEME_QUIC;proxy_info_.RemoveProxiesWithoutScheme(supported_proxies);if (proxy_info_.is_empty()) {// No proxies/direct to choose from. This happens when we don't support// any of the proxies in the returned list.result = ERR_NO_SUPPORTED_PROXIES;} else if (using_quic_ &&(!proxy_info_.is_quic() && !proxy_info_.is_direct())) {// QUIC can not be spoken to non-QUIC proxies. This error should not be// user visible, because the non-alternative Job should be resumed.result = ERR_NO_SUPPORTED_PROXIES;}}if (result != OK) {return result;}next_state_ = STATE_WAIT;return OK; }

Chromium net在對請求的代理的處理上比較靈活，它允許為請求設(shè)置一個標(biāo)記 LOAD_BYPASS_PROXY ，以使該請求的執(zhí)行總是繞過代理。在HttpStreamFactoryImpl::Job::DoResolveProxy() 中會首先檢查請求是否設(shè)置了這個標(biāo)記，若設(shè)置，則將與服務(wù)器直連而立即返回，不再執(zhí)行后面解析系統(tǒng)代理服務(wù)器設(shè)置系統(tǒng)的過程。否則繼續(xù)執(zhí)行。

對于代理的使用，用戶通常都可以設(shè)置一些規(guī)則，比如代理的類型，比如對設(shè)置對某些域名的訪問不使用代理等等。因而對于適當(dāng)?shù)拇淼倪x擇，是根據(jù)設(shè)置的規(guī)則和要訪問的URL進行的。Alternative-Service是一種用于支持新協(xié)議，比如HTTP2，SPDY和QUIC這種，的機制。這種機制通過服務(wù)器向客戶端返回一個 "Alt-Svc" 頭部字段以表明服務(wù)器期望客戶端采用的新協(xié)議。如果要使用新協(xié)議，則發(fā)送請求的URL可能會有一定的改變。在HttpStreamFactoryImpl::Job::DoResolveProxy() 中，若要使用 "Alt-Svc" SPDY/HTTP2，會先對原始的Url做一定的修飾，并以修飾后的Url為基礎(chǔ)去選擇代理。

最后通過ProxyService解析代理信息，選擇代理服務(wù)器。

解析代理之后，執(zhí)行的HttpStreamFactoryImpl::Job::DoResolveProxyComplete() 主要是對解析的結(jié)果做檢查。在這里會過濾掉不支持的代理，并返回最終的檢查結(jié)果。為了保持處理邏輯的簡便統(tǒng)一，即使沒有設(shè)置任何代理服務(wù)器，解析的代理服務(wù)器列表也不會是空的，而是包含一個類型為DIRECT的代理設(shè)置。

默認的ProxyService

HttpStreamFactoryImpl::Job::DoResolveProxy() 所用到的 ProxyService 來自于HttpNetworkSession。而 HttpNetworkSession 的 ProxyService 則是通過如下過程一步一步從 URLRequestContextBuilder 傳過來的：

HttpStreamFactoryImpl::Job::Job() <- DefaultJobFactory::CreateJob() <- HttpStreamFactoryImpl::HttpStreamFactoryImpl() <- HttpNetworkSession::HttpNetworkSession(const Params& params) <- URLRequestContextBuilder::Build()

在 URLRequestContextBuilder::Build() 中可以看到如下的幾行代碼：

void URLRequestContextBuilder::SetHttpNetworkSessionComponents(const URLRequestContext* context,HttpNetworkSession::Params* params) {params->host_resolver = context->host_resolver();params->cert_verifier = context->cert_verifier();params->transport_security_state = context->transport_security_state();params->cert_transparency_verifier = context->cert_transparency_verifier();params->ct_policy_enforcer = context->ct_policy_enforcer();params->proxy_service = context->proxy_service();params->ssl_config_service = context->ssl_config_service();params->http_auth_handler_factory = context->http_auth_handler_factory();params->http_server_properties = context->http_server_properties();params->net_log = context->net_log();params->channel_id_service = context->channel_id_service(); } . . . . . . std::unique_ptr<URLRequestContext> URLRequestContextBuilder::Build() {std::unique_ptr<ContainerURLRequestContext> context(new ContainerURLRequestContext(file_task_runner_));URLRequestContextStorage* storage = context->storage(); . . . . . .if (!proxy_service_) {// TODO(willchan): Switch to using this code when// ProxyService::CreateSystemProxyConfigService()'s signature doesn't suck. #if !defined(OS_LINUX) && !defined(OS_ANDROID)if (!proxy_config_service_) {proxy_config_service_ = ProxyService::CreateSystemProxyConfigService(base::ThreadTaskRunnerHandle::Get().get(),context->GetFileTaskRunner());} #endif // !defined(OS_LINUX) && !defined(OS_ANDROID)proxy_service_ = ProxyService::CreateUsingSystemProxyResolver(std::move(proxy_config_service_),0, // This results in using the default value.context->net_log());}storage->set_proxy_service(std::move(proxy_service_));

然而，對于Android而言，使用的并不是這里創(chuàng)建的 ProxyService 。ProxyConfigService 和 ProxyService 都是在更早的時候創(chuàng)建的。ProxyConfigService 創(chuàng)建的位置 (components/cronet/android/cronet_url_request_context_adapter.cc) 如下：

void CronetURLRequestContextAdapter::InitRequestContextOnMainThread(JNIEnv* env,const JavaParamRef<jobject>& jcaller) {base::android::ScopedJavaGlobalRef<jobject> jcaller_ref;jcaller_ref.Reset(env, jcaller);proxy_config_service_ = net::ProxyService::CreateSystemProxyConfigService(GetNetworkTaskRunner(), nullptr /* Ignored on Android */);net::ProxyConfigServiceAndroid* android_proxy_config_service =static_cast<net::ProxyConfigServiceAndroid*>(proxy_config_service_.get());// If a PAC URL is present, ignore it and use the address and port of// Android system's local HTTP proxy server. See: crbug.com/432539.// TODO(csharrison) Architect the wrapper better so we don't need to cast for// android ProxyConfigServices.android_proxy_config_service->set_exclude_pac_url(true);g_net_log.Get().EnsureInitializedOnMainThread();GetNetworkTaskRunner()->PostTask(FROM_HERE,base::Bind(&CronetURLRequestContextAdapter::InitializeOnNetworkThread,base::Unretained(this), base::Passed(&context_config_),jcaller_ref)); }

而 ProxyService 的創(chuàng)建位置 (components/cronet/android/cronet_url_request_context_adapter.cc) 則在 CronetURLRequestContextAdapter::InitializeOnNetworkThread()：

void CronetURLRequestContextAdapter::InitializeOnNetworkThread(std::unique_ptr<URLRequestContextConfig> config,const base::android::ScopedJavaGlobalRef<jobject>&jcronet_url_request_context) {DCHECK(GetNetworkTaskRunner()->BelongsToCurrentThread());DCHECK(!is_context_initialized_);DCHECK(proxy_config_service_);// TODO(mmenke): Add method to have the builder enable SPDY.net::URLRequestContextBuilder context_builder;std::unique_ptr<net::NetworkDelegate> network_delegate(new BasicNetworkDelegate()); #if defined(DATA_REDUCTION_PROXY_SUPPORT) . . . . . . #endif // defined(DATA_REDUCTION_PROXY_SUPPORT)context_builder.set_network_delegate(std::move(network_delegate));context_builder.set_net_log(g_net_log.Get().net_log());// Android provides a local HTTP proxy server that handles proxying when a PAC// URL is present. Create a proxy service without a resolver and rely on this// local HTTP proxy. See: crbug.com/432539.context_builder.set_proxy_service(net::ProxyService::CreateWithoutProxyResolver(std::move(proxy_config_service_), g_net_log.Get().net_log()));

ProxyConfigService 和 ProxyService 的實際創(chuàng)建過程（位于net/proxy/proxy_service.cc ）如下：

// static std::unique_ptr<ProxyService> ProxyService::CreateWithoutProxyResolver(std::unique_ptr<ProxyConfigService> proxy_config_service,NetLog* net_log) {return base::WrapUnique(new ProxyService(std::move(proxy_config_service),base::WrapUnique(new ProxyResolverFactoryForNullResolver), net_log)); } . . . . . . // static std::unique_ptr<ProxyConfigService> ProxyService::CreateSystemProxyConfigService(const scoped_refptr<base::SingleThreadTaskRunner>& io_task_runner,const scoped_refptr<base::SingleThreadTaskRunner>& file_task_runner) { #if defined(OS_WIN) . . . . . . #elif defined(OS_ANDROID)return base::WrapUnique(new ProxyConfigServiceAndroid(io_task_runner, base::ThreadTaskRunnerHandle::Get())); #elseLOG(WARNING) << "Failed to choose a system proxy settings fetcher ""for this platform.";return base::WrapUnique(new ProxyConfigServiceDirect()); #endif }

可見在Android平臺，默認的ProxyConfigService 為 ProxyConfigServiceAndroid， ProxyService 本身并不單單是接口，它在解析代理信息時，除了依賴靜態(tài)信息外，還會依賴 ProxyResolverFactory 和 ProxyResolver 去獲得代理信息。按照設(shè)計， ProxyResolver 將會填充用于特定URL的代理的列表。通常的 ProxyResolver 后端都是一個PAC腳本，但也不一定。一個 ProxyResolver 可以在同一時間為多個URL服務(wù)。

而在Android平臺 ProxyResolverFactory 和 ProxyResolver 的實現(xiàn)分別為 ProxyResolverFactoryForNullResolver 和 ProxyResolverNull。可以看一下ProxyResolverFactoryForNullResolver 和 ProxyResolverNull的實現(xiàn)（位于net/proxy/proxy_service.cc ）：

// Proxy resolver that fails every time. class ProxyResolverNull : public ProxyResolver {public:ProxyResolverNull() {}// ProxyResolver implementation.int GetProxyForURL(const GURL& url,ProxyInfo* results,const CompletionCallback& callback,RequestHandle* request,const BoundNetLog& net_log) override {return ERR_NOT_IMPLEMENTED;}void CancelRequest(RequestHandle request) override { NOTREACHED(); }LoadState GetLoadState(RequestHandle request) const override {NOTREACHED();return LOAD_STATE_IDLE;}}; . . . . . . class ProxyResolverFactoryForNullResolver : public ProxyResolverFactory {public:ProxyResolverFactoryForNullResolver() : ProxyResolverFactory(false) {}// ProxyResolverFactory overrides.int CreateProxyResolver(const scoped_refptr<ProxyResolverScriptData>& pac_script,std::unique_ptr<ProxyResolver>* resolver,const net::CompletionCallback& callback,std::unique_ptr<Request>* request) override {resolver->reset(new ProxyResolverNull());return OK;}private:DISALLOW_COPY_AND_ASSIGN(ProxyResolverFactoryForNullResolver); };

由此，可以認為在Android平臺是沒有 ProxyResolver 后端的，也就是代理解析，基本上只依賴系統(tǒng)的靜態(tài)配置信息。

ProxyService的初始化

在 ProxyService 創(chuàng)建的時候，會做一些初始化：

ProxyService::ProxyService(std::unique_ptr<ProxyConfigService> config_service,std::unique_ptr<ProxyResolverFactory> resolver_factory,NetLog* net_log): resolver_factory_(std::move(resolver_factory)),next_config_id_(1),current_state_(STATE_NONE),net_log_(net_log),stall_proxy_auto_config_delay_(TimeDelta::FromMilliseconds(kDelayAfterNetworkChangesMs)),quick_check_enabled_(true),sanitize_url_policy_(SanitizeUrlPolicy::SAFE) {NetworkChangeNotifier::AddIPAddressObserver(this);NetworkChangeNotifier::AddDNSObserver(this);ResetConfigService(std::move(config_service)); } . . . . . . ProxyService::State ProxyService::ResetProxyConfig(bool reset_fetched_config) {DCHECK(CalledOnValidThread());State previous_state = current_state_;permanent_error_ = OK;proxy_retry_info_.clear();script_poller_.reset();init_proxy_resolver_.reset();SuspendAllPendingRequests();resolver_.reset();config_ = ProxyConfig();if (reset_fetched_config)fetched_config_ = ProxyConfig();current_state_ = STATE_NONE;return previous_state; }void ProxyService::ResetConfigService(std::unique_ptr<ProxyConfigService> new_proxy_config_service) {DCHECK(CalledOnValidThread());State previous_state = ResetProxyConfig(true);// Release the old configuration service.if (config_service_.get())config_service_->RemoveObserver(this);// Set the new configuration service.config_service_ = std::move(new_proxy_config_service);config_service_->AddObserver(this);if (previous_state != STATE_NONE)ApplyProxyConfigIfAvailable(); }

這里主要是將 ProxyService 對象注冊為網(wǎng)絡(luò)狀態(tài)的監(jiān)聽者，以監(jiān)聽IP地址和 DNS 的改變，并注冊為 ProxyConfigService 的監(jiān)聽者以監(jiān)聽。由于創(chuàng)建初始，previous_state 為 STATE_NONE，因而并不會做更多別的事情。

ProxyConfigService的初始化

ProxyConfigService 是Android平臺中 ProxyService 獲取代理配置信息的關(guān)鍵，回頭再來看 ProxyConfigService 的創(chuàng)建及初始化過程。如我們前面看到的，創(chuàng)建對象的位置在CronetURLRequestContextAdapter::InitRequestContextOnMainThread()。具體的過程（ 位于net/proxy/proxy_config_service_android.cc ）如下：

ProxyConfigServiceAndroid::ProxyConfigServiceAndroid(const scoped_refptr<base::SequencedTaskRunner>& network_task_runner,const scoped_refptr<base::SequencedTaskRunner>& jni_task_runner): delegate_(new Delegate(network_task_runner, jni_task_runner, base::Bind(&GetJavaProperty))) {delegate_->SetupJNI();delegate_->FetchInitialConfig(); }

在這里主要是創(chuàng)建 ProxyConfigServiceAndroid::Delegate，并做初始化。初始化主要包括 SetupJNI() 和 FetchInitialConfig()，其中 SetupJNI() 是這樣的：

class JNIDelegateImpl : public ProxyConfigServiceAndroid::JNIDelegate {public:explicit JNIDelegateImpl(Delegate* delegate) : delegate_(delegate) {} . . . . . . class ProxyConfigServiceAndroid::Delegate: public base::RefCountedThreadSafe<Delegate> {public:Delegate(const scoped_refptr<base::SequencedTaskRunner>& network_task_runner,const scoped_refptr<base::SequencedTaskRunner>& jni_task_runner,const GetPropertyCallback& get_property_callback): jni_delegate_(this),network_task_runner_(network_task_runner),jni_task_runner_(jni_task_runner),get_property_callback_(get_property_callback),exclude_pac_url_(false) {}void SetupJNI() {DCHECK(OnJNIThread());JNIEnv* env = AttachCurrentThread();if (java_proxy_change_listener_.is_null()) {VLOG(1) << "ProxyConfigServiceAndroid::Delegate SetupJNI, try to create java_proxy_change_listener_ object";java_proxy_change_listener_.Reset(Java_ProxyChangeListener_create(env, base::android::GetApplicationContext()));CHECK(!java_proxy_change_listener_.is_null());}Java_ProxyChangeListener_start(env,java_proxy_change_listener_.obj(),reinterpret_cast<intptr_t>(&jni_delegate_));}

可以看到，它主要是創(chuàng)建了一個類型為org.chromium.net.ProxyChangeListener 的Java對象，并調(diào)用了該對象的 start(long nativePtr) 方法（ 位于net/android/java/src/org/chromium/net/ProxyChangeListener.java ）。來看這個Java類的實現(xiàn)：

private ProxyChangeListener(Context context) {mContext = context;} . . . . . .@CalledByNativepublic static ProxyChangeListener create(Context context) {return new ProxyChangeListener(context);} . . . . . .@CalledByNativepublic void start(long nativePtr) {assert mNativePtr == 0;mNativePtr = nativePtr;registerReceiver();} . . . . . .private void registerReceiver() {if (mProxyReceiver != null) {return;}IntentFilter filter = new IntentFilter();filter.addAction(Proxy.PROXY_CHANGE_ACTION);mProxyReceiver = new ProxyReceiver();mContext.getApplicationContext().registerReceiver(mProxyReceiver, filter);}

可以看到，這里主要是注冊了一個監(jiān)聽 Action 為 Proxy.PROXY_CHANGE_ACTION 的 BroadcastReceiver。再來看 FetchInitialConfig()：

// Returns whether the provided string was successfully converted to a port. bool ConvertStringToPort(const std::string& port, int* output) {url::Component component(0, port.size());int result = url::ParsePort(port.c_str(), component);if (result == url::PORT_INVALID || result == url::PORT_UNSPECIFIED)return false;*output = result;return true; }ProxyServer ConstructProxyServer(ProxyServer::Scheme scheme,const std::string& proxy_host,const std::string& proxy_port) {DCHECK(!proxy_host.empty());int port_as_int = 0;if (proxy_port.empty())port_as_int = ProxyServer::GetDefaultPortForScheme(scheme);else if (!ConvertStringToPort(proxy_port, &port_as_int))return ProxyServer();DCHECK(port_as_int > 0);return ProxyServer(scheme, HostPortPair(proxy_host, static_cast<uint16_t>(port_as_int))); }ProxyServer LookupProxy(const std::string& prefix,const GetPropertyCallback& get_property,ProxyServer::Scheme scheme) {DCHECK(!prefix.empty());std::string proxy_host = get_property.Run(prefix + ".proxyHost");if (!proxy_host.empty()) {std::string proxy_port = get_property.Run(prefix + ".proxyPort");return ConstructProxyServer(scheme, proxy_host, proxy_port);}// Fall back to default proxy, if any.proxy_host = get_property.Run("proxyHost");if (!proxy_host.empty()) {std::string proxy_port = get_property.Run("proxyPort");return ConstructProxyServer(scheme, proxy_host, proxy_port);}return ProxyServer(); }ProxyServer LookupSocksProxy(const GetPropertyCallback& get_property) {std::string proxy_host = get_property.Run("socksProxyHost");if (!proxy_host.empty()) {std::string proxy_port = get_property.Run("socksProxyPort");return ConstructProxyServer(ProxyServer::SCHEME_SOCKS5, proxy_host,proxy_port);}return ProxyServer(); }void AddBypassRules(const std::string& scheme,const GetPropertyCallback& get_property,ProxyBypassRules* bypass_rules) {// The format of a hostname pattern is a list of hostnames that are separated// by | and that use * as a wildcard. For example, setting the// http.nonProxyHosts property to *.android.com|*.kernel.org will cause// requests to http://developer.android.com to be made without a proxy.std::string non_proxy_hosts =get_property.Run(scheme + ".nonProxyHosts");if (non_proxy_hosts.empty())return;base::StringTokenizer tokenizer(non_proxy_hosts, "|");while (tokenizer.GetNext()) {std::string token = tokenizer.token();std::string pattern;base::TrimWhitespaceASCII(token, base::TRIM_ALL, &pattern);if (pattern.empty())continue;// '?' is not one of the specified pattern characters above.DCHECK_EQ(std::string::npos, pattern.find('?'));bypass_rules->AddRuleForHostname(scheme, pattern, -1);} }// Returns true if a valid proxy was found. bool GetProxyRules(const GetPropertyCallback& get_property,ProxyConfig::ProxyRules* rules) {// See libcore/luni/src/main/java/java/net/ProxySelectorImpl.java for the// mostly equivalent Android implementation. There is one intentional// difference: by default Chromium uses the HTTP port (80) for HTTPS// connections via proxy. This default is identical on other platforms.// On the opposite, Java spec suggests to use HTTPS port (443) by default (the// default value of https.proxyPort).rules->type = ProxyConfig::ProxyRules::TYPE_PROXY_PER_SCHEME;rules->proxies_for_http.SetSingleProxyServer(LookupProxy("http", get_property, ProxyServer::SCHEME_HTTP));rules->proxies_for_https.SetSingleProxyServer(LookupProxy("https", get_property, ProxyServer::SCHEME_HTTP));rules->proxies_for_ftp.SetSingleProxyServer(LookupProxy("ftp", get_property, ProxyServer::SCHEME_HTTP));rules->fallback_proxies.SetSingleProxyServer(LookupSocksProxy(get_property));rules->bypass_rules.Clear();AddBypassRules("ftp", get_property, &rules->bypass_rules);AddBypassRules("http", get_property, &rules->bypass_rules);AddBypassRules("https", get_property, &rules->bypass_rules);// We know a proxy was found if not all of the proxy lists are empty.return !(rules->proxies_for_http.IsEmpty() &&rules->proxies_for_https.IsEmpty() &&rules->proxies_for_ftp.IsEmpty() &&rules->fallback_proxies.IsEmpty()); };void GetLatestProxyConfigInternal(const GetPropertyCallback& get_property,ProxyConfig* config) {if (!GetProxyRules(get_property, &config->proxy_rules()))*config = ProxyConfig::CreateDirect(); }std::string GetJavaProperty(const std::string& property) {// Use Java System.getProperty to get configuration information.// TODO(pliard): Conversion to/from UTF8 ok here?JNIEnv* env = AttachCurrentThread();ScopedJavaLocalRef<jstring> str = ConvertUTF8ToJavaString(env, property);ScopedJavaLocalRef<jstring> result =Java_ProxyChangeListener_getProperty(env, str.obj());return result.is_null() ?std::string() : ConvertJavaStringToUTF8(env, result.obj()); } . . . . . .void FetchInitialConfig() {DCHECK(OnJNIThread());ProxyConfig proxy_config;GetLatestProxyConfigInternal(get_property_callback_, &proxy_config);network_task_runner_->PostTask(FROM_HERE,base::Bind(&Delegate::SetNewConfigOnNetworkThread, this, proxy_config));} . . . . . .// Called on the network thread.void SetNewConfigOnNetworkThread(const ProxyConfig& proxy_config) {DCHECK(OnNetworkThread());proxy_config_ = proxy_config;FOR_EACH_OBSERVER(Observer, observers_,OnProxyConfigChanged(proxy_config,ProxyConfigService::CONFIG_VALID));}

可以看到，這里做了兩件事，一是獲取系統(tǒng)的代理配置信息，方法主要還是通過讀取系統(tǒng)屬性完成；二是通知監(jiān)聽者，這主要是ProxyService。

對于 Action 為 Proxy.PROXY_CHANGE_ACTION 的 BroadcastReceiver，是在注冊完成之后幾乎立即就會得到通知的。ProxyReceiver的實現(xiàn)如下：

private class ProxyReceiver extends BroadcastReceiver {@Overridepublic void onReceive(Context context, Intent intent) {if (intent.getAction().equals(Proxy.PROXY_CHANGE_ACTION)) {proxySettingsChanged(extractNewProxy(intent));}}// Extract a ProxyConfig object from the supplied Intent's extra data// bundle. The android.net.ProxyProperties class is not exported from// the Android SDK, so we have to use reflection to get at it and invoke// methods on it. If we fail, return an empty proxy config (meaning// 'direct').// TODO(sgurun): once android.net.ProxyInfo is public, rewrite this.private ProxyConfig extractNewProxy(Intent intent) {try {final String getHostName = "getHost";final String getPortName = "getPort";final String getPacFileUrl = "getPacFileUrl";final String getExclusionList = "getExclusionList";String className;String proxyInfo;if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {className = "android.net.ProxyProperties";proxyInfo = "proxy";} else {className = "android.net.ProxyInfo";proxyInfo = "android.intent.extra.PROXY_INFO";}Object props = intent.getExtras().get(proxyInfo);if (props == null) {return null;}Class<?> cls = Class.forName(className);Method getHostMethod = cls.getDeclaredMethod(getHostName);Method getPortMethod = cls.getDeclaredMethod(getPortName);Method getExclusionListMethod = cls.getDeclaredMethod(getExclusionList);String host = (String) getHostMethod.invoke(props);int port = (Integer) getPortMethod.invoke(props);String[] exclusionList;if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {String s = (String) getExclusionListMethod.invoke(props);exclusionList = s.split(",");} else {exclusionList = (String[]) getExclusionListMethod.invoke(props);}// TODO(xunjieli): rewrite this once the API is public.if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT&& Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP) {Method getPacFileUrlMethod = cls.getDeclaredMethod(getPacFileUrl);String pacFileUrl = (String) getPacFileUrlMethod.invoke(props);if (!TextUtils.isEmpty(pacFileUrl)) {return new ProxyConfig(host, port, pacFileUrl, exclusionList);}} else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {Method getPacFileUrlMethod = cls.getDeclaredMethod(getPacFileUrl);Uri pacFileUrl = (Uri) getPacFileUrlMethod.invoke(props);if (!Uri.EMPTY.equals(pacFileUrl)) {return new ProxyConfig(host, port, pacFileUrl.toString(), exclusionList);}}return new ProxyConfig(host, port, null, exclusionList);} catch (ClassNotFoundException ex) {Log.e(TAG, "Using no proxy configuration due to exception:" + ex);return null;} catch (NoSuchMethodException ex) {Log.e(TAG, "Using no proxy configuration due to exception:" + ex);return null;} catch (IllegalAccessException ex) {Log.e(TAG, "Using no proxy configuration due to exception:" + ex);return null;} catch (InvocationTargetException ex) {Log.e(TAG, "Using no proxy configuration due to exception:" + ex);return null;} catch (NullPointerException ex) {Log.e(TAG, "Using no proxy configuration due to exception:" + ex);return null;}}}private void proxySettingsChanged(ProxyConfig cfg) {if (!sEnabled) {return;}if (mDelegate != null) {mDelegate.proxySettingsChanged();}if (mNativePtr == 0) {return;}// Note that this code currently runs on a MESSAGE_LOOP_UI thread, but// the C++ code must run the callbacks on the network thread.if (cfg != null) {nativeProxySettingsChangedTo(mNativePtr, cfg.mHost, cfg.mPort, cfg.mPacUrl,cfg.mExclusionList);} else {nativeProxySettingsChanged(mNativePtr);}}

這個Receiver在收到通知后，會將代理信息傳遞到C/C++層。最終調(diào)用ProxyConfigServiceAndroid::Delegate::JNIDelegateImpl：

// ProxyConfigServiceAndroid::JNIDelegate overrides.void ProxySettingsChangedTo(JNIEnv* env,const JavaParamRef<jobject>& jself,const JavaParamRef<jstring>& jhost,jint jport,const JavaParamRef<jstring>& jpac_url,const JavaParamRef<jobjectArray>& jexclusion_list) override {std::string host = ConvertJavaStringToUTF8(env, jhost);std::string pac_url;if (jpac_url)ConvertJavaStringToUTF8(env, jpac_url, &pac_url);std::vector<std::string> exclusion_list;base::android::AppendJavaStringArrayToStringVector(env, jexclusion_list, &exclusion_list);delegate_->ProxySettingsChangedTo(host, jport, pac_url, exclusion_list);}void ProxySettingsChanged(JNIEnv* env,const JavaParamRef<jobject>& self) override {delegate_->ProxySettingsChanged();}private:Delegate* const delegate_;};

繼而調(diào)用 ProxyConfigServiceAndroid::Delegate 的相應(yīng)方法：

void CreateStaticProxyConfig(const std::string& host,int port,const std::string& pac_url,const std::vector<std::string>& exclusion_list,ProxyConfig* config) {if (!pac_url.empty()) {config->set_pac_url(GURL(pac_url));config->set_pac_mandatory(false);} else if (port != 0) {std::string rules = base::StringPrintf("%s:%d", host.c_str(), port);config->proxy_rules().ParseFromString(rules);config->proxy_rules().bypass_rules.Clear();std::vector<std::string>::const_iterator it;for (it = exclusion_list.begin(); it != exclusion_list.end(); ++it) {std::string pattern;base::TrimWhitespaceASCII(*it, base::TRIM_ALL, &pattern);if (pattern.empty())continue;config->proxy_rules().bypass_rules.AddRuleForHostname("", pattern, -1);}} else {*config = ProxyConfig::CreateDirect();} } . . . . . .// Called on the JNI thread.void ProxySettingsChanged() {DCHECK(OnJNIThread());ProxyConfig proxy_config;GetLatestProxyConfigInternal(get_property_callback_, &proxy_config);network_task_runner_->PostTask(FROM_HERE,base::Bind(&Delegate::SetNewConfigOnNetworkThread, this, proxy_config));}// Called on the JNI thread.void ProxySettingsChangedTo(const std::string& host,int port,const std::string& pac_url,const std::vector<std::string>& exclusion_list) {DCHECK(OnJNIThread());ProxyConfig proxy_config;if (exclude_pac_url_) {CreateStaticProxyConfig(host, port, "", exclusion_list, &proxy_config);} else {CreateStaticProxyConfig(host, port, pac_url, exclusion_list,&proxy_config);}network_task_runner_->PostTask(FROM_HERE,base::Bind(&Delegate::SetNewConfigOnNetworkThread, this, proxy_config));}

ProxySettingsChanged()如同 FetchInitialConfig() 一樣，是從system property中獲取代理配置信息，并通知監(jiān)聽者。而 ProxySettingsChangedTo() 則是以傳入的代理配置信息構(gòu)造配置，并通知監(jiān)聽者。

可見，BroadcastReceiver 通知時的這次配置信息更新會沖掉最初通過 FetchInitialConfig() 獲取的那些。

總結(jié)一下，在Android中，chromium net獲取代理配置信息的方法是：

在 ProxyConfigServiceAndroid 創(chuàng)建過程中，從system property中讀取代理設(shè)置信息，同時注冊BroadcastReceiver以監(jiān)聽系統(tǒng)代理配置的改變。

在收到系統(tǒng)廣播消息的通知時，若廣播中包含詳細的代理配置信息，則以這些信息更新Chromium net的代理設(shè)置；否則，再次讀取system property獲取代理配置信息。

代理解析

ProxyConfigService 在代理配置發(fā)生改變時，會將新的代理配置通知給ProxyService：

void ProxyService::SetReady() {DCHECK(!init_proxy_resolver_.get());current_state_ = STATE_READY;// Make a copy in case |this| is deleted during the synchronous completion// of one of the requests. If |this| is deleted then all of the PacRequest// instances will be Cancel()-ed.PendingRequests pending_copy = pending_requests_;for (PendingRequests::iterator it = pending_copy.begin();it != pending_copy.end();++it) {PacRequest* req = it->get();if (!req->is_started() && !req->was_cancelled()) {req->net_log()->EndEvent(NetLog::TYPE_PROXY_SERVICE_WAITING_FOR_INIT_PAC);// Note that we re-check for synchronous completion, in case we are// no longer using a ProxyResolver (can happen if we fell-back to manual).req->StartAndCompleteCheckingForSynchronous();}} } . . . . . . void ProxyService::OnProxyConfigChanged(const ProxyConfig& config,ProxyConfigService::ConfigAvailability availability) {// Retrieve the current proxy configuration from the ProxyConfigService.// If a configuration is not available yet, we will get called back later// by our ProxyConfigService::Observer once it changes.ProxyConfig effective_config;switch (availability) {case ProxyConfigService::CONFIG_PENDING:// ProxyConfigService implementors should never pass CONFIG_PENDING.NOTREACHED() << "Proxy config change with CONFIG_PENDING availability!";return;case ProxyConfigService::CONFIG_VALID:effective_config = config;break;case ProxyConfigService::CONFIG_UNSET:effective_config = ProxyConfig::CreateDirect();break;}// Emit the proxy settings change to the NetLog stream.if (net_log_) {net_log_->AddGlobalEntry(NetLog::TYPE_PROXY_CONFIG_CHANGED,base::Bind(&NetLogProxyConfigChangedCallback,&fetched_config_, &effective_config));}// Set the new configuration as the most recently fetched one.fetched_config_ = effective_config;fetched_config_.set_id(1); // Needed for a later DCHECK of is_valid().InitializeUsingLastFetchedConfig(); }void ProxyService::InitializeUsingLastFetchedConfig() {ResetProxyConfig(false);DCHECK(fetched_config_.is_valid());// Increment the ID to reflect that the config has changed.fetched_config_.set_id(next_config_id_++);if (!fetched_config_.HasAutomaticSettings()) {config_ = fetched_config_;SetReady();return;}// Start downloading + testing the PAC scripts for this new configuration.current_state_ = STATE_WAITING_FOR_INIT_PROXY_RESOLVER;// If we changed networks recently, we should delay running proxy auto-config.TimeDelta wait_delay =stall_proxy_autoconfig_until_ - TimeTicks::Now();init_proxy_resolver_.reset(new InitProxyResolver());init_proxy_resolver_->set_quick_check_enabled(quick_check_enabled_);int rv = init_proxy_resolver_->Start(&resolver_, resolver_factory_.get(), proxy_script_fetcher_.get(),dhcp_proxy_script_fetcher_.get(), net_log_, fetched_config_, wait_delay,base::Bind(&ProxyService::OnInitProxyResolverComplete,base::Unretained(this)));if (rv != ERR_IO_PENDING)OnInitProxyResolverComplete(rv); }

在這里主要是將新的代理配置信息保存在 fetched_config_ 中，繼而將配置保存在 config_ 中，并設(shè)置狀態(tài)標(biāo)記 current_state_ 為 ready。

HttpStreamFactoryImpl::Job::DoResolveProxy() 通過 ProxyService 的 ResolveProxy() 來為特定的URL找到合適的代理服務(wù)器：

int ProxyService::ResolveProxy(const GURL& raw_url,const std::string& method,ProxyInfo* result,const CompletionCallback& callback,PacRequest** pac_request,ProxyDelegate* proxy_delegate,const BoundNetLog& net_log) {DCHECK(!callback.is_null());return ResolveProxyHelper(raw_url, method, result, callback, pac_request,proxy_delegate, net_log); }int ProxyService::ResolveProxyHelper(const GURL& raw_url,const std::string& method,ProxyInfo* result,const CompletionCallback& callback,PacRequest** pac_request,ProxyDelegate* proxy_delegate,const BoundNetLog& net_log) {DCHECK(CalledOnValidThread());net_log.BeginEvent(NetLog::TYPE_PROXY_SERVICE);// Notify our polling-based dependencies that a resolve is taking place.// This way they can schedule their polls in response to network activity.config_service_->OnLazyPoll();if (script_poller_.get())script_poller_->OnLazyPoll();if (current_state_ == STATE_NONE)ApplyProxyConfigIfAvailable();// Sanitize the URL before passing it on to the proxy resolver (i.e. PAC// script). The goal is to remove sensitive data (like embedded user names// and password), and local data (i.e. reference fragment) which does not need// to be disclosed to the resolver.GURL url = SanitizeUrl(raw_url, sanitize_url_policy_);// Check if the request can be completed right away. (This is the case when// using a direct connection for example).int rv = TryToCompleteSynchronously(url, proxy_delegate, result);if (rv != ERR_IO_PENDING) {rv = DidFinishResolvingProxy(url, method, proxy_delegate, result, rv, net_log,callback.is_null() ? TimeTicks() : TimeTicks::Now(), false);return rv;}if (callback.is_null())return ERR_IO_PENDING;scoped_refptr<PacRequest> req(new PacRequest(this, url, method, proxy_delegate, result, callback, net_log));if (current_state_ == STATE_READY) {// Start the resolve request.rv = req->Start();if (rv != ERR_IO_PENDING)return req->QueryDidComplete(rv);} else {req->net_log()->BeginEvent(NetLog::TYPE_PROXY_SERVICE_WAITING_FOR_INIT_PAC);}DCHECK_EQ(ERR_IO_PENDING, rv);DCHECK(!ContainsPendingRequest(req.get()));pending_requests_.insert(req);// Completion will be notified through |callback|, unless the caller cancels// the request using |pac_request|.if (pac_request)*pac_request = req.get();return rv; // ERR_IO_PENDING } . . . . . . int ProxyService::TryToCompleteSynchronously(const GURL& url,ProxyDelegate* proxy_delegate,ProxyInfo* result) {DCHECK_NE(STATE_NONE, current_state_);if (current_state_ != STATE_READY)return ERR_IO_PENDING; // Still initializing.DCHECK_NE(config_.id(), ProxyConfig::kInvalidConfigID);// If it was impossible to fetch or parse the PAC script, we cannot complete// the request here and bail out.if (permanent_error_ != OK)return permanent_error_;if (config_.HasAutomaticSettings())return ERR_IO_PENDING; // Must submit the request to the proxy resolver.// Use the manual proxy settings.config_.proxy_rules().Apply(url, result);result->config_source_ = config_.source();result->config_id_ = config_.id();return OK; }

這個過程應(yīng)用代理規(guī)則，選擇適當(dāng)?shù)拇矸?wù)器給調(diào)用者。

Done。

參考資料

Proxy server
教你在Android手機上使用全局代理

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