本文描述http client使用socks代理过程中需要注意的几个方面：1，socks5支持用户密码授权；2，支持https；3，支持让代理服务器解析DNS；
使用代理创建Socket
从原理上来看，不管用什么http客户端（httpclient，okhttp），最终都要转换到java.net.Socket的创建上去，看到代码：
package java.net;
public Socket(Proxy proxy) {
...
}这是JDK中对网络请求使用Socks代理的入口方法。（http代理是在http协议层之上的，不在此文讨论范围之内）。
HttpClient要实现socks代理，就需要塞进去一个Proxy对象，也就是定制两个类：org.apache.http.conn.ssl.SSLConnectionSocketFactory 和org.apache.http.conn.socket.PlainConnectionSocketFactory，分别对应https和http。
代码如下：
private class SocksSSLConnectionSocketFactory extends SSLConnectionSocketFactory {
public SocksSSLConnectionSocketFactory(SSLContext sslContext, HostnameVerifier hostnameVerifier) {
super(sslContext, hostnameVerifier);
}
@Override
public Socket createSocket(HttpContext context) throws IOException {
ProxyConfig proxyConfig = (ProxyConfig) context.getAttribute(ProxyConfigKey);
if (proxyConfig != null) {//需要代理
return new Socket(proxyConfig.getProxy());
} else {
return super.createSocket(context);
}
}
@Override
public Socket connectSocket(int connectTimeout, Socket socket, HttpHost host, InetSocketAddress remoteAddress,
InetSocketAddress localAddress, HttpContext context) throws IOException {
ProxyConfig proxyConfig = (ProxyConfig) context.getAttribute(ProxyConfigKey);
if (proxyConfig != null) {//make proxy server to resolve host in http url
remoteAddress = InetSocketAddress
.createUnresolved(host.getHostName(), host.getPort());
}
return super.connectSocket(connectTimeout, socket, host, remoteAddress, localAddress, context);
}
}和
private class SocksSSLConnectionSocketFactory extends SSLConnectionSocketFactory {
public SocksSSLConnectionSocketFactory(SSLContext sslContext, HostnameVerifier hostnameVerifier) {
super(sslContext, hostnameVerifier);
}
@Override
public Socket createSocket(HttpContext context) throws IOException {
ProxyConfig proxyConfig = (ProxyConfig) context.getAttribute(ProxyConfigKey);
if (proxyConfig != null) {
return new Socket(proxyConfig.getProxy());
} else {
return super.createSocket(context);
}
}
@Override
public Socket connectSocket(int connectTimeout, Socket socket, HttpHost host, InetSocketAddress remoteAddress,
InetSocketAddress localAddress, HttpContext context) throws IOException {
ProxyConfig proxyConfig = (ProxyConfig) context.getAttribute(ProxyConfigKey);
if (proxyConfig != null) {//make proxy server to resolve host in http url
remoteAddress = InetSocketAddress
.createUnresolved(host.getHostName(), host.getPort());
}
return super.connectSocket(connectTimeout, socket, host, remoteAddress, localAddress, context);
}
}然后在创建httpclient对象时，给HttpClientConnectionManager设置socketFactoryRegistry
Registry<ConnectionSocketFactory> socketFactoryRegistry = RegistryBuilder.<ConnectionSocketFactory>create()
.register(Protocol.HTTP.toString(), new SocksConnectionSocketFactory())
.register(Protocol.HTTPS.toString(), new SocksSSLConnectionSocketFactory(sslContext, NoopHostnameVerifier.INSTANCE))
.build();
PoolingHttpClientConnectionManager connectionManager = new PoolingHttpClientConnectionManager(socketFactoryRegistry);
让代理服务器解析域名
场景：运行httpClient的进程所在主机可能并不能上公网，大部分时候，也无法进行DNS解析，这时通常会出现域名无法解析的IO异常，下面介绍怎么避免在客户端解析域名。
上面有一行代码非常关键：
remoteAddress = InetSocketAddress
.createUnresolved(host.getHostName(), host.getPort());变量host是你发起http请求的目标主机和端口信息，这里创建了一个未解析(Unresolved)的SocketAddress，在socks协议握手阶段，InetSocketAddress信息会原封不动的发送到代理服务器，由代理服务器解析出具体的IP地址。
Socks的协议描述中有个片段：
The SOCKS request is formed as follows:
+----+-----+-------+------+----------+----------+
|VER | CMD | RSV | ATYP | DST.ADDR | DST.PORT |
+----+-----+-------+------+----------+----------+
| 1 | 1 | X'00' | 1 | Variable | 2 |
+----+-----+-------+------+----------+----------+
Where:
o VER protocol version: X'05'
o CMD
o CONNECT X'01'
o BIND X'02'
o UDP ASSOCIATE X'03'
o RSV RESERVED
o ATYP address type of following address
o IP V4 address: X'01'
o DOMAINNAME: X'03'
o IP V6 address: X'04'代码按上面方法写，协议握手发送的是ATYP=X'03'，即采用域名的地址类型。否则，HttpClient会尝试在客户端解析，然后发送ATYP=X'01'进行协商。当然，大多数时候HttpClient在解析域名的时候就挂了。
https中需要注意的问题
在使用httpclient访问https网站的时候，经常会遇到javax.net.ssl包中的异常，例如：
Caused by: javax.net.ssl.SSLException: Received fatal alert: internal_error
at sun.security.ssl.Alerts.getSSLException(Unknown Source) ~[na:1.7.0_80]
at sun.security.ssl.Alerts.getSSLException(Unknown Source) ~[na:1.7.0_80]一般需要做几个设置：
创建不校验证书链的SSLContext
SSLContext sslContext = null;
try {
sslContext = new SSLContextBuilder().loadTrustMaterial(null, new TrustStrategy() {
@Override
public boolean isTrusted(X509Certificate[] chain, String authType)
throws CertificateException {
return true;
}
}).build();
} catch (Exception e) {
throw new com.aliyun.oss.ClientException(e.getMessage());
}
...
new SocksSSLConnectionSocketFactory(sslContext, NoopHostnameVerifier.INSTANCE)创建不校验域名的HostnameVerifier
public class NoopHostnameVerifier implements javax.net.ssl.HostnameVerifier {
public static final NoopHostnameVerifier INSTANCE = new NoopHostnameVerifier();
@Override
public boolean verify(final String s, final SSLSession sslSession) {
return true;
}
}如何使用用户密码授权？
java SDK中给Socks代理授权有点特殊，不是按socket来的，而是在系统层面做的全局配置。比如，可以通过下面代码设置一个全局的Authenticator：
Authenticator.setDefault(new MyAuthenticator("userName", "Password"));
...
class MyAuthenticator extends java.net.Authenticator {
private String user ;
private String password ;
public MyAuthenticator(String user, String password) {
this.user = user;
this.password = password;
}
protected PasswordAuthentication getPasswordAuthentication() {
return new PasswordAuthentication(user, password.toCharArray());
}
}这种方法很简单，不过有些不方便的地方，如果你的产品中需要连接不同的Proxy服务器，而他们的用户名密码是不一样的，那么这个方法就不适用了。
基于ThreadLocal的Authenticator
public class ThreadLocalProxyAuthenticator extends Authenticator{
private ThreadLocal<PasswordAuthentication> credentials = null;
private static class SingletonHolder {
private static final ThreadLocalProxyAuthenticator instance = new ThreadLocalProxyAuthenticator();
}
public static final ThreadLocalProxyAuthenticator getInstance() {
return SingletonHolder.instance;
}
public void setCredentials(String user, String password) {
credentials.set(new PasswordAuthentication(user, password.toCharArray()));
}
public static void clearCredentials() {
ThreadLocalProxyAuthenticator authenticator = ThreadLocalProxyAuthenticator.getInstance();
Authenticator.setDefault(authenticator);
authenticator.credentials.set(null);
}
public PasswordAuthentication getPasswordAuthentication() {
return credentials.get();
}
}
这个类意味着，授权信息只会保存到当前调用者的线程中，其他线程的调用者无法访问，在创建Socket的线程中设置密钥和清理密钥，就可以做到授权按照Socket连接进行隔离。Java TheadLocal相关知识本文不赘述。
按连接隔离的授权
class ProxyHttpClient extends CloseableHttpClient{
private CloseableHttpClient httpClient;
public ProxyHttpClient(CloseableHttpClient httpClient){
this.httpClient=httpClient;
}
protected CloseableHttpResponse doExecute(HttpHost target, HttpRequest request, HttpContext context) throws IOException, ClientProtocolException {
ProxyConfig proxyConfig = //这里获取当前连接的代理配置信息
boolean clearCredentials = false;
if (proxyConfig != null) {
if (context == null) {
context = HttpClientContext.create();
}
context.setAttribute(ProxyConfigKey, proxyConfig);
if (proxyConfig.getAuthentication() != null) {
ThreadLocalProxyAuthenticator.setCredentials(proxyConfig.getAuthentication());//设置授权信息
clearCredentials = true;
}
}
try {
return httpClient.execute(target, request, context);
} finally {
if (clearCredentials) {//清理授权信息
ThreadLocalProxyAuthenticator.clearCredentials();
}
}
}
}另外，线程是可以复用的，因为每次调用完毕后，都清理了授权信息。
这里有个一POJO类ProxyConfig，保存的是socks代理的IP端口和用户密码信息。
public class ProxyConfig {
private Proxy proxy;
private PasswordAuthentication authentication;
}
