情景分析 現(xiàn)已存在一個(gè)可用穩(wěn)定的異步客戶端類http_client_base，該類基于boost asio實(shí)現(xiàn)了連接服務(wù)器，發(fā)送請(qǐng)求，獲取響應(yīng)和解析http數(shù)據(jù)等操作，該類的大致實(shí)現(xiàn)框架如下
1
class http_client_base
2
{
3
public:
4 http_client_base(boost::asio::io_service& io_service)
5 :resolver_(io_service),socket_(io_service)
6
{
7
}
8
9 void async_connect(const std::string& address,const std::string& port)
10 {
11 boost::asio::ip::tcp::resolver::query query(address, port);
12 resolver_.async_resolve(query,boost::bind(&http_client::handle_resolve, this,
13 asio::placeholders::error,asio::placeholders::iterator));
14 }
15
16 void async_write(const void* data,size_t size,bool in_place=false)
17 {
18 if(!in_place){
19 //do something
20 asio::async_write(socket_,request_,
21 boost::bind(&http_client::handle_write,this,boost::asio::placeholders::error));
22 }else
23 asio::async_write(socket_,asio::buffer(data,size),
24 boost::bind(&http_client::handle_write,this,boost::asio::placeholders::error));
25 }
26
27private:
28
29 void handle_connect(const boost::system::error_code& e)
30 {
31 if(!e)
32 onConnect();
33 else
34 onIoError(e);
35 }
36
37 void handle_write(const boost::system::error_code& e)
38 {
39 if(!e)
40 onWrite();
41 else
42 onIoError(e);
43 }
44
45protected:
46 virtual void onConnect(){}
47 virtual void onWrite(){}
48 virtual void onIoError(const boost::system::error_code& e){}
49
50private:
51 boost::asio::ip::tcp::socket socket_;
52 boost::asio::ip::tcp::resolver resolver_;
53 boost::asio::streambuf request_, response_;
54
}; 顯而易見(jiàn)，http_client_base使用tcp::socket作為底層實(shí)現(xiàn)，所以數(shù)據(jù)是非ssl傳輸?shù)摹，F(xiàn)因需求變更，為了數(shù)據(jù)安全要求使用ssl傳輸。但boost asio中的ssl::stream類接口和tcp::socket有所不同。其實(shí)在非ssl和ssl間，不同的只是讀寫(xiě)數(shù)據(jù)的方法，而數(shù)據(jù)處理邏輯不變，因此為了重用http_client_base的機(jī)制框架和對(duì)http數(shù)據(jù)的解析，那么怎么使http_client_base不作大的改動(dòng)就支持ssl呢？通過(guò)研究asio源碼發(fā)現(xiàn)，
async_xxx系列自由函數(shù)內(nèi)部要求讀寫(xiě)流實(shí)現(xiàn)read_some、async_read_some、write_some和async_write_some4個(gè)短讀寫(xiě)方法。由于tcp::socket已實(shí)現(xiàn)短讀寫(xiě)而且ssl::stream是tcp::socket的上層，因此只要設(shè)計(jì)一個(gè)抽象的基類流，使之支持read_some、async_some_read、w
rite_some和async_write_some即可，而實(shí)現(xiàn)使用dynamic_cast轉(zhuǎn)到兄弟基類tcp::socket或ssl::stream，再調(diào)用它們對(duì)應(yīng)的同名短讀寫(xiě)方法；另外還需要給出獲取最底層socket的接口，以支持async_connect和connect方法。因此針對(duì)這一設(shè)計(jì)實(shí)現(xiàn)，則要求派生類必須同時(shí)從抽象基類和其兄弟基類tcp::socket或ssl::stream繼承。
框架實(shí)現(xiàn) 基類模板
1
template<typename T>
2class boost_socket_base
3
{
4
public:
5 typedef boost::asio::ssl::stream<T> ssl_socket_base_t;
6 typedef T socket_base_t;
7
8protected:
9 boost_socket_base()
10 :tb_(boost::indeterminate)
11
{ }
12
13public:
14 virtual ~boost_socket_base()
15 { }
16
17 ssl_socket_base_t* get_ssl_socket()
18 {
19 if(tb_){
20 BOOST_ASSERT(ss_);
21 return ss_;
22
}else if(!tb_)
23 return NULL;
24 else{
25 if(ss_=dynamic_cast<ssl_socket_base_t*>(this))
26 tb_ = true;
27 return ss_;
28 }
29 }
30
31 socket_base_t* get_socket()
32 {
33 if(!tb_){
34 BOOST_ASSERT(s_);
35 return s_;
36 }else if(tb_)
37 return NULL;
38 else{
39 if(s_=dynamic_cast<socket_base_t*>(this))
40 tb_ = false;
41 return s_;
42 }
43 }
44
45 typename T::lowest_layer_type& lowest_layer()
46 {
47 ssl_socket_base_t* p = get_ssl_socket();
48 return p ? p->lowest_layer() : get_socket()->lowest_layer();
49 }
50
51 template <typename MutableBufferSequence>
52 std::size_t read_some(const MutableBufferSequence& buffers,boost::system::error_code& ec)
53 {
54 ssl_socket_base_t* p = get_ssl_socket();
55 return p ? p->read_some(buffers) : get_socket()->read_some(buffers,ec);
56 }
57
58 template <typename MutableBufferSequence>
59 std::size_t read_some(const MutableBufferSequence& buffers)
60 {
61 //與上面相同，但不帶ec
62 }
63
64 template <typename MutableBufferSequence, typename ReadHandler>
65 void async_read_some(const MutableBufferSequence& buffers,BOOST_ASIO_MOVE_ARG(ReadHandler) handler)
66 {
67 ssl_socket_base_t* p = get_ssl_socket();
68 return p ? p->async_read_some(buffers,handler) : get_socket()->async_read_some(buffers,handler);
69 }
70
71 template <typename ConstBufferSequence>
72 std::size_t write_some(const ConstBufferSequence& buffers,boost::system::error_code& ec)
73 {
74 ssl_socket_base_t* p = get_ssl_socket();
75 return p ? p->write_some(buffers,ec) : get_socket()->write_some(buffers,ec);
76 }
77
78 template <typename ConstBufferSequence>
79 std::size_t write_some(const ConstBufferSequence& buffers)
80 {
81 //與上面相同，但不帶ec
82 }
83
84 template <typename MutableBufferSequence, typename ReadHandler>
85 void async_write_some(const MutableBufferSequence& buffers,BOOST_ASIO_MOVE_ARG(ReadHandler) handler)
86 {
87 ssl_socket_base_t* p = get_ssl_socket();
88 return p ? p->async_write_some(buffers,handler) : get_socket()->async_write_some(buffers,handler);
89 }
90
91private:
92 boost::tribool tb_;
93 union {
94 ssl_socket_base_t* ss_;
95 socket_base_t* s_;
96 };
97
}; 考慮到dynamic_cast轉(zhuǎn)換的性能開(kāi)銷，因此增加了三態(tài)邏輯變量tb_和union指針，tb_表示當(dāng)前this實(shí)際指向的對(duì)象類型，初始化為indeterminate，true表示ssl socket對(duì)象，使用ss_；false表示普通socket對(duì)象，使用s_。這樣一來(lái)，當(dāng)且僅當(dāng)tb_為indeterminate時(shí)才dynamic_cast。由于這點(diǎn)優(yōu)化僅對(duì)基類指針操作有效，而對(duì)派生對(duì)象實(shí)無(wú)必要，所以tb_和union指針設(shè)為私有的；而且基類指針可以指向不同的子類對(duì)象，所以增加了reset方法重設(shè)tb_為indeterminate狀態(tài)，保證行為的正確性。
子類模板
1template<typename T>
2class boost_ssl_socket : public boost_socket_base<T>
3 , public boost::asio::ssl::stream<T>
4{
5public:
6 typedef boost::asio::ssl::stream<T> base2;
7
8 boost_ssl_socket(boost::asio::io_service& io_service,boost::asio::ssl::context& ctx)
9 :base2(io_service,ctx)
10 { }
11};
12
13template<typename T>
14class boost_socket : public boost_socket_base<T>
15 , public T
16{
17public:
18 typedef T base2;
19
20 boost_socket(boost::asio::io_service& io_service)
21 :base2(io_service)
22 { }
23}; boost_ssl_socket為ssl套接字類模板，boost_socket為普通套接字類模板，使用多重繼承，第1基類為boost_socket_base<T>，第2基類分別為asio:ssl:stream<T>和T。
應(yīng)用改進(jìn) 使用上面ssl socket框架后，只須5個(gè)地方稍作改動(dòng)即可。
1）成員變量：由原來(lái)的boost::asio::ip::tcp改為boost_socket_base<boost_tcp_socket>*類型。
1typedef boost::asio::ip::tcp::socket boost_tcp_socket;
2boost_socket_base<boost_tcp_socket>* socket_; 2）構(gòu)造函數(shù)：增加boost::asio::ssl::context* ctx參數(shù)，默認(rèn)為NULL，表示不使用ssl。
1http_client_base(boost::asio::io_service& io_service,boost::asio::ssl::context* ctx=NULL)
2 :resolver_(io_service)
3{
4 if(ctx)
5 socket_ = new boost_ssl_socket<boost_tcp_socket>(io_service,*ctx);
6 else
7 socket_ = new boost_socket<boost_tcp_socket>(io_service);
8}
3）握手處理：與非ssl不同的是，在連接后需要進(jìn)行握手，握手成功后才回調(diào)onConnect。
1void handle_connect(const boost::system::error_code& e)
2{
3 if(!e){
4 boost_socket_base<boost_tcp_socket>::ssl_socket_base_t* p = socket_->get_ssl_socket();
5 if(p)
6 p->async_handshake(boost::asio::ssl::stream_base::client,boost::bind(&http_client::handle_handshake,
7 this,boost::asio::placeholders::error));
8 else
9 onConnect();
10 }else
11 onIoError(e);
12}
13void handle_handshake(const boost::system::error_code& e)
14{
15 if(!e)
16 onConnect();
17 else
18 onIoError(e);
19} 4）異步連接：由于async_connect只接受boost::basic_socket類即最底層的socket作為參數(shù)，因此需要調(diào)用lowest_layer。
1void handle_resolve(const boost::system::error_code& e,boost::asio::ip::tcp::resolver::iterator endpoint_iterator)
2{
3 if (!e)
4 boost::asio::async_connect(socket_->lowest_layer(), endpoint_iterator,boost::bind(&http_client::handle_connect,this,boost::asio::placeholders::error));
5 else
6 onIoError(e);
7}
5）async_xxx調(diào)用：將參數(shù)socket_改為*socket_，例如下。
1void async_write(const void* data,size_t size,bool in_place=false)
2{
3 if(!in_place){
4 //do something
5 boost::asio::async_write(*socket_,request_,boost::bind(&http_client::handle_write,this,boost::asio::placeholders::error));
6 }else
7 boost::asio::async_write(*socket_,asio::buffer(data,size),boost::bind(&http_client::handle_write,this,boost::asio::placeholders::error));
8}
9void handle_write(const boost::system::error_code& e)
10{
11 if(!e)
12 boost::asio::async_read_until(*socket_, response_, "\r\n\r\n",
13 boost::bind(&http_client::handle_read_header,this,boost::asio::placeholders::error,asio::placeholders::bytes_transferred));
14 else
15 onIoError(e);
16}
posted on 2013-03-20 20:47
春秋十二月 閱讀(12310)
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