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1 | // |
2 | // third_party_lib.cpp | |
3 | // ~~~~~~~~~~~~~~~~~~~ | |
4 | // | |
1e59de90 | 5 | // Copyright (c) 2003-2022 Christopher M. Kohlhoff (chris at kohlhoff dot com) |
b32b8144 FG |
6 | // |
7 | // Distributed under the Boost Software License, Version 1.0. (See accompanying | |
8 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | |
9 | // | |
10 | ||
11 | #include <boost/asio.hpp> | |
12 | #include <array> | |
13 | #include <iostream> | |
14 | #include <memory> | |
15 | ||
16 | using boost::asio::ip::tcp; | |
17 | ||
18 | namespace third_party_lib { | |
19 | ||
20 | // Simulation of a third party library that wants to perform read and write | |
21 | // operations directly on a socket. It needs to be polled to determine whether | |
22 | // it requires a read or write operation, and notified when the socket is ready | |
23 | // for reading or writing. | |
24 | class session | |
25 | { | |
26 | public: | |
27 | session(tcp::socket& socket) | |
28 | : socket_(socket) | |
29 | { | |
30 | } | |
31 | ||
32 | // Returns true if the third party library wants to be notified when the | |
33 | // socket is ready for reading. | |
34 | bool want_read() const | |
35 | { | |
36 | return state_ == reading; | |
37 | } | |
38 | ||
39 | // Notify that third party library that it should perform its read operation. | |
40 | void do_read(boost::system::error_code& ec) | |
41 | { | |
42 | if (std::size_t len = socket_.read_some(boost::asio::buffer(data_), ec)) | |
43 | { | |
44 | write_buffer_ = boost::asio::buffer(data_, len); | |
45 | state_ = writing; | |
46 | } | |
47 | } | |
48 | ||
49 | // Returns true if the third party library wants to be notified when the | |
50 | // socket is ready for writing. | |
51 | bool want_write() const | |
52 | { | |
53 | return state_ == writing; | |
54 | } | |
55 | ||
56 | // Notify that third party library that it should perform its write operation. | |
57 | void do_write(boost::system::error_code& ec) | |
58 | { | |
59 | if (std::size_t len = socket_.write_some( | |
60 | boost::asio::buffer(write_buffer_), ec)) | |
61 | { | |
62 | write_buffer_ = write_buffer_ + len; | |
63 | state_ = boost::asio::buffer_size(write_buffer_) > 0 ? writing : reading; | |
64 | } | |
65 | } | |
66 | ||
67 | private: | |
68 | tcp::socket& socket_; | |
69 | enum { reading, writing } state_ = reading; | |
70 | std::array<char, 128> data_; | |
71 | boost::asio::const_buffer write_buffer_; | |
72 | }; | |
73 | ||
74 | } // namespace third_party_lib | |
75 | ||
76 | // The glue between asio's sockets and the third party library. | |
77 | class connection | |
78 | : public std::enable_shared_from_this<connection> | |
79 | { | |
80 | public: | |
81 | connection(tcp::socket socket) | |
82 | : socket_(std::move(socket)) | |
83 | { | |
84 | } | |
85 | ||
86 | void start() | |
87 | { | |
88 | // Put the socket into non-blocking mode. | |
89 | socket_.non_blocking(true); | |
90 | ||
91 | do_operations(); | |
92 | } | |
93 | ||
94 | private: | |
95 | void do_operations() | |
96 | { | |
97 | auto self(shared_from_this()); | |
98 | ||
99 | // Start a read operation if the third party library wants one. | |
100 | if (session_impl_.want_read() && !read_in_progress_) | |
101 | { | |
102 | read_in_progress_ = true; | |
103 | socket_.async_wait(tcp::socket::wait_read, | |
104 | [this, self](boost::system::error_code ec) | |
105 | { | |
106 | read_in_progress_ = false; | |
107 | ||
108 | // Notify third party library that it can perform a read. | |
109 | if (!ec) | |
110 | session_impl_.do_read(ec); | |
111 | ||
112 | // The third party library successfully performed a read on the | |
113 | // socket. Start new read or write operations based on what it now | |
114 | // wants. | |
115 | if (!ec || ec == boost::asio::error::would_block) | |
116 | do_operations(); | |
117 | ||
118 | // Otherwise, an error occurred. Closing the socket cancels any | |
119 | // outstanding asynchronous read or write operations. The | |
120 | // connection object will be destroyed automatically once those | |
121 | // outstanding operations complete. | |
122 | else | |
123 | socket_.close(); | |
124 | }); | |
125 | } | |
126 | ||
127 | // Start a write operation if the third party library wants one. | |
128 | if (session_impl_.want_write() && !write_in_progress_) | |
129 | { | |
130 | write_in_progress_ = true; | |
131 | socket_.async_wait(tcp::socket::wait_write, | |
132 | [this, self](boost::system::error_code ec) | |
133 | { | |
134 | write_in_progress_ = false; | |
135 | ||
136 | // Notify third party library that it can perform a write. | |
137 | if (!ec) | |
138 | session_impl_.do_write(ec); | |
139 | ||
140 | // The third party library successfully performed a write on the | |
141 | // socket. Start new read or write operations based on what it now | |
142 | // wants. | |
143 | if (!ec || ec == boost::asio::error::would_block) | |
144 | do_operations(); | |
145 | ||
146 | // Otherwise, an error occurred. Closing the socket cancels any | |
147 | // outstanding asynchronous read or write operations. The | |
148 | // connection object will be destroyed automatically once those | |
149 | // outstanding operations complete. | |
150 | else | |
151 | socket_.close(); | |
152 | }); | |
153 | } | |
154 | } | |
155 | ||
156 | private: | |
157 | tcp::socket socket_; | |
158 | third_party_lib::session session_impl_{socket_}; | |
159 | bool read_in_progress_ = false; | |
160 | bool write_in_progress_ = false; | |
161 | }; | |
162 | ||
163 | class server | |
164 | { | |
165 | public: | |
166 | server(boost::asio::io_context& io_context, unsigned short port) | |
167 | : acceptor_(io_context, {tcp::v4(), port}) | |
168 | { | |
169 | do_accept(); | |
170 | } | |
171 | ||
172 | private: | |
173 | void do_accept() | |
174 | { | |
175 | acceptor_.async_accept( | |
176 | [this](boost::system::error_code ec, tcp::socket socket) | |
177 | { | |
178 | if (!ec) | |
179 | { | |
180 | std::make_shared<connection>(std::move(socket))->start(); | |
181 | } | |
182 | ||
183 | do_accept(); | |
184 | }); | |
185 | } | |
186 | ||
187 | tcp::acceptor acceptor_; | |
188 | }; | |
189 | ||
190 | int main(int argc, char* argv[]) | |
191 | { | |
192 | try | |
193 | { | |
194 | if (argc != 2) | |
195 | { | |
196 | std::cerr << "Usage: third_party_lib <port>\n"; | |
197 | return 1; | |
198 | } | |
199 | ||
200 | boost::asio::io_context io_context; | |
201 | ||
202 | server s(io_context, std::atoi(argv[1])); | |
203 | ||
204 | io_context.run(); | |
205 | } | |
206 | catch (std::exception& e) | |
207 | { | |
208 | std::cerr << "Exception: " << e.what() << "\n"; | |
209 | } | |
210 | ||
211 | return 0; | |
212 | } |