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    <p>I've just started using <a href="https://developers.google.com/protocol-buffers" rel="nofollow noreferrer">Google Protocol Buffers (protobuf)</a> and also had problems sending (and receiving) messages over a computer network.</p> <p>In contrast to the Java API, the C++ API does not have a <a href="https://developers.google.com/protocol-buffers/docs/reference/java/com/google/protobuf/MessageLite" rel="nofollow noreferrer"><code>writeDelimitedTo</code></a> method to send a protobuf message with a delimiter. Without a delimiter we also have to send the size of the message, to be able to de-serialize it at the receive endpoint.</p> <p>The C++ API offers the class <a href="https://developers.google.com/protocol-buffers/docs/reference/cpp/google.protobuf.io.coded_stream" rel="nofollow noreferrer"><code>::google::protobuf::io::CodedOutputStream</code></a>, defined in the header file <code>google/protobuf/io/coded_stream.h</code>.</p> <p>The following source code demonstrates how-to send a delimited protobuf message via <a href="http://boost.org/doc/libs/1_55_0/doc/html/boost_asio.html" rel="nofollow noreferrer">Boost.Asio</a> over the wire. The example uses UDP. Since I haven't found a working example on the WWW, I share it here.</p> <pre><code>#include "boost/asio.hpp" #include "google/protobuf/io/coded_stream.h" #include "google/protobuf/io/zero_copy_stream_impl.h" using ::boost::asio::ip::udp; int main() { PlayerInfo message; message.set_name("Player 1"); // ... const boost::asio::ip::address_v4 kIpAddress = boost::asio::ip::address_v4::loopback(); const unsigned short kPortNumber = 65535; try { boost::asio::io_service io_service; udp::socket socket(io_service, boost::asio::ip::udp::v4()); udp::endpoint endpoint(kIpAddress, kPortNumber); boost::system::error_code error; boost::asio::streambuf stream_buffer; std::ostream output_stream(&amp;stream_buffer); { ::google::protobuf::io::OstreamOutputStream raw_output_stream(&amp;output_stream); ::google::protobuf::io::CodedOutputStream coded_output_stream(&amp;raw_output_stream); coded_output_stream.WriteVarint32(message.ByteSize()); message.SerializeToCodedStream(&amp;coded_output_stream); // IMPORTANT: In order to flush a CodedOutputStream it has to be deleted, // otherwise a 0 bytes package is send over the wire. } } size_t len = socket.send_to(stream_buffer.data(), endpoint, 0, error); if (error &amp;&amp; error != boost::asio::error::message_size) { throw boost::system::system_error(error); } std::cout &lt;&lt; "Sent " &lt;&lt; len &lt;&lt; " bytes data to " &lt;&lt; kIpAddress.to_string() &lt;&lt; "." &lt;&lt; std::endl; } catch (const std::exception&amp; ex) { std::cerr &lt;&lt; ex.what() &lt;&lt; std::endl; } </code></pre> <p>While writing this article, I've also discovered the following two questions:</p> <ul> <li><a href="https://stackoverflow.com/questions/8269452/google-protocol-buffers-parsedelimitedfrom-and-writedelimitedto-for-c">Google Protocol Buffers: parseDelimitedFrom and writeDelimitedTo for C++</a></li> <li><a href="https://stackoverflow.com/questions/5679764/boostasiostreambuf-empty">boost::asio::streambuf empty?</a></li> </ul> <p>Both are related to this question and also contain (partial) answers. I hope my answer may be useful anyway.</p>
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