So, one thing you need to do is catch OSError. Another important consideration in relation to errors is timeouts. You’ll see them discussed in many places in the documentation. Timeouts happen and are a so-called normal error. Hosts and routers are rebooted, switch ports go bad, cables go bad, cables get unplugged, you name it. You should be prepared for these and other errors, handling them in your code. template < class T > associated_allocator_t < T > get_associated_allocator ( const T & t ); template < class T , class ProtoAllocator > associated_allocator_t < T , ProtoAllocator > get_associated_allocator ( const T & t , const ProtoAllocator & a ); enum class fork_event { prepare , parent , child }; class execution_context ; class service_already_exists ; template < class Service > Service & use_service ( execution_context & ctx ); template < class Service , class ... Args > Service & make_service ( execution_context & ctx , Args &&... args ); template < class Service > bool has_service ( execution_context & ctx ) noexcept ; template < class T > struct is_executor : false_type {}; struct executor_arg_t { }; constexpr executor_arg_t executor_arg = executor_arg_t (); template < class T , class Executor > struct uses_executor ; template < class T , class Executor = system_executor > struct associated_executor ; template < class T , class Executor = system_executor > using associated_executor_t = typename associated_executor < T , Executor >:: type ; Running a traffic capture is a great way to watch how an application behaves on the network and gather evidence about what it sends and receives, and how often and how much. You’ll also be able to see when a client or server closes or aborts a connection or stops responding. This information can be extremely helpful when you’re troubleshooting. Now it’s time to run multiconn-server.py and multiconn-client.py. They both use command-line arguments. You can run them without arguments to see the options. When creating the dowel holes, you can make them level or create an angled hole by adjusting the drill press 10%. This will make the drill bits angle upwards a hair, which will help them not slid off when hung on a wall.

The request message is created and appended to the send buffer, which is then seen by and sent via ._write(). The state variable self._request_queued is set so that .queue_request() isn’t called again. template < class AsyncReadStream , class DynamicBuffer , class CompletionToken > DEDUCED async_read_until ( AsyncReadStream & s , DynamicBuffer && b , char delim , CompletionToken && token ); template < class AsyncReadStream , class DynamicBuffer , class CompletionToken > DEDUCED async_read_until ( AsyncReadStream & s , DynamicBuffer && b , string_view delim , CompletionToken && token );

port represents the TCP port number to accept connections on from clients. It should be an integer from 1 to 65535, as 0 is reserved. Some systems may require superuser privileges if the port number is less than 1024. class system_executor { public : // constructors: system_executor () {} // executor operations: execution_context & context () noexcept ; void on_work_started () noexcept {} void on_work_finished () noexcept {} template < class Func , class ProtoAllocator > void dispatch ( Func && f , const ProtoAllocator & a ); template < class Func , class ProtoAllocator > void post ( Func && f , const ProtoAllocator & a ); template < class Func , class ProtoAllocator > void defer ( Func && f , const ProtoAllocator & a ); }; bool operator ==( const system_executor &, const system_executor &) noexcept ; bool operator !=( const system_executor &, const system_executor &) noexcept ; Make sure that request data is sanitized and validated as much as possible prior to calling other code that processes it. Use fuzz tests for this and run them regularly.

template < class CompletionToken > auto async_xyz ( T1 t1 , T2 t2 , CompletionToken && token ) { completion_handler_type_t < decay_t < CompletionToken >, void ( R1 r1 , R2 r2 )> completion_handler ( forward < CompletionToken >( token )); async_result < decltype ( completion_handler )> result ( completion_handler ); // initiate the operation and cause completion_handler to be invoked with // the result return result . get (); } Inevitably, something won’t work, and you’ll be wondering what to do. Don’t worry, it happens to everyone. Hopefully, with the help of this tutorial, your debugger, and your favorite search engine, you’ll be able to get going again with the source code part. If you use multiple processes, the operating system is able to schedule your Python code to run in parallel on multiple processors or cores, without the GIL. For ideas and inspiration, see the PyCon talk John Reese - Thinking Outside the GIL with AsyncIO and Multiprocessing - PyCon 2018. After saving the message content to the data variable, .process_request() removes it from the receive buffer. Then, if the content type is JSON, .process_request() decodes and deserializes it. If it’s not, this example application assumes that it’s a binary request and simply prints the content type. An interesting thing to note with TCP is that it’s completely legal for the client or server to close their side of the connection while the other side remains open. This is referred to as a “half-open” connection. It’s the application’s decision whether or not this is desirable. In general, it’s not. In this state, the side that has closed their end of the connection can no longer send data. They can only receive it.libclient.py # ... class Message : # ... def queue_request ( self ): content = self . request [ "content" ] content_type = self . request [ "type" ] content_encoding = self . request [ "encoding" ] if content_type == "text/json" : req = { "content_bytes" : self . _json_encode ( content , content_encoding ), "content_type" : content_type , "content_encoding" : content_encoding , } else : req = { "content_bytes" : content , "content_type" : content_type , "content_encoding" : content_encoding , } message = self . _create_message ( ** req ) self . _send_buffer += message self . _request_queued = True # ... Copied! class my_service : public execution_context :: service { public : typedef my_service key_type ; explicit my_service ( execution_context & ctx ); my_service ( execution_context & ctx , int some_value ); private : virtual void shutdown () override ; There’s still a bit of a problem. You have a variable-length header, which is nice and flexible, but how do you know the length of the header when reading it with .recv()? namespace experimental template < class Allocator > struct uses_allocator < experimental ::network_v1 :: executor , Allocator > : true_type {}; } // namespace std