c++ - stdin pipe not closing when read with Boost.ASIO -

i'm reading stdin using boost.asio, when pipe expect pipe close when input has been consumed. i.e. i'm doing @ commmand line:

cat somefile.txt | myprog 

and i'd expect myprog see file close. instead waits forever.

the code looks this:

boost::asio::posix::stream_descriptor as_stdin(ios); {     boost::system::error_code error;     as_stdin.assign(dup(stdin_fileno), error);     if ( error ) {         exit(2);     } } auto proc = [&as_stdinr](auto yield) {         boost::asio::streambuf buffer;         while ( as_stdin.is_open() ) {             auto bytes = boost::asio::async_read_until(as_stdin, buffer, '\n', yield);             if ( bytes ) {                 buffer.commit(bytes);                 std::istream in(&buffer);                 std::string line;                 std::getline(in, line);                 std::cerr << line << std::endl;             } else {                 std::cerr << "no bytes read" << std::endl;             }         }         std::cerr << "done" << std::endl;     }; boost::asio::spawn(ios, proc); 

all of file content echoed, reading pipe works fine, neither of "no bytes read" or "done" messages ever printed. i've tried both , without dup system call.

am misunderstanding how pipe works, or doing wrong or missing else?

i think comes down "how detect eof when using coroutines?"

you catch exception async_read_until

size_t bytes = 0; bool eof = false; try {     bytes = boost::asio::async_read_until(as_stdin, buffer, '\n', yield); } catch(std::exception const& e) {     std::cerr << "exception: " << e.what() << "\n";     bytes = 0;     eof = true; } // ... if (eof) break; 

or use error_code:

boost::system::error_code ec; auto bytes = boost::asio::async_read_until(as_stdin, buffer, '\n', yield[ec]); // ... if (ec) {     std::cerr << "error: " << ec.message() << "\n";     break; } 

output similar in both cases

exception: end of file no bytes read done 

or

no bytes read error: end of file done 

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limitations

regular files cannot used posix stream_descriptor, see https://stackoverflow.com/a/23631715/85371