C++ socket never ready for write with poll - c++

Question

I am writing a C++ wrapper for sockets on Linux.
I can connect read/write to a http server my poll function works perfectly for reading but for some reason it won't work with writing. I have tried using gdb and it appears poll sets fd.revents to 0 when fd.events is POLLOUT
poll code:
/**
*#brief assigns request.reply based on fd.revents
*/
static void translate_request(mizaru::PollRequest &request, pollfd &fd)
{
assert( (fd.revents & POLLHUP) == 0);
assert( (fd.revents & POLLERR) == 0);
assert( (fd.revents & POLLNVAL) == 0);
switch(fd.revents)
{
case (POLLIN | POLLOUT) :
request.reply = mizaru::POLL_REPLY_RW;
break;
case POLLIN :
request.reply = mizaru::POLL_REPLY_READ;
break;
case POLLOUT :
request.reply = mizaru::POLL_REPLY_WRITE;
default :
request.reply = 0;
}
}
/**
* #fills in fd.events based on request.request
* and fd.fd based on request.sock
*/
static void prep_request(mizaru::PollRequest &request, pollfd &fd)
{
fd.fd = request.sock.get_handle();
switch(request.request)
{
case mizaru::PollType::POLL_READ :
fd.events = POLLIN;
break;
case mizaru::PollType::POLL_WRITE :
fd.events = POLLOUT;
break;
default :
fd.events = POLLIN | POLLOUT;
}
}
void mizaru::trans::poll(mizaru::PollRequest &request,const std::chrono::milliseconds& wait_time) noexcept
{
pollfd fd;
prep_request(request, fd);
poll(&fd, 1, wait_time.count());
translate_request(request, fd);
}
mizaru::PollRequest struct :
struct PollRequest
{
PollRequest(PollType request, const SyncSocket &sock) : sock(sock), request(request), reply(POLL_REPLY_FAIL) {}
const SyncSocket & sock;
PollType request;
uint8_t reply;
};
SyncSocket.get_handle() just returns the fd returned by socket(int,int,int) in sys/socket.h
test function :
bool test_poll()
{
mizaru::IPv4 ip ( "54.225.138.124" );
mizaru::SyncSocketTCP sock ( ip, 80 ,true);
mizaru::PollRequest request{mizaru::PollType::POLL_READ, sock};
std::chrono::milliseconds time(1000);
mizaru::poll(request, time);
if(request.reply == mizaru::POLL_REPLY_READ)
{
std::cout << "fail test_poll first read" <<std::endl;
return false;
}
request.request = mizaru::PollType::POLL_WRITE;
mizaru::poll(request, time);
if(request.reply != mizaru::POLL_REPLY_WRITE)
{
std::cout << "fail test_poll first write" << std::endl;
return false;
}
std::string toWrite ( "GET / http/1.1\nHost: httpbin.org\n\n" );
mizaru::byte_buffer write_buff;
for ( char c : toWrite )
{
write_buff.push_back ( c );
}
unsigned int r_value = sock.write ( write_buff );
if (r_value != toWrite.size())
{
std::cout << "fail test_poll r_value" << std::endl;
return false;
}
request.request = mizaru::PollType::POLL_READ;
mizaru::poll(request, time);
if(request.reply != mizaru::POLL_REPLY_READ)
{
std::cout << "fail test_poll second read" << std::endl;
return false;
}
request.request = mizaru::PollType::POLL_WRITE;
mizaru::poll(request, time);
if(request.reply != mizaru::POLL_REPLY_WRITE)
{
std::cout << "fail test_poll second write " << std::endl;
return false;
}
return true;
}
PollType enum :
enum PollType {POLL_READ, POLL_WRITE, POLL_RW};
POLL_REPLY_* constants :
constexpr uint8_t POLL_REPLY_READ = 0x01;
constexpr uint8_t POLL_REPLY_WRITE = 0x02;
constexpr uint8_t POLL_REPLY_RW = POLL_REPLY_READ | POLL_REPLY_WRITE;
constexpr uint8_t POLL_REPLY_FAIL = 0;
I am sorry that the sample code is not directly compilable I was trying to make it short,
Since I get a proper HTTP 200 OK reply you can assume connecting and read/write are handled properly. The test fails when polling for write

Answer 1

In translate_request():
switch(fd.revents)
{
case (POLLIN | POLLOUT) :
request.reply = mizaru::POLL_REPLY_RW;
break;
case POLLIN :
request.reply = mizaru::POLL_REPLY_READ;
break;
case POLLOUT :
request.reply = mizaru::POLL_REPLY_WRITE;
default :
request.reply = 0;
}
You are missing a break in both the POLLOUT and default cases. POLLOUT falls through to default, erasing the evidence that POLLOUT occurred.