Is it ok to invoke WSAAsyncSelect in the WM_CREATE message of a Window Process (WinProc), and then perform all recv actions inside the same WinProc (e.g. to recv and populate a control with the received byte data) under WM_SOCKET?
For example, I know that performing long tasks inside the WinProc can cause the window to be unresponsive (since it cannot handle other messages until this message is completed), but I've seen no examples that treat this recv I/O with a thread or event object. Is it completely unnecessary?
Here's the example case in the WinProc I've seen on the net, and also in Petzold the recv is handled in a similar fashion:
case WM_SOCKET:
{
if(WSAGETSELECTERROR(lParam))
{
MessageBox(hWnd,
"Connection to server failed",
"Error",
MB_OK|MB_ICONERROR);
SendMessage(hWnd,WM_DESTROY,NULL,NULL);
break;
}
switch(WSAGETSELECTEVENT(lParam))
{
case FD_READ:
{
char szIncoming[1024];
ZeroMemory(szIncoming,sizeof(szIncoming));
int inDataLength=recv(Socket,
(char*)szIncoming,
sizeof(szIncoming)/sizeof(szIncoming[0]),
0);
strncat(szHistory,szIncoming,inDataLength);
strcat(szHistory,"\r\n");
SendMessage(hEditIn,
WM_SETTEXT,
sizeof(szIncoming)-1,
reinterpret_cast<LPARAM>(&szHistory));
}
break;
case FD_CLOSE:
{
MessageBox(hWnd,
"Server closed connection",
"Connection closed!",
MB_ICONINFORMATION|MB_OK);
closesocket(Socket);
SendMessage(hWnd,WM_DESTROY,NULL,NULL);
}
break;
}
}
Yes, this is perfectly acceptable. Though typically you would wait until CreateWindow/Ex() exits before then calling WSAAsyncSelect(). But either way works fine. Just be sure to handle the case where recv() fails, or returns fewer bytes than you asked for.
Related
I am trying to test WiFi data transfer between cell phone and Esp32 (Arduino), when ESP32 reads file data via WiFi, even there is still data in, client.read() often return -1, I have to add other conditions to check reading finished or not.
My question is why there are so many failed reads, any ideas are highly appreciated.
void setup()
{
i=0;
Serial.begin(115200);
Serial.println("begin...");
// You can remove the password parameter if you want the AP to be open.
WiFi.softAP(ssid, password);
IPAddress myIP = WiFi.softAPIP();
Serial.print("AP IP address: ");
Serial.println(myIP);
server.begin();
Serial.println("Server started");
}
// the loop function runs over and over again until power down or reset
void loop()
{
WiFiClient client = server.available(); // listen for incoming clients
if(client) // if you get a client,
{
Serial.println("New Client."); // print a message out the serial port
Serial.println(client.remoteIP().toString());
while(client.connected()) // loop while the client's connected
{
while(client.available()>0) // if there's bytes to read from the client,
{
char c = client.read(); // read a byte, then
if(DOWNLOADFILE ==c){
pretime=millis();
uint8_t filename[32]={0};
uint8_t bFilesize[8];
long filesize;
int segment=0;
int remainder=0;
uint8_t data[512];
int len=0;
int totallen=0;
delay(50);
len=client.read(filename,32);
delay(50);
len=client.read(bFilesize,8);
filesize=BytesToLong(bFilesize);
segment=(int)filesize/512;
delay(50);
i=0; //succeed times
j=0; //fail times
////////////////////////////////////////////////////////////////////
//problem occures here, to many "-1" return value
// total read 24941639 bytes, succeed 49725 times, failed 278348 times
// if there were no read problems, it should only read 48,715 times and finish.
//But it total read 328,073 times, including 278,348 falied times, wasted too much time
while(((len=client.read(data,512))!=-1) || (totallen<filesize))
{
if(len>-1) {
totallen+=len;
i++;
}
else{
j++;
}
}
///loop read end , too many times read fail//////////////////////////////////////////////////////////////////
sprintf(toClient, "\nfile name %s,size %d, total read %d, segment %d, succeed %d times, failed %d times\n",filename,filesize,totallen,segment,i,j);
Serial.write(toClient);
curtime=millis();
sprintf(toClient, "time splashed %d ms, speed %d Bps\n", curtime-pretime, filesize*1000/(curtime-pretime));
Serial.write(toClient);
client.write(RETSUCCESS);
}
else
{
Serial.write("Unknow command\n");
}
}
}
// close the connection:
client.stop();
Serial.println("Client Disconnected.");
}
When you call available() and check for > 0, you are checking to see if there is one or more characters available to read. It will be true if just one character has arrived. You read one character, which is fine, but then you start reading more without stopping to see if there are more available.
TCP doesn't guarantee that if you write 100 characters to a socket that they all arrive at once. They can arrive in arbitrary "chunks" with arbitrary delays. All that's guaranteed is that they will eventually arrive in order (or if that's not possible because of networking issues, the connection will fail.)
In the absence of a blocking read function (I don't know if those exist) you have to do something like what you are doing. You have to read one character at a time and append it to a buffer, gracefully handing the possibility of getting a -1 (the next character isn't here yet, or the connection broke). In general you never want to try to read multiple characters in a single read(buf, len) unless you've just used available() to make sure len characters are actually available. And even that can fail if your buffers are really large. Stick to one-character-at-a-time.
It's a reasonable idea to call delay(1) when available() returns 0. In the places where you try to guess at something like delay(20) before reading a buffer you are rolling the dice - there's no promise that any amount of delay will guarantee bytes get delivered. Example: Maybe a drop of water fell on the chip's antenna and it won't work until the drop evaporates. Data could be delayed for minutes.
I don't know how available() behaves if the connection fails. You might have to do a read() and get back a -1 to diagnose a failed connection. The Arduino documentation is absolutely horrible, so you'll have to experiment.
TCP is much simpler to handle on platforms that have threads, blocking read, select() and other tools to manage data. Having only non-blocking read makes things harder, but there it is.
In some situations UDP is actually a lot simpler - there are more guarantees about getting messages of certain sizes in a single chunk. But of course whole messages can go missing or show up out of order. It's a trade-off.
I seem to be struggling with the std::io::TcpStream. I'm actually trying to open a TCP connection with another system but the below code emulates the problem exactly.
I have a Tcp server that simply writes "Hello World" to the TcpStream upon opening and then loops to keep the connection open.
fn main() {
let listener = io::TcpListener::bind("127.0.0.1", 8080);
let mut acceptor = listener.listen();
for stream in acceptor.incoming() {
match stream {
Err(_) => { /* connection failed */ }
Ok(stream) => spawn(proc() {
handle(stream);
})
}
}
drop(acceptor);
}
fn handle(mut stream: io::TcpStream) {
stream.write(b"Hello Connection");
loop {}
}
All the client does is attempt to read a single byte from the connection and print it.
fn main() {
let mut socket = io::TcpStream::connect("127.0.0.1", 8080).unwrap();
loop {
match socket.read_byte() {
Ok(i) => print!("{}", i),
Err(e) => {
println!("Error: {}", e);
break
}
}
}
}
Now the problem is my client remains blocked on the read until I kill the server or close the TCP connection. This is not what I want, I need to open a TCP connection for a very long time and send messages back and forth between client and server. What am I misunderstanding here? I have the exact same problem with the real system i'm communicating with - I only become unblocked once I kill the connection.
Unfortunately, Rust does not have any facility for asynchronous I/O now. There are some attempts to rectify the situation, but they are far from complete yet. That is, there is a desire to make truly asynchronous I/O possible (proposals include selecting over I/O sources and channels at the same time, which would allow waking tasks which are blocked inside an I/O operation via an event over a channel, though it is not clear how this should be implemented on all supported platforms), but there's still a lot to do and there's nothing really usable now, as far as I'm aware.
You can emulate this to some extent with timeouts, however. This is far from the best solution, but it works. It could look like this (simplified example from my code base):
let mut socket = UdpSocket::bind(address).unwrap();
let mut buf = [0u8, ..MAX_BUF_LEN];
loop {
socket.set_read_timeout(Some(5000));
match socket.recv_from(buf) {
Ok((amt, src)) => { /* handle successful read */ }
Err(ref e) if e.kind == TimedOut => {} // continue
Err(e) => fail!("error receiving data: {}", e) // bail out
}
// do other work, check exit flags, for example
}
Here recv_from will return IoError with kind set to TimedOut if there is no data available on the socket during 5 seconds inside recv_from call. You need to reset the timeout before inside each loop iteration since it is more like a "deadline" than a timeout - when it expires, all calls will start to fail with timeout error.
This is definitely not the way it should be done, but Rust currently does not provide anything better. At least it does its work.
Update
There is now an attempt to create an asynchronous event loop and network I/O based on it. It is called mio. It probably can be a good temporary (or even permanent, who knows) solution for asynchronous I/O.
NB: the OP confirms in the comment thread that the problem was due to a typo, not shown in the posted code.
I was expecting to get a notification using GetQueuedCompletionStatus after scheduling an overlapped disconnect with DisconnectEx. I never get one - is this by design? If I specify a manual reset event in the OVERLAPPED structure this is signalled to indicate that the disconnect is complete, but GetQueuedCompletionStatus never returns.
My call to DisconnectEx looks a bit like this (note that context has an operator LPOVERLAPPED and ol is the first element in the structure):
context.ol.hEvent = hEvent;
BOOL result = DisconnectEx(context.socket, context, TF_REUSE_SOCKET, 0);
if (result)
{
// we completed synchronously:
ProcessCompletion(0, context, 0);
}
else
{
int error = WSAGetLastError();
if (error != ERROR_IO_PENDING)
{
throw ServerSocketException("DisconnectEx failed");
}
WaitForSingleObject(hEvent, INFINITE);
std::cout << "disconnected - event signalled\n";
}
I added the WaitForSingleObject when I found that GetQueuedCompletionStatus didn't return. What is the correct way to detect DisconnectEx completing? I want to use the socket again in a call to AcceptEx.
It appears that this was because of a typo on the OP's part.
(Posting an answer so other people don't have to read the comment thread...)
Okay this is my first question here on Stack Overflow, so bare over with it if I'm not asking properly.
Basically I'm trying to code some asynchronous sockets using std.socket, but I'm not sure if I've understood the concept correct. I've only ever worked with asynchronous sockets in C# and in D it seem to be on a much lower level. I've researched a lot and looked up a lot of code, documentation etc. both for D and C/C++ to get an understanding, however I'm not sure if I understand the concept correctly and if any of you have some examples. I tried looking at splat, but it's very outdated and vibe seems to be too complex just for a simple asynchronous socket wrapper.
If I understood correctly there is no poll() function in std.socket so you'd have to use SocketSet with a single socket on select() to poll the status of the socket right?
So basically how I'd go about handling the sockets is polling to get the read status of the socket and if it has a success (value > 0) then I can call receive() which will return 0 for disconnection else the received value, but I'd have to keep doing this until the expected bytes are received.
Of course the socket is set to nonblocked!
Is that correct?
Here is the code I've made up so far.
void HANDLE_READ()
{
while (true)
{
synchronized
{
auto events = cast(AsyncObject[int])ASYNC_EVENTS_READ;
foreach (asyncObject; events)
{
int poll = pollRecv(asyncObject.socket.m_socket);
switch (poll)
{
case 0:
{
throw new SocketException("The socket had a time out!");
continue;
}
default:
{
if (poll <= -1)
{
throw new SocketException("The socket was interrupted!");
continue;
}
int recvGetSize = (asyncObject.socket.m_readBuffer.length - asyncObject.socket.readSize);
ubyte[] recvBuffer = new ubyte[recvGetSize];
int recv = asyncObject.socket.m_socket.receive(recvBuffer);
if (recv == 0)
{
removeAsyncObject(asyncObject.event_id, true);
asyncObject.socket.disconnect();
continue;
}
asyncObject.socket.m_readBuffer ~= recvBuffer;
asyncObject.socket.readSize += recv;
if (asyncObject.socket.readSize == asyncObject.socket.expectedReadSize)
{
removeAsyncObject(asyncObject.event_id, true);
asyncObject.event(asyncObject.socket);
}
break;
}
}
}
}
}
}
So basically how I'd go about handling the sockets is polling to get the read status of the socket
Not quite right. Usually, the idea is to build an event loop around select, so that your application is idle as long as there are no network or timer events that need to be handled. With polling, you'd have to check for new events continuously or on a timer, which leads to wasted CPU cycles, and events getting handled a bit later than they occur.
In the event loop, you populate the SocketSets with sockets whose events you are interested in. If you want to be notified of new received data on a socket, it goes to the "readable" set. If you have data to send, the socket should be in the "writable" set. And all sockets should be on the "error" set.
select will then block (sleep) until an event comes in, and fill the SocketSets with the sockets which have actionable events. Your application can then respond to them appropriately: receive data for readable sockets, send queued data for writable sockets, and perform cleanup for errored sockets.
Here's my D implementation of non-fiber event-based networking: ae.net.asockets.
I am implementing a server that sends xml to clients using boost. The problem I am facing is that the buffer doesn't get sent immediately and accumulates to a point then sends the whole thing. This cause a problem on my client side, when it parses the xml, it may have incomplete xml tag (incomplete message). Is there a way in boost to flush out the socket whenever it needs to send out a message? Below is server's write code.
void
ClientConnection::handle_write(const boost::system::error_code& error)
{
if (!error)
{
m_push_message_queue.pop_front ();
if (!m_push_message_queue.empty () && !m_disconnected)
{
boost::asio::async_write(m_socket,
boost::asio::buffer(m_push_message_queue.front().data(),
m_push_message_queue.front().length()),
boost::bind(&ClientConnection::handle_write, this,
boost::asio::placeholders::error));
}
}
else
{
std::err << "Error writting out message...\n";
m_disconnected = true;
m_server->DisconnectedClient (this);
}
}
Typically when creating applications using TCP byte streams the sender sends a fixed length header so the receiver knows how many bytes to expect. Then the receiver reads that many bytes and parses the resulting buffer into an XML object.
I assume you are using TCP connection. TCP is stream type, so you can't assume your packet will come in one big packet. You need to fix your communication design, by sending size length first like San Miller answer, or sending flag or delimiter after all xml data has been sent.
Assuming you are definitely going to have some data on the socket you want to clear, you could do something like this:
void fulsh_socket()
{
boost::asio::streambuf b;
boost::asio::streambuf::mutable_buffers_type bufs = b.prepare(BUFFER_SIZE);
std::size_t bytes = socket_.receive(bufs); // !!! This will block until some data becomes available
b.commit(bytes);
boost::asio::socket_base::bytes_readable command(true);
socket_.io_control(command);
while(command.get())
{
bufs = b.prepare(BUFFER_SIZE);
bytes = socket_.receive(bufs);
b.commit(bytes);
socket_.io_control(command); // reset for bytes pending
}
return;
}
where socket_ is a member variable.
HTH