通过 TCP 同时发送两个数据包时，一个丢失

Question

I use Java as a server, and PHP as a client, so after connecting to the server, I do socket_set_nonblock (so that the flow does not stop when socket_read), then through while() I accept packages (socket_read), but the trouble is, if you send two packages at once, the second one disappears.

// socket class
public function __construct(int $port) {
    if(!($this->socket = @socket_create(AF_INET, SOCK_STREAM, SOL_TCP)))
        var_dump('Ошибка при создании сокета: ' . socket_strerror(socket_last_error()) . PHP_EOL);
    if (!@socket_set_option($this->socket, SOL_SOCKET, SO_REUSEADDR, 1))
        var_dump('Не могу установить опцию на сокете: ' . socket_strerror(socket_last_error()) . PHP_EOL);
    if(!@socket_bind($this->socket, '127.0.0.1', $port))
        var_dump('Не удалось привязать адрес: ' . socket_strerror(socket_last_error()) . PHP_EOL);
}

public function connect(string $address, int $port): bool {
        if(($result = @socket_connect($this->socket, $address, $port)))
            if(!socket_set_nonblock($this->socket))
                var_dump('Не могу установить опцию: [nonblock] на сокете: ' . socket_strerror(socket_last_error()) . PHP_EOL);
        return $result;
    }

public function readData(): string {
    return socket_read($this->socket, ClientConst::MTU_SIZE);
}

// main class
public function main() {
    while(true) {
        if(($rawPacket = $this->primarySocket->readData()) !== '') {
            //todo: 
        }
    }
}

Answer 1

TCP does not have messages. TCP sends a stream of bytes. There is no guarantee that one 'send' results in one 'receive' at the other end. It could be that the receive call reads data from two sends; it could be that two receive calls each read only part of the data from one send.

If you want message boundaries you need to provide them. There are two common techniques: precede each message by a length, and read that many bytes; or use a delimiter (such as \n) and read up to the delimiter.