获取socket对应的接收缓冲区中的可读数据量

获取`socket`对应的接收缓冲区中的可读数据量

本文介绍如何获取当前socket对应的接收缓冲区的可读数据量

在Linux上可以使用ioctl函数

#include <sys/ioctl.h>int ioctl (int __fd, unsigned long int __request, ...)

来看一个例子:

#include <sys/types.h> 
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <fcntl.h>
#include <poll.h>
#include <iostream>
#include <string.h>
#include <vector>
#include <errno.h>//无效fd标记
#define INVALID_FD  -1int main(int argc, char* argv[])
{//创建一个侦听socketint listenfd = socket(AF_INET, SOCK_STREAM, 0);if (listenfd == INVALID_FD){std::cout << "create listen socket error." << std::endl;return -1;}//将侦听socket设置为非阻塞的int oldSocketFlag = fcntl(listenfd, F_GETFL, 0);int newSocketFlag = oldSocketFlag | O_NONBLOCK;if (fcntl(listenfd, F_SETFL,  newSocketFlag) == -1){close(listenfd);std::cout << "set listenfd to nonblock error." << std::endl;return -1;}//复用地址和端口号int on = 1;setsockopt(listenfd, SOL_SOCKET, SO_REUSEADDR, (char *)&on, sizeof(on));setsockopt(listenfd, SOL_SOCKET, SO_REUSEPORT, (char *)&on, sizeof(on));//初始化服务器地址struct sockaddr_in bindaddr;bindaddr.sin_family = AF_INET;bindaddr.sin_addr.s_addr = htonl(INADDR_ANY);bindaddr.sin_port = htons(3000);if (bind(listenfd, (struct sockaddr *)&bindaddr, sizeof(bindaddr)) == -1){std::cout << "bind listen socket error." << std::endl;close(listenfd);return -1;}//启动侦听if (listen(listenfd, SOMAXCONN) == -1){std::cout << "listen error." << std::endl;close(listenfd);return -1;}	std::vector<pollfd> fds;pollfd listen_fd_info;listen_fd_info.fd = listenfd;listen_fd_info.events = POLLIN;listen_fd_info.revents = 0;fds.push_back(listen_fd_info);//是否存在无效的fd标志bool exist_invalid_fd;int n;while (true){exist_invalid_fd = false;n = poll(&fds[0], fds.size(), 1000);if (n < 0){//被信号中断if (errno == EINTR)continue;//出错，退出break;}else if (n == 0){//超时，继续continue;}int size = fds.size();for (size_t i = 0; i < size; ++i){// 事件可读if (fds[i].revents & POLLIN){if (fds[i].fd == listenfd){//侦听socket，接受新连接struct sockaddr_in clientaddr;socklen_t clientaddrlen = sizeof(clientaddr);//接受客户端连接, 并加入到fds集合中int clientfd = accept(listenfd, (struct sockaddr *)&clientaddr, &clientaddrlen);if (clientfd != -1){//将客户端socket设置为非阻塞的int oldSocketFlag = fcntl(clientfd, F_GETFL, 0);int newSocketFlag = oldSocketFlag | O_NONBLOCK;if (fcntl(clientfd, F_SETFL,  newSocketFlag) == -1){close(clientfd);std::cout << "set clientfd to nonblock error." << std::endl;						} else{struct pollfd client_fd_info;client_fd_info.fd = clientfd;client_fd_info.events = POLLIN;client_fd_info.revents = 0;fds.push_back(client_fd_info);std::cout << "new client accepted, clientfd: " << clientfd << std::endl;}				}}else {//socket 可读时获取当前接收缓冲区中的字节数目ulong bytesToRecv = 0;if (ioctl(fds[i].fd, FIONREAD, &bytesToRecv) == 0){std::cout << "bytesToRecv: " << bytesToRecv << std::endl;}//普通clientfd,收取数据char buf[64] = { 0 };int m = recv(fds[i].fd, buf, 64, 0);if (m <= 0){if (errno != EINTR && errno != EWOULDBLOCK){//出错或对端关闭了连接，关闭对应的clientfd，并设置无效标志位	std::cout << "client disconnected, clientfd: " << fds[i].fd << std::endl;close(fds[i].fd);fds[i].fd = INVALID_FD;exist_invalid_fd = true;							}			}else{std::cout << "recv from client: " << buf << ", clientfd: " << fds[i].fd << std::endl;}}}else if (fds[i].revents & POLLERR){//TODO: 暂且不处理}}// end  outer-for-loopif (exist_invalid_fd){//统一清理无效的fdfor (std::vector<pollfd>::iterator iter = fds.begin(); iter != fds.end(); ){if (iter->fd == INVALID_FD)iter = fds.erase(iter);else++iter;}}	}// end  while-loop//关闭所有socketfor (std::vector<pollfd>::iterator iter = fds.begin(); iter != fds.end(); ++ iter)close(iter->fd);			return 0;
}