1:服务器将文件大小复制到缓冲区中并发送:
snprintf(t_buf, 255, "%" PRIu32, fsize);
if(send(f_sockd, t_buf, sizeof(t_buf), 0) < 0){
perror("error on sending file size\n");
onexit(f_sockd, m_sockd, 0, 2);
}
2:客户端接收到文件大小,放入fsize中:
if(recv(f_sockd, t_buf, sizeof(t_buf), 0) < 0){
perror("error on receiving file size");
onexit(f_sockd, 0 ,0 ,1);
}
fsize = atoi(t_buf);
----------------- 上面的代码使我的程序完美运行!
如果我编写此代码而不是上一个代码,则会出现问题:
1:服务器发送fsize:
if(send(f_sockd, &fsize, sizeof(fsize), 0) < 0){
perror("error on sending file size\n");
onexit(f_sockd, m_sockd, 0, 2);
}
2:客户端收到fsize:
if(recv(f_sockd, &fsize, sizeof(fsize), 0) < 0){
perror("error on receiving file size");
onexit(f_sockd, 0, 0, 1);
}
其中uint32_t fsize;
和char t_buf[256];
。
问题是,第一种方法可以正常工作,但第二种方法客户端不会收到所有文件,而只会收到其中的一部分。这段代码有什么问题?
谢谢!
最佳答案
recv(2)不一定填满完整的输出缓冲区 - 它可能返回更少的字节,具体取决于可用数据量:
The receive calls normally return any data available, up to the requested amount, rather than waiting for receipt of the full amount requested.
返回值(当 > 0 时)将是接收到的字节数,因此如果您想确保接收到所有内容,可以循环调用它。
或者,您可以传递 MSG_WAITALL
标志:
This flag requests that the operation block until the full request is satisfied. However, the call may still return less data than requested if a signal is caught, an error or disconnect occurs, or the next data to be received is of a different type than that returned.
因此,就您的情况而言,您可以执行以下操作:
ssize_t bytes = recv(f_sockd, &fsize, sizeof(fsize), MSG_WAITALL);
if(bytes == sizeof(fsize))
{
/* received everything */
}
else
{
/* something went wrong */
}
关于c套接字发送和接收int而不是char缓冲区,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/12175887/