C++ 如何知道我是否从非阻塞套接字读取所有内容

我接受了一个非阻塞连接套接字:

我有一个非阻塞套接字连接，在收到一包数据后，我try 使用recv读取更多内容.

struct sockaddr accepted_address;
socklen_t accepted_address_size = sizeof(accepted_address);

int fd = accept(server_fd, &accepted_address, &accepted_address_size);
make_nonblocking(fd);

... // wait when socket is ready to give me data

char buffer[BUF_SIZE];
int  used = 0;

while (true) {
    int bytes_received = recv(fd, buffer, BUF_SIZE, 0);
    if (bytes_received > 0) { /* OK */ }
    else if (bytes_received < 0) {
        if (errno == EAGAIN || errno == EWOULDBLOCK) {
            /* Should wait for more data, BUT I WILL WAIT INDEFINITELY!!! */
        } else {
            /* Handle error */
        }
    } else {
        /* EOF, OK, Process received data */
    }
}

当第一个recv调用检索到整个消息时，问题就出现了，但后续调用的结果是errno == EAGAIN，这导致了对更多永远不会到达的数据的无限期等待.

按每this answer 这是意料之中的行为.

我的问题是: How can I reliably determine that I have received the entire message if the second call to recv won't give me EOF but instead returns EAGAIN, leaving me waiting indefinitely?个