我的代码逻辑（C语言实现断点续传的demo）大概是
服务器将文件分片，每次向客户端只发送一个分片，只有等客户端返回应答才继续发送接下来的分片
现在我遇到的问题是
客户端发送的应答，能发送到套接字的输出缓冲区，可是，服务器这边却recv()不到这个应答
我想不到是什么原因，help me
代码
//服务器
//保存上次下载标识
int id;
//从tfp指向的文件即Temp.txt读取内容，默认为0，即从第一个片开始
id = fgetc(tfp);
int idsize = sizeof(id);
//需要一个接收客户端应答的缓冲区
char buffer[BUF_SIZE] = { 0 };
char *bp = buffer;
printf("Server will send files to the client\n\n\n\n");
int recvLen = 0,sendLen=0;
for ( i = 0; i < PIECE; i++)
{
//记录当前下载到哪一个片，保存到Temp.txt
fputc(i, tfp);
printf("the %d of for circle\n", i);
//上次下载到哪里，这一次便从那里开始
if (sli[i].grade == id) {
//每次发送一个分片
printf("\tserver will send the %d piece of the file\n",i+1);
if ((sendLen = send(sock, dp[i], tsize, 0)) < 0)
{
printf("\tsend a mess to client had failed, and the successful bytes is:%d\n", sendLen);
}
else
{
printf("\tsend a mess to client was succeeded, and the successful bytes is:%d\n", sendLen);
}
/*
*服务器每发送一个分片，必须根据客户端的应答进行判断
*1、客户端应答已收到(用字符'f'表示)——继续发送剩下的分片，并且显示传输进度
*2、客户端应答未收到(用字符'n'表示)——保存当前下载标识，结束传输
*/
//recv()的作用是阻塞，因为要接收客户端的应答
printf("\t\twait to receive respond from client\n");
if ((recvLen = recv(sock, buffer, nCount, 0)) > 0) {
printf("\tthe num to recv respond from client is %d,and the nCount is %d\n", i + 1, recvLen);
}
else
{
printf("receive respond failed! return:%d\n",recvLen);
}
//应答超时设置为6s，表示经过了6s以后，若客户端还没有应答，就不再等待该应答
//Sleep(6000);
if (*bp=='f')
{
//若客户端已收到应答
//表示已发送完毕一个分片，下载标识+1，并且打印传输进度
printf("Server gets the respond from client\n");
printf("\tthe rate of transported procession now is:%d%%\n", i * 100 / PIECE);
if (i % 10 == 0)
printf("\n");
id++;
}
else if(*bp=='n')
{
//若客户端收不到应答
//也就是当前分片也发送失败，即当前下载标识不需要自增1——记录当前下载标识
printf("Server misses the respond from client\n");
fputc(i, tfp);
break;
}
else
{
printf("nothing\n");
}
if (id == PIECE)
printf("\n传输完成！\n");
printf("\n");
}
}
客户端代码
//客户端
/*
*接收缓冲区是连续接受数据的
* 每次接收一个片就返回应答
* 同时写进文件(buffer->rfp)
*/
char buffer[BUF_SIZE] = { 0 };
//客户端用指向字符常量的指针来表示应答
char idNarr[2] = "n";
char idFarr[2] = "f";
const char *ip = idNarr;
//该应答标识的实际长度
int len = sizeof(ip) / sizeof(const char *);
//实际接收字节
int rLen = 0, i,nCount,fwLen;
printf("\n\n\n\n");
for (i = 0; i < PIECE; i++)
{
printf("the %d of for circle\n",i);
rLen = recv(clntSock, buffer, BUF_SIZE, 0);
buffer[rLen] = '\0';
//检验是否从套接字的输入缓冲区接收到数据
printf("receive from server is %s,the length is %d\n",buffer,rLen);
printf("ip point to the string is:%s\n",ip);
//接收到数据就把应答标识标志为f
ip =idFarr;
printf("ip point to the string is:%s\n",ip);
//发送应答标识，并检查是否发送成功
if ((nCount= send(clntSock, ip, len, 0))<0)
{
printf("send a mess to server had failed, and the successful bytes is:%d", nCount);
}
else
{
printf("send a mess to server was succeeded, and the successful bytes is:%d\n", nCount);
}
ip = idNarr;
//将接收到的数据写入本地文件，并检查是否写入成功
if((fwLen = fwrite(buffer, 1, rLen, fp)) > 0) {
printf("\tto write something into file of %d,and the nCount is %d\n", i + 1, rLen);
}
else
{
printf("fwrite failed!\n");
}
}
