0. pipe 与 dup
1. pipe
默认为阻塞， ` int socketpair(int domain, int type, int protocol, int sv[2]);`
2. dup
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int dup(int oldfd);
int dup2(int oldfd, int newfd);
3.demo
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int main(int argc,char *argv[]){
if (argc<=2){
printf("argc error");
return -1;
}
const char* ip = argv[1];
int port = atoi(argv[2]);
struct sockaddr_in address;
bzero(&address,sizeof(address));
address.sin_family = AF_INET;
inet_pton(AF_INET,ip,&address.sin_addr);
address.sin_port = htons(port);
int sock = socket(PF_INET,SOCK_STREAM,0);
assert(sock >= 0);
int ret = bind(sock,(struct sockaddr*)&address,sizeof(address));
assert(ret != -1);
ret = listen( sock, 5 );
assert( ret != -1 );
struct sockaddr_in client;
socklen_t client_addrlength = sizeof(client);
int connfd = accept(sock,(struct sockaddr*)&client,&client_addrlength);
if (connfd < 0){
perror("accept error");
} else{
close(STDOUT_FILENO);
dup(connfd);
printf("abcd\n");
close(connfd);
}
close(sock);
return 0;
}
1. readv 与 writev
readv: 将数据从文件描述符读到分散的内存块中。 writev: 将多块分散的内存数据一并写入到文件描述符中。
上面这么说可能有点抽象，这样举个例子比较好理解，Web服务器解析到一个请求后，要响应一个状态行、多个头部字段、以及返回的html文档内容。前两块可以放置在一块内存中，html文档放在另外一块内存中。我们并不需要将两个部分的内容拼接再发送，而是可以使用writev将他们同时写出。
一个demo，web服务器上的集中写
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// readv 核心代码
struct iovec iv[2];
iv[0].iov_base = header_buf;
iv[0].iov_len = strlen(header_buf);
iv[1].iov_base = file_buf;
iv[1].iov_len = strlen(file_buf);
完整代码：
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int main(int argc,char *argv[]){
if (argc <= 3){
printf("argc nums error");
return 1;
}
const char* ip = argv[1]; // ip
int port = atoi(argv[2]); // 端口
const char* file_name = argv[3]; // 目标文件
struct sockaddr_in address;
bzero(&address,sizeof(address));
address.sin_family = AF_INET;
inet_pton(AF_INET,ip,&address.sin_addr); // ip地址转换函数 绑定ip
address.sin_port = htons(port); // 绑定端口
int sock = socket(PF_INET,SOCK_STREAM,0); // tcp 链接sock
assert(sock >- 0);
int ret = bind(sock,(struct sockaddr*)&address,sizeof(address)); // sockt 与ip端口绑定
assert(ret != -1);
ret = listen(sock,5); // 开始监听
assert(ret != -1);
struct sockaddr_in client; // 客户端sockt
socklen_t client_addrlength = sizeof(client);
int connfd = accept(sock,(struct sockaddr*)&client,&client_addrlength);
if (connfd < 0){
printf("errno is %d\n",errno);
} else{
char header_buf[BUFFER_SIZE];
char *file_buf;
struct stat file_stat;
bool valid = true;
int len = 0;
if (stat(file_name,&file_stat) < 0){
valid = false;
} else{
if (S_ISDIR(file_stat.st_mode)){
valid = false; // 目标文件是一个目录
}else if (file_stat.st_mode & S_IROTH) // 当前用户有读取目标文件的权限
{
int fd = open(file_name,O_RDONLY);
file_buf = new char[file_stat.st_size+1];
memset(file_buf,'\0',file_stat.st_size+1); // 初始化
if (read(fd,file_buf,file_stat.st_size +1) < 0){
valid = false;
}
} else{
valid = false;
}
}
//如果目标文件夹有效，则发送正常的http应答
if (valid){
ret = snprintf( header_buf, BUFFER_SIZE-1, "%s %s\r\n", "HTTP/1.1", status_line[0] );
len += ret;
ret = snprintf( header_buf + len, BUFFER_SIZE-1-len,
"Content-Length: %d\r\n", file_stat.st_size );
len += ret;
ret = snprintf( header_buf + len, BUFFER_SIZE-1-len, "%s", "\r\n" );
struct iovec iv[2];
iv[0].iov_base = header_buf;
iv[0].iov_len = strlen(header_buf);
iv[1].iov_base = file_buf;
iv[1].iov_len = strlen(file_buf);
ret = writev(connfd,iv,2);
} else{
ret = snprintf( header_buf, BUFFER_SIZE-1, "%s %s\r\n", "HTTP/1.1", status_line[1] );
len += ret;
ret = snprintf( header_buf + len, BUFFER_SIZE-1-len, "%s", "\r\n" );
send( connfd, header_buf, strlen( header_buf ), 0 );
}
close(connfd);
delete[] file_buf;
}
close(sock);
return 0;
}
2. senfile 函数（零拷贝）
函数原型： ssize_t sendfile(int out_fd, int in_fd, off_t *offset, size_t count);
优势：Because this copying is done within the kernel,（完全在内核中）。
限制：out_fd must refer to a socket. Since Linux 2.6.33 it can be any file. in_fd 为文件，out_fd 为socket。
sendfile几乎是专门为网络上传输文件而设计。
demo
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int main(int argc,char* argv[]){
if (argc <= 3){
printf("argc nums error");
return 1;
const char* ip = argv[1];
int port = atoi(argv[2]);
const char *file_name = argv[3];
int filefd = open(file_name,O_RDONLY);
assert(filefd > 0);
struct stat stat_buf;
fstat(filefd,&stat_buf);
struct sockaddr_in address;
bzero(&address,sizeof(address));
address.sin_family = AF_INET;
inet_pton(AF_INET,ip,&address.sin_addr);
address.sin_port = htons(port);
int sock = socket(PF_INET,SOCK_STREAM,0);
assert(sock >= 0);
int ret = bind(sock,(struct sockaddr*)&address,sizeof(address));
assert(ret != -1);
ret = listen(sock,5);
assert(ret != -1);
struct sockaddr_in client;
socklen_t client_addrlength = sizeof(client);
int connfd = accept(sock,(struct sockaddr*)&client,&client_addrlength);
if (connfd < 0){
printf("errno is");
} else{
sendfile(connfd,filefd,NULL,stat_buf.st_size);
close(connfd);
}
close(sock);
return 0;
}
}
3. mmap 与 munmap函数
用于申请内存与释放内存，将这段内存可作为进程间通信的共享内存。暂略。
4. splice函数
两个文件描述符间的数据移动，零拷贝操作。 where one of the file descriptors must refer to a pipe.
demo
一个零拷贝的回射服务器，将客户端发送的数据原样的返回客户端。
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int mian(int argc,char* argv[]){
if (argc <= 2){
return 1;
}
const char* ip = argv[1];
int port = atoi(argv[2]);
struct sockaddr_in address;
bzero(&address,sizeof(address));
address.sin_family = AF_INET;
inet_pton(AF_INET,ip,&address.sin_addr);
address.sin_port = htons(port);
int sock = socket(PF_INET,SOCK_STREAM,0);
assert(sock >= 0);
int ret = bind(sock,(struct sockaddr*)&address,sizeof(address));
assert(ret != -1);
struct sockaddr_in client;
socklen_t client_addrlength = sizeof(client);
int connfd = accept(sock,(struct sockaddr*)&client,&client_addrlength);
if (connfd < 0){
printf("error");
} else{
int pipefd[2];
assert(ret != -1);
ret = pipe(pipefd);
ret = splice(connfd,NULL,pipefd[1],NULL,32768,SPLICE_F_MORE|SPLICE_F_MOVE);
assert(ret != -1);
ret = splice( pipefd[0], NULL, connfd, NULL, 32768, SPLICE_F_MORE | SPLICE_F_MOVE );
assert(ret != -1);
close(connfd);
}
close(sock);
return 0;
}
4. tee函数
两个管道间的文件描述符之间的复制数据。零拷贝操作。
5. fcntl函数
根据文件描述符更改属性
略。