我想使用能够发送和接收文件的套接字和C / C ++语言实现在Linux上运行的客户端 - 服务器体系结构。是否有任何库使这项任务变得简单？有人可以提供一个例子吗？
最便携的解决方案是以块的形式读取文件，然后在循环中将数据写入套接字（同样，在接收文件时反过来）。你将缓冲区read分配到缓冲区，并将write从缓冲区分配到你的套接字中（你也可以使用send和recv，它们是特定于套接字的写入和读取数据的方式）。大纲看起来像这样：
while (1) {
// Read data into buffer. We may not have enough to fill up buffer, so we
// store how many bytes were actually read in bytes_read.
int bytes_read = read(input_file, buffer, sizeof(buffer));
if (bytes_read == 0) // We're done reading from the file
break;
if (bytes_read < 0) {
// handle errors
}
// You need a loop for the write, because not all of the data may be written
// in one call; write will return how many bytes were written. p keeps
// track of where in the buffer we are, while we decrement bytes_read
// to keep track of how many bytes are left to write.
void *p = buffer;
while (bytes_read > 0) {
int bytes_written = write(output_socket, p, bytes_read);
if (bytes_written <= 0) {
// handle errors
}
bytes_read -= bytes_written;
p += bytes_written;
}
}
请务必仔细阅读read和write的文档，尤其是在处理错误时。一些错误代码意味着您应该再次尝试，例如只使用continue语句再次循环，而其他错误代码意味着某些东西被破坏而您需要停止。
为了将文件发送到套接字，有一个系统调用，sendfile可以满足您的需求。它告诉内核将文件从一个文件描述符发送到另一个文件描述符，然后内核可以处理其余的文件描述符。有一点需要注意，源文件描述符必须支持mmap（如实际文件，而不是套接字），并且目标必须是套接字（因此您不能使用它来复制文件，或直接从一个插座到另一个插座）;它旨在支持您描述的将文件发送到套接字的用法。但是，它对接收文件没有帮助;你需要自己做循环。我不能告诉你为什么有一个sendfile电话但没有类似的recvfile。
请注意sendfile是特定于Linux的;它不能移植到其他系统。其他系统经常有自己的sendfile版本，但确切的界面可能会有所不同（FreeBSD，Mac OS X，Solaris）。
在Linux 2.6.17中，splice系统调用是introduced，从2.6.23开始是used internally to implement sendfile。 splice是比sendfile更通用的API。有关splice和tee的详细描述，请参阅相当不错的explanation from Linus himself。他指出如何使用splice基本上就像上面的循环，使用read和write，除了缓冲区在内核中，因此数据不必在内核和用户空间之间传输，或者甚至可能都没有通过通过CPU（称为“零拷贝I / O”）。
做aman 2 sendfile。您只需要在服务器上的客户端和目标文件上打开源文件，然后调用sendfile，内核将切断并移动数据。
最小的可运行POSIX read + write示例
用法：
ifconfig查找服务器本地IP，例如192.168.0.10
跑：
./server output.tmp 12345
printf 'ab\ncd\n' > input.tmp
./client input.tmp 192.168.0.10 12345
output.tmp的服务器计算机上创建了一个文件qazxsw po！server.c
'ab\ncd\n'client.c
/*
Receive a file over a socket.
Saves it to output.tmp by default.
Interface:
./executable [<output_file> [<port>]]
Defaults:
- output_file: output.tmp
- port: 12345
*/
#define _XOPEN_SOURCE 700
#include <stdio.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <netdb.h> /* getprotobyname */
#include <netinet/in.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <unistd.h>
int main(int argc, char **argv) {
char *file_path = "output.tmp";
char buffer[BUFSIZ];
char protoname[] = "tcp";
int client_sockfd;
int enable = 1;
int filefd;
int i;
int server_sockfd;
socklen_t client_len;
ssize_t read_return;
struct protoent *protoent;
struct sockaddr_in client_address, server_address;
unsigned short server_port = 12345u;
if (argc > 1) {
file_path = argv[1];
if (argc > 2) {
server_port = strtol(argv[2], NULL, 10);
}
}
/* Create a socket and listen to it.. */
protoent = getprotobyname(protoname);
if (protoent == NULL) {
perror("getprotobyname");
exit(EXIT_FAILURE);
}
server_sockfd = socket(
AF_INET,
SOCK_STREAM,
protoent->p_proto
);
if (server_sockfd == -1) {
perror("socket");
exit(EXIT_FAILURE);
}
if (setsockopt(server_sockfd, SOL_SOCKET, SO_REUSEADDR, &enable, sizeof(enable)) < 0) {
perror("setsockopt(SO_REUSEADDR) failed");
exit(EXIT_FAILURE);
}
server_address.sin_family = AF_INET;
server_address.sin_addr.s_addr = htonl(INADDR_ANY);
server_address.sin_port = htons(server_port);
if (bind(
server_sockfd,
(struct sockaddr*)&server_address,
sizeof(server_address)
) == -1
) {
perror("bind");
exit(EXIT_FAILURE);
}
if (listen(server_sockfd, 5) == -1) {
perror("listen");
exit(EXIT_FAILURE);
}
fprintf(stderr, "listening on port %d\n", server_port);
while (1) {
client_len = sizeof(client_address);
puts("waiting for client");
client_sockfd = accept(
server_sockfd,
(struct sockaddr*)&client_address,
&client_len
);
filefd = open(file_path,
O_WRONLY | O_CREAT | O_TRUNC,
S_IRUSR | S_IWUSR);
if (filefd == -1) {
perror("open");
exit(EXIT_FAILURE);
}
do {
read_return = read(client_sockfd, buffer, BUFSIZ);
if (read_return == -1) {
perror("read");
exit(EXIT_FAILURE);
}
if (write(filefd, buffer, read_return) == -1) {
perror("write");
exit(EXIT_FAILURE);
}
} while (read_return > 0);
close(filefd);
close(client_sockfd);
}
return EXIT_SUCCESS;
}
/*
Send a file over a socket.
Interface:
./executable [<input_path> [<sever_hostname> [<port>]]]
Defaults:
- input_path: input.tmp
- server_hostname: 127.0.0.1
- port: 12345
*/
#define _XOPEN_SOURCE 700
#include <stdio.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <fcntl.h>
#include <netdb.h> /* getprotobyname */
#include <netinet/in.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <unistd.h>
int main(int argc, char **argv) {
char protoname[] = "tcp";
struct protoent *protoent;
char *file_path = "input.tmp";
char *server_hostname = "127.0.0.1";
char *server_reply = NULL;
char *user_input = NULL;
char buffer[BUFSIZ];
in_addr_t in_addr;
in_addr_t server_addr;
int filefd;
int sockfd;
ssize_t i;
ssize_t read_return;
struct hostent *hostent;
struct sockaddr_in sockaddr_in;
unsigned short server_port = 12345;
if (argc > 1) {
file_path = argv[1];
if (argc > 2) {
server_hostname = argv[2];
if (argc > 3) {
server_port = strtol(argv[3], NULL, 10);
}
}
}
filefd = open(file_path, O_RDONLY);
if (filefd == -1) {
perror("open");
exit(EXIT_FAILURE);
}
/* Get socket. */
protoent = getprotobyname(protoname);
if (protoent == NULL) {
perror("getprotobyname");
exit(EXIT_FAILURE);
}
sockfd = socket(AF_INET, SOCK_STREAM, protoent->p_proto);
if (sockfd == -1) {
perror("socket");
exit(EXIT_FAILURE);
}
/* Prepare sockaddr_in. */
hostent = gethostbyname(server_hostname);
if (hostent == NULL) {
fprintf(stderr, "error: gethostbyname(\"%s\")\n", server_hostname);
exit(EXIT_FAILURE);
}
in_addr = inet_addr(inet_ntoa(*(struct in_addr*)*(hostent->h_addr_list)));
if (in_addr == (in_addr_t)-1) {
fprintf(stderr, "error: inet_addr(\"%s\")\n", *(hostent->h_addr_list));
exit(EXIT_FAILURE);
}
sockaddr_in.sin_addr.s_addr = in_addr;
sockaddr_in.sin_family = AF_INET;
sockaddr_in.sin_port = htons(server_port);
/* Do the actual connection. */
if (connect(sockfd, (struct sockaddr*)&sockaddr_in, sizeof(sockaddr_in)) == -1) {
perror("connect");
return EXIT_FAILURE;
}
while (1) {
read_return = read(filefd, buffer, BUFSIZ);
if (read_return == 0)
break;
if (read_return == -1) {
perror("read");
exit(EXIT_FAILURE);
}
/* TODO use write loop: https://stackoverflow.com/questions/24259640/writing-a-full-buffer-using-write-system-call */
if (write(sockfd, buffer, read_return) == -1) {
perror("write");
exit(EXIT_FAILURE);
}
}
free(user_input);
free(server_reply);
close(filefd);
exit(EXIT_SUCCESS);
}
。
进一步评论
可能的改进：
output.tmp。
或者，我们可以创建一个哈希文件的服务器来查找文件名，并保留从原始路径到磁盘上的哈希（在数据库上）的映射。accept或poll是一些选择：select一个简单的HTTP How to implement a timeout in read function call?实现如下所示：wget
在Ubuntu 15.10上测试过。
这个文件将作为一个很好的How to make an HTTP get request in C without libcurl?示例：sendfile