我有一个客户端和服务器,服务器是通过以下方式设置的:
int listenS = socket(AF_INET, SOCK_STREAM, 0);
struct sockaddr_in s = { 0 };
s.sin_family = AF_INET;
s.sin_port = htons(PORT);
s.sin_addr.s_addr = htonl(IP_ADDR);
bind(listenS, (struct sockaddr*)&s, sizeof(s));
listen(listenS, QUEUE_LEN);
struct sockaddr_in clientIn;
int clientInSize = sizeof clientIn;
while (1)
{
int newfd = accept(listenS, (struct sockaddr*)&clientIn, (socklen_t*)&clientInSize);
//......
(我只是删除了一些测试以使代码更易读)
客户就是:
int sock = socket(AF_INET, SOCK_STREAM, 0), nrecv;
struct sockaddr_in s = { 0 };
s.sin_family = AF_INET;
s.sin_port = htons(PORT);
s.sin_addr.s_addr = htonl(IP_ADDR);
if (connect(sock, (struct sockaddr*)&s, sizeof(s)) < 0)
{ //......
我建立了连接,并且一切正常,服务器recv
第一次从客户端发送消息,但是当我尝试向服务器发送send
另一条消息时,服务器不会阻止recv
调用并且什么都不会得到(返回缓冲区大小,而不是0 )
这是客户端代码:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <sys/sendfile.h>
#include <sys/stat.h>
#define PORT 0x0da2
#define IP_ADDR 0x7f000001
#define MAX_BUFFER_SIZE 1024
int send_all(int socket, void* buffer, size_t length)
{
char *ptr = (char*)buffer;
while (length > 0)
{
int i = send(socket, ptr, length, 0);
if (i < 1) return -1;
ptr += i;
length -= i;
}
return 0;
}
int main(int argc, char** argv)
{
if (argc > 1)
{
if ((strcmp(argv[1], "list-files") != 0) &&
(strcmp(argv[1], "upload-file") != 0) &&
(strcmp(argv[1], "download-file") != 0) &&
(strcmp(argv[1], "search") != 0))
{
perror("The arguments are incorrect.");
}
int sock = socket(AF_INET, SOCK_STREAM, 0), nrecv;
struct sockaddr_in s = { 0 };
s.sin_family = AF_INET;
s.sin_port = htons(PORT);
s.sin_addr.s_addr = htonl(IP_ADDR);
if (connect(sock, (struct sockaddr*)&s, sizeof(s)) < 0)
{
perror("connect");
return 1;
}
printf("Successfully connected.\n");
char sendBuffer[MAX_BUFFER_SIZE];
int lenOfArgv = strlen(argv[1]);
int sendBufferIndex = 0;
for (int i = 0;
i < lenOfArgv && sendBufferIndex < MAX_BUFFER_SIZE;
i++, sendBufferIndex++)
{
sendBuffer[sendBufferIndex] = argv[1][i];
}
if (argc == 3)
{
sendBuffer[sendBufferIndex++] = ' ';
int lenOfArgv = strlen(argv[2]);
for (int i = 0;
i < lenOfArgv && sendBufferIndex < MAX_BUFFER_SIZE;
i++, sendBufferIndex++)
{
sendBuffer[sendBufferIndex] = argv[2][i];
}
}
sendBuffer[sendBufferIndex] = 0;
// + 1 for terminating null
if (send_all(sock, sendBuffer, strlen(sendBuffer) + 1) < 0)
{
perror("send buffer to server failed");
return 1;
}
if(strcmp(argv[1], "download-file") == 0)
{
char sizeBuffer[256];
recv(sock, sizeBuffer, 256, 0);
int fileSize = atoi(sizeBuffer);
if(fileSize > 0)
{
FILE* recievedFile = fopen(argv[2], "w");
if(recievedFile != NULL)
{
int remainData = fileSize;
size_t len;
char fileBuffer[MAX_BUFFER_SIZE];
while(((len = recv(sock, fileBuffer, MAX_BUFFER_SIZE, 0)) > 0 && (remainData > 0)))
{
fwrite(fileBuffer, sizeof(char), len, recievedFile);
remainData -= len;
printf("Received %d bytes, %d is left..\n", len, remainData);
}
fclose(recievedFile);
printf("File downloaded!\n");
}
else
{
perror("Failed to download file\n");
}
}
}
else if(strcmp(argv[1], "upload-file") == 0)
{
char filePath[MAX_BUFFER_SIZE];
sprintf(filePath, "%s", argv[2]);
int fd = open(filePath, O_RDONLY);
int downloadFailed = 0;
if (fd != -1)
{
struct stat file_stat;
if(fstat(fd, &file_stat) >= 0)
{
char fileSize[256];
sprintf(fileSize, "%d", (int)file_stat.st_size);
int len = send(sock, fileSize, sizeof(fileSize), 0);
if(len >= 0)
{
int remainData = file_stat.st_size;
off_t offset = 0;
int sent_bytes = 0;
while(((sent_bytes = sendfile(sock, fd, &offset, MAX_BUFFER_SIZE)) > 0) && (remainData > 0))
{
remainData -= sent_bytes;
printf("sent %d bytes, %d is left...\n", sent_bytes, remainData);
}
}else {downloadFailed = 1;}
}else {downloadFailed = 1;}
}else {downloadFailed = 1;}
if(downloadFailed == 1)
{
perror("Failed to download file!\n");
}
}
else
{
char someBuffer[MAX_BUFFER_SIZE];
// nrecv is the number of bytes that we recieved
if ((nrecv = recv(sock, someBuffer, MAX_BUFFER_SIZE, 0)) < 0)
{
perror("recv");
return 1;
}
printf("%s\n", someBuffer);
}
close(sock);
return 0;
}
else
{
perror("The arguments are incorrect.");
}
}
这是服务器代码:
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <sys/wait.h>
#include <math.h>
#include <dirent.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/sendfile.h>
#define PORT 0x0da2 // 3490
#define IP_ADDR 0x7f000001 // 127.0.0.1
#define QUEUE_LEN 20
#define MAX_BUFFER_SIZE 1024
int send_all(int socket, void* buffer, int length)
{
char *ptr = (char*)buffer;
while (length > 0)
{
int i = send(socket, ptr, length, 0);
if (i < 1) return -1;
ptr += i;
length -= i;
}
return 0;
}
void list_dir()
{
DIR * directory;
struct dirent* dir;
directory = opendir(".");
if (directory)
{
while ((dir = readdir(directory)) != NULL)
{
printf("%s\n", dir->d_name); // /home/text.txt, text.txt
// get filesize (in bytes0 with dir->d_name
}
}
}
void list_files(char* buffer, int withBytes = 0)
{
DIR* d;
struct dirent* dir;
d = opendir("data");
int bufferIndex = 0;
while((dir = readdir(d)) != NULL)
{
char tempFilename[256] = "data/";
int tempIndex = 5;
char* scan = dir->d_name;
while(*scan)
{
tempFilename[tempIndex++] = *scan;
buffer[bufferIndex++] = *scan++;
}
tempFilename[tempIndex] = 0;
struct stat st = {0};
stat(tempFilename, &st);
int fileSize = st.st_size;
if(withBytes == 1)
{
// Adding file size to the buffer
bufferIndex += sprintf(&buffer[bufferIndex], " %d bytes", fileSize);
}
buffer[bufferIndex++] = '\n';
}
buffer[bufferIndex] = 0;
closedir(d);
}
int main(void)
{
int listenS = socket(AF_INET, SOCK_STREAM, 0);
if (listenS < 0)
{
perror("socket");
return 1;
}
struct sockaddr_in s = { 0 };
s.sin_family = AF_INET;
s.sin_port = htons(PORT);
s.sin_addr.s_addr = htonl(IP_ADDR);
if (bind(listenS, (struct sockaddr*)&s, sizeof(s)) < 0)
{
perror("bind");
return 1;
}
if (listen(listenS, QUEUE_LEN) < 0)
{
perror("listen");
return 1;
}
struct sockaddr_in clientIn;
int clientInSize = sizeof clientIn;
struct stat st = {0};
if(stat("data", &st) == -1)
{
mkdir("data", 0700);
}
while (1)
{
int newfd = accept(listenS, (struct sockaddr*)&clientIn, (socklen_t*)&clientInSize);
if (newfd < 0)
{
perror("accept");
return 1;
}
int pid = fork(); // creating new thread
if (pid == 0)
{
close(listenS); // duplicate=> thats why we need to close the socket
char someBuffer[MAX_BUFFER_SIZE];
int nrecv;
if ((nrecv = recv(newfd, someBuffer, MAX_BUFFER_SIZE, 0)) < 0)
{
perror("recv");
return 1;
}
printf("Message recieved: %s\n", someBuffer);
// Here we read the command the argument and split them
// into seperate variables
char command[256];
char argument[256];
int commandHasBeenSet = 0;
char* token = strtok(someBuffer, " ");
while(token != NULL)
{
if(commandHasBeenSet == 0)
{
strcpy(command, token);
commandHasBeenSet = 1;
}
else
{
strcpy(argument, token);
}
token = strtok(NULL, " ");
}
if (strcmp(command, "list-files") == 0)
{
char buffer[MAX_BUFFER_SIZE];
list_files(buffer, 1);
if (send_all(newfd, buffer, strlen(buffer) + 1) < 0)
{
perror("send buffer to client failed");
return 1;
}
printf("Sent a message to a client!\n");
}
else if (strcmp(command, "upload-file") == 0)
{
printf("Uploading file %s\n", argument);
char sizeBuffer[256];
recv(newfd, sizeBuffer, 256, 0);
int fileSize = atoi(sizeBuffer);
if(fileSize > 0)
{
char filePath[MAX_BUFFER_SIZE];
sprintf(filePath, "data/%s", argument);
printf("Downloading to %s", filePath);
FILE* recievedFile = fopen(filePath, "w");
if(recievedFile != NULL)
{
int remainData = fileSize;
size_t len;
char fileBuffer[MAX_BUFFER_SIZE];
while(((len = recv(newfd, fileBuffer, MAX_BUFFER_SIZE, 0)) > 0 && (remainData > 0)))
{
fwrite(fileBuffer, sizeof(char), len, recievedFile);
remainData -= len;
printf("Received %d bytes, %d is left..\n", len, remainData);
}
fclose(recievedFile);
printf("File downloaded!\n");
}
else
{
perror("Failed to download file\n");
}
}else
{
perror("Failed to get file size for download\n");
}
}
else if (strcmp(command, "download-file") == 0)
{
char filePath[MAX_BUFFER_SIZE];
sprintf(filePath, "data/%s", argument);
int fd = open(filePath, O_RDONLY);
int downloadFailed = 0;
if (fd != -1)
{
struct stat file_stat;
if(fstat(fd, &file_stat) >= 0)
{
char fileSize[256];
sprintf(fileSize, "%d", (int)file_stat.st_size);
int len = send(newfd, fileSize, sizeof(fileSize), 0);
if(len >= 0)
{
int remainData = file_stat.st_size;
off_t offset = 0;
int sent_bytes = 0;
while(((sent_bytes = sendfile(newfd, fd, &offset, MAX_BUFFER_SIZE)) > 0) && (remainData > 0))
{
remainData -= sent_bytes;
printf("Server sent %d bytes, %d is left...\n", sent_bytes, remainData);
}
}else {downloadFailed = 1;}
}else {downloadFailed = 1;}
}else {downloadFailed = 1;}
if(downloadFailed == 1)
{
perror("Failed to download file!\n");
}
}
else if (strcmp(command, "search") == 0)
{
char buffer[MAX_BUFFER_SIZE];
char result[MAX_BUFFER_SIZE];
int resultIndex = 0;
list_files(buffer);
result[0] = 0;
char tempBuffer[MAX_BUFFER_SIZE];
strcpy(tempBuffer, buffer);
token = strtok(tempBuffer, "\n");
while(token != NULL)
{
char* scanToken = token;
char* scanArgument = argument;
int found = 1;
while(*scanToken && *scanArgument)
{
if(*scanToken++ != *scanArgument++)
{
found = 0;
break;
}
}
if(found == 1)
{
if(resultIndex > 0)
{
result[resultIndex++] = ' ';
}
strcpy(&result[resultIndex], token);
resultIndex += strlen(token);
result[resultIndex] = 0;
}
token = strtok(NULL, "\n");
}
if (send_all(newfd, result, strlen(result) + 1) < 0)
{
perror("send buffer to client failed");
return 1;
}
printf("Sent a message to a client!\n");
}
close(newfd);
exit(0);
}
else
close(newfd);
}
close(listenS);
return 0;
}
如果您运行服务器,然后使用以下命令运行客户端:
./client list-files
./client download-file test.txt
它将正常工作,客户端将从服务器接收消息,反之亦然。
当我尝试运行时出现问题:
./client upload-file test.txt
与download-file
命令基本相同,只是从客户端复制并粘贴到服务器(相同的逻辑,应该工作相同),除了不同。
具体来说,程序在服务器(recv(newfd, sizeBuffer, 256, 0);
)的第175行失败,它的值为0,而不是客户端发送的值。
知道我缺少什么吗?
(我尝试在线搜索,但未找到任何内容)
答案 0 :(得分:1)
TCP是流协议。没有消息边界,并且服务器的recv
与客户端的send
不对应。
客户端使用以下命令发送命令
send_all(sock, sendBuffer, strlen(sendBuffer) + 1)
OTOH,服务器尝试通过以下方式接收它
nrecv = recv(newfd, someBuffer, MAX_BUFFER_SIZE, 0))
recv
不在乎流是否包含'\0'
。它盲目地等待MAX_BUFFER_SIZE
字节的到来。客户端发送的某些(有价值的)数据位于命令后面的someBuffer
中,但服务器忽略了。
服务器必须更加认真地解析答复。为此,您可能需要更详细的协议(例如,为每个字符串加上长度)。
答案 1 :(得分:0)
您假设流套接字将保留您的消息边界。它不会。因此,您发送的内容如下:
upload-file filename\0
NNN\0\0\0...\0 [256 bytes containing filesize]
<content of filename>
因此,您可能在服务器端执行的第recv
个字节(MAX_BUFFER_SIZE
个字节)不仅接收命令字符串和文件名,还接收文件大小块和整个文件内容。也就是说,您已经收到所有内容,并且它位于someBuffer
中。您的初始命令字符串以null终止,因此除非您选中nrecv
,否则您将不知道它的其余部分。因此,您的下一个recv
调用将获得文件结尾,因为客户端已完成并且已关闭其连接的结尾。
要通过TCP发送已定义的记录,您需要确切地知道每个点需要多少字节,并准确地接收(或准备解析接收到的数据)。另请参见https://stackoverflow.com/a/47440054/1076479