如何解决sendto在发送数据包时创建分段错误
我正在尝试通过UDP发送数据包,但是在198行出现了段错误:
sendto(socketfd,buffer_str,total_len,res->ai_addr,res->ai_addrlen);
我不太确定是什么原因造成的。我已经通过GDB运行了该程序,并且所有参数似乎都没有问题。我尝试发送的文件只是一个简单的txt文件,其中包含文本“ Lorem ipsum dolor sit amet”。
第76行的第一个sendto可以正常工作,第78行的recv也可以。当我尝试用类似76的代码替换198上的sendto时,我得到了相同的段错误。
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netdb.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/time.h>
struct packet {
unsigned int total_frag;
unsigned int frag_no;
unsigned int size;
char* filename;
char filedata[1000];
};
struct node {
struct node* next;
struct packet data;
};
struct list {
struct node* head;
};
int main(int argc,char *argv[]) {
printf("ftp <file name>\n");
struct sockaddr_storage their_addr;
socklen_t addr_size = sizeof(their_addr);
struct addrinfo hints,*res;
char* port = "5050";//argv[2];
struct sockaddr_in *serverAddr;
serverAddr = malloc(sizeof(struct sockaddr_in));
memset(&hints,sizeof(hints));
memset(serverAddr,sizeof(*serverAddr));
serverAddr->sin_family = AF_INET;
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_DGRAM;
hints.ai_addr = (struct sockaddr *) serverAddr;
getaddrinfo("ug168.eecg.utoronto.ca"/*argv[1]*/,port,&hints,&res);
int socketfd = socket(PF_INET,SOCK_DGRAM,0);
char fileName[100];
scanf("%s",fileName);
int fd = open(fileName,O_RDWR);
if(fd == -1) {
return 0;
}
struct timeval pre_time,post_time;
gettimeofday(&pre_time,NULL);
sendto(socketfd,(char*)"ftp",3,res->ai_addrlen);
char buf[1000];
int length = recvfrom(socketfd,buf,1000,(struct sockaddr *)&serverAddr,&addr_size);
gettimeofday(&post_time,NULL);
buf[length] = '\0';
if(strcmp("yes",buf) == 0) {
printf("A file transfer can start\n");
}
printf("seconds : %ld\nmicro seconds : %ld\n",post_time.tv_sec - pre_time.tv_sec,post_time.tv_usec - pre_time.tv_usec);
FILE *file;
file = fopen(fileName,"rb"); //rb = read as binary
fseek(file,SEEK_END);
int fileLength = ftell(file);
fseek(file,SEEK_SET);
char buffer[fileLength];
fread(buffer,fileLength,1,file);
fclose(file);
int frag_total = fileLength / 1000;
if(fileLength % 1000 != 0) {
frag_totaL++;
}
struct list packet_list;
packet_list.head = malloc(sizeof(struct node));
struct node* curr = packet_list.head;
for(int i = 0; i < frag_total; i++) {
curr->data.total_frag = frag_total;
curr->data.frag_no = i + 1;
if(i == frag_total - 1) {
curr->data.size = fileLength % 1000;
} else {
curr->data.size = 1000;
}
curr->data.filename = malloc(sizeof(char) * (strlen(fileName) + 1));
strcpy(curr->data.filename,fileName);
if(i == frag_total - 1) {
//copy data equal to remainder
for(int j = 0; j < fileLength % 1000; j++) {
curr->data.filedata[j] = buffer[1000 * i + j];
}
} else {
//copy 1000 bytes
for(int j = 0; j < 1000; j++) {
curr->data.filedata[j] = buffer[1000 * i + j];
}
}
if(i < frag_total - 1) {
curr->next = malloc(sizeof(struct node));
curr = curr->next;
}
}
curr = packet_list.head;
while(curr != NULL) {
int j = curr->data.total_frag;
int frag_total_len = 0;
while(j != 0) {
j /= 10;
frag_total_len++;
}
j = curr->data.frag_no;
int frag_no_len = 0;
while(j != 0) {
j /= 10;
frag_no_len++;
}
j = curr->data.size;
int size_len = 0;
while(j != 0) {
j /= 10;
size_len++;
}
int name_len = strlen(curr->data.filename);
int total_len = frag_total_len + frag_no_len + size_len + name_len + 4 + curr->data.size; //4 bc 4 colons
char buffer_str[total_len];
j = 0;
char strbuf[total_len];
sprintf(strbuf,"%d",curr->data.total_frag);
for(int k = j; k < j + frag_total_len; k++) {
buffer_str[k] = strbuf[k-j];
}
j += frag_total_len;
buffer_str[j] = ':';
j++;
sprintf(strbuf,curr->data.frag_no);
for(int k = j; k < j + frag_no_len; k++) {
buffer_str[k] = strbuf[k-j];
}
j += frag_no_len;
buffer_str[j] = ':';
j++;
sprintf(strbuf,curr->data.size);
for(int k = j; k < j + size_len; k++) {
buffer_str[k] = strbuf[k-j];
}
j += size_len;
buffer_str[j] = ':';
j++;
for(int k = 0 ; k < name_len; k++,j++) {
buffer_str[j] = curr->data.filename[k];
}
buffer_str[j] = ':';
j++;
for(int k = 0; k < curr->data.size; k++,j++) {
buffer_str[j] = curr->data.filedata[k];
}
sendto(socketfd,res->ai_addrlen);
curr = curr->next;
}
return 0;
}
我不确定是什么原因造成的
解决方法
原始发布的代码省略了对getaddrinfo()
的错误检查,这将返回错误代码,而res
保持不变;导致在调用sendto()
时取消引用未初始化的指针;修订示例:
int rv = getaddrinfo("ug168.eecg.utoronto.ca"/*argv[1]*/,port,&hints,&res);
if (rv) {
fprintf(stderr,"getaddrinfo error,rv %d\n",rv);
return (1);
}
,
本地变量res
被调用覆盖
int length = recvfrom(socketfd,buf,1000,(struct sockaddr *)&serverAddr,&addr_size);
这是因为传递了指针serverAddr
的地址而不是指针的值:
int length = recvfrom(socketfd,(struct sockaddr *)serverAddr,&addr_size);
您可能会发现该程序现在由于另一个原因而发生段错误:对于少于两个片段的短文件,缓冲区处理失败,因为curr->next
未初始化。
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