C - Check if str is null - c

In my code C, I have **line and I need check if *line is NULL, I wrote following code can crash the program and I don't know why
How I can check if *line is NULL or not ?
( I have 0 warnings, 0 errors: -Wall -Werror -Wextra )
Source code:
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include "libft/libft.h"
# define BUFF_SIZE 16
int read_buffer(int const fd, int ret, char **endl, char **buffer)
{
char buff[BUFF_SIZE + 1];
ret = read(fd, buff, BUFF_SIZE);
buff[ret] = '\0';
if (ret > 0)
{
*buffer = ft_strjoin(*buffer, buff);
*endl = ft_strchr(*buffer, '\n');
}
return (ret);
}
int get_next_line(int const fd, char **line)
{
static char *buffer;
char *endl;
int ret;
if (!buffer && !(buffer = ft_memalloc(BUFF_SIZE + 1)))
return (-1);
if (!*line) // HERE, program crash
*line = my_strdup("");
ret = 1;
endl = ft_strchr(buffer, '\n');
while (ret > 0)
{
ret = read_buffer(fd, ret, &endl, &buffer);
if (endl)
{
buffer[endl - buffer] = '\0';
*line = my_strdup(buffer);
buffer = my_strdup(endl + 1);
return (1);
}
if (ret == 0)
{
if (ft_strcmp("", *line) == 0)
{
*line = my_strdup(buffer);
return (1);
}
return (0);
}
}
return (ret);
}
int main(void)
{
int fd;
int ret;
char *line;
if ((fd = open("b.txt", O_RDONLY)) < 3 && fd != 0)
return (-1);
printf("%d\n", fd);
ret = get_next_line(fd, &line);
printf("%d - %s\n", ret, line);
ret = get_next_line(fd, &line);
printf("%d - %s\n", ret, line);
ret = get_next_line(fd, &line);
printf("%d - %s\n", ret, line);
ret = get_next_line(fd, &line);
printf("%d - %s\n", ret, line);
return (0);
}

You're testing whether *line is null correctly in get_next_line(). The problem is that you never initialized line to NULL in main(). Since it's uninitialized, you get undefined behavior when trying to use it.
Change
char *line;
to
char *line = NULL;

Related

Why am I getting heap-buffer-overflow in this C code?

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
char *get_next_line(int fd);
int main (void)
{
int i = 0;
char *s;
int fd;
fd = open("./text", O_RDONLY);
s = get_next_line (fd);
}
char *get_next_line(int fd)
{
char *buf;
char c;
int nread;
int cnt;
if (fd < 0 || BUFFER_SIZE < 1)
return (NULL);
buf = (char*)malloc(BUFFER_SIZE + 1);
if (!buf)
return (NULL);
while(nread = (read(fd, &c, 1)) > 0)
{
*buf = c;
buf++;
cnt++;
if (c == '\n')
break;
}
if (nread < 0)
return (NULL);
*buf = '\n';
printf("%s\n", buf);
return (buf - cnt - 1);
}
When I compile with no flags, I just get two empty line. Compiling with -fsanitize=address and I know heap-buffer-overflow happens at the line printf("%s\n", buf);
But I don't know why this happen. I tried STDIN to fix it but didn't work. Can someone check this please?
You are not terminating the buf with null character.
*buf = '\n';
*buf = '\0';
Make sure you reserve the space for null character while allocating memory to buf.
Free the memory if number of bytes read are less than 0.
if (nread < 0) {
return (NULL);
}
to
if (nread < 0) {
free(startAddress);
return (NULL);
}
You can have temporary pointer to preserve the starting address of buf instead of calculating the starting address.
char *get_next_line(int fd)
{
char *buf;
char c;
int nread;
if (fd < 0 || BUFFER_SIZE < 1)
return (NULL);
buf = (char*)malloc(BUFFER_SIZE + 2);
if (!buf)
return (NULL);
char *startAddress = buf;
while(nread = (read(fd, &c, 1)) > 0)
{
*buf = c;
buf++;
if (c == '\n')
break;
}
if (nread < 0) {
free(startAddress);
return (NULL);
}
*buf = '\0';
printf("%s\n", buf);
return startAddress;
}

How to get a line from csv file with a custom fgets

I'm currently writing a program in C that reads in from a CSV file, I have a defined buffer size but am having trouble separating each line from the buffer. I can see where the line ends by checking for a '\n' char. I cannot extract that line from the buffer for parsing however. Anybody have some ideas?
#ifndef BUFFSIZE
#define BUFFSIZE 4096
#endif
int main() {
int fd;
int fdBin;
char * buf = malloc(BUFFSIZE);
int count = 0;
bool EOFFlag = false;
fd = open("SongCSV.csv", O_RDONLY);
fdBin = open("BinarySongData.bin", O_CREAT | O_WRONLY, "0600");
if (fd == -1) {
printf("failed to open a file\n");
exit(1);
}
off_t offset = 0;
off_t offsetOld = 0;
int readBytes;
while (!EOFFlag) {
offsetOld = offset;
offset = lseek(fd, offset - offsetOld, SEEK_CUR);
readBytes = read(fd, buf, BUFFSIZE);
printf("\n\n%lld\n\n", (offset));
int i = 0;
int commaCounter = 0;
while (i < readBytes) {
if (buf[i] != '\n') {
}
if (buf[i] == '\n') {
printf("\t\t THIS IS END OF LINE \t%d", i);
commaCounter = 0;
}
if (buf[i] == ',') {
commaCounter++;
if (commaCounter == 4) {
printf("****Album Name****");
}
}
write(fdBin, buf, BUFFSIZE);
printf("%c", buf[i]);
i++;
}
if (readBytes < BUFFSIZE) {
EOFFlag = true;
printf("\nREACHED END OF FILE");
}
printf("\n");
printf("AA: END OF LINE ****%d*****", count);
count++;
}
close(fd);
close(fdBin);
return 0;
}
I do it this way, easy and simple. I just did it quickly, any doubts just ask me, Cheers.
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
int main()
{
int len = sending();
char *firstline;
int i = 0;
char buf[0];
int rd ;
int fd = open("hey.csv", O_RDONLY);
rd = read(fd, buf, 1);
firstline = malloc(sizeof(char) * len);
while (i != len)
{
firstline[i] = buf[0];
i++;
rd = read(fd, buf, 1);
}
firstline[i] = '\0';
printf("%s\n", firstline);
return (0);
}
int sending()
{
int fd = open("hey.csv", O_RDONLY);
char buf[1];
int r = 0;
r = read(fd, buf, 1);
int len = 0;
while (buf[0] != '\n')//getting exact size to malloc
{
len++;
r = read(fd, buf, 1);
}
return len;
}

C - Read a file line by line

I'm trying to read a file line by line with any value to BUFF_SIZE, but it doesn't work.
The returned value:
3
1 - #include <stdio.h>
#
1 - include <stdlib.h>
#
1 - include <fcntl.h>
#i
1 - nclude "libft/libft.h"
Why they missing chars in my strings ?
My source code (main.c):
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include "libft/libft.h"
# define BUFF_SIZE 3
int get_next_line(int const fd, char **line)
{
static char *buffer;
char *tmp;
int ret;
char *endl;
if (!buffer && !(buffer = ft_memalloc(BUFF_SIZE + 1)))
return (-1);
tmp = ft_strnew(0);
endl = ft_strchr(buffer, '\n');
while (endl == NULL)
{
if ((ret = read(fd, buffer, BUFF_SIZE)) > 0)
{
buffer[ret] = '\0';
endl = ft_strchr(buffer, '\n');
tmp = ft_strjoin(tmp, buffer);
}
else if (ret < 0)
return (-1);
else if (ret == 0)
{
if ((endl = ft_strchr(buffer, '\0')) == buffer)
return (0);
}
}
*line = ft_strdup(tmp);
ft_memmove(buffer, endl + 1, ft_strlen(endl + 1) + 1);
return (1);
}
int main(void)
{
int fd;
int ret;
char *line;
if ((fd = open("main.c", O_RDONLY)) < 3 && fd != 0)
return (-1);
printf("%d\n", fd);
ret = get_next_line(fd, &line);
printf("%d - %s\n", ret, line);
ret = get_next_line(fd, &line);
printf("%d - %s\n", ret, line);
ret = get_next_line(fd, &line);
printf("%d - %s\n", ret, line);
ret = get_next_line(fd, &line);
printf("%d - %s\n", ret, line);
return (0);
}
Someone can help me to resole this ?

C socket: recv and send all data

I would like to obtain a behavior similar to this:
Server run
Client run
Client type a command like "help" or other
Server responds appropriately
go to 3
The problem is that when my function excCommand("help") run just a little text is received and printed.
My text file is this:
COMMAND HELP:
help - Display help
quit - Shutdown client
only COMMAND HELP is printed.
Another problem is that when i type a command nothing is printed and after 2 command client exit.
This is the piece in particular:
while (quit)
{
getLine("client> ", command, 10);
if (strcmp(command, "quit") == 0)
quit = 0;
else
excCommand(command);
}
This is the server:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "common.h"
int main(int argc, char *argv[])
{
if (argc != 2)
ErrorWithUserMessage("Parameter(s)", "<Server Port>");
char *service = argv[1];
int servSock = SetupTCPServerSocket(service);
if (servSock < 0)
ErrorWithUserMessage("SetupTCPServerSocket() failed: ", "unable to establish");
unsigned int childProcessCount = 0;
while (1)
{
int clntSock = AcceptTCPConnection(servSock);
pid_t processID = fork();
if (processID < 0)
ErrorWithSystemMessage("fork() failed");
else if (processID == 0)
{
close(servSock);
HandleTCPClient(clntSock);
exit(EXIT_SUCCESS);
}
printf("with child process: %d\n", processID);
close(clntSock);
childProcessCount++;
//clean up zombies
while (childProcessCount)
{
processID = waitpid((pid_t) - 1, NULL, WNOHANG);
if (processID < 0)
ErrorWithSystemMessage("waitpid() failed");
else if (processID == 0)
break;
else
childProcessCount--;
}
}
}
Handler:
void HandleTCPClient(int clntSock)
{
char buffer[BUFSIZE];
ssize_t numBytesRcvd = recv(clntSock, buffer, BUFSIZE, 0);
buffer[numBytesRcvd] = '\0';
if (numBytesRcvd < 0)
ErrorWithSystemMessage("recv() failed");
if (strcmp(buffer, "help") == 0)
{
FILE *fp = fopen("help.txt", "r");
if (fp)
{
char line[128];
while (fgets(line, sizeof(line), fp) != NULL)
{
if (send(clntSock, line, sizeof(line), 0) < 0)
ErrorWithSystemMessage("send() failed");
}
fclose(fp);
}
}
close(clntSock);
}
and this is my client:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include "common.h"
int sock;
void getLine(char *message, char *buf, int maxLen)
{
printf("%s", message);
fgets(buf, maxLen, stdin);
buf[strlen(buf) - 1] = 0;
}
void excCommand(char *command)
{
if ( send(sock, command, strlen(command), 0) < 0)
ErrorWithSystemMessage("send() failed");
char replyMessage[BUFSIZE];
ssize_t numBytesRecv = 0;
do
{
numBytesRecv = recv(sock, replyMessage, BUFSIZE, 0);
if ( numBytesRecv < 0)
ErrorWithSystemMessage("recv() failed");
printf("%s\n", replyMessage);
memset(&replyMessage, 0, sizeof(replyMessage));
}
while (numBytesRecv > 0);
}
void PrintFile(const char *filename)
{
FILE *fp;
fp = fopen(filename, "r");
if (fp)
{
char line[128];
while (fgets(line, sizeof(line), fp) != NULL)
fputs(line, stdout);
fputs("\n", stdout);
fclose(fp);
}
}
int main(int argc, char *argv[])
{
int quit = 1;
char command[10];
if (argc < 2 || argc > 3)
{
ErrorWithUserMessage("Parameter(s)", "<Server Address> <Server Port>");
}
char *server = argv[1];
char *service = argv[2];
sock = SetupTCPClientSocket(server, service);
if (sock < 0)
ErrorWithUserMessage("SetupTCPClientSocket() failed: ", "unable to connect");
printf("Connection established!\n\n");
PrintFile("menu.txt");
excCommand("help");
while (quit)
{
getLine("client> ", command, 10);
if (strcmp(command, "quit") == 0)
quit = 0;
else
excCommand(command);
}
fputs("\n", stdout);
close(sock);
exit(EXIT_SUCCESS);
}
sorry for being so long-winded
The recv() and send() functions do not guarantee to send/recv all data (see man recv, man send)
You need to implement your own send_all() and recv_all(), something like
bool send_all(int socket, void *buffer, size_t length)
{
char *ptr = (char*) buffer;
while (length > 0)
{
int i = send(socket, ptr, length);
if (i < 1) return false;
ptr += i;
length -= i;
}
return true;
}
The following guide may help you Beej's Guide to Network Programming
Usual problems.
void excCommand(char *command)
{
if ( send(sock, command, strlen(command), 0) < 0)
ErrorWithSystemMessage("send() failed");
char replyMessage[BUFSIZE];
ssize_t numBytesRecv = 0;
do
{
numBytesRecv = recv(sock, replyMessage, BUFSIZE, 0);
if ( numBytesRecv < 0)
ErrorWithSystemMessage("recv() failed");
printf("%s\n", replyMessage);
Invalid. numBytesRecv could have been zero, in which case there is no message at all, otherwise at this point must be positive, as you've already tested for negative, and it indicates the actual length of the message, which isn't necessarily null-terminated. Change to:
if (numBytesRecv == 0)
break;
printf("%.*s\n", numBytesRecv, replyMessage);
and then:
memset(&replyMessage, 0, sizeof(replyMessage));
Pointless. Remove.
}
while (numBytesRecv > 0);
At this point you should check for numBytesRecv < 0 and call perror() or one of its friends.
I choose to send before each send() if i have to continue or not.
so i first have 3 define
#define BUFFSIZE 1024
#define CONT "CONT"
#define DONE "DONE"
Then to send my data
int send_to_socket(int sock, char *msg)
{
size_t len;
int ret[2];
len = strlen(msg);
ret[0] = send(sock, (len <= BUFFSIZE) ? DONE : CONT, 4, 0);
ret[1] = send(sock, msg, BUFFSIZE, 0);
if (ret[0] <= 0 || ret[1] <= 0)
{
perror("send_to_socket");
return (-1);
}
if (len > BUFFSIZE)
return (send_to_socket(sock, msg + BUFFSIZE));
return (1);
}
And to receive it :
char *recv_from_socket(int cs)
{
char state[5];
char buff[BUFFSIZE+1];
char *msg;
int ret[2];
msg = NULL;
while (42)
{
bzero(state, 5);
bzero(buff, BUFFSIZE+1);
ret[0] = recv(cs, state, 4, 0);
ret[1] = recv(cs, buff, BUFFSIZE, 0);
if (ret[0] <= 0 || ret[1] <= 0)
{
perror("recv_from_socket");
return (NULL);
}
// strfljoin() is selfmade
// join the string and free the left argument to prevent memory leaks.
// return fresh new string
msg = (msg) ? ft_strfljoin(msg, buff) : strdup(buff);
if (strncmp(state, DONE, 4) == 0)
break ;
i++;
}
return (msg);
}

Read line by line from a socket buffer

I want to write a function that read line by line from a socket buffer obtained from third parameter from read() function from unistd.h header.
I have wrote this:
int sgetline(int fd, char ** out)
{
int buf_size = 128;
int bytesloaded = 0;
char buf[2];
char * buffer = malloc(buf_size);
char * newbuf;
int size = 0;
assert(NULL != buffer);
while( read(fd, buf, 1) > 0 )
{
strcat(buffer, buf);
buf[1] = '\0';
bytesloaded += strlen(buf);
size = size + buf_size;
if(buf[0] == '\n')
{
*out = buffer;
return bytesloaded;
}
if(bytesloaded >= size)
{
size = size + buf_size;
newbuf = realloc(buffer, size);
if(NULL != newbuf)
{
buffer = newbuf;
}
else
{
printf("sgetline() allocation failed!\n");
exit(1);
}
}
}
*out = buffer;
return bytesloaded;
}
but I have some problems with this function, for example, if the input is something like:
HTTP/1.1 301 Moved Permanently\r\n
Cache-Control:no-cache\r\n
Content-Length:0\r\n
Location\r\nhttp://bing.com/\r\n
\r\n\r\n
and I do
int sockfd = socket( ... );
//....
char* tbuf;
while(sgetline(sockfd, &tbuf) > 0)
{
if(strcmp(tbuf,"\r\n\r\n") == 0)
{
printf("End of Headers detected.\n");
}
}
the above C application does not output "End of Header detected.". Why is this, and how can I fix this?
It's not OK to read one byte at a time, because you are making too many system calls - better is to use a buffer, read a chunk and check if you got \n. After getting a line, the rest of the bytes read remains in the buffer, so you cannot mix read/recv with read_line. Another version of read n bytes using this kind of buffer can be write...
My version to read a line, and a little example to use it.
#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <unistd.h>
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <string.h>
#define CBSIZE 2048
typedef struct cbuf {
char buf[CBSIZE];
int fd;
unsigned int rpos, wpos;
} cbuf_t;
int read_line(cbuf_t *cbuf, char *dst, unsigned int size)
{
unsigned int i = 0;
ssize_t n;
while (i < size) {
if (cbuf->rpos == cbuf->wpos) {
size_t wpos = cbuf->wpos % CBSIZE;
//if ((n = read(cbuf->fd, cbuf->buf + wpos, (CBSIZE - wpos))) < 0) {
if((n = recv(cbuf->fd, cbuf->buf + wpos, (CBSIZE - wpos), 0)) < 0) {
if (errno == EINTR)
continue;
return -1;
} else if (n == 0)
return 0;
cbuf->wpos += n;
}
dst[i++] = cbuf->buf[cbuf->rpos++ % CBSIZE];
if (dst[i - 1] == '\n')
break;
}
if(i == size) {
fprintf(stderr, "line too large: %d %d\n", i, size);
return -1;
}
dst[i] = 0;
return i;
}
int main()
{
cbuf_t *cbuf;
char buf[512];
struct sockaddr_in saddr;
struct hostent *h;
char *ip;
char host[] = "www.google.com";
if(!(h = gethostbyname(host))) {
perror("gethostbyname");
return NULL;
}
ip = inet_ntoa(*(struct in_addr*)h->h_addr);
cbuf = calloc(1, sizeof(*cbuf));
fprintf(stdout, "Connecting to ip: %s\n", ip);
if((cbuf->fd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
perror("socket");
return 1;
}
memset(&saddr, 0, sizeof(saddr));
saddr.sin_family = AF_INET;
saddr.sin_port = htons(80);
inet_aton(ip, &saddr.sin_addr);
if(connect(cbuf->fd, (struct sockaddr*)&saddr, sizeof(saddr)) < 0) {
perror("connect");
return 1;
}
snprintf(buf, sizeof(buf), "GET / HTTP/1.1\r\nHost: %s\r\nConnection: close\r\n\r\n", host);
write(cbuf->fd, buf, strlen(buf));
while(read_line(cbuf, buf, sizeof(buf)) > 0) {
// if it's an empty \r\n on a line, header ends //
if(buf[0]=='\r' && buf[1] == '\n') {
printf("------------------------\n");
}
printf("[%s]", buf);
}
close(cbuf->fd);
free(cbuf);
return 0;
}
Try this implementation instead:
int sgetline(int fd, char ** out)
{
int buf_size = 0;
int in_buf = 0;
int ret;
char ch;
char * buffer = NULL;
char * new_buffer;
do
{
// read a single byte
ret = read(fd, &ch, 1);
if (ret < 1)
{
// error or disconnect
free(buffer);
return -1;
}
// has end of line been reached?
if (ch == '\n')
break; // yes
// is more memory needed?
if ((buf_size == 0) || (in_buf == buf_size))
{
buf_size += 128;
new_buffer = realloc(buffer, buf_size);
if (!new_buffer)
{
free(buffer);
return -1;
}
buffer = new_buffer;
}
buffer[in_buf] = ch;
++in_buf;
}
while (true);
// if the line was terminated by "\r\n", ignore the
// "\r". the "\n" is not in the buffer
if ((in_buf > 0) && (buffer[in_buf-1] == '\r'))
--in_buf;
// is more memory needed?
if ((buf_size == 0) || (in_buf == buf_size))
{
++buf_size;
new_buffer = realloc(buffer, buf_size);
if (!new_buffer)
{
free(buffer);
return -1;
}
buffer = new_buffer;
}
// add a null terminator
buffer[in_buf] = '\0';
*out = buffer; // complete line
return in_buf; // number of chars in the line, not counting the line break and null terminator
}
int sockfd = socket( ... );
//....
char* tbuf;
int ret;
// keep reading until end of headers is detected.
// headers are terminated by a 0-length line
do
{
// read a single line
ret = sgetline(sockfd, &tbuf);
if (ret < 0)
break; // error/disconnect
// is it a 0-length line?
if (ret == 0)
{
printf("End of Headers detected.\n");
free(tbuf);
break;
}
// tbuf contains a header line, use as needed...
free(tbuf);
}
while (true);
You are making things more difficult for yourself than they need to be. You really don't need to do strcats to get the single character you read on each read added at the current position.
But your bug is that the routine returns as soon as it sees a \n, so the string it returns can never contain anything following the first \n.

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