Reading a file from a specific point problem - c

I'm using TCP server/client C application to send a file from server to client. File must be sent in parts (one part per one connection). I successfully send file from server to client, that's not the problem. The problem is with the one part per connection, getting the right part to be sent. I'm using fseek() to find the size of whole file and divided it by 4. That's the size of chunk that I want to be sent to client. A problem persists because I get more chunk than I actually expect.
// Retrieve file size
fSize = fileSize(filePtr);
// How much bytes to send
if (fSize >= 4)
{
leftToSend = fSize / SEND_DENOM;
}
else
{
leftToSend = fSize;
}
int fpOffset = leftToSend * (partToSend - 1);
fseek(filePtr, fpOffset, SEEK_SET);
int i = 0;
char cFromFile;
while(leftToSend != 0 || feof(filePtr))
{
cFromFile = fgetc(filePtr);
dataBuffer[i++] = cFromFile;
leftToSend--;
bytesSent++;
if (strlen(dataBuffer) == (BUFFER_SIZE - 1) || leftToSend == 0)
{
// Send message to client
iResult = sendto(clientSocket,
dataBuffer,
strlen(dataBuffer),
0,
(SOCKADDR *)&clientAddress,
sizeof(clientAddress));
if (iResult == SOCKET_ERROR)
{
printf("sendto failed with error: %d\n", WSAGetLastError());
closesocket(clientSocket);
WSACleanup();
ExitThread(100);
}
// Set whole buffer to zero
memset(dataBuffer, 0, BUFFER_SIZE);
i = 0;
}
}
Find file size function:
unsigned long long int fileSize (FILE* filePtr)
{
unsigned long long int fSize = 0;
fseek(filePtr, 0, SEEK_END);
fSize = ftell(filePtr);
rewind(filePtr);
return fSize;
}
Example (How it should look):
This is a problem...
chunk - This_
chunk - is_a_
chunk - probl
chunk - em...
And this is something I get:
chunk - This_is_a
chunk - is_a_prob
chunk - problem..
chunk - em...
where _ represents blank space

From the comments you've mentioned, try the following code.
I'll assume you calculate the leftToSend variable correctly.
while((leftToSend >= 0) || feof(filePtr))
{
cFromFile = fgetc(filePtr);
dataBuffer[i] = cFromFile;
i++;
leftToSend--;
if ((i >= (BUFFER_SIZE - 1)) || (0 == leftToSend) || (i >= (SEND_DENOM + 1)))
{
// Send message to client
iResult = sendto(clientSocket,
dataBuffer,
i,
0,
(SOCKADDR *)&clientAddress,
sizeof(clientAddress));
if (SOCKET_ERROR == iResult)
{
printf("sendto failed with error: %d\n", WSAGetLastError());
closesocket(clientSocket);
WSACleanup();
ExitThread(100);
}
// Set whole buffer to zero
memset(dataBuffer, 0, BUFFER_SIZE);
bytesSent += i;
i = 0;
}
}

Related

Can not Transmit last packet with recv() Server/Client C file Transmiting over TCP

I have been trying to transfer files over TCP\IP on a windows client to Linux server.
This has been a major issue for the passed few days due to a lack of understanding why the last packet is not received on the server side, which brakes the writing of the file.
What I want to achieve is downloading images(JPG,PNG), programs (EXE) and etc`..
Output
Client
lltoa(size.QuadPart,container,10);
//Send file size
send(sock, container, sizeof(container), 0);
bzero(container,1024);
//End of file size
unsigned __int64 uiPos = 0;
unsigned __int64 uiRemaining = ul.QuadPart;
while (uiRemaining > 0)
{
ul.QuadPart = uiPos;
ov.Offset = ul.LowPart;
ov.OffsetHigh = ul.HighPart;
DWORD dwNumToSend = (uiRemaining <= 3) ? 1 :1024; //(DWORD)uiRemaining;
if (!TransmitFile(sock,get_file, dwNumToSend, 0, &ov, NULL, 0))
{
if ((GetLastError() != ERROR_IO_PENDING) && (WSAGetLastError() != WSA_IO_PENDING))
break;
WaitForSingleObject(ov.hEvent, INFINITE);
}
uiPos += dwNumToSend;
uiRemaining -= dwNumToSend;
//Sleep(1);
}
CloseHandle(ov.hEvent);
CloseHandle(get_file);
Server
file_size = atoi(response);
printf("File size: %lli \n",file_size);
bzero(response,18384);
//End of file size
//First packet of file
len = recv(client_socket,response,sizeof(response)<file_size?(sizeof(response)):file_size,MSG_WAITALL);
printf("Received: %i \n",len);
if (len == 0)
{
printf("Error downloading file!");
goto jump;
}
file_size = file_size - len;
int counter = 0;
while(file_size > 0)
{
//Start getting the file
fwrite(response,1,len,new_file);
bzero(response,18384);
len = recv(client_socket,response,((file_size <= 1024) || (len < 1024))?file_size:sizeof(response),MSG_WAITALL);
printf("Received: %i\t|",len);
if(len <= 0)
{
break;
}
//Check if this is the last packet
file_size = file_size - len;
printf("Response #%i\tbytes_received: %i\tbytes remain:%li \n",counter,len,file_size);
counter += 1;
}
if(file_size > 0)
{
printf("\t\t\tError downloading file! bytes left:%li \n",file_size);
}
else
{
printf("Successfully downloaded file! \n");
}
fclose(new_file);
goto jump;
With error handeling for recv():
If more of the server side code is needed please comment.. I think that this will do though..
Thank You!!
Based on code you have showed, found some problems. After edited as below it works for me. You can have a try. (Please show ul.QuadPart, ul.LowPart and ul.HighPart related code if you still have issues.)
At client side:
Change DWORD dwNumToSend = (uiRemaining <= 3) ? 1 :1024; to DWORD dwNumToSend = (uiRemaining <= 1024) ? uiRemaining : 1024;
At server side:
Change ((file_size <= 1024) || (len < 1024))?file_size:sizeof(response) to (file_size <= sizeof(response))?file_size:sizeof(response)

how to send image files through http?

I'm learning the socket programming and trying to write a simple http server with c. My program can load html/css/javascript files correctly, but the image files can't be loaded. For example, the website icon favicon.ico and <img> of the html file always failed to load. I'm using the code as below to build my simple server:
server.c:
#define CYAN(format, ...) \
printf("\033[1;36m" format "\33[0m\n", ## __VA_ARGS__)
struct sockaddr_in s_addr;
struct sockaddr_in c_addr;
socklen_t c_addr_size;
int s_sock;// server socket
int c_sock;// clinet socket
char buf[4096];// user agent
char msg[4096];// file content
char head[1024];// http header
char file[128];// which file requested
void init_server();
void read_request();
void send_file();
int main()
{
init_server();
while (1) {
c_sock = accept(s_sock, NULL, NULL);
if (c_sock != -1) {
int nread = recv(c_sock, buf, sizeof(buf), 0);
read_request();// TODO
CYAN("%d", nread);
CYAN("%s", buf);
send_file();
close(c_sock);
}
}
close(s_sock);
return 0;
}
void init_server()
{
s_sock = socket(AF_INET, SOCK_STREAM, 0);
assert(s_sock != -1);
s_addr.sin_family = AF_INET;
s_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
s_addr.sin_port = htons(8000);
int res = bind(s_sock, (struct sockaddr*)&s_addr, sizeof(s_addr));
if (res == -1) { perror("cannot bind"); exit(-1); }
listen(s_sock, 10);// TODO
c_addr_size = sizeof(c_addr);
}
void read_request()
{
int buf_len = strlen(buf);
int i = 0, j = 0;
for (i = 0; i < buf_len - 10; i ++) {
if (buf[i] == 'G' && buf[i + 1] == 'E' && buf[i + 2] == 'T') {// `GET` keyword
i = i + 4;// skip space
while (buf[i] != ' ') {
file[j] = buf[i];
j ++, i ++;
}
file[j] = '\0';
CYAN("%s", file);
return;
}
}
}
void send_file()
{
if (strcmp(file, "/") == 0) {
sprintf(file, "index.html");
is_html = 1;
} else {
sprintf(file, "%s", file + 1);// skip `/`
}
FILE *fp = fopen(file, "r");
// count file length
int file_len = 0;
while (fgets(msg, 1000, fp)) {// read by lines
file_len += strlen(msg);
}
// send http header
sprintf(head,
"HTTP/1.1 200 OK\n"
// "Content-Type: text/html\n"
"Content-Length: %d\n"
"\n", file_len
);
// send file content
CYAN("%d", fseek(fp, 0, SEEK_SET));
memset(msg, 0, sizeof(msg));
send(c_sock, head, strlen(head), 0);
while (fgets(msg, 1000, fp)) {// read by lines
send(c_sock, msg, strlen(msg), 0);
}
fclose(fp);
}
I'm not familiar with http, and I don't know whether I should change the content of the http header when sending images files. How to correct my code, can anyone help me?
FILE *fp = fopen(file, "r");
// count file length
int file_len = 0;
while (fgets(msg, 1000, fp)) {// read by lines
file_len += strlen(msg);
}
No. No. No. No. Never use text processing on binary data.
File length is easy.
FILE *fp = fopen(file, "rb");
fseek(fp, 0, SEEK_END);
long file_len = ftell(fp);
fseek(fp, 0, SEEK_SET);
Now to send it:
send_helper(c_sock, head, strlen(head), 0); /* send header */
while (file_len > 4096) {
int delta = fread(msg, 4096, 1, fp);
if (delta == 0) {
/* handle error */
fclose(fp);
/* need to refactor here; c_sock is useless and needs to be closed */
return;
}
send_helper(c_sock, msg, delta);
file_len -= delta;
}
if (file_len > 0) {
/* last chunk; fread only returns a short count on an actual error so no loop here */
int delta = fread(msg, 4096, 1, fp);
if (delta == 0) {
/* handle error */
fclose(fp);
/* need to refactor here; c_sock is useless and needs to be closed */
return;
}
send_helper(c_sock, msg, delta);
}
fclose(fp);
Unlike fread, send needs a loop to ensure all bytes are sent.
void send_helper(int c_sock, char *msg, size_t size)
{
while (size > 0)
{
ssize_t delta = sendto(c_sock, msg, size, 0);
/*
* not bothering to handle error well--
* we'll just error a few more times and drop out of loop anyway.
* You probably should come back and fix this later though
*/
if (delta <= 0) return;
size -= (size_t)delta;
msg += (size_t)delta;
}
}

Not sending file correctly. Sockets. C

I am writing a program that a client can ask for files to a server. Then the server will send them in chunks of 512 bytes. The problem is that when the client read the file:
*Sometimes the first 512 bytes are different from the original file. The total read file also has a different size (and obviously it also ends different from the original file) and therefore the client loop that writes to the new file does never end.
*Sometimes it works perfectly and i don't know why.
Server:
/* Check if file exists */
if(access(retrFileName, F_OK) == 0){
/* Open file */
fd = open(retrFileName, O_RDONLY);
lseek(fd, 0, SEEK_SET);
if (fd == -1){
fprintf(stderr, "Error opening file --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
/* Get file stats */
if (fstat(fd, &fileStat) < 0){
fprintf(stderr, "Error fstat --> %s", strerror(errno));
exit(EXIT_FAILURE);
}
sprintf(fileSize, "%li", fileStat.st_size);
/* Sending file data */
offset = 0;
remainData = fileStat.st_size;
while (((sentBytes = sendfile(clientSock, fd, &offset, 512)) == 512) && (remainData > 0)) {
remainData -= sentBytes;
fprintf(stdout, "Server envio %d bytes del file, offset ahora vale: %li y quedan = %d bytes\n", sentBytes, offset, remainData);
}
remainData -= sentBytes;
fprintf(stdout, "Server envio %d bytes del file, offset ahora vale: %li y quedan = %d bytes\n", sentBytes, offset, remainData);//do while
close(fd);////////////////////////
send(clientSock, NICETRANSFER, sizeof(NICETRANSFER), 0); //LO METE AL ARCHIVO
printf("send\n");
//close(clientSock);///////////
}
else{
send(clientSock, FILEERROR, sizeof(FILEERROR), 0);
printf("send\n");
}
}
Client:
/* Open file */
receivedFile = fopen("r.txt", "wb");
if (receivedFile == NULL){
fprintf(stderr, "Failed to open file --> %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
/* Write to the file */
int contador = 0;
int remainData = fileSize;
do{
if(remainData < 512)
bytesLeidos = recv(clientSock, readingBuffer, remainData, 0);
else
bytesLeidos = recv(clientSock, readingBuffer, 512, 0);
fwrite(readingBuffer, bytesLeidos, 1, receivedFile);
remainData -= 512;
contador += 512;
printf("bytesleidos: %li, contador: %d:\n%s\n\n", bytesLeidos, contador, readingBuffer);
}while(contador < fileSize);
fclose(receivedFile);
Golden rule of socket programming: Always check the return value from recv. It's not always what you think it will be.
Even though you "send" 512 bytes at a time, you are in no way guaranteed that TCP will deliver the same number of bytes at a time to the receiver. TCP segmentation, IP fragmentation, and general Internet weirdness will cause the recv side to get an arbitrary number of bytes at a time.
Hence, your hardcoded assumption that recv will always return 512 is incorrect:
remainData -= 512;
contador += 512;
Instead, you should be saying:
remainData -= bytesLeidos;
contador += bytesLeidos;
An you need to check for errors and socket closing too.
This is an improved main loop for your client code:
while (remainData > 0)
{
size_t recvSize = (remainData >= 512) ? 512 : remainData;
bytesLeidos = recv(clientSock, readingBuffer, recvSize, 0);
if (bytesLeidos > 0)
{
fwrite(readingBuffer, bytesLeidos, 1, receivedFile);
remainData -= bytesLeidos;
contador += bytesLeidos;
/* null terminate readingBuffer so garbage isn't printed.*/
/* Make sure readingBuffer is allocated to be at least */
/* N+1 bytes (513) to account for this character being appended. */
readingBuffer[bytesLeidos] = '\0';
printf("bytesleidos: %li, contador: %d:\n%s\n\n", bytesLeidos, contador, readingBuffer);
}
else if (bytesLeidos == 0)
{
/* remote side closed connection */
printf("Remote side exited connection\n");
break;
}
else if (bytesLeidos < 0)
{
/* connection error */
printf("Connection error\n");
break;
}
}
I solved my problem!! I needed to sync both client and server. To do so, the server send the size of the file and waits for an answer for the client with recv. When the client recieve the file size, it send a "" message.
I don't know if this is the correct solution, but this way you can sync server and client.
After sync, the server send the respective file normally with sendfile

recv() on socket by dynamically allocating space

I'm trying to get the source code of my website using c, I'm able to connect and everything but when I implement the recv() code, it only receives the last few bytes of the source code. I'd like to dynamically allocate space for the buffer to receive more using the C functions malloc and realloc.
This is the code I have so far:
char *buffer = NULL;
unsigned int i = 0;
unsigned long LEN = 200;
unsigned long cur_size = 0;
buffer = (char*)malloc(sizeof(char)*LEN);
do
{
if( status >= LEN )
{
cur_size += status;
buffer = (char*)realloc(buffer, cur_size);
}
status = recv(cSocket, buffer, LEN, 0);
if( status == 0 )
{
printf("Bye\n");
}
else if( status > 0 )
{
printf("%d\n", status);
}
else
{
printf("socket error=%d\n", WSAGetLastError());
break;
}
}while( status > 0 );
printf("%s\n", buffer);
It still doesn't print the whole source code. How should I go about this?
Pseudocode:
buffer = 'len chars';
loop:
if( status >= buffer ) buffer = 'resize to status chars';
status = recv(sock, buffer, len, 0);
end loop
As you resize the buffer in advance this needs to be reflected by its size. Which currently is not the case.
To fix this you could, for example, initialise cur_size with LEN by changing
unsigned long cur_size = 0;
to
unsigned long cur_size = LEN;
Assuming the fix above, you want to append to the buffer and not overwrite it with every call to recv().
To do so change this line
status = recv(cSocket, buffer, LEN, 0);
to be
status = recv(cSocket, buffer + cur_size - LEN, LEN, 0);
A more straight forward approach would be to not track the size of the buffer, but the number of bytes received and just always increase the buffer by a constant size.
Also the two calls to allocate memory can be replaced by one:
char *buffer = NULL;
unsigned long LEN = 200;
unsigned long bytes_received = 0;
unsigned long cur_size = 0;
int status = 0;
do
{
if (bytes_received >= cur_size)
{
char * tmp;
cur_size += LEN;
tmp = realloc(buffer, cur_size);
if (NULL == tmp)
{
fprintf(stderr, "realloc error=%d\n", WSAGetLastError());
break;
}
buffer = tmp;
}
status = recv(cSocket, buffer + bytes_received, LEN, 0);
if (status == 0)
{
printf("Bye\n");
}
else if (status > 0)
{
bytes_received += status;
printf("%d\n", status);
}
else /* < 0 */
{
fprintf(stderr, "socket error=%d\n", WSAGetLastError());
}
} while (status > 0);
printf("%s\n", buffer);
Well, after a bit of research, I came across this website and finally found what I was looking for.
Binary tides
Although it uses linux's fcntl, the windows equivalent is ioctlsocket which is used to set the socket's non-blocking mode.
To see the exact function, visit the website. I modified the version and set my socket to blocking mode.
int total_recv(SOCKET s)
{
int size_recv = 0, total_size = 0, block = 00;
char chunk[BUFLEN];
ioctlsocket(s, FIONBIO, (unsigned long*)&block); // set mode to block
// not necessary but clarification of function, mode is block by
// default
while( 1 )
{
memset(chunk, 0, BUFLEN);
if( ( size_recv = recv(s, chunk, BUFLEN, 0) ) == SOCKET_ERROR )
{
printf("Error receiving\n");
}
else if( size_recv == 0 )
{
break;
}
else
{
total_size += size_recv;
// i used file since console wouldn't show full source code
FILE *fp = NULL;
fp = fopen("source.txt", "a");
fprintf(fp, chunk);
fclose(fp);
}
}
return total_size;
}

Client reads lesser bytes than Server is sending on sockets

My server code is as follows:
while(bytes_written < filesize){
//Send from send_ptr
bw = send(child_socket, send_ptr, newLength, 0);
printf("%d bytes written\n", (int)bw);
//Increment bytes written
bytes_written += bw;
//Move send pointer
send_ptr = send_ptr + bw;
}
And my client code is as follows:
while((num_bytes_recv = read(sd, jpgBufferPointer, BUFFER_LENGTH))>0){
total_bytes_recv += num_bytes_recv;
printf("Read %d bytes\n",num_bytes_recv);
//Check for error
if(jpgError == NULL)
jpgError = strstr(jpgBufferPointer, "404 Not Found");
if(jpgError != NULL){
//Forwarding error response
if(send(sd, jpgBuffer, num_bytes_recv, 0) == -1){
error("Failed to send response message to client");
}
}
else{
//Find content size
contentSizeBuffer = strstr(jpgBufferPointer,"Content-Length");
if(contentSizeBuffer != NULL){
contentSizeBuffer=contentSizeBuffer+16;
contentSize=atoi(contentSizeBuffer);
jpgBuffer=(char*)realloc(jpgBuffer,(contentSize+FILE_NAME_LENGTH*2)*sizeof(char));
jpgBufferPointer=jpgBuffer;
}
jpgBufferPointer+=num_bytes_recv;
}
}
The server is saying it has sent all 43000 bytes, but client says it has received only 32768 bytes.
Appreciate any help! Thanks
You have a bug in the sending part, you should update newLength, because if you have 1 byte left to send from the file, it will send more, going out of the memory area where the content you want to send is stored. You should fix in this way:
bw = send(child_socket, send_ptr, newLength<(filesize-bytes_written)?newLength:(filesize-bytes_written), 0);
In this way the last send will have the correct size.
Also, use write instead of send if you are not using any flags.
You need to have the similar loop as you have on the writing side (bytes_written < filesize) on the reading side (i.e., while you can read more bytes, you should read them and append them).
The network doesn't guarantee that one read() call will return all available data.
The best way of writing client-server socket programming is to have a header before your data. The header should state the amount of data that it is going to transfer.
For example, To send data "Hello World", then send it as "0011+HELLO WORLD"
Here 11 stands for the size of the data the sender is planning to send now. The receiver on reading the first 4 bytes can understand that he should be ready to read next 11 bytes of data from the sender.
So reader will do two read:
hRead = 5 /* With 5 you are saying it can read upto max of 9999 bytes from data".
read(sd, buff, hRead);
dRead = atoi(buff);
readn(sd, buff, dRead);
For Example : Server
size_t sendn(int fd, const void *vptr, size_t n) {
size_t nleft;
size_t nwritten;
const char *ptr;
ptr = vptr;
nleft = n;
while (nleft > 0) {
if ((nwritten = send(fd, vptr, nleft, 0)) <= 0) {
if (errno == EINTR)
nwritten = 0;
else {
fprintf(stderr, "send failed %d - %s\n", fd, strerror(errno));
return (-1);
}
}
nleft -= nwritten;
ptr += nwritten;
}
return (n);
}
To send message:
sprintf(buff, "%d + %d + %s\r\n", MSG_LOGIN, strlen("Hello World"), Hello World);
sendn(sd, buff, strlen(buff));
Client:
size_t readn(int fd, void *vptr, size_t n) {
size_t nleft;
size_t nread;
char *ptr;
ptr = vptr;
nleft = n;
while (nleft > 0) {
if ((nread = recv(fd, ptr, nleft, 0)) < 0) {
if (errno == EINTR)
nread = 0;
else {
fprintf(stderr, "read failed %d - %s\n", fd, strerror(errno));
return (-1);
}
} else if (nread == 0)
break;
nleft -= nread;
ptr += nread;
}
return (n - nleft);
}

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