recv() on socket by dynamically allocating space

Question

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

Answer 1

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);

Answer 2

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;
}