Question

I’m trying to store some binary data obtained from read() in my buffer using the memcpy() function.

Basically, I want to store buf in my buffer:

#define MAX_BUFFER_SIZE 256
//...
char *
httpget(const char * domain, const int port, const char * headers)
{
    int sockfd;
    int buf_size = MAX_BUFFER_SIZE;

    struct sockaddr_in  sock_addr; 
    struct hostent  *   host;

    char * buffer;
    char * newbuf;
    char * tbuf;

    sockfd = socket(AF_INET,SOCK_STREAM,0);

    if( sockfd == -1 )
    {
        return NULL;
    }

    host = gethostbyname(domain);

    if( NULL == host )
    {
        close(sockfd);
        return NULL;
    }

    memset(&sock_addr, '\0', sizeof(sock_addr));
    sock_addr.sin_family = AF_INET;
    memcpy( &sock_addr.sin_addr.s_addr,
            host -> h_addr,
            host -> h_length );

    sock_addr.sin_port = htons(port);

    if( connect(sockfd, (struct sockaddr *) &sock_addr, sizeof(sock_addr)) == -1)
    {
        close(sockfd);
        return NULL;
    }

    if( write(sockfd, headers, strlen(headers) + 1) == -1)
    {
        close(sockfd);
        return NULL;
    }

    buffer = malloc( MAX_BUFFER_SIZE );
    tbuf = malloc( MAX_BUFFER_SIZE );

    if(buffer == NULL || tbuf == NULL)
    {
        return NULL;
    }

    int bytesloaded = 0;
    int readed;

    while( (readed = read(sockfd, tbuf, MAX_BUFFER_SIZE)) > 0 )
    {   
        if(bytesloaded + readed >= buf_size)
        {
            buf_size = buf_size + MAX_BUFFER_SIZE;  
            newbuf = realloc(buffer, buf_size);

            if(newbuf != NULL)
            {
                buffer = newbuf; 
            }
            else 
            {
                return NULL;
            }
        }

        memcpy(buffer, tbuf, readed);
        bytesloaded += readed;
    }

    close(sockfd);
    printf("buffer = %s", buffer);
    return buffer;
}

but when I printf(“%s”,buffer); I get only the HTTP Headers and �PNG characteres from binary that have 7007 content-length. how to fix this? I hope this is clear for you. any help is very appreciated.Thanks in advance.

Answer 1

I think you want:

memcpy(buffer + bytesloaded, buf, readed);

You aren’t seeing the entire response when you try to dump it using printf("%s",buffer) because the .png image being sent in the response is binary data that’s likely to contain a null '\0' byte, and the printf() will stop at that point.

You have all sorts of other options to examine the data returned in the response (or information about it): look at buffer in the debugger, dump the bytesloaded variable, dump buffer using a function that will convert it to hex for display, and/or write the response body (after the headers and the CR/LF that follows the headers) to a .png file and take a look at it in something that will display an image.