Question

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?

Answer 1

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.