read_buffer

#include <sys/select.h>
#include <errno.h>
 
int read_buffer(int fd, unsigned char* buffer, int length, unsigned int timeout_ms) {
    int ret, left, bytes = 0;
    fd_set rfds;
    struct timeval sleep;
    struct timeval *psleep = &sleep;
 
    left = length;
    FD_ZERO(&rfds);
    FD_SET(this->serial_fd, &rfds);
 
    if (timeout_ms != 0) {
        sleep.tv_sec = (timeout_ms / 1000);
        sleep.tv_usec = 1000 * (timeout_ms % 1000);
    } else {
        psleep = NULL;
    }
 
    while (true) {
        while (true) {
            if ((ret = select((fd + 1), &rfds, NULL, NULL, psleep)) > 0)
                break;
 
            if (ret == 0)
                return TIMEOUT; 
 
            if ((ret < 0) && (errno != EINTR))
                return SELECT_ERROR;	
        }
 
        if ((ret = read(this->serial_fd, (buffer + bytes), left)) < 0)
            return READ_ERROR;
 
        bytes += ret;
        left  -= ret;
 
        if (bytes >= length)
            break;
 
        if (ret == 0) 
            return EOF;
    }
 
    return bytes;
}