resolver.c 4.01 KB
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/*
 * resolver.c:
 *
 */

#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>
#include <errno.h>
#include <string.h>

#include "ns_hash.h"

#define RESOLVE_QUEUE_LENGTH 20

struct in_addr resolve_queue[RESOLVE_QUEUE_LENGTH];

pthread_cond_t resolver_queue_cond;
pthread_mutex_t resolver_queue_mutex;
pthread_mutex_t resolver_queue_access_mutex;

hash_type* ns_hash;

int head;
int tail;

void resolver_worker(void* ptr) {
    struct timespec delay;
    delay.tv_sec = 0;
    delay.tv_nsec = 500;
    while(1) {
        /* Wait until we are told that an address has been added to the 
         * queue
         */
        pthread_cond_wait(&resolver_queue_cond, &resolver_queue_mutex);

        /* Keep resolving until the queue is empty */
        pthread_mutex_lock(&resolver_queue_access_mutex);
        while(head != tail) {
            struct in_addr addr = resolve_queue[tail];
            struct hostent hostbuf, *hp;
            size_t hstbuflen;
            char *tmphstbuf;
            int res;
            int herr;

            /* mutex always locked at this point */

            tail = (tail + 1) % RESOLVE_QUEUE_LENGTH;

            pthread_mutex_unlock(&resolver_queue_access_mutex);


            hstbuflen = 1024;
            /* Allocate buffer, remember to free it to avoid memory leakage.  */            
            tmphstbuf = malloc (hstbuflen);

            while ((res = gethostbyaddr_r (&addr, sizeof(addr), AF_INET,
                                           &hostbuf, tmphstbuf, hstbuflen,
                                           &hp, &herr)) == ERANGE) {
                /* Enlarge the buffer.  */
                hstbuflen *= 2;
                tmphstbuf = realloc (tmphstbuf, hstbuflen);
              }

            /*
             * Store the result in ns_hash
             */
            pthread_mutex_lock(&resolver_queue_access_mutex);

            /*  Check for errors.  */
            if (res || hp == NULL) {
                /* failed */
                //printf("[ Did not resolve %s ]\n", inet_ntoa(addr));
                /* Leave the unresolved IP in the hash */
            }
            else {
                /* success */
                char* hostname;
                //printf("[ Resolved: %s ]\n", hp->h_name);
                if(hash_find(ns_hash, &addr, (void**)&hostname) == HASH_STATUS_OK) {
                    hash_delete(ns_hash, &addr);
                    free(hostname);
                }
                else {
                    //printf("[ Warning: Could not find hash entry for key: %s ]\n", inet_ntoa(addr));
                }
                hostname = strdup(hp->h_name);
                hash_insert(ns_hash, &addr, (void*)hostname);

            }
            free(tmphstbuf);
        }
        pthread_mutex_unlock(&resolver_queue_access_mutex);
    }
}

void resolver_initialise() {
    pthread_t thread;
    head = tail = 0;

    ns_hash = ns_hash_create();
    
    pthread_mutex_init(&resolver_queue_mutex, NULL);
    pthread_mutex_init(&resolver_queue_access_mutex, NULL);
    pthread_cond_init(&resolver_queue_cond, NULL);

    pthread_create(&thread, NULL, (void*)&resolver_worker, NULL);

}

void resolve(struct in_addr* addr, char* result, int buflen) {
    char* hostname;

    pthread_mutex_lock(&resolver_queue_access_mutex);

    if(hash_find(ns_hash, addr, (void**)&hostname) == HASH_STATUS_OK) {
        /* Found => already resolved, or on the queue */
    }
    else {
        hostname = strdup(inet_ntoa(*addr));
        hash_insert(ns_hash, addr, hostname);

        if(((head + 1) % RESOLVE_QUEUE_LENGTH) == tail) {
            /* queue full */
        }
        else {
            resolve_queue[head] = *addr;
            head = (head + 1) % RESOLVE_QUEUE_LENGTH;
            pthread_cond_signal(&resolver_queue_cond);
        }
    }
    pthread_mutex_unlock(&resolver_queue_access_mutex);

    if(result != NULL && buflen > 1) {
        strncpy(result, hostname, buflen - 1);
        result[buflen - 1] = '\0';
    }
}