dns resolving using c-ares library

diff --git a/emi.canl.canl-c/src/canl_dns.c b/emi.canl.canl-c/src/canl_dns.c
new file mode 100644 (file)
index 0000000..2110a95
--- /dev/null
+++ b/emi.canl.canl-c/src/canl_dns.c
@@ -0,0 +1,157 @@
+#include <ares.h>
+#include <sys/socket.h>
+#include <netdb.h>
+#include <sys/time.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <string.h>
+#include "canl_locl.h"
+
+static void free_hostent(struct hostent *h);
+static int decrement_timeout(struct timeval *timeout, struct timeval before, struct timeval after);
+
+#if ARES_VERSION >= 0x010500
+static void callback_ares_gethostbyname(void *arg, int status, int timeouts, struct hostent *h)
+#else
+static void callback_ares_gethostbyname(void *arg, int status, struct hostent *h)
+#endif
+{
+    struct asyn_result *arp = (struct asyn_result *) arg;
+    int n_addr = 0;
+    int i = 0;
+
+    switch (status) {
+        case ARES_SUCCESS:
+            if (h == NULL || h->h_addr_list[0] == NULL){
+                arp->err = NO_DATA;
+                break;
+            }
+            /*how many addresses are there in h->h_addr_list*/
+            while (h->h_addr_list[n_addr])
+                n_addr++;
+
+            arp->ent->h_addr_list = (char **) calloc((n_addr+1), sizeof(char *));
+            if (arp->ent->h_addr_list == NULL) {
+                arp->err = NETDB_INTERNAL;
+                break;
+            }
+            for (i = 0; i < n_addr; i++) {
+                arp->ent->h_addr_list[i] = malloc(h->h_length);
+                if (arp->ent->h_addr_list[i] == NULL) {
+                    free_hostent (arp->ent);
+                    arp->ent = NULL;
+                    arp->err = NETDB_INTERNAL;
+                    break;
+                }
+                memcpy(arp->ent->h_addr_list[i], h->h_addr_list[i],
+                        h->h_length);
+            }
+            /* rest of h members might be assigned here(name,aliases), not necessery now */
+            arp->ent->h_addr_list[n_addr] = NULL;
+            arp->ent->h_addrtype = h->h_addrtype;
+            arp->ent->h_length = h->h_length;
+            arp->err = NETDB_SUCCESS;
+            break;
+        case ARES_EBADNAME:
+        case ARES_ENOTFOUND:
+            arp->err = HOST_NOT_FOUND;
+            break;
+        case ARES_ENOTIMP:
+            arp->err = NO_RECOVERY;
+            break;
+        case ARES_ENOMEM:
+        case ARES_EDESTRUCTION:
+        default:
+            arp->err = NETDB_INTERNAL;
+            break;
+    }
+}
+
+static int decrement_timeout(struct timeval *timeout, struct timeval before, struct timeval after)
+{
+    (*timeout).tv_sec = (*timeout).tv_sec - (after.tv_sec - before.tv_sec);
+    (*timeout).tv_usec = (*timeout).tv_usec - (after.tv_usec - before.tv_usec);
+    while ( (*timeout).tv_usec < 0) {
+        (*timeout).tv_sec--;
+        (*timeout).tv_usec += 1000000;
+    }
+    if ( ((*timeout).tv_sec < 0) || (((*timeout).tv_sec == 0) && ((*timeout).tv_usec == 0)) ) return(1);
+    else return(0);
+}
+
+
+static void free_hostent(struct hostent *h)
+{
+    int i;
+
+    if (h) {
+        if (h->h_name) free(h->h_name);
+        if (h->h_aliases) {
+            for (i=0; h->h_aliases[i]; i++) free(h->h_aliases[i]);
+            free(h->h_aliases);
+        }
+        if (h->h_addr_list) {
+            for (i=0; h->h_addr_list[i]; i++) free(h->h_addr_list[i]);
+            free(h->h_addr_list);
+        }
+        free(h);
+    }
+}
+
+int asyn_getservbyname(int a_family, struct asyn_result *ares_result,char const *name, 
+        struct timeval *timeout)
+{
+    int err;
+    ares_channel channel;
+    int nfds;
+    fd_set readers, writers;
+    struct timeval tv, *tvp;
+    struct timeval start_time,check_time;
+
+    /* start timer */
+    gettimeofday(&start_time,0);
+
+    /* ares init */
+    if ( ares_init(&channel) != ARES_SUCCESS )
+        return(NETDB_INTERNAL); //TODO return value...
+
+    /* query DNS server asynchronously */
+    ares_gethostbyname(channel, name, a_family, callback_ares_gethostbyname, 
+            (void *) ares_result);
+
+    /* wait for result */
+    while (1) {
+        FD_ZERO(&readers);
+        FD_ZERO(&writers);
+        nfds = ares_fds(channel, &readers, &writers);
+        if (nfds == 0)
+            break;
+
+        gettimeofday(&check_time,0);
+        if (timeout && decrement_timeout(timeout, start_time, check_time)) {
+            ares_destroy(channel);
+            return(TRY_AGAIN);
+        }
+        start_time = check_time;
+
+        tvp = ares_timeout(channel, timeout, &tv);
+
+        switch ( select(nfds, &readers, &writers, NULL, tvp) ) {
+            case -1: if (errno != EINTR) {
+                         ares_destroy(channel);
+                         return NETDB_INTERNAL;
+                     } else
+                         continue;
+            case 0:
+                     FD_ZERO(&readers);
+                     FD_ZERO(&writers);
+                     /* fallthrough */
+            default: ares_process(channel, &readers, &writers);
+        }
+    }
+    err = ares_result->err;
+
+    ares_destroy(channel);
+
+    return err;
+}