iftop

resolver.c

@@ -0,0 +1,143 @@
+/*
+ * 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';
+    }
+}