Build with -Wextra and modernise the capture device setup

src/Makefile

@@ -5,7 +5,7 @@ all: $(PROG)
 
 CC = gcc
 OPTIMIZATION ?= -O2
-CFLAGS = -g $(OPTIMIZATION) -Wall
+CFLAGS = -g $(OPTIMIZATION) -Wall -Wextra
 
 # SANITIZE=address builds the binary and the test suite under ASan/UBSan.
 ifdef SANITIZE

src/hashtable.c

@@ -26,7 +26,9 @@ unsigned int hash_function(const void *key, int len) {
   const unsigned char *data = (const unsigned char *)key;
 
   while(len >= 4) {
-    uint32_t k = *(uint32_t*)data;
+    uint32_t k;
+
+    memcpy(&k, data, sizeof(k));
 
     k *= m;
     k ^= k >> r;
@@ -90,11 +92,12 @@ void hashtable_destroy(hashtable *ht) {
 }
 
 void *hashtable_add(hashtable *ht, char *key, void *value) {
-    int bucket, key_size;
+    int bucket;
+    size_t key_size;
     entry *current;
 
     key_size = strlen(key);
-    bucket = hash_function(key, strlen(key)) % ht->nbucket;
+    bucket = hash_function(key, (int)key_size) % ht->nbucket;
     current = ht->buckets[bucket];
     while (current) {
        if (key_size == strlen(current->key) && !strncmp(key, current->key, key_size)) {
@@ -117,11 +120,12 @@ void *hashtable_add(hashtable *ht, char *key, void *value) {
 }
 
 void *hashtable_get(hashtable *ht, char *key) {
-    int bucket, key_size;
+    int bucket;
+    size_t key_size;
     entry *current;
 
     key_size = strlen(key);
-    bucket = hash_function(key, key_size) % ht->nbucket;
+    bucket = hash_function(key, (int)key_size) % ht->nbucket;
     current = ht->buckets[bucket];
     while(current) {
         if (strlen(current->key) == key_size && !strncmp(key, current->key, key_size)) {
@@ -133,10 +137,11 @@ void *hashtable_get(hashtable *ht, char *key) {
 }
 
 int hashtable_del(hashtable *ht, char *key) {
-    int bucket, key_size = strlen(key);
+    int bucket;
+    size_t key_size = strlen(key);
     entry *current, *prev = NULL;
 
-    bucket = hash_function(key, key_size) % ht->nbucket;
+    bucket = hash_function(key, (int)key_size) % ht->nbucket;
     current = ht->buckets[bucket];
     while (current) {
         if (key_size == strlen(current->key) && !strncmp(key, current->key, key_size)) {

src/sniffer.c

@@ -37,6 +37,24 @@ static void free_request(void *v) {
     free(req);
 }
 
+/* pcap_lookupdev is deprecated and returns a shared buffer; the caller owns
+ * the name this returns. Loopback is a last resort, not a first guess. */
+static char *first_capture_device(char *err) {
+    pcap_if_t *devices, *d;
+    char *name = NULL;
+
+    if (pcap_findalldevs(&devices, err) == -1) return NULL;
+    for (d = devices; d; d = d->next) {
+        if (d->flags & PCAP_IF_LOOPBACK) continue;
+        name = strdup(d->name);
+        break;
+    }
+    if (!name && devices) name = strdup(devices->name);
+    pcap_freealldevs(devices);
+    if (!name) snprintf(err, MAX_ERR_BUFF_SIZE, "no capture device available");
+    return name;
+}
+
 struct bpf_program *sniffer_compile(pcap_t *pcap, const char *filter, char *err) {
     struct bpf_program *bpf;
 
@@ -94,11 +112,13 @@ struct sniffer *sniffer_create(struct options *opts, char *err) {
         pcap = sniffer_offline(opts->offline_file, err);
     } else {
         pcap = sniffer_online(opts->dev, opts->snaplen, opts->buf_size, err);
-        if (!strcmp(opts->dev, "any") && !pcap) {
-            if ((dev = pcap_lookupdev(err)) != NULL) {
+        if (!pcap && !strcmp(opts->dev, "any")) {
+            if ((dev = first_capture_device(err)) != NULL) {
                 pcap = sniffer_online(dev, opts->snaplen, opts->buf_size, err);
                 free(opts->dev);
-                opts->dev = strdup(dev);
+                free(sniffer->dev);
+                opts->dev = dev;
+                sniffer->dev = strdup(dev);
             }
         }
     }
@@ -161,13 +181,8 @@ pcap_t *sniffer_offline(const char *file, char *err) {
 pcap_t *sniffer_online(const char *dev, int snaplen, int buf_size, char *err) {
     int status;
     pcap_t *pcap;
-    bpf_u_int32 net = 0, mask = 0;
-    const char *new_dev = dev;
 
-    if (pcap_lookupnet(dev, &net, &mask, err) == -1) {
-        return NULL;
-    }
-    pcap = pcap_create(new_dev, err);
+    pcap = pcap_create(dev, err);
     if (!pcap) return NULL;
     status = pcap_set_snaplen(pcap, snaplen);
     if (status < 0) goto error;