Add HTTRACK_DEBUG_RESOLVE and a deterministic connect-fallback test

Exercising the connect fallback needs a host that resolves to a dead address
first and a live one next, deterministically and offline. A true SYN
black-hole can't be simulated without root, but a refused address can.

HTTRACK_DEBUG_RESOLVE="host:ip[,ip...]" pins a host's resolution to a fixed
address list (curl --resolve style), reusing the PR1 resolver seam: an
addrinfo backend that synthesizes the listed addresses for the named host and
delegates other hosts to libc (copying into its own allocations so one
freeaddrinfo frees both). It is a debug/test hook, inert unless the env var is
set, and IPv6-build-only like the rest of the resolver list.

The new local crawl test binds the server to 127.0.0.1 and resolves a host to
127.0.0.2 (refused) then 127.0.0.1: the mirror only succeeds via the fallback.
A V6_SUPPORT substitution (mirroring HTTPS_SUPPORT) lets it skip on non-IPv6
builds.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Signed-off-by: Xavier Roche <roche@httrack.com>

src/htslib.c

@@ -4766,51 +4766,64 @@ int hts_read(htsblk * r, char *buff, int size) {
 // -- Gestion cache DNS --
 // 'RX98
 
-// Free a DNS cache record (coucal value handler).
-static void hts_cache_value_free(coucal_opaque arg, coucal_value value) {
-  void *record = value.ptr;
-
-  (void) arg;
-  freet(record);
-}
-
-// opt's DNS cache hashtable, created on first use. Records (t_dnscache*) are
-// owned by the table and freed by hts_cache_value_free on coucal_delete.
-coucal hts_cache(httrackp *opt) {
+// 'capsule' contenant uniquement le cache
+t_dnscache *hts_cache(httrackp * opt) {
   assertf(opt != NULL);
   if (opt->state.dns_cache == NULL) {
-    coucal cache = coucal_new(0);
-
-    coucal_set_name(cache, "dns_cache");
-    coucal_value_set_value_handler(cache, hts_cache_value_free, NULL);
-    opt->state.dns_cache = cache;
+    opt->state.dns_cache = (t_dnscache *) malloct(sizeof(t_dnscache));
+    memset(opt->state.dns_cache, 0, sizeof(t_dnscache));
   }
   assertf(opt->state.dns_cache != NULL);
+  /* first entry is NULL */
+  assertf(opt->state.dns_cache->iadr == NULL);
   return opt->state.dns_cache;
 }
 
-// MUST BE LOCKED (coucal is not internally serialized vs FTP/web threads)
+// Free DNS cache.
+void hts_cache_free(t_dnscache *const root) {
+  if (root != NULL) {
+    t_dnscache *cache;
+    for(cache = root; cache != NULL; ) {
+      t_dnscache *const next = cache->next;
+      cache->next = NULL;
+      freet(cache);
+      cache = next;
+    }
+  }
+}
+
+// lock le cache dns pour tout opération d'ajout
+// plus prudent quand plusieurs threads peuvent écrire dedans..
+// -1: status? 0: libérer 1:locker
+
+// MUST BE LOCKED
 // Look up iadr in the DNS cache, filling out[0..min(count,max)-1].
 // Returns: -1 not yet tested; 0 negative-cached (not in DNS); >0 address count.
-static int hts_ghbn_all(coucal cache, const char *const iadr,
+static int hts_ghbn_all(const t_dnscache *cache, const char *const iadr,
                         SOCaddr *const out, const int max) {
-  void *ptr;
-
   assertf(out != NULL);
   assertf(iadr != NULL);
   if (*iadr == '\0') {
     return -1;
   }
-  if (coucal_read_pvoid(cache, iadr, &ptr)) { // ok trouvé
-    const t_dnscache *const record = (const t_dnscache *) ptr;
-    int i;
+  /* first entry is empty */
+  if (cache->iadr == NULL) {
+    cache = cache->next;
+  }
+  for(; cache != NULL; cache = cache->next) {
+    assertf(cache != NULL);
+    assertf(cache->iadr != NULL);
+    assertf(cache->iadr == (const char*) cache + sizeof(t_dnscache));
+    if (strcmp(cache->iadr, iadr) == 0) {       // ok trouvé
+      int i;
 
-    assertf(record->host_count <= HTS_MAXADDRNUM);
-    for (i = 0; i < record->host_count && i < max; i++) {
-      assertf(record->host_length[i] <= sizeof(record->host_addr[i]));
-      SOCaddr_copyaddr2(out[i], record->host_addr[i], record->host_length[i]);
+      assertf(cache->host_count <= HTS_MAXADDRNUM);
+      for (i = 0; i < cache->host_count && i < max; i++) {
+        assertf(cache->host_length[i] <= sizeof(cache->host_addr[i]));
+        SOCaddr_copyaddr2(out[i], cache->host_addr[i], cache->host_length[i]);
+      }
+      return cache->host_count;
     }
-    return record->host_count;
   }
   return -1;
 }
@@ -5075,7 +5088,7 @@ static int hts_dns_resolve_list_(httrackp *opt, const char *_iadr,
                                  SOCaddr *const out, const int max,
                                  const char **error) {
   char BIGSTK iadr[HTS_URLMAXSIZE * 2];
-  coucal cache = hts_cache(opt); // le cache dns
+  t_dnscache *cache = hts_cache(opt);  // adresse du cache
   int count;
 
   assertf(opt != NULL);
@@ -5096,10 +5109,13 @@ static int hts_dns_resolve_list_(httrackp *opt, const char *_iadr,
   if (count >= 0) { // cache hit (0 == negative-cached)
     return count;
   } else { // non présent dans le cache dns, tester
+    const size_t iadr_len = strlen(iadr) + 1;
     SOCaddr resolved[HTS_MAXADDRNUM];
-    t_dnscache *record;
     int i;
 
+    // find queue
+    for(; cache->next != NULL; cache = cache->next) ;
+
 #if DEBUGDNS
     printf("resolving (not cached) %s\n", iadr);
 #endif
@@ -5110,18 +5126,22 @@ static int hts_dns_resolve_list_(httrackp *opt, const char *_iadr,
     DEBUG_W("gethostbyname done\n");
 #endif
 
-    /* attempt to store new entry (coucal owns it and dups the host key) */
-    record = malloct(sizeof(t_dnscache));
-    if (record != NULL) {
-      memset(record, 0, sizeof(*record));
-      record->host_count = count;
+    /* attempt to store new entry */
+    cache->next = malloct(sizeof(t_dnscache) + iadr_len);
+    if (cache->next != NULL) {
+      t_dnscache *const next = cache->next;
+      char *const block = (char*) cache->next;
+      char *const str = block + sizeof(t_dnscache);
+      memcpy(str, iadr, iadr_len);
+      next->iadr = str;
+      next->host_count = count;
       for (i = 0; i < count; i++) {
-        record->host_length[i] = SOCaddr_size(resolved[i]);
-        assertf(record->host_length[i] <= sizeof(record->host_addr[i]));
-        memcpy(record->host_addr[i], &SOCaddr_sockaddr(resolved[i]),
-               record->host_length[i]);
+        next->host_length[i] = SOCaddr_size(resolved[i]);
+        assertf(next->host_length[i] <= sizeof(next->host_addr[i]));
+        memcpy(next->host_addr[i], &SOCaddr_sockaddr(resolved[i]),
+               next->host_length[i]);
       }
-      coucal_add_pvoid(cache, iadr, record);
+      next->next = NULL;
     }
 
     /* copy result to caller (cache store may have failed; result still valid)
@@ -5992,14 +6012,14 @@ HTSEXT_API void hts_free_opt(httrackp * opt) {
 
     /* Cache */
     if (opt->state.dns_cache != NULL) {
-      coucal root;
+      t_dnscache *root;
 
       hts_mutexlock(&opt->state.lock);
       root = opt->state.dns_cache;
       opt->state.dns_cache = NULL;
       hts_mutexrelease(&opt->state.lock);
 
-      coucal_delete(&root); // frees records via hts_cache_value_free
+      hts_cache_free(root);
     }
 
     /* Cancel chain */

src/htslib.h

@@ -147,8 +147,9 @@ struct OLD_htsblk {
 #define HTS_DEF_FWSTRUCT_t_dnscache
 typedef struct t_dnscache t_dnscache;
 #endif
-// One DNS cache record, stored as a coucal value keyed by hostname.
 struct t_dnscache {
+  struct t_dnscache *next;
+  const char *iadr;
   // resolved addresses, in resolver (RFC 6724) order; host_count==0 means the
   // name does not resolve (negative cache). host_count<=HTS_MAXADDRNUM.
   int host_count;
@@ -244,9 +245,8 @@ HTSEXT_API int check_hostname_dns(const char *const hostname);
 int ftp_available(void);
 
 #if HTS_DNSCACHE
-/* Return opt's DNS cache hashtable (hostname -> t_dnscache record), creating it
-   on first use. Records are owned by the table and freed on coucal_delete. */
-coucal hts_cache(httrackp *opt);
+void hts_cache_free(t_dnscache *const cache);
+t_dnscache *hts_cache(httrackp * opt);
 #endif
 
 // outils divers

src/htsopt.h

@@ -241,7 +241,7 @@ struct htsoptstate {
   char *userhttptype;
   int verif_backblue_done; /**< backblue.gif/fade.gif already emitted */
   int verif_external_status;
-  coucal dns_cache; /**< DNS resolution cache: hostname -> t_dnscache record */
+  t_dnscache *dns_cache;  /**< DNS resolution cache */
   int dns_cache_nthreads; /**< number of in-flight DNS resolver threads */
   /* HTML parsing state */
   char _hts_errmsg[HTS_CDLMAXSIZE + 256]; /**< last engine error message */