nodejs/node · error

%s: %s

Error message

%s: %s

What it means

Printed by ahost's callback() at ahost.c:217 when the DNS lookup initiated by ares_gethostbyname or ares_gethostbyaddr completes with a non-success status. The callback receives (arg, status, timeouts, host) where arg is the original hostname/IP string. The message formats as 'hostname: ares-error-string'. The callback returns without printing addresses since none are available.

Source

Thrown at deps/cares/src/tools/ahost.c:217

  ares_destroy(channel);

  ares_library_cleanup();

#ifdef USE_WINSOCK
  WSACleanup();
#endif

  return 0;
}

static void callback(void *arg, int status, int timeouts, struct hostent *host)
{
  char **p;

  (void)timeouts;

  if (status != ARES_SUCCESS) {
    fprintf(stderr, "%s: %s\n", (char *)arg, ares_strerror(status));
    return;
  }

  for (p = host->h_addr_list; *p; p++) {
    char addr_buf[46] = "??";

    ares_inet_ntop(host->h_addrtype, *p, addr_buf, sizeof(addr_buf));
    printf("%-32s\t%s", host->h_name, addr_buf);
    puts("");
  }
}

static void ai_callback(void *arg, int status, int timeouts,
                        struct ares_addrinfo *result)
{
  struct ares_addrinfo_node *node = NULL;
  (void)timeouts;

View on GitHub (pinned to 1b2de5e052)

Solutions

  1. Check the ares_strerror() portion of the message: ENOTFOUND means the name does not exist, ETIMEOUT means the resolver is unreachable.
  2. Verify the domain name is spelled correctly and exists in DNS (cross-check with 'dig' or 'nslookup').
  3. For AAAA failures, confirm the domain actually has IPv6 records (try -t a instead of -t aaaa).
  4. If timeouts persist, verify network connectivity to the DNS server and try an alternate resolver (-s 8.8.8.8).

Example fix

// before: querying AAAA for IPv4-only domain
ahost -t aaaa ipv4-only.example.com
// -> 'ipv4-only.example.com: ...'

// after: query the correct record type
ahost -t a ipv4-only.example.com
Defensive patterns

Strategy: fallback

Validate before calling

// Pre-check domain existence is not practical for DNS.
// Instead, validate name syntax before querying:
validate_domain() {
    local name="$1"
    [ ${#name} -le 253 ] || return 1
    return 0
}
validate_domain "$DOMAIN" || { echo "invalid name" >&2; exit 1; }

Try / catch

// In the callback, handle non-success gracefully
static void callback(void *arg, int status, int timeouts, struct hostent *host) {
    if (status != ARES_SUCCESS) {
        fprintf(stderr, "%s: %s\n", (char *)arg, ares_strerror(status));
        // fall back to alternate resolver or report gracefully
        return;
    }
    // process host->h_addr_list
}

Prevention

When it happens

Trigger: The callback registered with ares_gethostbyname/ares_gethostbyaddr is invoked by c-ares with status != ARES_SUCCESS. Triggered when the DNS server returns NXDOMAIN (ARES_ENOTFOUND), a SERVFAIL (ARES_ESERVFAIL), a timeout (ARES_ETIMEOUT after all retries), or when the name cannot be resolved for the requested family (e.g., querying AAAA for a name with only A records returns ARES_ENODATA).

Common situations: Looking up a nonexistent domain (NXDOMAIN). The DNS server is unreachable (timeout). Querying AAAA records for an IPv4-only domain. The domain exists but has no records of the requested type. Network connectivity issues prevent reaching the configured DNS resolver.

Related errors

AI-assisted analysis of nodejs/node@1b2de5e052 (2026-08-13). Data as JSON: /api/errors/c3fa8c426720d015. Report an issue: GitHub.