diff -up cups-2.2.0/cups/auth.c.resolv_reload cups-2.2.0/cups/auth.c

--- cups-2.2.0/cups/auth.c.resolv_reload	2017-05-09 10:36:47.764075800 +0200

+++ cups-2.2.0/cups/auth.c	2017-05-09 10:40:50.074052694 +0200

@@ -519,6 +519,18 @@ cups_gss_getname(

   DEBUG_printf(("7cups_gss_getname(http=%p, service_name=\"%s\")", http,

                 service_name));

+#ifdef HAVE_RES_INIT

+ /*

+  * Check if /etc/resolv.conf is modified.

+  * If so, reload resolver.

+  */

+

+  dns_resolver_reload_rv retval;

+

+  retval = dnsReloadResolver();

+  if (retval.status == DNS_RESOLVER_RELOAD_ERROR)

+    DEBUG_printf(("1cups_gss_getname: dnsReloadResolver() failed - %s.", strerror(retval.errnum)));

+#endif /* HAVE_RES_INIT */

  /*

   * Get the hostname...

diff -up cups-2.2.0/cups/http-addr.c.resolv_reload cups-2.2.0/cups/http-addr.c

--- cups-2.2.0/cups/http-addr.c.resolv_reload	2017-05-09 10:36:58.094989545 +0200

+++ cups-2.2.0/cups/http-addr.c	2017-05-09 10:43:51.958516333 +0200

@@ -361,6 +361,20 @@ httpAddrLookup(

 #ifdef HAVE_RES_INIT

  /*

+  * Check if /etc/resolv.conf is modified.

+  * If so, reload resolver and set need_res_init to 0.

+  */

+

+  dns_resolver_reload_rv retval;

+

+  retval = dnsReloadResolver();

+

+  if (retval.status == DNS_RESOLVER_RELOAD_RELOADED && cg->need_res_init == 1)

+    cg->need_res_init = 0;

+

+  if (retval.status == DNS_RESOLVER_RELOAD_ERROR)

+    DEBUG_printf(("1httpAddrLookup: dnsReloadResolver() failed - %s.", strerror(retval.errnum)));

+ /*

   * STR #2920: Initialize resolver after failure in cups-polld

   *

   * If the previous lookup failed, re-initialize the resolver to prevent

diff -up cups-2.2.0/cups/http-addrlist.c.resolv_reload cups-2.2.0/cups/http-addrlist.c

--- cups-2.2.0/cups/http-addrlist.c.resolv_reload	2017-05-09 10:37:03.834941621 +0200

+++ cups-2.2.0/cups/http-addrlist.c	2017-05-09 10:45:10.426832540 +0200

@@ -483,6 +483,20 @@ httpAddrGetList(const char *hostname,	/*

 #ifdef HAVE_RES_INIT

  /*

+  * Check if /etc/resolv.conf is modified.

+  * If so, reload resolver and set cg->need_res_init to 0

+  */

+

+  dns_resolver_reload_rv retval;

+

+  retval = dnsReloadResolver();

+

+  if (retval.status == DNS_RESOLVER_RELOAD_RELOADED && cg->need_res_init == 1)

+    cg->need_res_init = 0;

+

+  if (retval.status == DNS_RESOLVER_RELOAD_ERROR)

+    DEBUG_printf(("1httpAddrGetList: dnsReloadResolver() failed - %s.", strerror(retval.errnum)));

+ /*

   * STR #2920: Initialize resolver after failure in cups-polld

   *

   * If the previous lookup failed, re-initialize the resolver to prevent

diff -up cups-2.2.0/cups/http.c.resolv_reload cups-2.2.0/cups/http.c

--- cups-2.2.0/cups/http.c.resolv_reload	2017-05-09 10:37:23.282779246 +0200

+++ cups-2.2.0/cups/http.c	2017-05-09 10:47:21.406691147 +0200

@@ -107,7 +107,9 @@ static const char * const http_fields[]

 			  "Allow",

 			  "Server"

 			};

-

+#ifdef HAVE_RES_INIT

+time_t resolv_conf_modtime = 0;

+#endif /* HAVE_RES_INIT */

 /*

  * 'httpAcceptConnection()' - Accept a new HTTP client connection from the

@@ -4811,3 +4813,107 @@ http_write_chunk(http_t     *http,	/* I

   return (bytes);

 }

+

+#ifdef HAVE_RES_INIT

+/*

+ * Function to check modification time of resolv.conf. 

+ * If time is changed, it reloads resolver. 

+ * If /etc/resolv.conf doesn't exist, it tries to reload resolver with local nameserver, if it wasn't reloaded before

+ * If even reloading resolver with local nameserver doesn't work, it ends with error.

+ * Global variable resolv_conf_modtime is set to -1 before the first call of this function - this is for prevention of resolver's reloading when cupsd is just started and resolv.conf exists - cupsd has current configuration in that case.

+ */

+

+dns_resolver_reload_rv

+dnsReloadResolver()

+{

+  dns_resolver_reload_rv retval, lstat_retval, stat_retval, res_init_retval;

+  struct stat resolv_conf_stat, resolv_conf_lstat, resolv_conf_status;

+  retval.status = DNS_RESOLVER_RELOAD_OK;

+  retval.errnum = 0;

+  stat_retval.errnum = 0;

+  lstat_retval.errnum = 0;

+  res_init_retval.errnum = 0;

+

+  /* Variable to store /etc/resolv.conf modification time - initialized by actual time*/

+  static time_t resolv_conf_modtime = -1;

+

+  /* This part of code is to ensure we get modification time of symlink and original file - we will decide which is newer later */

+  stat_retval.status = stat(DNS_RESOLV_CONF_PATH, &resolv_conf_stat);

+  stat_retval.errnum = errno;

+  lstat_retval.status = lstat(DNS_RESOLV_CONF_PATH, &resolv_conf_lstat);

+  lstat_retval.errnum = errno;

+

+  /* symlink /etc/resolv.conf or original file couldn't be stated because it doesn't exist, try resolver on localhost 

+   * Covers cases:

+   * - resolv.conf and original file existed and it doesn't now - resolv_conf_modtime has different value than 0  - reload resolver with local nameserver

+   * - resolv.conf and original file didn't exist and still doesn't exist - resolv_conf_modtime is set to 0 - do nothing

+   */

+  if (stat_retval.status == -1 && lstat_retval.status == -1 && stat_retval.errnum == ENOENT && lstat_retval.errnum == ENOENT)

+  {

+    /* if resolv_conf_modtime is set to 0, it means previous reload was for resolver with local nameserver - no need to reload again */

+    if (resolv_conf_modtime != 0)

+    {

+      res_init_retval.status = res_init();

+      res_init_retval.errnum = errno;

+      if (res_init_retval.status == 0)

+      {

+        resolv_conf_modtime = 0;

+        retval.status = DNS_RESOLVER_RELOAD_RELOADED;

+      }

+      else

+        retval.status = res_init_retval.status;

+

+      retval.errnum = res_init_retval.errnum;

+    }

+    else

+    {

+      retval.status = DNS_RESOLVER_RELOAD_OK;

+      retval.errnum = ENOENT;

+    }

+

+    return (retval);

+  }

+

+  /* If stat ends with different errno, return status - it should return both statuses and errnos, but for simplification it returns only stat */

+  if (stat_retval.status == -1 && lstat_retval.status == -1)

+  {

+    retval.errnum = stat_retval.errnum;

+    retval.status = stat_retval.status;

+    return (retval);

+  }

+

+  /* Here we compare modification times from lstat and stat to decide which is newer - if they are equal, lstat modification time is used. We are checking only stat() errno, because case with errors in both lstat() and stat() functions is checked before */

+  if (stat_retval.errnum == 0)

+    if (resolv_conf_stat.st_mtime > resolv_conf_lstat.st_mtime)

+      resolv_conf_status = resolv_conf_stat;

+    else

+      resolv_conf_status = resolv_conf_lstat;

+  else

+    resolv_conf_status = resolv_conf_lstat;

+

+  /* If /etc/resolv.conf exists and modification times are different, reload resolver.

+   * Covers cases:

+   * - resolv.conf or original file exists and it was modified - resolv_conf_modtime has different value than resolv_conf_status.st_mtime - reload resolver with nameserver from /etc/resolv.conf 

+   * - resolv.conf or original file didn't exist and it does now - resolv_conf_modtime is set to 0 and resolv_conf_status.st_mtime has value - reload resolver with nameserver form /etc/resolv.conf

+   * - resolv.conf or original file exists and it wasn't modified - resolv_conf_modtime is equal to resolv_conf_status.st_mtime - do nothing

+   */

+  if (resolv_conf_status.st_mtime != resolv_conf_modtime)

+  {

+    res_init_retval.status = res_init();

+    res_init_retval.errnum = errno;

+    if (res_init_retval.status == 0)

+    {

+      retval.status = DNS_RESOLVER_RELOAD_RELOADED;

+    }

+    else

+      retval.status = res_init_retval.status;

+

+    retval.errnum = res_init_retval.errnum;

+  }

+

+  resolv_conf_modtime = resolv_conf_status.st_mtime;

+

+  return (retval);

+}

+#endif /* HAVE_RES_INIT */

+

diff -up cups-2.2.0/cups/http.h.resolv_reload cups-2.2.0/cups/http.h

--- cups-2.2.0/cups/http.h.resolv_reload	2017-05-09 10:37:41.108630413 +0200

+++ cups-2.2.0/cups/http.h	2017-05-09 12:20:16.115333557 +0200

@@ -55,6 +55,12 @@ typedef off_t ssize_t;			/* @private@ */

 #      define SO_PEERCRED LOCAL_PEERCRED

 #    endif /* LOCAL_PEERCRED && !SO_PEERCRED */

 #  endif /* WIN32 */

+#  ifdef HAVE_RES_INIT

+#    include <sys/stat.h>

+#    include <unistd.h>

+#    include <arpa/nameser.h>

+#    include <resolv.h>

+#  endif /* HAVE_RES_INIT */

 /*

@@ -95,6 +101,13 @@ extern "C" {

 #endif /* AF_INET6 && !s6_addr32 */

+#ifdef HAVE_RES_INIT

+/*

+ * Global variable for storing old modification time of resolv.conf 

+ */

+  extern time_t resolv_conf_modtime;

+#endif /* HAVE_RES_INIT */

+

 /*

  * Limits...

  */

@@ -103,6 +116,9 @@ extern "C" {

 #  define HTTP_MAX_HOST		256	/* Max length of hostname string */

 #  define HTTP_MAX_BUFFER	2048	/* Max length of data buffer */

 #  define HTTP_MAX_VALUE	256	/* Max header field value length */

+#  ifdef HAVE_RES_INIT

+#    define DNS_RESOLV_CONF_PATH	"/etc/resolv.conf" /* Path to resolv.conf */

+#  endif /* HAVE_RES_INIT */

 /*

@@ -406,6 +422,15 @@ typedef enum http_version_e		/**** HTTP

 #  endif /* !_CUPS_NO_DEPRECATED */

 } http_version_t;

+#ifdef HAVE_RES_INIT

+typedef enum dns_resolver_reload_e

+{

+  DNS_RESOLVER_RELOAD_ERROR = -1,

+  DNS_RESOLVER_RELOAD_OK = 0,

+  DNS_RESOLVER_RELOAD_RELOADED = 1

+} dns_resolver_reload_t;

+#endif /* HAVE_RES_INIT */

+

 typedef union _http_addr_u		/**** Socket address union, which

 					 **** makes using IPv6 and other

 					 **** address types easier and

@@ -444,6 +469,13 @@ typedef struct http_credential_s	/**** H

 typedef int (*http_timeout_cb_t)(http_t *http, void *user_data);

 					/**** HTTP timeout callback @since CUPS 1.5/macOS 10.7@ ****/

+#ifdef HAVE_RES_INIT

+typedef struct dns_resolver_reload_retval

+{

+  dns_resolver_reload_t status;

+  int errnum;

+} dns_resolver_reload_rv;

+#endif /* HAVE_RES_INIT */

 /*

@@ -590,6 +622,10 @@ extern http_version_t	httpGetVersion(htt

 extern int		httpReconnect2(http_t *http, int msec, int *cancel)

 			               _CUPS_API_1_6;

+/**** Prototype of function to check modification time of /etc/resolv.conf ****/

+#ifdef HAVE_RES_INIT

+extern dns_resolver_reload_rv	dnsReloadResolver();

+#endif /* HAVE_RES_INIT */

 /**** New in CUPS 1.7/macOS 10.9 ****/

 extern http_t		*httpAcceptConnection(int fd, int blocking)

diff -up cups-2.2.0/cups/http-support.c.resolv_reload cups-2.2.0/cups/http-support.c

--- cups-2.2.0/cups/http-support.c.resolv_reload	2017-05-09 10:38:11.314378218 +0200

+++ cups-2.2.0/cups/http-support.c	2017-05-09 12:21:40.455565953 +0200

@@ -2258,6 +2258,18 @@ http_resolve_cb(

     http_addrlist_t	*addrlist,	/* List of addresses */

 			*addr;		/* Current address */

+#ifdef HAVE_RES_INIT

+   /*

+    * Check if resolv.conf is modified, if so, reload resolver

+    */

+

+    dns_resolver_reload_rv retval;

+

+    retval = dnsReloadResolver();

+    if (retval.status == DNS_RESOLVER_RELOAD_ERROR)

+      DEBUG_printf(("1http_resolve_cb: dnsReloadResolver() failed - %s.", strerror(retval.errnum)));

+#endif /* HAVE_RES_INIT */

+

     DEBUG_printf(("5http_resolve_cb: Looking up \"%s\".", hostTarget));

     snprintf(fqdn, sizeof(fqdn), "%d", ntohs(port));

diff -up cups-2.2.0/scheduler/conf.c.resolv_reload cups-2.2.0/scheduler/conf.c

--- cups-2.2.0/scheduler/conf.c.resolv_reload	2017-05-09 10:38:29.869223299 +0200

+++ cups-2.2.0/scheduler/conf.c	2017-05-09 12:22:40.442020000 +0200

@@ -937,6 +937,15 @@ cupsdReadConfiguration(void)

   if (!RemotePort)

     BrowseLocalProtocols = 0;		/* Disable sharing - no remote access */

+#ifdef HAVE_RES_INIT

+  dns_resolver_reload_rv retval;	/* Return status of dnsReloadResolver() */

+

+  retval = dnsReloadResolver();

+

+  if (retval.status == DNS_RESOLVER_RELOAD_ERROR)

+    syslog(LOG_LPR, "1cupsdReadConfiguration: dnsReloadResolver() failed - %s.", strerror(retval.errnum));

+#endif /* HAVE_RES_INIT */

+

  /*

   * See if the ServerName is an IP address...

   */

diff -up cups-2.2.0/scheduler/main.c.resolv_reload cups-2.2.0/scheduler/main.c

--- cups-2.2.0/scheduler/main.c.resolv_reload	2017-05-09 10:38:37.699157925 +0200

+++ cups-2.2.0/scheduler/main.c	2017-05-09 12:23:36.280514244 +0200

@@ -136,6 +136,14 @@ main(int  argc,				/* I - Number of comm

   long			tmo_delay;	/* Time before it must be called */

 #endif /* HAVE_AVAHI */

+#ifdef HAVE_RES_INIT

+  dns_resolver_reload_rv retval;	/* Return status from dnsReloadResolver() */

+

+  retval = dnsReloadResolver();

+  if (retval.status == DNS_RESOLVER_RELOAD_ERROR)

+    fprintf(stderr, "cupsd: Cannot reload a resolver - %s , using old configuration now.\n", strerror(retval.errnum));

+#endif /* HAVE_RES_INIT */

+

 #ifdef HAVE_GETEUID

  /*

   * Check for setuid invocation, which we do not support!