Configurable hosts path for file_lookup (#465)

This changeset adds support for configurable hosts file
ARES_OPT_HOSTS_FILE (similar to ARES_OPT_RESOLVCONF).

Co-authored-by: Manish Mehra (@mmehra)

docs/ares_init_options.3

@@ -41,6 +41,7 @@ struct ares_options {
   int nsort;
   int ednspsz;
   char *resolvconf_path;
+  char *hosts_path;
 };
 
 int ares_init_options(ares_channel *\fIchannelptr\fP,
@@ -195,6 +196,16 @@ should be set to a path string, and will be honoured on *nix like systems. The
 default is
 .B /etc/resolv.conf
 .br
+.TP 18
+.B ARES_OPT_HOSTS_FILE
+.B char *\fIhosts_path\fP;
+.br
+The path to use for reading the hosts file. The
+.I hosts_path
+should be set to a path string, and will be honoured on *nix like systems. The
+default is
+.B /etc/hosts
+.br
 .PP
 The \fIoptmask\fP parameter also includes options without a corresponding
 field in the

include/ares.h

@@ -175,6 +175,7 @@ extern "C" {
 #define ARES_OPT_EDNSPSZ        (1 << 15)
 #define ARES_OPT_NOROTATE       (1 << 16)
 #define ARES_OPT_RESOLVCONF     (1 << 17)
+#define ARES_OPT_HOSTS_FILE     (1 << 18)
 
 /* Nameinfo flag values */
 #define ARES_NI_NOFQDN                  (1 << 0)
@@ -284,6 +285,7 @@ struct ares_options {
   int nsort;
   int ednspsz;
   char *resolvconf_path;
+  char *hosts_path;
 };
 
 struct hostent;

src/lib/ares_destroy.c

@@ -38,6 +38,8 @@ void ares_destroy_options(struct ares_options *options)
     ares_free(options->lookups);
   if(options->resolvconf_path)
     ares_free(options->resolvconf_path);
+  if(options->hosts_path)
+    ares_free(options->hosts_path);
 }
 
 void ares_destroy(ares_channel channel)
@@ -90,6 +92,9 @@ void ares_destroy(ares_channel channel)
   if (channel->resolvconf_path)
     ares_free(channel->resolvconf_path);
 
+  if (channel->hosts_path)
+    ares_free(channel->hosts_path);
+
   ares_free(channel);
 }
 

src/lib/ares_getaddrinfo.c

@@ -416,6 +416,11 @@ static int file_lookup(struct host_query *hquery)
       path_hosts = getenv("CARES_HOSTS");
     }
 
+  if (hquery->channel->hosts_path)
+    {
+      path_hosts = hquery->channel->hosts_path;
+    }
+
   if (!path_hosts)
     {
 #ifdef WIN32

src/lib/ares_init.c

@@ -164,6 +164,7 @@ int ares_init_options(ares_channel *channelptr, struct ares_options *options,
   channel->sock_funcs = NULL;
   channel->sock_func_cb_data = NULL;
   channel->resolvconf_path = NULL;
+  channel->hosts_path = NULL;
 
   channel->last_server = 0;
   channel->last_timeout_processed = (time_t)now.tv_sec;
@@ -239,6 +240,8 @@ done:
         ares_free(channel->lookups);
       if(channel->resolvconf_path)
         ares_free(channel->resolvconf_path);
+      if(channel->hosts_path)
+        ares_free(channel->hosts_path);
       ares_free(channel);
       return status;
     }
@@ -350,6 +353,9 @@ int ares_save_options(ares_channel channel, struct ares_options *options,
   if (channel->resolvconf_path)
     (*optmask) |= ARES_OPT_RESOLVCONF;
 
+  if (channel->hosts_path)
+    (*optmask) |= ARES_OPT_HOSTS_FILE;
+
   /* Copy easy stuff */
   options->flags   = channel->flags;
 
@@ -429,6 +435,13 @@ int ares_save_options(ares_channel channel, struct ares_options *options,
       return ARES_ENOMEM;
   }
 
+  /* copy path for hosts file */
+  if (channel->hosts_path) {
+    options->hosts_path = ares_strdup(channel->hosts_path);
+    if (!options->hosts_path)
+      return ARES_ENOMEM;
+  }
+
   return ARES_SUCCESS;
 }
 
@@ -545,6 +558,14 @@ static int init_by_options(ares_channel channel,
         return ARES_ENOMEM;
     }
 
+  /* Set path for hosts file, if given. */
+  if ((optmask & ARES_OPT_HOSTS_FILE) && !channel->hosts_path)
+    {
+      channel->hosts_path = ares_strdup(options->hosts_path);
+      if (!channel->hosts_path && options->hosts_path)
+        return ARES_ENOMEM;
+    }
+
   channel->optmask = optmask;
 
   return ARES_SUCCESS;
@@ -1661,6 +1682,11 @@ static int init_by_defaults(ares_channel channel)
       ares_free(channel->resolvconf_path);
       channel->resolvconf_path = NULL;
     }
+
+    if(channel->hosts_path) {
+      ares_free(channel->hosts_path);
+      channel->hosts_path = NULL;
+    }
   }
 
   if(hostname)

src/lib/ares_private.h

@@ -339,6 +339,9 @@ struct ares_channeldata {
 
   /* Path for resolv.conf file, configurable via ares_options */
   char *resolvconf_path;
+
+  /* Path for hosts file, configurable via ares_options */
+  char *hosts_path;
 };
 
 /* Does the domain end in ".onion" or ".onion."? Case-insensitive. */

test/ares-test-init.cc

@@ -88,6 +88,8 @@ TEST_F(LibraryTest, OptionsChannelInit) {
   optmask |= ARES_OPT_ROTATE;
   opts.resolvconf_path = strdup("/etc/resolv.conf");
   optmask |= ARES_OPT_RESOLVCONF;
+  opts.hosts_path = strdup("/etc/hosts");
+  optmask |= ARES_OPT_HOSTS_FILE;
 
   ares_channel channel = nullptr;
   EXPECT_EQ(ARES_SUCCESS, ares_init_options(&channel, &opts, optmask));
@@ -115,6 +117,7 @@ TEST_F(LibraryTest, OptionsChannelInit) {
   EXPECT_EQ(std::string(opts.domains[1]), std::string(opts2.domains[1]));
   EXPECT_EQ(std::string(opts.lookups), std::string(opts2.lookups));
   EXPECT_EQ(std::string(opts.resolvconf_path), std::string(opts2.resolvconf_path));
+  EXPECT_EQ(std::string(opts.hosts_path), std::string(opts2.hosts_path));
 
   ares_destroy_options(&opts);
   ares_destroy_options(&opts2);
@@ -174,6 +177,8 @@ TEST_F(LibraryTest, OptionsChannelAllocFail) {
   optmask |= ARES_OPT_ROTATE;
   opts.resolvconf_path = strdup("/etc/resolv.conf");
   optmask |= ARES_OPT_RESOLVCONF;
+  opts.hosts_path = strdup("/etc/hosts");
+  optmask |= ARES_OPT_HOSTS_FILE;
 
   ares_channel channel = nullptr;
   for (int ii = 1; ii <= 8; ii++) {
@@ -430,6 +435,32 @@ CONTAINED_TEST_F(LibraryTest, ContainerMyResolvConfInit,
   return HasFailure();
 }
 
+// Allow hosts path to be configurable
+NameContentList myhosts = {
+  {"/tmp/hosts", "10.0.12.26     foobar\n"
+                 "2001:A0:C::1A  foobar\n"}};
+CONTAINED_TEST_F(LibraryTest, ContainerMyHostsInit,
+                 "myhostname", "mydomain.org", myhosts) {
+  char filename[] = "/tmp/hosts";
+  ares_channel channel = nullptr;
+  struct ares_options options = {0};
+  options.hosts_path = strdup(filename);
+  int optmask = ARES_OPT_HOSTS_FILE;
+  EXPECT_EQ(ARES_SUCCESS, ares_init_options(&channel, &options, optmask));
+
+  optmask = 0;
+  free(options.hosts_path);
+  options.hosts_path = NULL;
+
+  EXPECT_EQ(ARES_SUCCESS, ares_save_options(channel, &options, &optmask));
+  EXPECT_EQ(ARES_OPT_HOSTS_FILE, (optmask & ARES_OPT_HOSTS_FILE));
+  EXPECT_EQ(std::string(filename), std::string(options.hosts_path));
+
+  ares_destroy_options(&options);
+  ares_destroy(channel);
+  return HasFailure();
+}
+
 NameContentList hostconf = {
   {"/etc/resolv.conf", "nameserver 1.2.3.4\n"
                        "sortlist1.2.3.4\n"  // malformed line