1 files changed, 116 insertions, 0 deletions
diff --git a/functions.c b/functions.c
index 54e2663..35be8e4 100644
--- a/functions.c
+++ b/functions.c
@@ -1710,3 +1710,119 @@ void strlower(char *string) {
     string[i] = tolower(string[i]);
   }
 }
+
+// Gets a single TXT record from DNS for "dnsname" and stores the result in "record"
+// Returns 1 on success or 0 on failure
+// TODO: If this is ever used for more than just version checks, then it needs to do more than a single record.
+int gettxtrecordsingle(char *dnsname, char *record) {
+  debugprint(DEBUG_FULL, "gettxtrecordsingle(): given '%s'.\n", dnsname);
+
+  unsigned char buffer[8000] = {0};
+  char result[MAXDNSTXTLEN] = {0};
+  const unsigned char *presult = NULL;
+  struct __res_state resState = {0};
+  ns_msg nsMsg = {0};
+  ns_rr rr;
+
+  int type = 0;
+  int ret = 0;
+  int size = 0;
+  int count = 0;
+  long unsigned int len = 0;
+  int res_init = 0;
+
+  ret = res_ninit(&resState);
+
+  if (ret) {
+    debugprint(DEBUG_CRIT, "gettxtrecordsingle(): res_ninit() returned failure (it returned %d)!  Returning 0.\n", ret);
+    return 0;
+  } else {
+    res_init = 1;
+  }
+
+  memset(buffer, 0, sizeof (buffer));
+  size = res_nquery(&resState, dnsname, C_IN, T_TXT, buffer, sizeof(buffer) - 1);
+
+  if (size < 1) {
+    res_nclose(&resState);
+    debugprint(DEBUG_CRIT, "gettxtrecordsingle(): res_nquery() returned zero-length or failure (it returend %d)!  Returning 0.\n", size);
+    return 0;
+  }
+
+  ret = ns_initparse(buffer, size, &nsMsg);
+
+  if (ret) {
+    res_nclose(&resState);
+    debugprint(DEBUG_CRIT, "gettxtrecordsingle(): ns_initparse() returned failure (failed to parse the buffer buffer?) (it returned %d)!  Returning 0.\n", ret);
+    return 0;
+  }
+
+  count = ns_msg_count(nsMsg, ns_s_an);
+
+  for (int i = 0; i < count; i++) {
+    ret = ns_parserr(&nsMsg, ns_s_an, i , &rr);
+
+    if (ret) {
+      res_nclose(&resState);
+      return 0;
+    }
+
+    type = ns_rr_type(rr);
+    if (ns_t_txt == type) {
+      len = ns_rr_rdlen(rr);
+      presult = ns_rr_rdata(rr);
+
+      if ((len > 1) && (len < sizeof(result))) {
+        len--;
+        memcpy (result, presult+1, len);
+        result[len] = '\0';
+        debugprint(DEBUG_FULL, "gettxtrecordsingle(): record '%d' from DNS is '%s'.\n", i, result);
+
+        // Only using the first result
+        if (i == 0) {
+          strncpy(record, result, sizeof(result) - 1);
+        }
+      }
+   }
+  }
+
+  debugprint(DEBUG_FULL, "gettxtrecordsingle(): using record '%s'.\n", result);
+
+  if (res_init) {
+    res_nclose (&resState);
+  }
+
+  return 1;
+}
+
+// Gets the latest blabouncer version string from DNS and stores it in "version"
+// Ignores the Git version portion (everything after the first '-') of VERSION, if present
+// Returns 1 if local VERSION is current, -1 if local VERSION is not current, or 0 on failure
+int checkversion(char *version) {
+  if (!gettxtrecordsingle(VERSIONTXTNAME, version)) {
+    debugprint(DEBUG_CRIT, "checkversion(): gettxtrecordsingle() failure and the buffer contains '%s', returning 0.\n", version);
+    return 0;
+  } else {
+    debugprint(DEBUG_FULL, "checkversion(): gettxtrecordsingle() success and the returned record is '%s'.\n", version);
+  }
+
+  // Ignore the Git version portion (everything after the first '-') of VERSION, if present
+  char localversion[MAXDNSTXTLEN];
+  strncpy(localversion, VERSION, sizeof(localversion) - 1);
+
+  for (size_t i = 0; i < strlen(localversion); i++) {
+    if (localversion[i] == '-') {
+      localversion[i] = '\0';
+      debugprint(DEBUG_FULL, "checkversion(): Trimmed local VERSION string to '%s'.\n", localversion);
+      break;
+    }
+  }
+
+  if (strncmp(localversion, version, sizeof(localversion))) {
+    debugprint(DEBUG_SOME, "checkversion(): Returned version '%s' doesn't match expected '%s', returning -1.\n", version, localversion);
+    return -1;
+  } else {
+    debugprint(DEBUG_FULL, "checkversion(): Returned version '%s' matches expected '%s', returning 1.\n", version, localversion);
+    return 1;
+  }
+}