Improve IPv6 support and system DNS servers discovery

.pubnub.yml

@@ -1,8 +1,33 @@
 name: c-core
 schema: 1
-version: "6.1.0"
+version: "6.2.0"
 scm: github.com/pubnub/c-core
 changelog:
+  - date: 2025-12-10
+    version: v6.2.0
+    changes:
+      - type: feature
+        text: "Add working IPv6 route detection to decide the preferable connection interface."
+      - type: feature
+        text: "When built with `PUBNUB_DNS_SERVERS_VALIDATION_TIMEOUT` set to delay in milliseconds, system DNS servers' discovery will make an actual DNS query, and the value will be used as a request timeout."
+      - type: feature
+        text: "Add handling of the IPv6 proxy address provided by automated (or PAC) proxy discovery API."
+      - type: bug
+        text: "Fix issue because of which `pubnub_await` wasn't waiting after `pubnub_cancel` has been called."
+      - type: bug
+        text: "Fix `WinHttpGetProxyForUrl` usage with URL with schema instead of domain only."
+      - type: bug
+        text: "Fix issue with `/etc/resolv.conf` parsing where untrimmed string produced wrong address."
+      - type: bug
+        text: "Some Windows-related interfaces, because of different `pubnub_` struct layouts caused by different  `pubnub_config.h` type aliases and pre-processing macros, accessed and modified wrong fields."
+      - type: bug
+        text: "Fix `set_from_url4proxy` for proper `lpszProxy` parsing."
+      - type: improvement
+        text: "Add defaults for `PUBNUB_ADVANCED_KEEP_ALIVE` in all related `pubnub_config.h` files."
+      - type: improvement
+        text: "When built with IPv6 support, first try to use any of the user-provided IPv6 DNS servers before falling back to the user-provided IPv4 before falling back to the address provided by a well-known DNS provider."
+      - type: improvement
+        text: "When built with IPv6 support, SDK will send two queries to receive both records and decide which will be most suitable for currently available routing."
   - date: 2025-11-17
     version: v6.1.0
     changes:
@@ -1065,7 +1090,7 @@ sdks:
             distribution-type: source code
             distribution-repository: GitHub release
             package-name: C-Core
-            location: https://github.com/pubnub/c-core/releases/tag/v6.1.0
+            location: https://github.com/pubnub/c-core/releases/tag/v6.2.0
             requires:
               -
                 name: "miniz"
@@ -1131,7 +1156,7 @@ sdks:
             distribution-type: source code
             distribution-repository: GitHub release
             package-name: C-Core
-            location: https://github.com/pubnub/c-core/releases/tag/v6.1.0
+            location: https://github.com/pubnub/c-core/releases/tag/v6.2.0
             requires:
               -
                 name: "miniz"
@@ -1197,7 +1222,7 @@ sdks:
             distribution-type: source code
             distribution-repository: GitHub release
             package-name: C-Core
-            location: https://github.com/pubnub/c-core/releases/tag/v6.1.0
+            location: https://github.com/pubnub/c-core/releases/tag/v6.2.0
             requires:
               -
                 name: "miniz"
@@ -1259,7 +1284,7 @@ sdks:
             distribution-type: source code
             distribution-repository: GitHub release
             package-name: C-Core
-            location: https://github.com/pubnub/c-core/releases/tag/v6.1.0
+            location: https://github.com/pubnub/c-core/releases/tag/v6.2.0
             requires:
               -
                 name: "miniz"
@@ -1320,7 +1345,7 @@ sdks:
             distribution-type: source code
             distribution-repository: GitHub release
             package-name: C-Core
-            location: https://github.com/pubnub/c-core/releases/tag/v6.1.0
+            location: https://github.com/pubnub/c-core/releases/tag/v6.2.0
             requires:
               -
                 name: "miniz"
@@ -1376,7 +1401,7 @@ sdks:
             distribution-type: source code
             distribution-repository: GitHub release
             package-name: C-Core
-            location: https://github.com/pubnub/c-core/releases/tag/v6.1.0
+            location: https://github.com/pubnub/c-core/releases/tag/v6.2.0
             requires:
               -
                 name: "miniz"
@@ -1429,7 +1454,7 @@ sdks:
             distribution-type: source code
             distribution-repository: GitHub release
             package-name: C-Core
-            location: https://github.com/pubnub/c-core/releases/tag/v6.1.0
+            location: https://github.com/pubnub/c-core/releases/tag/v6.2.0
             requires:
               -
                 name: "miniz"

CHANGELOG.md

@@ -1,3 +1,23 @@
+## v6.2.0
+December 10 2025
+
+#### Added
+- Add working IPv6 route detection to decide the preferable connection interface.
+- When built with `PUBNUB_DNS_SERVERS_VALIDATION_TIMEOUT` set to delay in milliseconds, system DNS servers' discovery will make an actual DNS query, and the value will be used as a request timeout.
+- Add handling of the IPv6 proxy address provided by automated (or PAC) proxy discovery API.
+
+#### Fixed
+- Fix issue because of which `pubnub_await` wasn't waiting after `pubnub_cancel` has been called.
+- Fix `WinHttpGetProxyForUrl` usage with URL with schema instead of domain only.
+- Fix issue with `/etc/resolv.conf` parsing where untrimmed string produced wrong address.
+- Some Windows-related interfaces, because of different `pubnub_` struct layouts caused by different  `pubnub_config.h` type aliases and pre-processing macros, accessed and modified wrong fields.
+- Fix `set_from_url4proxy` for proper `lpszProxy` parsing.
+
+#### Modified
+- Add defaults for `PUBNUB_ADVANCED_KEEP_ALIVE` in all related `pubnub_config.h` files.
+- When built with IPv6 support, first try to use any of the user-provided IPv6 DNS servers before falling back to the user-provided IPv4 before falling back to the address provided by a well-known DNS provider.
+- When built with IPv6 support, SDK will send two queries to receive both records and decide which will be most suitable for currently available routing.
+
 ## v6.1.0
 November 17 2025
 

core/pubnub_dns_servers.h

@@ -21,7 +21,7 @@ struct pubnub_ipv6_address {
 };
 
 /* primary, secondary(ipv4, ipv6) and default dns server */
-#define PUBNUB_MAX_DNS_SERVERS_MASK 0x10 
+#define PUBNUB_MAX_DNS_SERVERS_MASK 0x10
 #else
 /* primary, secondary(ipv4) and default dns server */
 #define PUBNUB_MAX_DNS_SERVERS_MASK 0x04
@@ -122,13 +122,12 @@ PUBNUB_EXTERN int pubnub_get_dns_secondary_server_ipv4(struct pubnub_ipv4_addres
 
     @param[out] o_ipv4 The array where to put the system DNS servers.
                        allocated by the caller for @p n elements.
-
     @param[in] n The number of elements allocated for the @p o_ipv4
     @retval -1: error, can't read DNS server configuration
     @retval otherwise: number of DNS servers read
   */
 PUBNUB_EXTERN int pubnub_dns_read_system_servers_ipv4(struct pubnub_ipv4_address* o_ipv4,
-                                        size_t                      n);
+                                                      size_t n);
 #if PUBNUB_USE_IPV6
 /** Sets the primary DNS server IPv6 address to use when
     resolving the Pubnub origin, in binary form(network order).
@@ -162,7 +161,7 @@ PUBNUB_EXTERN int pubnub_dns_set_secondary_server_ipv6(struct pubnub_ipv6_addres
 /** Sets the primary DNS server IPv6 address from the corresponding
     'numbers-and-colons' notation string to use when resolving the Pubnub origin.
     Applies to all subsequent DNS queries, if successful.
-    (Note: All DNS servers are initially set to zeros) 
+    (Note: All DNS servers are initially set to zeros)
 
     @param ipv6_str The IPv6 address string of the server to use. Set all
                     zeros("::0", or "0::") to not use this DNS server.
@@ -178,7 +177,7 @@ PUBNUB_EXTERN int pubnub_dns_set_primary_server_ipv6_str(char const* ipv6_str);
     Applies to all subsequent DNS queries, if successful and if
     using secondary server is supported. Secondary server, if
     used at all, is used if a query to the primary server fails.
-    (Note: All DNS servers are initially set to zeros) 
+    (Note: All DNS servers are initially set to zeros)
 
     @param ipv6_str The IPv6 address string of the server to use. Set all
                     zeros("::0", or "0::") to not use this DNS server.
@@ -207,10 +206,28 @@ PUBNUB_EXTERN int pubnub_get_dns_primary_server_ipv6(struct pubnub_ipv6_address*
             the secondary Ipv6 DNS server
   */
 PUBNUB_EXTERN int pubnub_get_dns_secondary_server_ipv6(struct pubnub_ipv6_address* o_ipv6);
-#endif /* PUBNUB_USE_IPV6 */
 
-#else
+/** Reads the DNS servers in the system configuration. Will read
+    at most @p n servers, even if more are configured. Keep in
+    mind that modern systems have complex configurations and
+    often this will yield just one DNS server which listens on the
+    loopback IP address, while the "real" DNS configuration is
+    not available through standard means.
+
+    On POSIX systems, this will read from `/etc/resolv.conf`,
+    looking for `nameserver` lines. On Windows, this will use OS
+    functions to get the info.
 
+    @param[out] o_ipv6 The array where to put the system DNS servers.
+                       allocated by the caller for @p n elements.
+    @param[in] n The number of elements allocated for the @p o_ipv6
+    @retval -1: error, can't read DNS server configuration
+    @retval otherwise: number of DNS servers read
+  */
+PUBNUB_EXTERN int pubnub_dns_read_system_servers_ipv6(struct pubnub_ipv6_address* o_ipv6,
+                                                      size_t n);
+#endif /* PUBNUB_USE_IPV6 */
+#else  /* PUBNUB_SET_DNS_SERVERS */
 #define pubnub_dns_set_primary_server_ipv4(ipv4) -1
 #define pubnub_dns_set_secondary_server_ipv4(ipv4) -1
 #define pubnub_dns_set_primary_server_ipv4_str(ipv4_str) -1
@@ -225,6 +242,7 @@ PUBNUB_EXTERN int pubnub_get_dns_secondary_server_ipv6(struct pubnub_ipv6_addres
 #define pubnub_dns_set_secondary_server_ipv6_str(ipv6_str) -1
 #define pubnub_get_dns_primary_server_ipv6(o_ipv6) -1
 #define pubnub_get_dns_secondary_server_ipv6(o_ipv6) -1
+#define pubnub_dns_read_system_servers_ipv6(o_ipv4, n) -1
 #endif /* PUBNUB_USE_IPV6 */
-#endif /* PUBNUB_SET_DNS_SERVERS */
+#endif /* !PUBNUB_SET_DNS_SERVERS */
 #endif /* !defined INC_PUBNUB_DNS_SERVERS */