* Pushed tag to 4.0.1.PRE

* Restconf RFC 8040 increased feature compliance
  * Cache-Control: no-cache added in HTTP responses (RFC Section 5.5)
  * Restconf monitoring capabilities (RFC Section 9.1)
* Added support for Yang extensions
  * New plugin callback: ca_extension
  * Main backend example includes example code on how to implement a Yang extension in a plugin.
* JSON changes
  * Non-pretty-print output removed all extra spaces.
    * Example: `{"nacm-example:x": 42}` --> {"nacm-example:x":42}`
  * Empty JSON container changed from `null` to `{}`.
    * Empty list and leafs remain as `null`
* Removed unnecessary configure dependencies
  * libnsl, libcrypt, libm, if_vlan,...
* pseudo-plugin added, to enable callbacks also for main programs. Useful for extensions
* Yang Unique statements with multiple schema identifiers did not work on some platforms due to memory error.

example/main/Makefile.in

@@ -79,7 +79,7 @@ all:	$(PLUGINS)
 
 CLISPECS = $(APPNAME)_cli.cli
 
-YANGSPECS	 = clixon-example@2019-01-13.yang
+YANGSPECS	 = clixon-example@2019-07-23.yang
 
 # Backend plugin
 BE_SRC   = $(APPNAME)_backend.c

example/main/README.md

@@ -7,6 +7,7 @@
   * [Streams](#streams)
   * [RPC Operations](#rpc-operations)
   * [State data](#state-data)
+  * [Extensions](#extension)
   * [Authentication and NACM](#authentication-and-nacm)
   * [Systemd](#systemd)
   * [Docker](#docker)
@@ -270,6 +271,33 @@ The example contains some stubs for authorization according to [RFC8341(NACM)](h
 * A basic auth HTTP callback, see: example_restconf_credentials() containing three example users: andy, wilma, and guest, according to the examples in Appendix A in [RFC8341](https://tools.ietf.org/html/rfc8341).
 * A NACM backend plugin reporting the mandatory NACM state variables.
 
+## Extensions
+
+Clixon supports Yang extensions, but you need to write plugin code.
+The example backend implements an "example:e4" Yang extension, as follows:
+```
+    extension e4 {
+       description
+	   "The first child of the ex:e4 (unknown) statement is replaced with its first
+            child. This means that 'uses bar;' in the ex:e4 statement below is a valid
+            data node";
+       argument arg;
+    }
+    ex:e4 arg1{
+      uses bar;
+    }
+```
+
+The backend plugin code registers an extension callback in the init struct:
+```
+    .ca_extension=example_extension,        /* yang extensions */
+```
+
+The callback then receives a callback on all "unknown" Yang statements
+during yang parsing. If the extension matches "example:e4", it applies
+the extension. In the example, it replaces the "ex:e4" statements with
+its first child, making it a proper yang statement.
+
 ## Systemd
 
 Example systemd files for backend and restconf daemons are found under the systemd directory. Install them under /etc/systemd/system for example.

example/main/clixon-example@2019-07-23.yang

@@ -2,9 +2,11 @@ module clixon-example {
     yang-version 1.1;
     namespace "urn:example:clixon";
     prefix ex;
+    revision 2019-07-23 {
+	description "Extension e4. Released in Clixon 4.1.0";
+    }
     revision 2019-01-13 {
-	description
-	    "Released in Clixon 3.9";
+	description "Released in Clixon 3.9";
     }
     import ietf-interfaces {
 	prefix if;
@@ -40,6 +42,23 @@ module clixon-example {
             type string;
          }
     }
+    /* yang extension implemented by the example backend code. */
+    extension e4 {
+       description
+	   "The first child of the ex:e4 (unknown) statement is replaced with its first
+            child. This means that 'uses bar;' in the ex:e4 statement below is a valid
+            data node";
+       argument arg;
+    }
+    grouping bar {
+      leaf bar{
+        type string;
+      }
+    }
+    ex:e4 arg1{
+      uses bar;
+    }
+
     /* Example notification as used in RFC 5277 and RFC 8040 */
     notification event {
          description "Example notification event.";

example/main/example_backend.c

@@ -351,6 +351,42 @@ example_statedata(clicon_handle h,
     return retval;
 }
 
+/*! Callback for yang extensions example:e4
+ * 
+ * @param[in] h    Clixon handle
+ * @param[in] yext Yang node of extension 
+ * @param[in] ys   Yang node of (unknown) statement belonging to extension
+ * @retval     0   OK, all callbacks executed OK
+ * @retval    -1   Error in one callback
+ */
+int
+example_extension(clicon_handle h,     
+		  yang_stmt    *yext,
+		  yang_stmt    *ys)
+{
+    int        retval = -1;
+    char      *extname;
+    char      *modname;
+    yang_stmt *ymod;
+    yang_stmt *yc;
+    
+    ymod = ys_module(yext);
+    modname = yang_argument_get(ymod);
+    extname = yang_argument_get(yext);
+    if (strcmp(modname, "example") != 0 || strcmp(extname, "e4") != 0)
+	goto ok;
+    clicon_debug(1, "%s Enabled extension:%s:%s", __FUNCTION__, modname, extname);
+    if ((yc = ys_prune(ys, 0)) == NULL)
+	goto done;
+    if (yn_insert(yang_parent_get(ys), yc) < 0)
+	goto done;
+ ok:
+    retval = 0;
+ done:
+    return retval;
+}
+
+
 /*! Testcase upgrade function moving interfaces-state to interfaces
  * @param[in]  h       Clicon handle 
  * @param[in]  xn      XML tree to be updated
@@ -616,6 +652,7 @@ static clixon_plugin_api api = {
     clixon_plugin_init,                     /* init - must be called clixon_plugin_init */
     example_start,                          /* start */
     example_exit,                           /* exit */
+    .ca_extension=example_extension,        /* yang extensions */
     .ca_reset=example_reset,                /* reset */
     .ca_statedata=example_statedata,        /* statedata */
     .ca_trans_begin=main_begin,             /* trans begin */