res_ari: Add support for channel variables in ARI events.

This works the same as for AMI manager variables. Set
"channelvars=foo,bar" in your ari.conf general section, and then the
channel variables "foo" and "bar" (along with their values), will
appear in every Stasis websocket channel event.

ASTERISK-26492 #close
patches:
  ari_vars.diff submitted by Mark Michelson

Change-Id: I5609ba239259577c0948645df776d7f3bc864229

include/asterisk/channel.h

@@ -4339,6 +4339,36 @@ void ast_channel_set_manager_vars(size_t varc, char **vars);
  */
 struct varshead *ast_channel_get_manager_vars(struct ast_channel *chan);
 
+/*!
+ * \since 14.2.0
+ * \brief Return whether or not any ARI variables have been set
+ *
+ * \retval 0 if no ARI variables are expected
+ * \retval 1 if ARI variables are expected
+ */
+int ast_channel_has_ari_vars(void);
+
+/*!
+ * \since 14.2.0
+ * \brief Sets the variables to be stored in the \a ari_vars field of all
+ * snapshots.
+ * \param varc Number of variable names.
+ * \param vars Array of variable names.
+ */
+void ast_channel_set_ari_vars(size_t varc, char **vars);
+
+/*!
+ * \since 14.2.0
+ * \brief Gets the variables for a given channel, as specified by ast_channel_set_ari_vars().
+ *
+ * The returned variable list is an AO2 object, so ao2_cleanup() to free it.
+ *
+ * \param chan Channel to get variables for.
+ * \return List of channel variables.
+ * \return \c NULL on error
+ */
+struct varshead *ast_channel_get_ari_vars(struct ast_channel *chan);
+
 /*!
  * \since 12
  * \brief Gets the variables for a given channel, as set using pbx_builtin_setvar_helper().

include/asterisk/json.h

@@ -1076,6 +1076,18 @@ enum ast_json_to_ast_vars_code {
  */
 enum ast_json_to_ast_vars_code ast_json_to_ast_variables(struct ast_json *json_variables, struct ast_variable **variables);
 
+struct varshead;
+
+/*!
+ * \brief Construct a JSON object from a \c ast_var_t list
+ * \since 14.2.0
+ *
+ * \param channelvars The list of \c ast_var_t to represent as JSON
+ *
+ * \return JSON object with variable names as keys and variable values as values
+ */
+struct ast_json *ast_json_channel_vars(struct varshead *channelvars);
+
 /*!@}*/
 
 #endif /* _ASTERISK_JSON_H */

include/asterisk/stasis_channels.h

@@ -73,6 +73,7 @@ struct ast_channel_snapshot {
 	struct ast_flags softhangup_flags;      /*!< softhangup channel flags */
 	struct varshead *manager_vars;          /*!< Variables to be appended to manager events */
 	int tech_properties;                    /*!< Properties of the channel's technology */
+	struct varshead *ari_vars;              /*!< Variables to be appended to ARI events */
 };
 
 /*!