ODS.ODSPubSubHubBubDownstream

ODS PubSubHubBub? Downstream API

What

The API is used in the ODS Application Downstream UI part and can be called as:

PSH.DBA.ods_cli_subscribe 
  (
    in inst_id int, 
    in hub varchar, 
    in mode varchar, 
    in topic varchar
)

Parameters

The API entry parameters are as follows:

• inst_id: the ODS instance Id integer
• hub: the hub url
• mode: 'subscribe' or 'unsubscribe'
• topic: the feed URL to subscribe

Why

The API should be called in the ODS Applications downstream UIs in order to allow push subscriptions. For ex. it is used in ODS Weblog in downstream ui.

How

When subscribed, a record into following table will be added so the UI can show them and to be possible to unsubscribe :

create table "DB"."DBA"."WA_PSH_SUBSCRIPTIONS"
(
  "PS_INST_ID" INTEGER, -- ODS instance Id
  "PS_URL" VARCHAR, -- the feed Url
  "PS_TS" TIMESTAMP, -- modification date/time
  "PS_HUB" VARCHAR, -- the Hub endpoint Url
  PRIMARY KEY ("PS_INST_ID", "PS_URL")
);

Also the ODS define it's own callback:

</psh/odscb.vsp?inst=<instanceid>

This should not be used separately as subscription API already use it.

Since every application defines own tables to import data from feeds every application should have a stored procedure in following pattern :

PSH.DBA.ods_<application type>_psh_cbk (feed_url, content, instance_id)

<application type>is one of :

• weblog,
• calendar,
• mail, etc.

same convention used in the ods rdf views and sioc data.

The above will be called when Hub pushes the feed changes, thus every application should call inside whatever logic it has to make new record.

Code

create procedure PSH.DBA.ods_cli_subscribe 
  (
    in inst_id int, 
    in hub varchar, 
    in mode varchar, 
    in topic varchar
  )
{
  declare token, subsu, callback, head, ret varchar;

  if (__proc_exists ('PSH.DBA.cli_subscribe') is null)
    signal ('42000', 'The PubSubHub package is not installed');

  if (hub is not null)
    {
      token := md5 (uuid ());

      callback := sprintf ('http://%s/psh/odscb.vsp?inst=%d', WA_GET_HOST (), inst_id);

      PSH..cli_subscribe ('dba', mode, topic, 'feed', null, token);

      subsu := sprintf ('%s?hub.callback=%U&hub.mode=%U&hub.topic=%U&hub.verify=sync&hub.verify_token=%U', hub, callback, mode, topic, token);
      commit work;	     

      ret := http_get (subsu, head);

      if (head[0] not like 'HTTP/1._ 20_ %')
	{
	  signal ('39000', 'The Hub rejects subscription request, please verify you are allowed to use it.');
	}
    }

  if (mode = 'subscribe')
    insert replacing DB.DBA.WA_PSH_SUBSCRIPTIONS (PS_INST_ID, PS_HUB, PS_URL) values (inst_id, hub, topic);
  else
    delete from DB.DBA.WA_PSH_SUBSCRIPTIONS where PS_INST_ID = inst_id and PS_URL = topic;
  commit work;	     
}
;

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