Calling RESTful Web Services from PostgreSQL procedure/function

Question

I have been provided RESTful web services to push data into a remote DB of another application. I need to call these services to push data from PostgreSQL DB by sending data in JSON format as GET/POST parameters to the web service. Is it possible to call these web services from the PostgreSQL functions (periodically) which push data into my database in the first place, or write JAVA code to call these web services that run queries on PostgreSQL database and call web services to pass them to the remote DB.

Answer 1

Yes, it is possible, althought not directly from Postgresql itself. I don't know about Java but the fastest way is to use plperlu with REST::Client package, e.g.:

CREATE OR REPLACE FUNCTION restful.put(auri character varying, ajson_text text)
 RETURNS text
 LANGUAGE plperlu
 SECURITY DEFINER
AS $function$
  use REST::Client;  
  use Encode qw(encode);
  my $client = REST::Client->new();    
  $client->getUseragent()->proxy( 'https', 'http://some-proxy/' ); # use for proxy authentication
  $client->addHeader('Content-Type', 'application/json');          # headers
  $client->POST( $_[0], encode('UTF-8', $_[1]));                   # encoding
  return $client->responseContent();  
$function$

Answer 2

Using plpython2u language:

Solution 1: (using urllib2)

CREATE OR REPLACE FUNCTION public.py_pgrest(uri text, body text DEFAULT NULL::text, content_type text DEFAULT 'application/json'::text)
 RETURNS text
 LANGUAGE plpython2u
AS $function$
    import urllib2
    from urllib2 import Request, urlopen, URLError, HTTPError
    req = Request(uri)
    if body:
        req.add_data(body)
    if content_type:
        req.add_header('Content-Type', content_type)
    try:
        data = urlopen(req)
    except HTTPError as e:
        return e
    except URLError as e:
        if hasattr(e, 'reason'):
            return e.reason
        elif hasattr(e, 'code'):
            return e.code
        else:
            return e
    else:
        return data.read()
$function$
;

Solution 2: (using requests)

CREATE OR REPLACE FUNCTION public.py_pgrest(p_url text, p_method text DEFAULT 'GET'::text, p_data text DEFAULT ''::text, p_headers text DEFAULT '{"Content-Type": "application/json"}'::text)
 RETURNS text
 LANGUAGE plpython2u
AS $function$
    import requests, json
    try:
        r = requests.request(method=p_method, url=p_url, data=p_data, headers=json.loads(p_headers))
    except Exception as e:
        return e
    else:
        return r.content
$function$
;