Add postgresql DSN formatter

Author: ovv

README.md

@@ -120,18 +120,19 @@ def format_my_service(credentials):
     return "some string based on 'credentials'."
 
 # Call this in setup
-config.register_formatter('my_service', 'format_my_service')
+config.register_formatter('my_service', format_my_service)
 
 # Then call this method to get the formatted version
 formatted = config.formatted_credentials('database', 'my_service')
 ```
 
 The first parameter is the name of a relationship defined in `.platform.app.yaml`.  The second is a formatter that was previously registered with `register_formatter()`.  If either the service or formatter is missing an exception will be thrown.  The type of `formatted` will depend on the formatter function and can be safely passed directly to the client library.
 
-Two formatters are included out of the box:
+Three formatters are included out of the box:
 
 * `pymongo` returns a DSN appropriate for using `pymongo` to connect to MongoDB. Note that `pymongo` will still need the username and password from the credentials dictionary passed as separate parameters.
-* `pysolr`  returns a DSN appropriate for using `pysolr` to connect to Apache Solr. 
+* `pysolr`  returns a DSN appropriate for using `pysolr` to connect to Apache Solr.
+* `postgresql_dsn` returns a DSN appropriate for postgresql connection.
 
 ### Reading Platform.sh variables
 

platformshconfig/config.py

@@ -150,6 +150,7 @@ def __init__(self, environment_variables=None, env_prefix='PLATFORM_'):
 
                 self.register_formatter('pymongo', pymongo_formatter)
                 self.register_formatter('pysolr', pysolr_formatter)
+                self.register_formatter('postgresql_dsn', posgresql_dsn_formatter)
 
             if self['VARIABLES']:
                 variables = self['VARIABLES']
@@ -577,6 +578,24 @@ def pysolr_formatter(credentials):
                                        credentials['path'])
 
 
+def posgresql_dsn_formatter(credentials):
+    """
+    Returns formatted Posgresql credentials as DSN.
+
+    Args:
+        credentials (dict):
+            The credentials dictionary from the relationships.
+
+    Returns:
+        (string) A formatted postgresql DSN.
+    """
+
+    return "postgresql://{0}:{1}@{2}:{3}/{4}".format(credentials["username"],
+                                                     credentials["password"],
+                                                     credentials["host"],
+                                                     credentials["port"],
+                                                     credentials["path"])
+
 class BuildTimeVariableAccessException(RuntimeError):
     pass