Add HTTP proxy support to ceilometer client

There is a need for HTTP Proxy support in Ceilometer client
It's used in the case when Ceilometer API is not directly available
Proxy url is taken from environment variables http_proxy or https_proxy

Implements: blueprint proxy-support

Change-Id: I839d704a7fa16521292205166d7cbea56497842b

ceilometerclient/common/http.py

@@ -48,6 +48,7 @@ class HTTPClient(object):
         self.endpoint = endpoint
         self.auth_token = kwargs.get('token')
         self.connection_params = self.get_connection_params(endpoint, **kwargs)
+        self.proxy_url = self.get_proxy_url()
 
     @staticmethod
     def get_connection_params(endpoint, **kwargs):
@@ -74,8 +75,13 @@ class HTTPClient(object):
     def get_connection(self):
         _class = self.connection_params[0]
         try:
-            return _class(*self.connection_params[1][0:2],
-                          **self.connection_params[2])
+            if self.proxy_url:
+                proxy_parts = urlutils.urlparse(self.proxy_url)
+                return _class(proxy_parts.hostname, proxy_parts.port,
+                              **self.connection_params[2])
+            else:
+                return _class(*self.connection_params[1][0:2],
+                              **self.connection_params[2])
         except httplib.InvalidURL:
             raise exc.InvalidEndpoint()
 
@@ -137,7 +143,10 @@ class HTTPClient(object):
         conn = self.get_connection()
 
         try:
-            conn_url = self._make_connection_url(url)
+            if self.proxy_url:
+                conn_url = self.endpoint + self._make_connection_url(url)
+            else:
+                conn_url = self._make_connection_url(url)
             conn.request(method, conn_url, **kwargs)
             resp = conn.getresponse()
         except socket.gaierror as e:
@@ -202,6 +211,15 @@ class HTTPClient(object):
                                      'application/octet-stream')
         return self._http_request(url, method, **kwargs)
 
+    def get_proxy_url(self):
+        scheme = urlutils.urlparse(self.endpoint).scheme
+        if scheme == 'https':
+            return os.environ.get('https_proxy')
+        elif scheme == 'http':
+            return os.environ.get('http_proxy')
+        msg = 'Unsupported scheme: %s' % scheme
+        raise exc.InvalidEndpoint(msg)
+
 
 class VerifiedHTTPSConnection(httplib.HTTPSConnection):
     """httplib-compatibile connection using client-side SSL authentication