Telemetry: devtools_http should reuse its http connection.

tools/telemetry/telemetry/core/backends/chrome_inspector/devtools_http.py

Index: tools/telemetry/telemetry/core/backends/chrome_inspector/devtools_http.py
diff --git a/tools/telemetry/telemetry/core/backends/chrome_inspector/devtools_http.py b/tools/telemetry/telemetry/core/backends/chrome_inspector/devtools_http.py
index f5fd8afdb9ef2449ad13925020e6d2d955f77526..50271048c8bf3fc0683cfdbf4248e0c68ba37800 100644
--- a/tools/telemetry/telemetry/core/backends/chrome_inspector/devtools_http.py
+++ b/tools/telemetry/telemetry/core/backends/chrome_inspector/devtools_http.py
@@ -2,11 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import contextlib
+import errno
 import httplib
 import json
 import socket
-import urllib2
+import sys
 
 
 class DevToolsClientConnectionError(Exception):
@@ -18,13 +18,48 @@ class DevToolsClientUrlError(DevToolsClientConnectionError):
 
 
 class DevToolsHttp(object):
-  """A helper class to send and parse DevTools HTTP requests."""
+  """A helper class to send and parse DevTools HTTP requests.
+
+  This class maintains a persistent http connection to Chrome devtools.
+  Ideally, owners of instances of this class should call Disconnect() before
+  disposing of the instance. Otherwise, the connection will not be closed until
+  the instance is garbage collected.
+  """
 
   def __init__(self, devtools_port):
     self._devtools_port = devtools_port
+    self._conn = None
+
+  def __del__(self):
+    self.Disconnect()
+
+  def _Connect(self, timeout):
+    """Attempts to establish a connection to Chrome devtools."""
+    assert not self._conn
+    try:
+      host_port = '127.0.0.1:%i' % self._devtools_port
+      self._conn = httplib.HTTPConnection(host_port, timeout=timeout)
+    except (socket.error, httplib.HTTPException) as e:
+      raise DevToolsClientConnectionError, (e,), sys.exc_info()[2]
+
+  def Disconnect(self):
+    """Closes the HTTP connection."""
+    if not self._conn:
+      return
+
+    try:
+      self._conn.close()
+    except (socket.error, httplib.HTTPException) as e:
+      raise DevToolsClientConnectionError, (e,), sys.exc_info()[2]
+    finally:
+      self._conn = None
 
   def Request(self, path, timeout=30):
-    """
+    """Sends a request to Chrome devtools.
+
+    This method lazily creates an HTTP connection, if one does not already
+    exist.
+
     Args:
       path: The DevTools URL path, without the /json/ prefix.
       timeout: Timeout defaults to 30 seconds.
@@ -32,18 +67,27 @@ class DevToolsHttp(object):
     Raises:
       DevToolsClientConnectionError: If the connection fails.
     """
-    url = 'http://127.0.0.1:%i/json' % self._devtools_port
+    if not self._conn:
+      self._Connect(timeout)
+
+    endpoint = '/json'
     if path:
-      url += '/' + path
+      endpoint += '/' + path
+    if self._conn.sock:
+      self._conn.sock.settimeout(timeout)
+    else:
+      self._conn.timeout = timeout
+
     try:
-      proxy_handler = urllib2.ProxyHandler({})  # Bypass any system proxy.
-      opener = urllib2.build_opener(proxy_handler)
-      with contextlib.closing(opener.open(url, timeout=timeout)) as req:
-        return req.read()
-    except urllib2.URLError as e:
-      raise DevToolsClientUrlError(e)
-    except (socket.error, httplib.BadStatusLine) as e:
-      raise DevToolsClientConnectionError(e)
+      # By default, httplib avoids going through the default system proxy.
+      self._conn.request('GET', endpoint)
+      response = self._conn.getresponse()
+      return response.read()
+    except (socket.error, httplib.HTTPException) as e:
+      self.Disconnect()
+      if isinstance(e, socket.error) and e.errno == errno.ECONNREFUSED:
+        raise DevToolsClientUrlError, (e,), sys.exc_info()[2]
+      raise DevToolsClientConnectionError, (e,), sys.exc_info()[2]
 
   def RequestJson(self, path, timeout=30):
     """Sends a request and parse the response as JSON.