File use_curl.patch of Package ecmwfapi

Use an external call to "curl" to retrieve data. This way we get
a robust and fast download procedure and the user can set additional retrieval
options in $CURL_HOME/.curlrc or ~/.curlrc such as proxies, rate limiting or timeouts.

--- ecmwfapi/api.py.old	2018-06-05 14:16:49.561786478 +0000
+++ ecmwfapi/api.py	2018-06-05 15:23:16.000972875 +0000
@@ -17,6 +17,7 @@ import time
 import traceback
 import textwrap
 from contextlib import closing
+from subprocess import Popen, PIPE
 
 # python 2 and 3 compatible urllib and httplib imports
 try:
@@ -459,14 +460,9 @@ class APIRequest(object):
     def _transfer(self, url, path, size):
         start = time.time()
         existing_size = 0
-        req = Request(url)
 
         if os.path.exists(path):
-            mode = "ab"
             existing_size = os.path.getsize(path)
-            req.add_header("Range", "bytes=%s-" % existing_size)
-        else:
-            mode = "wb"
 
         self.log(
             "Transfering %s into %s" % (self._bytename(size - existing_size), path)
@@ -475,15 +471,13 @@ class APIRequest(object):
         sys.stdout.flush()
         sys.stderr.flush()
 
-        bytes_transferred = 0
-        with open(path, mode) as f:
-            with closing(urlopen(req)) as http:
-                while True:
-                    chunk = http.read(1048576)  # 1MB chunks
-                    if not chunk:
-                        break
-                    f.write(chunk)
-                    bytes_transferred += len(chunk)
+        proc = Popen(["curl","-fsS","-C-","-w","%{size_download}",url,"-o",path], stdout=PIPE)
+        exitcode = proc.wait()
+        if exitcode != 0:
+            self.log("Transfer not successful, exit code %d" % exitcode)
+            sys.stdout.flush()
+            sys.stderr.flush()
+        bytes_transferred = int(proc.stdout.read())
 
         end = time.time()