fall back to downloading using the requests Python package (if installed) when urllib2 fails due to SSL error

.travis.yml

@@ -51,7 +51,7 @@ before_install:
     # autopep8 1.3.4 is last one to support Python 2.6
     - if [ "x$TRAVIS_PYTHON_VERSION" == 'x2.6' ]; then pip install 'autopep8<1.3.5'; else pip install autopep8; fi
     # optional Python packages for EasyBuild
-    - pip install GC3Pie pycodestyle python-graph-dot python-hglib PyYAML
+    - pip install GC3Pie pycodestyle python-graph-dot python-hglib PyYAML requests
     # git config is required to make actual git commits (cfr. tests for GitRepository)
     - git config --global user.name "Travis CI"
     - git config --global user.email "[email protected]"

easybuild/tools/filetools.py

@@ -60,6 +60,11 @@
 from easybuild.tools.config import build_option
 from easybuild.tools import run
 
+try:
+    import requests
+    HAVE_REQUESTS = True
+except ImportError:
+    HAVE_REQUESTS = False
 
 _log = fancylogger.getLogger('filetools', fname=False)
 
@@ -460,26 +465,47 @@ def download_file(filename, url, path, forced=False):
     attempt_cnt = 0
 
     # use custom HTTP header
-    url_req = urllib2.Request(url, headers={'User-Agent': 'EasyBuild',  "Accept" : "*/*"})
+    headers = {'User-Agent': 'EasyBuild', 'Accept': '*/*'}
+    # for backward compatibility, and to avoid relying on 3rd party Python library 'requests'
+    url_req = urllib2.Request(url, headers=headers)
+    used_urllib = urllib2
 
     while not downloaded and attempt_cnt < max_attempts:
         try:
-            # urllib2 does the right thing for http proxy setups, urllib does not!
-            url_fd = urllib2.urlopen(url_req, timeout=timeout)
-            _log.debug('response code for given url %s: %s' % (url, url_fd.getcode()))
+            if used_urllib is urllib2:
+                # urllib2 does the right thing for http proxy setups, urllib does not!
+                url_fd = urllib2.urlopen(url_req, timeout=timeout)
+                status_code = url_fd.getcode()
+            else:
+                response = requests.get(url, headers=headers, stream=True, timeout=timeout)
+                status_code = response.status_code
+                response.raise_for_status()
+                url_fd = response.raw
+                url_fd.decode_content = True
+            _log.debug('response code for given url %s: %s' % (url, status_code))
             write_file(path, url_fd.read(), forced=forced, backup=True)
             _log.info("Downloaded file %s from url %s to %s" % (filename, url, path))
             downloaded = True
             url_fd.close()
-        except urllib2.HTTPError as err:
-            if 400 <= err.code <= 499:
-                _log.warning("URL %s was not found (HTTP response code %s), not trying again" % (url, err.code))
+        except used_urllib.HTTPError as err:
+            if used_urllib is urllib2:
+                status_code = err.code
+            if 400 <= status_code <= 499:
+                _log.warning("URL %s was not found (HTTP response code %s), not trying again" % (url, status_code))
                 break
             else:
                 _log.warning("HTTPError occurred while trying to download %s to %s: %s" % (url, path, err))
                 attempt_cnt += 1
         except IOError as err:
             _log.warning("IOError occurred while trying to download %s to %s: %s" % (url, path, err))
+            error_re = re.compile(r"<urlopen error \[Errno 1\] _ssl.c:.*: error:.*:"
+                                  "SSL routines:SSL23_GET_SERVER_HELLO:sslv3 alert handshake failure>")
+            if error_re.match(str(err)):
+                if not HAVE_REQUESTS:
+                    raise EasyBuildError("SSL issues with urllib2. If you are using RHEL/CentOS 6.x please "
+                                         "install the python-requests and pyOpenSSL RPM packages and try again.")
+                _log.info("Downloading using requests package instead of urllib2")
+                used_urllib = requests
             attempt_cnt += 1
         except Exception, err:
             raise EasyBuildError("Unexpected error occurred when trying to download %s to %s: %s", url, path, err)

test/framework/filetools.py

@@ -59,6 +59,18 @@ class FileToolsTest(EnhancedTestCase):
         ('0_foo+0x0x#-$__', 'EB_0_underscore_foo_plus_0x0x_hash__minus__dollar__underscore__underscore_'),
     ]
 
+    def setUp(self):
+        """Test setup."""
+        super(FileToolsTest, self).setUp()
+
+        self.orig_filetools_urllib2_urlopen = ft.urllib2.urlopen
+
+    def tearDown(self):
+        """Cleanup."""
+        super(FileToolsTest, self).tearDown()
+
+        ft.urllib2.urlopen = self.orig_filetools_urllib2_urlopen
+
     def test_extract_cmd(self):
         """Test various extract commands."""
         tests = [
@@ -317,7 +329,7 @@ def test_download_file(self):
         opts = init_config(args=['--download-timeout=5.3'])
         init_config(build_options={'download_timeout': opts.download_timeout})
         target_location = os.path.join(self.test_prefix, 'jenkins_robots.txt')
-        url = 'https://jenkins1.ugent.be/robots.txt'
+        url = 'https://raw.githubusercontent.com/easybuilders/easybuild-framework/master/README.rst'
         try:
             urllib2.urlopen(url)
             res = ft.download_file(fn, url, target_location)
@@ -349,6 +361,30 @@ def test_download_file(self):
         self.assertTrue(os.path.exists(target_location))
         self.assertTrue(os.path.samefile(path, target_location))
 
+    def test_download_file_requests_fallback(self):
+        """Test fallback to requests in download_file function."""
+        url = 'https://raw.githubusercontent.com/easybuilders/easybuild-framework/master/README.rst'
+        fn = 'README.rst'
+        target = os.path.join(self.test_prefix, fn)
+
+        # replace urllib2.urlopen with function that raises SSL error
+        def fake_urllib2_open(*args, **kwargs):
+            error_msg = "<urlopen error [Errno 1] _ssl.c:510: error:12345:"
+            error_msg += "SSL routines:SSL23_GET_SERVER_HELLO:sslv3 alert handshake failure>"
+            raise IOError(error_msg)
+
+        ft.urllib2.urlopen = fake_urllib2_open
+
+        # if requests is available, file is downloaded
+        if ft.HAVE_REQUESTS:
+            res = ft.download_file(fn, url, target)
+            self.assertTrue(res and os.path.exists(res))
+            self.assertTrue("https://easybuilders.github.io/easybuild" in ft.read_file(res))
+
+        # without requests being available, error is raised
+        ft.HAVE_REQUESTS = False
+        self.assertErrorRegex(EasyBuildError, "SSL issues with urllib2", ft.download_file, fn, url, target)
+
     def test_mkdir(self):
         """Test mkdir function."""