1 files changed, 89 insertions, 0 deletions
diff --git a/Lib/test/support/socket_helper.py b/Lib/test/support/socket_helper.py
index 5f4a7f19a3..b09c248cfc 100644
--- a/Lib/test/support/socket_helper.py
+++ b/Lib/test/support/socket_helper.py
@@ -1,7 +1,11 @@
+import contextlib
 import errno
 import socket
 import unittest
 
+from .. import support
+
+
 HOST = "localhost"
 HOSTv4 = "127.0.0.1"
 HOSTv6 = "::1"
@@ -175,3 +179,88 @@ def get_socket_conn_refused_errs():
     if not IPV6_ENABLED:
         errors.append(errno.EAFNOSUPPORT)
     return errors
+
+
+_NOT_SET = object()
+
+@contextlib.contextmanager
+def transient_internet(resource_name, *, timeout=_NOT_SET, errnos=()):
+    """Return a context manager that raises ResourceDenied when various issues
+    with the Internet connection manifest themselves as exceptions."""
+    import nntplib
+    import urllib.error
+    if timeout is _NOT_SET:
+        timeout = support.INTERNET_TIMEOUT
+
+    default_errnos = [
+        ('ECONNREFUSED', 111),
+        ('ECONNRESET', 104),
+        ('EHOSTUNREACH', 113),
+        ('ENETUNREACH', 101),
+        ('ETIMEDOUT', 110),
+        # socket.create_connection() fails randomly with
+        # EADDRNOTAVAIL on Travis CI.
+        ('EADDRNOTAVAIL', 99),
+    ]
+    default_gai_errnos = [
+        ('EAI_AGAIN', -3),
+        ('EAI_FAIL', -4),
+        ('EAI_NONAME', -2),
+        ('EAI_NODATA', -5),
+        # Encountered when trying to resolve IPv6-only hostnames
+        ('WSANO_DATA', 11004),
+    ]
+
+    denied = support.ResourceDenied("Resource %r is not available" % resource_name)
+    captured_errnos = errnos
+    gai_errnos = []
+    if not captured_errnos:
+        captured_errnos = [getattr(errno, name, num)
+                           for (name, num) in default_errnos]
+        gai_errnos = [getattr(socket, name, num)
+                      for (name, num) in default_gai_errnos]
+
+    def filter_error(err):
+        n = getattr(err, 'errno', None)
+        if (isinstance(err, socket.timeout) or
+            (isinstance(err, socket.gaierror) and n in gai_errnos) or
+            (isinstance(err, urllib.error.HTTPError) and
+             500 <= err.code <= 599) or
+            (isinstance(err, urllib.error.URLError) and
+                 (("ConnectionRefusedError" in err.reason) or
+                  ("TimeoutError" in err.reason) or
+                  ("EOFError" in err.reason))) or
+            n in captured_errnos):
+            if not support.verbose:
+                sys.stderr.write(denied.args[0] + "\n")
+            raise denied from err
+
+    old_timeout = socket.getdefaulttimeout()
+    try:
+        if timeout is not None:
+            socket.setdefaulttimeout(timeout)
+        yield
+    except nntplib.NNTPTemporaryError as err:
+        if support.verbose:
+            sys.stderr.write(denied.args[0] + "\n")
+        raise denied from err
+    except OSError as err:
+        # urllib can wrap original socket errors multiple times (!), we must
+        # unwrap to get at the original error.
+        while True:
+            a = err.args
+            if len(a) >= 1 and isinstance(a[0], OSError):
+                err = a[0]
+            # The error can also be wrapped as args[1]:
+            #    except socket.error as msg:
+            #        raise OSError('socket error', msg).with_traceback(sys.exc_info()[2])
+            elif len(a) >= 2 and isinstance(a[1], OSError):
+                err = a[1]
+            else:
+                break
+        filter_error(err)
+        raise
+    # XXX should we catch generic exceptions and look for their
+    # __cause__ or __context__?
+    finally:
+        socket.setdefaulttimeout(old_timeout)